1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
use std::collections::HashSet;

use bevy_ecs::entity::EntityHashMap;
use bevy_ecs::prelude::*;
use bevy_math::{
    AspectRatio, Mat4, UVec2, UVec3, Vec2, Vec3, Vec3A, Vec3Swizzles, Vec4, Vec4Swizzles,
};
use bevy_reflect::prelude::*;
use bevy_render::{
    camera::{Camera, CameraProjection},
    color::Color,
    extract_component::ExtractComponent,
    extract_resource::ExtractResource,
    primitives::{Aabb, CascadesFrusta, CubemapFrusta, Frustum, HalfSpace, Sphere},
    render_resource::BufferBindingType,
    renderer::RenderDevice,
    view::{InheritedVisibility, RenderLayers, ViewVisibility, VisibleEntities},
};
use bevy_transform::components::{GlobalTransform, Transform};
use bevy_utils::tracing::warn;

use crate::*;

/// Constants for operating with the light units: lumens, and lux.
pub mod light_consts {
    /// Approximations for converting the wattage of lamps to lumens.
    ///
    /// The **lumen** (symbol: **lm**) is the unit of [luminous flux], a measure
    /// of the total quantity of [visible light] emitted by a source per unit of
    /// time, in the [International System of Units] (SI).
    ///
    /// For more information, see [wikipedia](https://en.wikipedia.org/wiki/Lumen_(unit))
    ///
    /// [luminous flux]: https://en.wikipedia.org/wiki/Luminous_flux
    /// [visible light]: https://en.wikipedia.org/wiki/Visible_light
    /// [International System of Units]: https://en.wikipedia.org/wiki/International_System_of_Units
    pub mod lumens {
        pub const LUMENS_PER_LED_WATTS: f32 = 90.0;
        pub const LUMENS_PER_INCANDESCENT_WATTS: f32 = 13.8;
        pub const LUMENS_PER_HALOGEN_WATTS: f32 = 19.8;
    }

    /// Predefined for lux values in several locations.
    ///
    /// The **lux** (symbol: **lx**) is the unit of [illuminance], or [luminous flux] per unit area,
    /// in the [International System of Units] (SI). It is equal to one lumen per square metre.
    ///
    /// For more information, see [wikipedia](https://en.wikipedia.org/wiki/Lux)
    ///
    /// [illuminance]: https://en.wikipedia.org/wiki/Illuminance
    /// [luminous flux]: https://en.wikipedia.org/wiki/Luminous_flux
    /// [International System of Units]: https://en.wikipedia.org/wiki/International_System_of_Units
    pub mod lux {
        /// The amount of light (lux) in a moonless, overcast night sky. (starlight)
        pub const MOONLESS_NIGHT: f32 = 0.0001;
        /// The amount of light (lux) during a full moon on a clear night.
        pub const FULL_MOON_NIGHT: f32 = 0.05;
        /// The amount of light (lux) during the dark limit of civil twilight under a clear sky.
        pub const CIVIL_TWILIGHT: f32 = 3.4;
        /// The amount of light (lux) in family living room lights.
        pub const LIVING_ROOM: f32 = 50.;
        /// The amount of light (lux) in an office building's hallway/toilet lighting.
        pub const HALLWAY: f32 = 80.;
        /// The amount of light (lux) in very dark overcast day
        pub const DARK_OVERCAST_DAY: f32 = 100.;
        /// The amount of light (lux) in an office.
        pub const OFFICE: f32 = 320.;
        /// The amount of light (lux) during sunrise or sunset on a clear day.
        pub const CLEAR_SUNRISE: f32 = 400.;
        /// The amount of light (lux) on a overcast day; typical TV studio lighting
        pub const OVERCAST_DAY: f32 = 1000.;
        /// The amount of light (lux) from ambient daylight (not direct sunlight).
        pub const AMBIENT_DAYLIGHT: f32 = 10_000.;
        /// The amount of light (lux) in full daylight (not direct sun).
        pub const FULL_DAYLIGHT: f32 = 20_000.;
        /// The amount of light (lux) in direct sunlight.
        pub const DIRECT_SUNLIGHT: f32 = 100_000.;
    }
}

/// A light that emits light in all directions from a central point.
///
/// Real-world values for `intensity` (luminous power in lumens) based on the electrical power
/// consumption of the type of real-world light are:
///
/// | Luminous Power (lumen) (i.e. the intensity member) | Incandescent non-halogen (Watts) | Incandescent halogen (Watts) | Compact fluorescent (Watts) | LED (Watts |
/// |------|-----|----|--------|-------|
/// | 200  | 25  |    | 3-5    | 3     |
/// | 450  | 40  | 29 | 9-11   | 5-8   |
/// | 800  | 60  |    | 13-15  | 8-12  |
/// | 1100 | 75  | 53 | 18-20  | 10-16 |
/// | 1600 | 100 | 72 | 24-28  | 14-17 |
/// | 2400 | 150 |    | 30-52  | 24-30 |
/// | 3100 | 200 |    | 49-75  | 32    |
/// | 4000 | 300 |    | 75-100 | 40.5  |
///
/// Source: [Wikipedia](https://en.wikipedia.org/wiki/Lumen_(unit)#Lighting)
#[derive(Component, Debug, Clone, Copy, Reflect)]
#[reflect(Component, Default)]
pub struct PointLight {
    pub color: Color,
    /// Luminous power in lumens, representing the amount of light emitted by this source in all directions.
    pub intensity: f32,
    pub range: f32,
    pub radius: f32,
    pub shadows_enabled: bool,
    pub shadow_depth_bias: f32,
    /// A bias applied along the direction of the fragment's surface normal. It is scaled to the
    /// shadow map's texel size so that it can be small close to the camera and gets larger further
    /// away.
    pub shadow_normal_bias: f32,
}

impl Default for PointLight {
    fn default() -> Self {
        PointLight {
            color: Color::rgb(1.0, 1.0, 1.0),
            // 1,000,000 lumens is a very large "cinema light" capable of registering brightly at Bevy's
            // default "very overcast day" exposure level. For "indoor lighting" with a lower exposure,
            // this would be way too bright.
            intensity: 1_000_000.0,
            range: 20.0,
            radius: 0.0,
            shadows_enabled: false,
            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
        }
    }
}

impl PointLight {
    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.02;
    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.6;
}

#[derive(Resource, Clone, Debug, Reflect)]
#[reflect(Resource)]
pub struct PointLightShadowMap {
    pub size: usize,
}

impl Default for PointLightShadowMap {
    fn default() -> Self {
        Self { size: 1024 }
    }
}

/// A light that emits light in a given direction from a central point.
/// Behaves like a point light in a perfectly absorbent housing that
/// shines light only in a given direction. The direction is taken from
/// the transform, and can be specified with [`Transform::looking_at`](Transform::looking_at).
#[derive(Component, Debug, Clone, Copy, Reflect)]
#[reflect(Component, Default)]
pub struct SpotLight {
    pub color: Color,
    /// Luminous power in lumens, representing the amount of light emitted by this source in all directions.
    pub intensity: f32,
    pub range: f32,
    pub radius: f32,
    pub shadows_enabled: bool,
    pub shadow_depth_bias: f32,
    /// A bias applied along the direction of the fragment's surface normal. It is scaled to the
    /// shadow map's texel size so that it can be small close to the camera and gets larger further
    /// away.
    pub shadow_normal_bias: f32,
    /// Angle defining the distance from the spot light direction to the outer limit
    /// of the light's cone of effect.
    /// `outer_angle` should be < `PI / 2.0`.
    /// `PI / 2.0` defines a hemispherical spot light, but shadows become very blocky as the angle
    /// approaches this limit.
    pub outer_angle: f32,
    /// Angle defining the distance from the spot light direction to the inner limit
    /// of the light's cone of effect.
    /// Light is attenuated from `inner_angle` to `outer_angle` to give a smooth falloff.
    /// `inner_angle` should be <= `outer_angle`
    pub inner_angle: f32,
}

impl SpotLight {
    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.02;
    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 1.8;
}

impl Default for SpotLight {
    fn default() -> Self {
        // a quarter arc attenuating from the center
        Self {
            color: Color::rgb(1.0, 1.0, 1.0),
            // 1,000,000 lumens is a very large "cinema light" capable of registering brightly at Bevy's
            // default "very overcast day" exposure level. For "indoor lighting" with a lower exposure,
            // this would be way too bright.
            intensity: 1_000_000.0,
            range: 20.0,
            radius: 0.0,
            shadows_enabled: false,
            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
            inner_angle: 0.0,
            outer_angle: std::f32::consts::FRAC_PI_4,
        }
    }
}

/// A Directional light.
///
/// Directional lights don't exist in reality but they are a good
/// approximation for light sources VERY far away, like the sun or
/// the moon.
///
/// The light shines along the forward direction of the entity's transform. With a default transform
/// this would be along the negative-Z axis.
///
/// Valid values for `illuminance` are:
///
/// | Illuminance (lux) | Surfaces illuminated by                        |
/// |-------------------|------------------------------------------------|
/// | 0.0001            | Moonless, overcast night sky (starlight)       |
/// | 0.002             | Moonless clear night sky with airglow          |
/// | 0.05–0.3          | Full moon on a clear night                     |
/// | 3.4               | Dark limit of civil twilight under a clear sky |
/// | 20–50             | Public areas with dark surroundings            |
/// | 50                | Family living room lights                      |
/// | 80                | Office building hallway/toilet lighting        |
/// | 100               | Very dark overcast day                         |
/// | 150               | Train station platforms                        |
/// | 320–500           | Office lighting                                |
/// | 400               | Sunrise or sunset on a clear day.              |
/// | 1000              | Overcast day; typical TV studio lighting       |
/// | 10,000–25,000     | Full daylight (not direct sun)                 |
/// | 32,000–100,000    | Direct sunlight                                |
///
/// Source: [Wikipedia](https://en.wikipedia.org/wiki/Lux)
///
/// ## Shadows
///
/// To enable shadows, set the `shadows_enabled` property to `true`.
///
/// Shadows are produced via [cascaded shadow maps](https://developer.download.nvidia.com/SDK/10.5/opengl/src/cascaded_shadow_maps/doc/cascaded_shadow_maps.pdf).
///
/// To modify the cascade set up, such as the number of cascades or the maximum shadow distance,
/// change the [`CascadeShadowConfig`] component of the [`DirectionalLightBundle`].
///
/// To control the resolution of the shadow maps, use the [`DirectionalLightShadowMap`] resource:
///
/// ```
/// # use bevy_app::prelude::*;
/// # use bevy_pbr::DirectionalLightShadowMap;
/// App::new()
///     .insert_resource(DirectionalLightShadowMap { size: 2048 });
/// ```
#[derive(Component, Debug, Clone, Reflect)]
#[reflect(Component, Default)]
pub struct DirectionalLight {
    pub color: Color,
    /// Illuminance in lux (lumens per square meter), representing the amount of
    /// light projected onto surfaces by this light source. Lux is used here
    /// instead of lumens because a directional light illuminates all surfaces
    /// more-or-less the same way (depending on the angle of incidence). Lumens
    /// can only be specified for light sources which emit light from a specific
    /// area.
    pub illuminance: f32,
    pub shadows_enabled: bool,
    pub shadow_depth_bias: f32,
    /// A bias applied along the direction of the fragment's surface normal. It is scaled to the
    /// shadow map's texel size so that it is automatically adjusted to the orthographic projection.
    pub shadow_normal_bias: f32,
}

impl Default for DirectionalLight {
    fn default() -> Self {
        DirectionalLight {
            color: Color::rgb(1.0, 1.0, 1.0),
            illuminance: light_consts::lux::AMBIENT_DAYLIGHT,
            shadows_enabled: false,
            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
        }
    }
}

impl DirectionalLight {
    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.02;
    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 1.8;
}

/// Controls the resolution of [`DirectionalLight`] shadow maps.
#[derive(Resource, Clone, Debug, Reflect)]
#[reflect(Resource)]
pub struct DirectionalLightShadowMap {
    pub size: usize,
}

impl Default for DirectionalLightShadowMap {
    fn default() -> Self {
        Self { size: 2048 }
    }
}

/// Controls how cascaded shadow mapping works.
/// Prefer using [`CascadeShadowConfigBuilder`] to construct an instance.
///
/// ```
/// # use bevy_pbr::CascadeShadowConfig;
/// # use bevy_pbr::CascadeShadowConfigBuilder;
/// # use bevy_utils::default;
/// #
/// let config: CascadeShadowConfig = CascadeShadowConfigBuilder {
///   maximum_distance: 100.0,
///   ..default()
/// }.into();
/// ```
#[derive(Component, Clone, Debug, Reflect)]
#[reflect(Component, Default)]
pub struct CascadeShadowConfig {
    /// The (positive) distance to the far boundary of each cascade.
    pub bounds: Vec<f32>,
    /// The proportion of overlap each cascade has with the previous cascade.
    pub overlap_proportion: f32,
    /// The (positive) distance to the near boundary of the first cascade.
    pub minimum_distance: f32,
}

impl Default for CascadeShadowConfig {
    fn default() -> Self {
        CascadeShadowConfigBuilder::default().into()
    }
}

fn calculate_cascade_bounds(
    num_cascades: usize,
    nearest_bound: f32,
    shadow_maximum_distance: f32,
) -> Vec<f32> {
    if num_cascades == 1 {
        return vec![shadow_maximum_distance];
    }
    let base = (shadow_maximum_distance / nearest_bound).powf(1.0 / (num_cascades - 1) as f32);
    (0..num_cascades)
        .map(|i| nearest_bound * base.powf(i as f32))
        .collect()
}

/// Builder for [`CascadeShadowConfig`].
pub struct CascadeShadowConfigBuilder {
    /// The number of shadow cascades.
    /// More cascades increases shadow quality by mitigating perspective aliasing - a phenomenon where areas
    /// nearer the camera are covered by fewer shadow map texels than areas further from the camera, causing
    /// blocky looking shadows.
    ///
    /// This does come at the cost increased rendering overhead, however this overhead is still less
    /// than if you were to use fewer cascades and much larger shadow map textures to achieve the
    /// same quality level.
    ///
    /// In case rendered geometry covers a relatively narrow and static depth relative to camera, it may
    /// make more sense to use fewer cascades and a higher resolution shadow map texture as perspective aliasing
    /// is not as much an issue. Be sure to adjust `minimum_distance` and `maximum_distance` appropriately.
    pub num_cascades: usize,
    /// The minimum shadow distance, which can help improve the texel resolution of the first cascade.
    /// Areas nearer to the camera than this will likely receive no shadows.
    ///
    /// NOTE: Due to implementation details, this usually does not impact shadow quality as much as
    /// `first_cascade_far_bound` and `maximum_distance`. At many view frustum field-of-views, the
    /// texel resolution of the first cascade is dominated by the width / height of the view frustum plane
    /// at `first_cascade_far_bound` rather than the depth of the frustum from `minimum_distance` to
    /// `first_cascade_far_bound`.
    pub minimum_distance: f32,
    /// The maximum shadow distance.
    /// Areas further from the camera than this will likely receive no shadows.
    pub maximum_distance: f32,
    /// Sets the far bound of the first cascade, relative to the view origin.
    /// In-between cascades will be exponentially spaced relative to the maximum shadow distance.
    /// NOTE: This is ignored if there is only one cascade, the maximum distance takes precedence.
    pub first_cascade_far_bound: f32,
    /// Sets the overlap proportion between cascades.
    /// The overlap is used to make the transition from one cascade's shadow map to the next
    /// less abrupt by blending between both shadow maps.
    pub overlap_proportion: f32,
}

impl CascadeShadowConfigBuilder {
    /// Returns the cascade config as specified by this builder.
    pub fn build(&self) -> CascadeShadowConfig {
        assert!(
            self.num_cascades > 0,
            "num_cascades must be positive, but was {}",
            self.num_cascades
        );
        assert!(
            self.minimum_distance >= 0.0,
            "maximum_distance must be non-negative, but was {}",
            self.minimum_distance
        );
        assert!(
            self.num_cascades == 1 || self.minimum_distance < self.first_cascade_far_bound,
            "minimum_distance must be less than first_cascade_far_bound, but was {}",
            self.minimum_distance
        );
        assert!(
            self.maximum_distance > self.minimum_distance,
            "maximum_distance must be greater than minimum_distance, but was {}",
            self.maximum_distance
        );
        assert!(
            (0.0..1.0).contains(&self.overlap_proportion),
            "overlap_proportion must be in [0.0, 1.0) but was {}",
            self.overlap_proportion
        );
        CascadeShadowConfig {
            bounds: calculate_cascade_bounds(
                self.num_cascades,
                self.first_cascade_far_bound,
                self.maximum_distance,
            ),
            overlap_proportion: self.overlap_proportion,
            minimum_distance: self.minimum_distance,
        }
    }
}

impl Default for CascadeShadowConfigBuilder {
    fn default() -> Self {
        if cfg!(all(
            feature = "webgl",
            target_arch = "wasm32",
            not(feature = "webgpu")
        )) {
            // Currently only support one cascade in webgl.
            Self {
                num_cascades: 1,
                minimum_distance: 0.1,
                maximum_distance: 100.0,
                first_cascade_far_bound: 5.0,
                overlap_proportion: 0.2,
            }
        } else {
            Self {
                num_cascades: 4,
                minimum_distance: 0.1,
                maximum_distance: 1000.0,
                first_cascade_far_bound: 5.0,
                overlap_proportion: 0.2,
            }
        }
    }
}

impl From<CascadeShadowConfigBuilder> for CascadeShadowConfig {
    fn from(builder: CascadeShadowConfigBuilder) -> Self {
        builder.build()
    }
}

#[derive(Component, Clone, Debug, Default, Reflect)]
#[reflect(Component)]
pub struct Cascades {
    /// Map from a view to the configuration of each of its [`Cascade`]s.
    pub(crate) cascades: EntityHashMap<Vec<Cascade>>,
}

#[derive(Clone, Debug, Default, Reflect)]
pub struct Cascade {
    /// The transform of the light, i.e. the view to world matrix.
    pub(crate) view_transform: Mat4,
    /// The orthographic projection for this cascade.
    pub(crate) projection: Mat4,
    /// The view-projection matrix for this cascade, converting world space into light clip space.
    /// Importantly, this is derived and stored separately from `view_transform` and `projection` to
    /// ensure shadow stability.
    pub(crate) view_projection: Mat4,
    /// Size of each shadow map texel in world units.
    pub(crate) texel_size: f32,
}

pub fn clear_directional_light_cascades(mut lights: Query<(&DirectionalLight, &mut Cascades)>) {
    for (directional_light, mut cascades) in lights.iter_mut() {
        if !directional_light.shadows_enabled {
            continue;
        }
        cascades.cascades.clear();
    }
}

pub fn build_directional_light_cascades<P: CameraProjection + Component>(
    directional_light_shadow_map: Res<DirectionalLightShadowMap>,
    views: Query<(Entity, &GlobalTransform, &P, &Camera)>,
    mut lights: Query<(
        &GlobalTransform,
        &DirectionalLight,
        &CascadeShadowConfig,
        &mut Cascades,
    )>,
) {
    let views = views
        .iter()
        .filter_map(|(entity, transform, projection, camera)| {
            if camera.is_active {
                Some((entity, projection, transform.compute_matrix()))
            } else {
                None
            }
        })
        .collect::<Vec<_>>();

    for (transform, directional_light, cascades_config, mut cascades) in &mut lights {
        if !directional_light.shadows_enabled {
            continue;
        }

        // It is very important to the numerical and thus visual stability of shadows that
        // light_to_world has orthogonal upper-left 3x3 and zero translation.
        // Even though only the direction (i.e. rotation) of the light matters, we don't constrain
        // users to not change any other aspects of the transform - there's no guarantee
        // `transform.compute_matrix()` will give us a matrix with our desired properties.
        // Instead, we directly create a good matrix from just the rotation.
        let light_to_world = Mat4::from_quat(transform.compute_transform().rotation);
        let light_to_world_inverse = light_to_world.inverse();

        for (view_entity, projection, view_to_world) in views.iter().copied() {
            let camera_to_light_view = light_to_world_inverse * view_to_world;
            let view_cascades = cascades_config
                .bounds
                .iter()
                .enumerate()
                .map(|(idx, far_bound)| {
                    // Negate bounds as -z is camera forward direction.
                    let z_near = if idx > 0 {
                        (1.0 - cascades_config.overlap_proportion)
                            * -cascades_config.bounds[idx - 1]
                    } else {
                        -cascades_config.minimum_distance
                    };
                    let z_far = -far_bound;

                    let corners = projection.get_frustum_corners(z_near, z_far);

                    calculate_cascade(
                        corners,
                        directional_light_shadow_map.size as f32,
                        light_to_world,
                        camera_to_light_view,
                    )
                })
                .collect();
            cascades.cascades.insert(view_entity, view_cascades);
        }
    }
}

/// Returns a [`Cascade`] for the frustum defined by `frustum_corners`.
/// The corner vertices should be specified in the following order:
/// first the bottom right, top right, top left, bottom left for the near plane, then similar for the far plane.
fn calculate_cascade(
    frustum_corners: [Vec3A; 8],
    cascade_texture_size: f32,
    light_to_world: Mat4,
    camera_to_light: Mat4,
) -> Cascade {
    let mut min = Vec3A::splat(f32::MAX);
    let mut max = Vec3A::splat(f32::MIN);
    for corner_camera_view in frustum_corners {
        let corner_light_view = camera_to_light.transform_point3a(corner_camera_view);
        min = min.min(corner_light_view);
        max = max.max(corner_light_view);
    }

    // NOTE: Use the larger of the frustum slice far plane diagonal and body diagonal lengths as this
    //       will be the maximum possible projection size. Use the ceiling to get an integer which is
    //       very important for floating point stability later. It is also important that these are
    //       calculated using the original camera space corner positions for floating point precision
    //       as even though the lengths using corner_light_view above should be the same, precision can
    //       introduce small but significant differences.
    // NOTE: The size remains the same unless the view frustum or cascade configuration is modified.
    let cascade_diameter = (frustum_corners[0] - frustum_corners[6])
        .length()
        .max((frustum_corners[4] - frustum_corners[6]).length())
        .ceil();

    // NOTE: If we ensure that cascade_texture_size is a power of 2, then as we made cascade_diameter an
    //       integer, cascade_texel_size is then an integer multiple of a power of 2 and can be
    //       exactly represented in a floating point value.
    let cascade_texel_size = cascade_diameter / cascade_texture_size;
    // NOTE: For shadow stability it is very important that the near_plane_center is at integer
    //       multiples of the texel size to be exactly representable in a floating point value.
    let near_plane_center = Vec3A::new(
        (0.5 * (min.x + max.x) / cascade_texel_size).floor() * cascade_texel_size,
        (0.5 * (min.y + max.y) / cascade_texel_size).floor() * cascade_texel_size,
        // NOTE: max.z is the near plane for right-handed y-up
        max.z,
    );

    // It is critical for `world_to_cascade` to be stable. So rather than forming `cascade_to_world`
    // and inverting it, which risks instability due to numerical precision, we directly form
    // `world_to_cascde` as the reference material suggests.
    let light_to_world_transpose = light_to_world.transpose();
    let world_to_cascade = Mat4::from_cols(
        light_to_world_transpose.x_axis,
        light_to_world_transpose.y_axis,
        light_to_world_transpose.z_axis,
        (-near_plane_center).extend(1.0),
    );

    // Right-handed orthographic projection, centered at `near_plane_center`.
    // NOTE: This is different from the reference material, as we use reverse Z.
    let r = (max.z - min.z).recip();
    let cascade_projection = Mat4::from_cols(
        Vec4::new(2.0 / cascade_diameter, 0.0, 0.0, 0.0),
        Vec4::new(0.0, 2.0 / cascade_diameter, 0.0, 0.0),
        Vec4::new(0.0, 0.0, r, 0.0),
        Vec4::new(0.0, 0.0, 1.0, 1.0),
    );

    let cascade_view_projection = cascade_projection * world_to_cascade;
    Cascade {
        view_transform: world_to_cascade.inverse(),
        projection: cascade_projection,
        view_projection: cascade_view_projection,
        texel_size: cascade_texel_size,
    }
}

/// An ambient light, which lights the entire scene equally.
///
/// This resource is inserted by the [`PbrPlugin`] and by default it is set to a low ambient light.
///
/// # Examples
///
/// Make ambient light slightly brighter:
///
/// ```
/// # use bevy_ecs::system::ResMut;
/// # use bevy_pbr::AmbientLight;
/// fn setup_ambient_light(mut ambient_light: ResMut<AmbientLight>) {
///    ambient_light.brightness = 100.0;
/// }
/// ```
#[derive(Resource, Clone, Debug, ExtractResource, Reflect)]
#[reflect(Resource)]
pub struct AmbientLight {
    pub color: Color,
    /// A direct scale factor multiplied with `color` before being passed to the shader.
    pub brightness: f32,
}

impl Default for AmbientLight {
    fn default() -> Self {
        Self {
            color: Color::WHITE,
            brightness: 80.0,
        }
    }
}
impl AmbientLight {
    pub const NONE: AmbientLight = AmbientLight {
        color: Color::WHITE,
        brightness: 0.0,
    };
}

/// Add this component to make a [`Mesh`](bevy_render::mesh::Mesh) not cast shadows.
#[derive(Component, Reflect, Default)]
#[reflect(Component, Default)]
pub struct NotShadowCaster;
/// Add this component to make a [`Mesh`](bevy_render::mesh::Mesh) not receive shadows.
///
/// **Note:** If you're using diffuse transmission, setting [`NotShadowReceiver`] will
/// cause both “regular” shadows as well as diffusely transmitted shadows to be disabled,
/// even when [`TransmittedShadowReceiver`] is being used.
#[derive(Component, Reflect, Default)]
#[reflect(Component, Default)]
pub struct NotShadowReceiver;
/// Add this component to make a [`Mesh`](bevy_render::mesh::Mesh) using a PBR material with [`diffuse_transmission`](crate::pbr_material::StandardMaterial::diffuse_transmission)`> 0.0`
/// receive shadows on its diffuse transmission lobe. (i.e. its “backside”)
///
/// Not enabled by default, as it requires carefully setting up [`thickness`](crate::pbr_material::StandardMaterial::thickness)
/// (and potentially even baking a thickness texture!) to match the geometry of the mesh, in order to avoid self-shadow artifacts.
///
/// **Note:** Using [`NotShadowReceiver`] overrides this component.
#[derive(Component, Reflect, Default)]
#[reflect(Component, Default)]
pub struct TransmittedShadowReceiver;

/// Add this component to a [`Camera3d`](bevy_core_pipeline::core_3d::Camera3d)
/// to control how to anti-alias shadow edges.
///
/// The different modes use different approaches to
/// [Percentage Closer Filtering](https://developer.nvidia.com/gpugems/gpugems/part-ii-lighting-and-shadows/chapter-11-shadow-map-antialiasing).
///
/// Currently does not affect point lights.
#[derive(Component, ExtractComponent, Reflect, Clone, Copy, PartialEq, Eq, Default)]
#[reflect(Component, Default)]
pub enum ShadowFilteringMethod {
    /// Hardware 2x2.
    ///
    /// Fast but poor quality.
    Hardware2x2,
    /// Method by Ignacio Castaño for The Witness using 9 samples and smart
    /// filtering to achieve the same as a regular 5x5 filter kernel.
    ///
    /// Good quality, good performance.
    #[default]
    Castano13,
    /// Method by Jorge Jimenez for Call of Duty: Advanced Warfare using 8
    /// samples in spiral pattern, randomly-rotated by interleaved gradient
    /// noise with spatial variation.
    ///
    /// Good quality when used with
    /// [`TemporalAntiAliasSettings`](bevy_core_pipeline::experimental::taa::TemporalAntiAliasSettings)
    /// and good performance.
    Jimenez14,
}

#[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
pub enum SimulationLightSystems {
    AddClusters,
    AssignLightsToClusters,
    UpdateDirectionalLightCascades,
    UpdateLightFrusta,
    CheckLightVisibility,
}

// Clustered-forward rendering notes
// The main initial reference material used was this rather accessible article:
// http://www.aortiz.me/2018/12/21/CG.html
// Some inspiration was taken from “Practical Clustered Shading” which is part 2 of:
// https://efficientshading.com/2015/01/01/real-time-many-light-management-and-shadows-with-clustered-shading/
// (Also note that Part 3 of the above shows how we could support the shadow mapping for many lights.)
// The z-slicing method mentioned in the aortiz article is originally from Tiago Sousa's Siggraph 2016 talk about Doom 2016:
// http://advances.realtimerendering.com/s2016/Siggraph2016_idTech6.pdf

/// Configure the far z-plane mode used for the furthest depth slice for clustered forward
/// rendering
#[derive(Debug, Copy, Clone, Reflect)]
pub enum ClusterFarZMode {
    /// Calculate the required maximum z-depth based on currently visible lights.
    /// Makes better use of available clusters, speeding up GPU lighting operations
    /// at the expense of some CPU time and using more indices in the cluster light
    /// index lists.
    MaxLightRange,
    /// Constant max z-depth
    Constant(f32),
}

/// Configure the depth-slicing strategy for clustered forward rendering
#[derive(Debug, Copy, Clone, Reflect)]
#[reflect(Default)]
pub struct ClusterZConfig {
    /// Far `Z` plane of the first depth slice
    pub first_slice_depth: f32,
    /// Strategy for how to evaluate the far `Z` plane of the furthest depth slice
    pub far_z_mode: ClusterFarZMode,
}

impl Default for ClusterZConfig {
    fn default() -> Self {
        Self {
            first_slice_depth: 5.0,
            far_z_mode: ClusterFarZMode::MaxLightRange,
        }
    }
}

/// Configuration of the clustering strategy for clustered forward rendering
#[derive(Debug, Copy, Clone, Component, Reflect)]
#[reflect(Component)]
pub enum ClusterConfig {
    /// Disable light cluster calculations for this view
    None,
    /// One single cluster. Optimal for low-light complexity scenes or scenes where
    /// most lights affect the entire scene.
    Single,
    /// Explicit `X`, `Y` and `Z` counts (may yield non-square `X/Y` clusters depending on the aspect ratio)
    XYZ {
        dimensions: UVec3,
        z_config: ClusterZConfig,
        /// Specify if clusters should automatically resize in `X/Y` if there is a risk of exceeding
        /// the available cluster-light index limit
        dynamic_resizing: bool,
    },
    /// Fixed number of `Z` slices, `X` and `Y` calculated to give square clusters
    /// with at most total clusters. For top-down games where lights will generally always be within a
    /// short depth range, it may be useful to use this configuration with 1 or few `Z` slices. This
    /// would reduce the number of lights per cluster by distributing more clusters in screen space
    /// `X/Y` which matches how lights are distributed in the scene.
    FixedZ {
        total: u32,
        z_slices: u32,
        z_config: ClusterZConfig,
        /// Specify if clusters should automatically resize in `X/Y` if there is a risk of exceeding
        /// the available cluster-light index limit
        dynamic_resizing: bool,
    },
}

impl Default for ClusterConfig {
    fn default() -> Self {
        // 24 depth slices, square clusters with at most 4096 total clusters
        // use max light distance as clusters max `Z`-depth, first slice extends to 5.0
        Self::FixedZ {
            total: 4096,
            z_slices: 24,
            z_config: ClusterZConfig::default(),
            dynamic_resizing: true,
        }
    }
}

impl ClusterConfig {
    fn dimensions_for_screen_size(&self, screen_size: UVec2) -> UVec3 {
        match &self {
            ClusterConfig::None => UVec3::ZERO,
            ClusterConfig::Single => UVec3::ONE,
            ClusterConfig::XYZ { dimensions, .. } => *dimensions,
            ClusterConfig::FixedZ {
                total, z_slices, ..
            } => {
                let aspect_ratio: f32 =
                    AspectRatio::from_pixels(screen_size.x, screen_size.y).into();
                let mut z_slices = *z_slices;
                if *total < z_slices {
                    warn!("ClusterConfig has more z-slices than total clusters!");
                    z_slices = *total;
                }
                let per_layer = *total as f32 / z_slices as f32;

                let y = f32::sqrt(per_layer / aspect_ratio);

                let mut x = (y * aspect_ratio) as u32;
                let mut y = y as u32;

                // check extremes
                if x == 0 {
                    x = 1;
                    y = per_layer as u32;
                }
                if y == 0 {
                    x = per_layer as u32;
                    y = 1;
                }

                UVec3::new(x, y, z_slices)
            }
        }
    }

    fn first_slice_depth(&self) -> f32 {
        match self {
            ClusterConfig::None | ClusterConfig::Single => 0.0,
            ClusterConfig::XYZ { z_config, .. } | ClusterConfig::FixedZ { z_config, .. } => {
                z_config.first_slice_depth
            }
        }
    }

    fn far_z_mode(&self) -> ClusterFarZMode {
        match self {
            ClusterConfig::None => ClusterFarZMode::Constant(0.0),
            ClusterConfig::Single => ClusterFarZMode::MaxLightRange,
            ClusterConfig::XYZ { z_config, .. } | ClusterConfig::FixedZ { z_config, .. } => {
                z_config.far_z_mode
            }
        }
    }

    fn dynamic_resizing(&self) -> bool {
        match self {
            ClusterConfig::None | ClusterConfig::Single => false,
            ClusterConfig::XYZ {
                dynamic_resizing, ..
            }
            | ClusterConfig::FixedZ {
                dynamic_resizing, ..
            } => *dynamic_resizing,
        }
    }
}

#[derive(Component, Debug, Default)]
pub struct Clusters {
    /// Tile size
    pub(crate) tile_size: UVec2,
    /// Number of clusters in `X` / `Y` / `Z` in the view frustum
    pub(crate) dimensions: UVec3,
    /// Distance to the far plane of the first depth slice. The first depth slice is special
    /// and explicitly-configured to avoid having unnecessarily many slices close to the camera.
    pub(crate) near: f32,
    pub(crate) far: f32,
    pub(crate) lights: Vec<VisiblePointLights>,
}

impl Clusters {
    fn update(&mut self, screen_size: UVec2, requested_dimensions: UVec3) {
        debug_assert!(
            requested_dimensions.x > 0 && requested_dimensions.y > 0 && requested_dimensions.z > 0
        );

        let tile_size = (screen_size.as_vec2() / requested_dimensions.xy().as_vec2())
            .ceil()
            .as_uvec2()
            .max(UVec2::ONE);
        self.tile_size = tile_size;
        self.dimensions = (screen_size.as_vec2() / tile_size.as_vec2())
            .ceil()
            .as_uvec2()
            .extend(requested_dimensions.z)
            .max(UVec3::ONE);

        // NOTE: Maximum 4096 clusters due to uniform buffer size constraints
        debug_assert!(self.dimensions.x * self.dimensions.y * self.dimensions.z <= 4096);
    }
    fn clear(&mut self) {
        self.tile_size = UVec2::ONE;
        self.dimensions = UVec3::ZERO;
        self.near = 0.0;
        self.far = 0.0;
        self.lights.clear();
    }
}

fn clip_to_view(inverse_projection: Mat4, clip: Vec4) -> Vec4 {
    let view = inverse_projection * clip;
    view / view.w
}

pub fn add_clusters(
    mut commands: Commands,
    cameras: Query<(Entity, Option<&ClusterConfig>, &Camera), Without<Clusters>>,
) {
    for (entity, config, camera) in &cameras {
        if !camera.is_active {
            continue;
        }

        let config = config.copied().unwrap_or_default();
        // actual settings here don't matter - they will be overwritten in assign_lights_to_clusters
        commands
            .entity(entity)
            .insert((Clusters::default(), config));
    }
}

#[derive(Clone, Component, Debug, Default)]
pub struct VisiblePointLights {
    pub(crate) entities: Vec<Entity>,
    pub point_light_count: usize,
    pub spot_light_count: usize,
}

impl VisiblePointLights {
    #[inline]
    pub fn iter(&self) -> impl DoubleEndedIterator<Item = &Entity> {
        self.entities.iter()
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.entities.len()
    }

    #[inline]
    pub fn is_empty(&self) -> bool {
        self.entities.is_empty()
    }
}

// NOTE: Keep in sync with bevy_pbr/src/render/pbr.wgsl
fn view_z_to_z_slice(
    cluster_factors: Vec2,
    z_slices: u32,
    view_z: f32,
    is_orthographic: bool,
) -> u32 {
    let z_slice = if is_orthographic {
        // NOTE: view_z is correct in the orthographic case
        ((view_z - cluster_factors.x) * cluster_factors.y).floor() as u32
    } else {
        // NOTE: had to use -view_z to make it positive else log(negative) is nan
        ((-view_z).ln() * cluster_factors.x - cluster_factors.y + 1.0) as u32
    };
    // NOTE: We use min as we may limit the far z plane used for clustering to be closer than
    // the furthest thing being drawn. This means that we need to limit to the maximum cluster.
    z_slice.min(z_slices - 1)
}

// NOTE: Keep in sync as the inverse of view_z_to_z_slice above
fn z_slice_to_view_z(
    near: f32,
    far: f32,
    z_slices: u32,
    z_slice: u32,
    is_orthographic: bool,
) -> f32 {
    if is_orthographic {
        return -near - (far - near) * z_slice as f32 / z_slices as f32;
    }

    // Perspective
    if z_slice == 0 {
        0.0
    } else {
        -near * (far / near).powf((z_slice - 1) as f32 / (z_slices - 1) as f32)
    }
}

fn ndc_position_to_cluster(
    cluster_dimensions: UVec3,
    cluster_factors: Vec2,
    is_orthographic: bool,
    ndc_p: Vec3,
    view_z: f32,
) -> UVec3 {
    let cluster_dimensions_f32 = cluster_dimensions.as_vec3();
    let frag_coord = (ndc_p.xy() * VEC2_HALF_NEGATIVE_Y + VEC2_HALF).clamp(Vec2::ZERO, Vec2::ONE);
    let xy = (frag_coord * cluster_dimensions_f32.xy()).floor();
    let z_slice = view_z_to_z_slice(
        cluster_factors,
        cluster_dimensions.z,
        view_z,
        is_orthographic,
    );
    xy.as_uvec2()
        .extend(z_slice)
        .clamp(UVec3::ZERO, cluster_dimensions - UVec3::ONE)
}

const VEC2_HALF: Vec2 = Vec2::splat(0.5);
const VEC2_HALF_NEGATIVE_Y: Vec2 = Vec2::new(0.5, -0.5);

/// Calculate bounds for the light using a view space aabb.
/// Returns a `(Vec3, Vec3)` containing minimum and maximum with
///     `X` and `Y` in normalized device coordinates with range `[-1, 1]`
///     `Z` in view space, with range `[-inf, -f32::MIN_POSITIVE]`
fn cluster_space_light_aabb(
    inverse_view_transform: Mat4,
    view_inv_scale: Vec3,
    projection_matrix: Mat4,
    light_sphere: &Sphere,
) -> (Vec3, Vec3) {
    let light_aabb_view = Aabb {
        center: Vec3A::from(inverse_view_transform * light_sphere.center.extend(1.0)),
        half_extents: Vec3A::from(light_sphere.radius * view_inv_scale.abs()),
    };
    let (mut light_aabb_view_min, mut light_aabb_view_max) =
        (light_aabb_view.min(), light_aabb_view.max());

    // Constrain view z to be negative - i.e. in front of the camera
    // When view z is >= 0.0 and we're using a perspective projection, bad things happen.
    // At view z == 0.0, ndc x,y are mathematically undefined. At view z > 0.0, i.e. behind the camera,
    // the perspective projection flips the directions of the axes. This breaks assumptions about
    // use of min/max operations as something that was to the left in view space is now returning a
    // coordinate that for view z in front of the camera would be on the right, but at view z behind the
    // camera is on the left. So, we just constrain view z to be < 0.0 and necessarily in front of the camera.
    light_aabb_view_min.z = light_aabb_view_min.z.min(-f32::MIN_POSITIVE);
    light_aabb_view_max.z = light_aabb_view_max.z.min(-f32::MIN_POSITIVE);

    // Is there a cheaper way to do this? The problem is that because of perspective
    // the point at max z but min xy may be less xy in screenspace, and similar. As
    // such, projecting the min and max xy at both the closer and further z and taking
    // the min and max of those projected points addresses this.
    let (
        light_aabb_view_xymin_near,
        light_aabb_view_xymin_far,
        light_aabb_view_xymax_near,
        light_aabb_view_xymax_far,
    ) = (
        light_aabb_view_min,
        light_aabb_view_min.xy().extend(light_aabb_view_max.z),
        light_aabb_view_max.xy().extend(light_aabb_view_min.z),
        light_aabb_view_max,
    );
    let (
        light_aabb_clip_xymin_near,
        light_aabb_clip_xymin_far,
        light_aabb_clip_xymax_near,
        light_aabb_clip_xymax_far,
    ) = (
        projection_matrix * light_aabb_view_xymin_near.extend(1.0),
        projection_matrix * light_aabb_view_xymin_far.extend(1.0),
        projection_matrix * light_aabb_view_xymax_near.extend(1.0),
        projection_matrix * light_aabb_view_xymax_far.extend(1.0),
    );
    let (
        light_aabb_ndc_xymin_near,
        light_aabb_ndc_xymin_far,
        light_aabb_ndc_xymax_near,
        light_aabb_ndc_xymax_far,
    ) = (
        light_aabb_clip_xymin_near.xyz() / light_aabb_clip_xymin_near.w,
        light_aabb_clip_xymin_far.xyz() / light_aabb_clip_xymin_far.w,
        light_aabb_clip_xymax_near.xyz() / light_aabb_clip_xymax_near.w,
        light_aabb_clip_xymax_far.xyz() / light_aabb_clip_xymax_far.w,
    );
    let (light_aabb_ndc_min, light_aabb_ndc_max) = (
        light_aabb_ndc_xymin_near
            .min(light_aabb_ndc_xymin_far)
            .min(light_aabb_ndc_xymax_near)
            .min(light_aabb_ndc_xymax_far),
        light_aabb_ndc_xymin_near
            .max(light_aabb_ndc_xymin_far)
            .max(light_aabb_ndc_xymax_near)
            .max(light_aabb_ndc_xymax_far),
    );

    // clamp to ndc coords without depth
    let (aabb_min_ndc, aabb_max_ndc) = (
        light_aabb_ndc_min.xy().clamp(NDC_MIN, NDC_MAX),
        light_aabb_ndc_max.xy().clamp(NDC_MIN, NDC_MAX),
    );

    // pack unadjusted z depth into the vecs
    (
        aabb_min_ndc.extend(light_aabb_view_min.z),
        aabb_max_ndc.extend(light_aabb_view_max.z),
    )
}

fn screen_to_view(screen_size: Vec2, inverse_projection: Mat4, screen: Vec2, ndc_z: f32) -> Vec4 {
    let tex_coord = screen / screen_size;
    let clip = Vec4::new(
        tex_coord.x * 2.0 - 1.0,
        (1.0 - tex_coord.y) * 2.0 - 1.0,
        ndc_z,
        1.0,
    );
    clip_to_view(inverse_projection, clip)
}
const NDC_MIN: Vec2 = Vec2::NEG_ONE;
const NDC_MAX: Vec2 = Vec2::ONE;

// Calculate the intersection of a ray from the eye through the view space position to a z plane
fn line_intersection_to_z_plane(origin: Vec3, p: Vec3, z: f32) -> Vec3 {
    let v = p - origin;
    let t = (z - Vec3::Z.dot(origin)) / Vec3::Z.dot(v);
    origin + t * v
}

#[allow(clippy::too_many_arguments)]
fn compute_aabb_for_cluster(
    z_near: f32,
    z_far: f32,
    tile_size: Vec2,
    screen_size: Vec2,
    inverse_projection: Mat4,
    is_orthographic: bool,
    cluster_dimensions: UVec3,
    ijk: UVec3,
) -> Aabb {
    let ijk = ijk.as_vec3();

    // Calculate the minimum and maximum points in screen space
    let p_min = ijk.xy() * tile_size;
    let p_max = p_min + tile_size;

    let cluster_min;
    let cluster_max;
    if is_orthographic {
        // Use linear depth slicing for orthographic

        // Convert to view space at the cluster near and far planes
        // NOTE: 1.0 is the near plane due to using reverse z projections
        let mut p_min = screen_to_view(screen_size, inverse_projection, p_min, 0.0).xyz();
        let mut p_max = screen_to_view(screen_size, inverse_projection, p_max, 0.0).xyz();

        // calculate cluster depth using z_near and z_far
        p_min.z = -z_near + (z_near - z_far) * ijk.z / cluster_dimensions.z as f32;
        p_max.z = -z_near + (z_near - z_far) * (ijk.z + 1.0) / cluster_dimensions.z as f32;

        cluster_min = p_min.min(p_max);
        cluster_max = p_min.max(p_max);
    } else {
        // Convert to view space at the near plane
        // NOTE: 1.0 is the near plane due to using reverse z projections
        let p_min = screen_to_view(screen_size, inverse_projection, p_min, 1.0);
        let p_max = screen_to_view(screen_size, inverse_projection, p_max, 1.0);

        let z_far_over_z_near = -z_far / -z_near;
        let cluster_near = if ijk.z == 0.0 {
            0.0
        } else {
            -z_near * z_far_over_z_near.powf((ijk.z - 1.0) / (cluster_dimensions.z - 1) as f32)
        };
        // NOTE: This could be simplified to:
        // cluster_far = cluster_near * z_far_over_z_near;
        let cluster_far = if cluster_dimensions.z == 1 {
            -z_far
        } else {
            -z_near * z_far_over_z_near.powf(ijk.z / (cluster_dimensions.z - 1) as f32)
        };

        // Calculate the four intersection points of the min and max points with the cluster near and far planes
        let p_min_near = line_intersection_to_z_plane(Vec3::ZERO, p_min.xyz(), cluster_near);
        let p_min_far = line_intersection_to_z_plane(Vec3::ZERO, p_min.xyz(), cluster_far);
        let p_max_near = line_intersection_to_z_plane(Vec3::ZERO, p_max.xyz(), cluster_near);
        let p_max_far = line_intersection_to_z_plane(Vec3::ZERO, p_max.xyz(), cluster_far);

        cluster_min = p_min_near.min(p_min_far).min(p_max_near.min(p_max_far));
        cluster_max = p_min_near.max(p_min_far).max(p_max_near.max(p_max_far));
    }

    Aabb::from_min_max(cluster_min, cluster_max)
}

// Sort lights by
// - point-light vs spot-light, so that we can iterate point lights and spot lights in contiguous blocks in the fragment shader,
// - then those with shadows enabled first, so that the index can be used to render at most `point_light_shadow_maps_count`
//   point light shadows and `spot_light_shadow_maps_count` spot light shadow maps,
// - then by entity as a stable key to ensure that a consistent set of lights are chosen if the light count limit is exceeded.
pub(crate) fn point_light_order(
    (entity_1, shadows_enabled_1, is_spot_light_1): (&Entity, &bool, &bool),
    (entity_2, shadows_enabled_2, is_spot_light_2): (&Entity, &bool, &bool),
) -> std::cmp::Ordering {
    is_spot_light_1
        .cmp(is_spot_light_2) // pointlights before spot lights
        .then_with(|| shadows_enabled_2.cmp(shadows_enabled_1)) // shadow casters before non-casters
        .then_with(|| entity_1.cmp(entity_2)) // stable
}

// Sort lights by
// - those with shadows enabled first, so that the index can be used to render at most `directional_light_shadow_maps_count`
//   directional light shadows
// - then by entity as a stable key to ensure that a consistent set of lights are chosen if the light count limit is exceeded.
pub(crate) fn directional_light_order(
    (entity_1, shadows_enabled_1): (&Entity, &bool),
    (entity_2, shadows_enabled_2): (&Entity, &bool),
) -> std::cmp::Ordering {
    shadows_enabled_2
        .cmp(shadows_enabled_1) // shadow casters before non-casters
        .then_with(|| entity_1.cmp(entity_2)) // stable
}

#[derive(Clone, Copy)]
// data required for assigning lights to clusters
pub(crate) struct PointLightAssignmentData {
    entity: Entity,
    transform: GlobalTransform,
    range: f32,
    shadows_enabled: bool,
    spot_light_angle: Option<f32>,
    render_layers: RenderLayers,
}

impl PointLightAssignmentData {
    pub fn sphere(&self) -> Sphere {
        Sphere {
            center: self.transform.translation_vec3a(),
            radius: self.range,
        }
    }
}

#[derive(Resource, Default)]
pub struct GlobalVisiblePointLights {
    entities: HashSet<Entity>,
}

impl GlobalVisiblePointLights {
    #[inline]
    pub fn iter(&self) -> impl Iterator<Item = &Entity> {
        self.entities.iter()
    }

    #[inline]
    pub fn contains(&self, entity: Entity) -> bool {
        self.entities.contains(&entity)
    }
}

// NOTE: Run this before update_point_light_frusta!
#[allow(clippy::too_many_arguments)]
pub(crate) fn assign_lights_to_clusters(
    mut commands: Commands,
    mut global_lights: ResMut<GlobalVisiblePointLights>,
    mut views: Query<(
        Entity,
        &GlobalTransform,
        &Camera,
        &Frustum,
        &ClusterConfig,
        &mut Clusters,
        Option<&RenderLayers>,
        Option<&mut VisiblePointLights>,
    )>,
    point_lights_query: Query<(
        Entity,
        &GlobalTransform,
        &PointLight,
        Option<&RenderLayers>,
        &ViewVisibility,
    )>,
    spot_lights_query: Query<(
        Entity,
        &GlobalTransform,
        &SpotLight,
        Option<&RenderLayers>,
        &ViewVisibility,
    )>,
    mut lights: Local<Vec<PointLightAssignmentData>>,
    mut cluster_aabb_spheres: Local<Vec<Option<Sphere>>>,
    mut max_point_lights_warning_emitted: Local<bool>,
    render_device: Option<Res<RenderDevice>>,
) {
    let Some(render_device) = render_device else {
        return;
    };

    global_lights.entities.clear();
    lights.clear();
    // collect just the relevant light query data into a persisted vec to avoid reallocating each frame
    lights.extend(
        point_lights_query
            .iter()
            .filter(|(.., visibility)| visibility.get())
            .map(
                |(entity, transform, point_light, maybe_layers, _visibility)| {
                    PointLightAssignmentData {
                        entity,
                        transform: GlobalTransform::from_translation(transform.translation()),
                        shadows_enabled: point_light.shadows_enabled,
                        range: point_light.range,
                        spot_light_angle: None,
                        render_layers: maybe_layers.copied().unwrap_or_default(),
                    }
                },
            ),
    );
    lights.extend(
        spot_lights_query
            .iter()
            .filter(|(.., visibility)| visibility.get())
            .map(
                |(entity, transform, spot_light, maybe_layers, _visibility)| {
                    PointLightAssignmentData {
                        entity,
                        transform: *transform,
                        shadows_enabled: spot_light.shadows_enabled,
                        range: spot_light.range,
                        spot_light_angle: Some(spot_light.outer_angle),
                        render_layers: maybe_layers.copied().unwrap_or_default(),
                    }
                },
            ),
    );

    let clustered_forward_buffer_binding_type =
        render_device.get_supported_read_only_binding_type(CLUSTERED_FORWARD_STORAGE_BUFFER_COUNT);
    let supports_storage_buffers = matches!(
        clustered_forward_buffer_binding_type,
        BufferBindingType::Storage { .. }
    );
    if lights.len() > MAX_UNIFORM_BUFFER_POINT_LIGHTS && !supports_storage_buffers {
        lights.sort_by(|light_1, light_2| {
            point_light_order(
                (
                    &light_1.entity,
                    &light_1.shadows_enabled,
                    &light_1.spot_light_angle.is_some(),
                ),
                (
                    &light_2.entity,
                    &light_2.shadows_enabled,
                    &light_2.spot_light_angle.is_some(),
                ),
            )
        });

        // check each light against each view's frustum, keep only those that affect at least one of our views
        let frusta: Vec<_> = views
            .iter()
            .map(|(_, _, _, frustum, _, _, _, _)| *frustum)
            .collect();
        let mut lights_in_view_count = 0;
        lights.retain(|light| {
            // take one extra light to check if we should emit the warning
            if lights_in_view_count == MAX_UNIFORM_BUFFER_POINT_LIGHTS + 1 {
                false
            } else {
                let light_sphere = light.sphere();
                let light_in_view = frusta
                    .iter()
                    .any(|frustum| frustum.intersects_sphere(&light_sphere, true));

                if light_in_view {
                    lights_in_view_count += 1;
                }

                light_in_view
            }
        });

        if lights.len() > MAX_UNIFORM_BUFFER_POINT_LIGHTS && !*max_point_lights_warning_emitted {
            warn!(
                "MAX_UNIFORM_BUFFER_POINT_LIGHTS ({}) exceeded",
                MAX_UNIFORM_BUFFER_POINT_LIGHTS
            );
            *max_point_lights_warning_emitted = true;
        }

        lights.truncate(MAX_UNIFORM_BUFFER_POINT_LIGHTS);
    }

    for (
        view_entity,
        camera_transform,
        camera,
        frustum,
        config,
        clusters,
        maybe_layers,
        mut visible_lights,
    ) in &mut views
    {
        let view_layers = maybe_layers.copied().unwrap_or_default();
        let clusters = clusters.into_inner();

        if matches!(config, ClusterConfig::None) {
            if visible_lights.is_some() {
                commands.entity(view_entity).remove::<VisiblePointLights>();
            }
            clusters.clear();
            continue;
        }

        let Some(screen_size) = camera.physical_viewport_size() else {
            clusters.clear();
            continue;
        };

        let mut requested_cluster_dimensions = config.dimensions_for_screen_size(screen_size);

        let view_transform = camera_transform.compute_matrix();
        let view_inv_scale = camera_transform.compute_transform().scale.recip();
        let view_inv_scale_max = view_inv_scale.abs().max_element();
        let inverse_view_transform = view_transform.inverse();
        let is_orthographic = camera.projection_matrix().w_axis.w == 1.0;

        let far_z = match config.far_z_mode() {
            ClusterFarZMode::MaxLightRange => {
                let inverse_view_row_2 = inverse_view_transform.row(2);
                lights
                    .iter()
                    .map(|light| {
                        -inverse_view_row_2.dot(light.transform.translation().extend(1.0))
                            + light.range * view_inv_scale.z
                    })
                    .reduce(f32::max)
                    .unwrap_or(0.0)
            }
            ClusterFarZMode::Constant(far) => far,
        };
        let first_slice_depth = match (is_orthographic, requested_cluster_dimensions.z) {
            (true, _) => {
                // NOTE: Based on glam's Mat4::orthographic_rh(), as used to calculate the orthographic projection
                // matrix, we can calculate the projection's view-space near plane as follows:
                // component 3,2 = r * near and 2,2 = r where r = 1.0 / (near - far)
                // There is a caveat here that when calculating the projection matrix, near and far were swapped to give
                // reversed z, consistent with the perspective projection. So,
                // 3,2 = r * far and 2,2 = r where r = 1.0 / (far - near)
                // rearranging r = 1.0 / (far - near), r * (far - near) = 1.0, r * far - 1.0 = r * near, near = (r * far - 1.0) / r
                // = (3,2 - 1.0) / 2,2
                (camera.projection_matrix().w_axis.z - 1.0) / camera.projection_matrix().z_axis.z
            }
            (false, 1) => config.first_slice_depth().max(far_z),
            _ => config.first_slice_depth(),
        };
        let first_slice_depth = first_slice_depth * view_inv_scale.z;

        // NOTE: Ensure the far_z is at least as far as the first_depth_slice to avoid clustering problems.
        let far_z = far_z.max(first_slice_depth);
        let cluster_factors = calculate_cluster_factors(
            first_slice_depth,
            far_z,
            requested_cluster_dimensions.z as f32,
            is_orthographic,
        );

        if config.dynamic_resizing() {
            let mut cluster_index_estimate = 0.0;
            for light in &lights {
                let light_sphere = light.sphere();

                // Check if the light is within the view frustum
                if !frustum.intersects_sphere(&light_sphere, true) {
                    continue;
                }

                // calculate a conservative aabb estimate of number of clusters affected by this light
                // this overestimates index counts by at most 50% (and typically much less) when the whole light range is in view
                // it can overestimate more significantly when light ranges are only partially in view
                let (light_aabb_min, light_aabb_max) = cluster_space_light_aabb(
                    inverse_view_transform,
                    view_inv_scale,
                    camera.projection_matrix(),
                    &light_sphere,
                );

                // since we won't adjust z slices we can calculate exact number of slices required in z dimension
                let z_cluster_min = view_z_to_z_slice(
                    cluster_factors,
                    requested_cluster_dimensions.z,
                    light_aabb_min.z,
                    is_orthographic,
                );
                let z_cluster_max = view_z_to_z_slice(
                    cluster_factors,
                    requested_cluster_dimensions.z,
                    light_aabb_max.z,
                    is_orthographic,
                );
                let z_count =
                    z_cluster_min.max(z_cluster_max) - z_cluster_min.min(z_cluster_max) + 1;

                // calculate x/y count using floats to avoid overestimating counts due to large initial tile sizes
                let xy_min = light_aabb_min.xy();
                let xy_max = light_aabb_max.xy();
                // multiply by 0.5 to move from [-1,1] to [-0.5, 0.5], max extent of 1 in each dimension
                let xy_count = (xy_max - xy_min)
                    * 0.5
                    * Vec2::new(
                        requested_cluster_dimensions.x as f32,
                        requested_cluster_dimensions.y as f32,
                    );

                // add up to 2 to each axis to account for overlap
                let x_overlap = if xy_min.x <= -1.0 { 0.0 } else { 1.0 }
                    + if xy_max.x >= 1.0 { 0.0 } else { 1.0 };
                let y_overlap = if xy_min.y <= -1.0 { 0.0 } else { 1.0 }
                    + if xy_max.y >= 1.0 { 0.0 } else { 1.0 };
                cluster_index_estimate +=
                    (xy_count.x + x_overlap) * (xy_count.y + y_overlap) * z_count as f32;
            }

            if cluster_index_estimate > ViewClusterBindings::MAX_INDICES as f32 {
                // scale x and y cluster count to be able to fit all our indices

                // we take the ratio of the actual indices over the index estimate.
                // this not not guaranteed to be small enough due to overlapped tiles, but
                // the conservative estimate is more than sufficient to cover the
                // difference
                let index_ratio = ViewClusterBindings::MAX_INDICES as f32 / cluster_index_estimate;
                let xy_ratio = index_ratio.sqrt();

                requested_cluster_dimensions.x =
                    ((requested_cluster_dimensions.x as f32 * xy_ratio).floor() as u32).max(1);
                requested_cluster_dimensions.y =
                    ((requested_cluster_dimensions.y as f32 * xy_ratio).floor() as u32).max(1);
            }
        }

        clusters.update(screen_size, requested_cluster_dimensions);
        clusters.near = first_slice_depth;
        clusters.far = far_z;

        // NOTE: Maximum 4096 clusters due to uniform buffer size constraints
        debug_assert!(
            clusters.dimensions.x * clusters.dimensions.y * clusters.dimensions.z <= 4096
        );

        let inverse_projection = camera.projection_matrix().inverse();

        for lights in &mut clusters.lights {
            lights.entities.clear();
            lights.point_light_count = 0;
            lights.spot_light_count = 0;
        }
        let cluster_count =
            (clusters.dimensions.x * clusters.dimensions.y * clusters.dimensions.z) as usize;
        clusters
            .lights
            .resize_with(cluster_count, VisiblePointLights::default);

        // initialize empty cluster bounding spheres
        cluster_aabb_spheres.clear();
        cluster_aabb_spheres.extend(std::iter::repeat(None).take(cluster_count));

        // Calculate the x/y/z cluster frustum planes in view space
        let mut x_planes = Vec::with_capacity(clusters.dimensions.x as usize + 1);
        let mut y_planes = Vec::with_capacity(clusters.dimensions.y as usize + 1);
        let mut z_planes = Vec::with_capacity(clusters.dimensions.z as usize + 1);

        if is_orthographic {
            let x_slices = clusters.dimensions.x as f32;
            for x in 0..=clusters.dimensions.x {
                let x_proportion = x as f32 / x_slices;
                let x_pos = x_proportion * 2.0 - 1.0;
                let view_x = clip_to_view(inverse_projection, Vec4::new(x_pos, 0.0, 1.0, 1.0)).x;
                let normal = Vec3::X;
                let d = view_x * normal.x;
                x_planes.push(HalfSpace::new(normal.extend(d)));
            }

            let y_slices = clusters.dimensions.y as f32;
            for y in 0..=clusters.dimensions.y {
                let y_proportion = 1.0 - y as f32 / y_slices;
                let y_pos = y_proportion * 2.0 - 1.0;
                let view_y = clip_to_view(inverse_projection, Vec4::new(0.0, y_pos, 1.0, 1.0)).y;
                let normal = Vec3::Y;
                let d = view_y * normal.y;
                y_planes.push(HalfSpace::new(normal.extend(d)));
            }
        } else {
            let x_slices = clusters.dimensions.x as f32;
            for x in 0..=clusters.dimensions.x {
                let x_proportion = x as f32 / x_slices;
                let x_pos = x_proportion * 2.0 - 1.0;
                let nb = clip_to_view(inverse_projection, Vec4::new(x_pos, -1.0, 1.0, 1.0)).xyz();
                let nt = clip_to_view(inverse_projection, Vec4::new(x_pos, 1.0, 1.0, 1.0)).xyz();
                let normal = nb.cross(nt);
                let d = nb.dot(normal);
                x_planes.push(HalfSpace::new(normal.extend(d)));
            }

            let y_slices = clusters.dimensions.y as f32;
            for y in 0..=clusters.dimensions.y {
                let y_proportion = 1.0 - y as f32 / y_slices;
                let y_pos = y_proportion * 2.0 - 1.0;
                let nl = clip_to_view(inverse_projection, Vec4::new(-1.0, y_pos, 1.0, 1.0)).xyz();
                let nr = clip_to_view(inverse_projection, Vec4::new(1.0, y_pos, 1.0, 1.0)).xyz();
                let normal = nr.cross(nl);
                let d = nr.dot(normal);
                y_planes.push(HalfSpace::new(normal.extend(d)));
            }
        }

        let z_slices = clusters.dimensions.z;
        for z in 0..=z_slices {
            let view_z = z_slice_to_view_z(first_slice_depth, far_z, z_slices, z, is_orthographic);
            let normal = -Vec3::Z;
            let d = view_z * normal.z;
            z_planes.push(HalfSpace::new(normal.extend(d)));
        }

        let mut update_from_light_intersections = |visible_lights: &mut Vec<Entity>| {
            for light in &lights {
                // check if the light layers overlap the view layers
                if !view_layers.intersects(&light.render_layers) {
                    continue;
                }

                let light_sphere = light.sphere();

                // Check if the light is within the view frustum
                if !frustum.intersects_sphere(&light_sphere, true) {
                    continue;
                }

                // NOTE: The light intersects the frustum so it must be visible and part of the global set
                global_lights.entities.insert(light.entity);
                visible_lights.push(light.entity);

                // note: caching seems to be slower than calling twice for this aabb calculation
                let (light_aabb_xy_ndc_z_view_min, light_aabb_xy_ndc_z_view_max) =
                    cluster_space_light_aabb(
                        inverse_view_transform,
                        view_inv_scale,
                        camera.projection_matrix(),
                        &light_sphere,
                    );

                let min_cluster = ndc_position_to_cluster(
                    clusters.dimensions,
                    cluster_factors,
                    is_orthographic,
                    light_aabb_xy_ndc_z_view_min,
                    light_aabb_xy_ndc_z_view_min.z,
                );
                let max_cluster = ndc_position_to_cluster(
                    clusters.dimensions,
                    cluster_factors,
                    is_orthographic,
                    light_aabb_xy_ndc_z_view_max,
                    light_aabb_xy_ndc_z_view_max.z,
                );
                let (min_cluster, max_cluster) =
                    (min_cluster.min(max_cluster), min_cluster.max(max_cluster));

                // What follows is the Iterative Sphere Refinement algorithm from Just Cause 3
                // Persson et al, Practical Clustered Shading
                // http://newq.net/dl/pub/s2015_practical.pdf
                // NOTE: A sphere under perspective projection is no longer a sphere. It gets
                // stretched and warped, which prevents simpler algorithms from being correct
                // as they often assume that the widest part of the sphere under projection is the
                // center point on the axis of interest plus the radius, and that is not true!
                let view_light_sphere = Sphere {
                    center: Vec3A::from(inverse_view_transform * light_sphere.center.extend(1.0)),
                    radius: light_sphere.radius * view_inv_scale_max,
                };
                let spot_light_dir_sin_cos = light.spot_light_angle.map(|angle| {
                    let (angle_sin, angle_cos) = angle.sin_cos();
                    (
                        (inverse_view_transform * light.transform.back().extend(0.0))
                            .truncate()
                            .normalize(),
                        angle_sin,
                        angle_cos,
                    )
                });
                let light_center_clip =
                    camera.projection_matrix() * view_light_sphere.center.extend(1.0);
                let light_center_ndc = light_center_clip.xyz() / light_center_clip.w;
                let cluster_coordinates = ndc_position_to_cluster(
                    clusters.dimensions,
                    cluster_factors,
                    is_orthographic,
                    light_center_ndc,
                    view_light_sphere.center.z,
                );
                let z_center = if light_center_ndc.z <= 1.0 {
                    Some(cluster_coordinates.z)
                } else {
                    None
                };
                let y_center = if light_center_ndc.y > 1.0 {
                    None
                } else if light_center_ndc.y < -1.0 {
                    Some(clusters.dimensions.y + 1)
                } else {
                    Some(cluster_coordinates.y)
                };
                for z in min_cluster.z..=max_cluster.z {
                    let mut z_light = view_light_sphere.clone();
                    if z_center.is_none() || z != z_center.unwrap() {
                        // The z plane closer to the light has the larger radius circle where the
                        // light sphere intersects the z plane.
                        let z_plane = if z_center.is_some() && z < z_center.unwrap() {
                            z_planes[(z + 1) as usize]
                        } else {
                            z_planes[z as usize]
                        };
                        // Project the sphere to this z plane and use its radius as the radius of a
                        // new, refined sphere.
                        if let Some(projected) = project_to_plane_z(z_light, z_plane) {
                            z_light = projected;
                        } else {
                            continue;
                        }
                    }
                    for y in min_cluster.y..=max_cluster.y {
                        let mut y_light = z_light.clone();
                        if y_center.is_none() || y != y_center.unwrap() {
                            // The y plane closer to the light has the larger radius circle where the
                            // light sphere intersects the y plane.
                            let y_plane = if y_center.is_some() && y < y_center.unwrap() {
                                y_planes[(y + 1) as usize]
                            } else {
                                y_planes[y as usize]
                            };
                            // Project the refined sphere to this y plane and use its radius as the
                            // radius of a new, even more refined sphere.
                            if let Some(projected) =
                                project_to_plane_y(y_light, y_plane, is_orthographic)
                            {
                                y_light = projected;
                            } else {
                                continue;
                            }
                        }
                        // Loop from the left to find the first affected cluster
                        let mut min_x = min_cluster.x;
                        loop {
                            if min_x >= max_cluster.x
                                || -get_distance_x(
                                    x_planes[(min_x + 1) as usize],
                                    y_light.center,
                                    is_orthographic,
                                ) + y_light.radius
                                    > 0.0
                            {
                                break;
                            }
                            min_x += 1;
                        }
                        // Loop from the right to find the last affected cluster
                        let mut max_x = max_cluster.x;
                        loop {
                            if max_x <= min_x
                                || get_distance_x(
                                    x_planes[max_x as usize],
                                    y_light.center,
                                    is_orthographic,
                                ) + y_light.radius
                                    > 0.0
                            {
                                break;
                            }
                            max_x -= 1;
                        }
                        let mut cluster_index = ((y * clusters.dimensions.x + min_x)
                            * clusters.dimensions.z
                            + z) as usize;

                        if let Some((view_light_direction, angle_sin, angle_cos)) =
                            spot_light_dir_sin_cos
                        {
                            for x in min_x..=max_x {
                                // further culling for spot lights
                                // get or initialize cluster bounding sphere
                                let cluster_aabb_sphere = &mut cluster_aabb_spheres[cluster_index];
                                let cluster_aabb_sphere = if let Some(sphere) = cluster_aabb_sphere
                                {
                                    &*sphere
                                } else {
                                    let aabb = compute_aabb_for_cluster(
                                        first_slice_depth,
                                        far_z,
                                        clusters.tile_size.as_vec2(),
                                        screen_size.as_vec2(),
                                        inverse_projection,
                                        is_orthographic,
                                        clusters.dimensions,
                                        UVec3::new(x, y, z),
                                    );
                                    let sphere = Sphere {
                                        center: aabb.center,
                                        radius: aabb.half_extents.length(),
                                    };
                                    *cluster_aabb_sphere = Some(sphere);
                                    cluster_aabb_sphere.as_ref().unwrap()
                                };

                                // test -- based on https://bartwronski.com/2017/04/13/cull-that-cone/
                                let spot_light_offset = Vec3::from(
                                    view_light_sphere.center - cluster_aabb_sphere.center,
                                );
                                let spot_light_dist_sq = spot_light_offset.length_squared();
                                let v1_len = spot_light_offset.dot(view_light_direction);

                                let distance_closest_point = (angle_cos
                                    * (spot_light_dist_sq - v1_len * v1_len).sqrt())
                                    - v1_len * angle_sin;
                                let angle_cull =
                                    distance_closest_point > cluster_aabb_sphere.radius;

                                let front_cull = v1_len
                                    > cluster_aabb_sphere.radius + light.range * view_inv_scale_max;
                                let back_cull = v1_len < -cluster_aabb_sphere.radius;

                                if !angle_cull && !front_cull && !back_cull {
                                    // this cluster is affected by the spot light
                                    clusters.lights[cluster_index].entities.push(light.entity);
                                    clusters.lights[cluster_index].spot_light_count += 1;
                                }
                                cluster_index += clusters.dimensions.z as usize;
                            }
                        } else {
                            for _ in min_x..=max_x {
                                // all clusters within range are affected by point lights
                                clusters.lights[cluster_index].entities.push(light.entity);
                                clusters.lights[cluster_index].point_light_count += 1;
                                cluster_index += clusters.dimensions.z as usize;
                            }
                        }
                    }
                }
            }
        };

        // reuse existing visible lights Vec, if it exists
        if let Some(visible_lights) = visible_lights.as_mut() {
            visible_lights.entities.clear();
            update_from_light_intersections(&mut visible_lights.entities);
        } else {
            let mut entities = Vec::new();
            update_from_light_intersections(&mut entities);
            commands.entity(view_entity).insert(VisiblePointLights {
                entities,
                ..Default::default()
            });
        }
    }
}

// NOTE: This exploits the fact that a x-plane normal has only x and z components
fn get_distance_x(plane: HalfSpace, point: Vec3A, is_orthographic: bool) -> f32 {
    if is_orthographic {
        point.x - plane.d()
    } else {
        // Distance from a point to a plane:
        // signed distance to plane = (nx * px + ny * py + nz * pz + d) / n.length()
        // NOTE: For a x-plane, ny and d are 0 and we have a unit normal
        //                          = nx * px + nz * pz
        plane.normal_d().xz().dot(point.xz())
    }
}

// NOTE: This exploits the fact that a z-plane normal has only a z component
fn project_to_plane_z(z_light: Sphere, z_plane: HalfSpace) -> Option<Sphere> {
    // p = sphere center
    // n = plane normal
    // d = n.p if p is in the plane
    // NOTE: For a z-plane, nx and ny are both 0
    // d = px * nx + py * ny + pz * nz
    //   = pz * nz
    // => pz = d / nz
    let z = z_plane.d() / z_plane.normal_d().z;
    let distance_to_plane = z - z_light.center.z;
    if distance_to_plane.abs() > z_light.radius {
        return None;
    }
    Some(Sphere {
        center: Vec3A::from(z_light.center.xy().extend(z)),
        // hypotenuse length = radius
        // pythagoras = (distance to plane)^2 + b^2 = radius^2
        radius: (z_light.radius * z_light.radius - distance_to_plane * distance_to_plane).sqrt(),
    })
}

// NOTE: This exploits the fact that a y-plane normal has only y and z components
fn project_to_plane_y(
    y_light: Sphere,
    y_plane: HalfSpace,
    is_orthographic: bool,
) -> Option<Sphere> {
    let distance_to_plane = if is_orthographic {
        y_plane.d() - y_light.center.y
    } else {
        -y_light.center.yz().dot(y_plane.normal_d().yz())
    };

    if distance_to_plane.abs() > y_light.radius {
        return None;
    }
    Some(Sphere {
        center: y_light.center + distance_to_plane * y_plane.normal(),
        radius: (y_light.radius * y_light.radius - distance_to_plane * distance_to_plane).sqrt(),
    })
}

pub fn update_directional_light_frusta(
    mut views: Query<
        (
            &Cascades,
            &DirectionalLight,
            &ViewVisibility,
            &mut CascadesFrusta,
        ),
        (
            // Prevents this query from conflicting with camera queries.
            Without<Camera>,
        ),
    >,
) {
    for (cascades, directional_light, visibility, mut frusta) in &mut views {
        // The frustum is used for culling meshes to the light for shadow mapping
        // so if shadow mapping is disabled for this light, then the frustum is
        // not needed.
        if !directional_light.shadows_enabled || !visibility.get() {
            continue;
        }

        frusta.frusta = cascades
            .cascades
            .iter()
            .map(|(view, cascades)| {
                (
                    *view,
                    cascades
                        .iter()
                        .map(|c| Frustum::from_view_projection(&c.view_projection))
                        .collect::<Vec<_>>(),
                )
            })
            .collect();
    }
}

// NOTE: Run this after assign_lights_to_clusters!
pub fn update_point_light_frusta(
    global_lights: Res<GlobalVisiblePointLights>,
    mut views: Query<
        (Entity, &GlobalTransform, &PointLight, &mut CubemapFrusta),
        Or<(Changed<GlobalTransform>, Changed<PointLight>)>,
    >,
) {
    let projection =
        Mat4::perspective_infinite_reverse_rh(std::f32::consts::FRAC_PI_2, 1.0, POINT_LIGHT_NEAR_Z);
    let view_rotations = CUBE_MAP_FACES
        .iter()
        .map(|CubeMapFace { target, up }| Transform::IDENTITY.looking_at(*target, *up))
        .collect::<Vec<_>>();

    for (entity, transform, point_light, mut cubemap_frusta) in &mut views {
        // The frusta are used for culling meshes to the light for shadow mapping
        // so if shadow mapping is disabled for this light, then the frusta are
        // not needed.
        // Also, if the light is not relevant for any cluster, it will not be in the
        // global lights set and so there is no need to update its frusta.
        if !point_light.shadows_enabled || !global_lights.entities.contains(&entity) {
            continue;
        }

        // ignore scale because we don't want to effectively scale light radius and range
        // by applying those as a view transform to shadow map rendering of objects
        // and ignore rotation because we want the shadow map projections to align with the axes
        let view_translation = Transform::from_translation(transform.translation());
        let view_backward = transform.back();

        for (view_rotation, frustum) in view_rotations.iter().zip(cubemap_frusta.iter_mut()) {
            let view = view_translation * *view_rotation;
            let view_projection = projection * view.compute_matrix().inverse();

            *frustum = Frustum::from_view_projection_custom_far(
                &view_projection,
                &transform.translation(),
                &view_backward,
                point_light.range,
            );
        }
    }
}

pub fn update_spot_light_frusta(
    global_lights: Res<GlobalVisiblePointLights>,
    mut views: Query<
        (Entity, &GlobalTransform, &SpotLight, &mut Frustum),
        Or<(Changed<GlobalTransform>, Changed<SpotLight>)>,
    >,
) {
    for (entity, transform, spot_light, mut frustum) in &mut views {
        // The frusta are used for culling meshes to the light for shadow mapping
        // so if shadow mapping is disabled for this light, then the frusta are
        // not needed.
        // Also, if the light is not relevant for any cluster, it will not be in the
        // global lights set and so there is no need to update its frusta.
        if !spot_light.shadows_enabled || !global_lights.entities.contains(&entity) {
            continue;
        }

        // ignore scale because we don't want to effectively scale light radius and range
        // by applying those as a view transform to shadow map rendering of objects
        let view_backward = transform.back();

        let spot_view = spot_light_view_matrix(transform);
        let spot_projection = spot_light_projection_matrix(spot_light.outer_angle);
        let view_projection = spot_projection * spot_view.inverse();

        *frustum = Frustum::from_view_projection_custom_far(
            &view_projection,
            &transform.translation(),
            &view_backward,
            spot_light.range,
        );
    }
}

pub fn check_light_mesh_visibility(
    visible_point_lights: Query<&VisiblePointLights>,
    mut point_lights: Query<(
        &PointLight,
        &GlobalTransform,
        &CubemapFrusta,
        &mut CubemapVisibleEntities,
        Option<&RenderLayers>,
    )>,
    mut spot_lights: Query<(
        &SpotLight,
        &GlobalTransform,
        &Frustum,
        &mut VisibleEntities,
        Option<&RenderLayers>,
    )>,
    mut directional_lights: Query<
        (
            &DirectionalLight,
            &CascadesFrusta,
            &mut CascadesVisibleEntities,
            Option<&RenderLayers>,
            &mut ViewVisibility,
        ),
        Without<SpotLight>,
    >,
    mut visible_entity_query: Query<
        (
            Entity,
            &InheritedVisibility,
            &mut ViewVisibility,
            Option<&RenderLayers>,
            Option<&Aabb>,
            Option<&GlobalTransform>,
        ),
        (Without<NotShadowCaster>, Without<DirectionalLight>),
    >,
) {
    fn shrink_entities(visible_entities: &mut VisibleEntities) {
        // Check that visible entities capacity() is no more than two times greater than len()
        let capacity = visible_entities.entities.capacity();
        let reserved = capacity
            .checked_div(visible_entities.entities.len())
            .map_or(0, |reserve| {
                if reserve > 2 {
                    capacity / (reserve / 2)
                } else {
                    capacity
                }
            });

        visible_entities.entities.shrink_to(reserved);
    }

    // Directional lights
    for (directional_light, frusta, mut visible_entities, maybe_view_mask, light_view_visibility) in
        &mut directional_lights
    {
        // Re-use already allocated entries where possible.
        let mut views_to_remove = Vec::new();
        for (view, cascade_view_entities) in &mut visible_entities.entities {
            match frusta.frusta.get(view) {
                Some(view_frusta) => {
                    cascade_view_entities.resize(view_frusta.len(), Default::default());
                    cascade_view_entities
                        .iter_mut()
                        .for_each(|x| x.entities.clear());
                }
                None => views_to_remove.push(*view),
            };
        }
        for (view, frusta) in &frusta.frusta {
            visible_entities
                .entities
                .entry(*view)
                .or_insert_with(|| vec![VisibleEntities::default(); frusta.len()]);
        }
        for v in views_to_remove {
            visible_entities.entities.remove(&v);
        }

        // NOTE: If shadow mapping is disabled for the light then it must have no visible entities
        if !directional_light.shadows_enabled || !light_view_visibility.get() {
            continue;
        }

        let view_mask = maybe_view_mask.copied().unwrap_or_default();

        for (
            entity,
            inherited_visibility,
            mut view_visibility,
            maybe_entity_mask,
            maybe_aabb,
            maybe_transform,
        ) in &mut visible_entity_query
        {
            if !inherited_visibility.get() {
                continue;
            }

            let entity_mask = maybe_entity_mask.copied().unwrap_or_default();
            if !view_mask.intersects(&entity_mask) {
                continue;
            }

            // If we have an aabb and transform, do frustum culling
            if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
                for (view, view_frusta) in &frusta.frusta {
                    let view_visible_entities = visible_entities
                        .entities
                        .get_mut(view)
                        .expect("Per-view visible entities should have been inserted already");

                    for (frustum, frustum_visible_entities) in
                        view_frusta.iter().zip(view_visible_entities)
                    {
                        // Disable near-plane culling, as a shadow caster could lie before the near plane.
                        if !frustum.intersects_obb(aabb, &transform.affine(), false, true) {
                            continue;
                        }

                        view_visibility.set();
                        frustum_visible_entities.entities.push(entity);
                    }
                }
            } else {
                view_visibility.set();
                for view in frusta.frusta.keys() {
                    let view_visible_entities = visible_entities
                        .entities
                        .get_mut(view)
                        .expect("Per-view visible entities should have been inserted already");

                    for frustum_visible_entities in view_visible_entities {
                        frustum_visible_entities.entities.push(entity);
                    }
                }
            }
        }

        for (_, cascade_view_entities) in &mut visible_entities.entities {
            cascade_view_entities.iter_mut().for_each(shrink_entities);
        }
    }

    for visible_lights in &visible_point_lights {
        for light_entity in visible_lights.entities.iter().copied() {
            // Point lights
            if let Ok((
                point_light,
                transform,
                cubemap_frusta,
                mut cubemap_visible_entities,
                maybe_view_mask,
            )) = point_lights.get_mut(light_entity)
            {
                for visible_entities in cubemap_visible_entities.iter_mut() {
                    visible_entities.entities.clear();
                }

                // NOTE: If shadow mapping is disabled for the light then it must have no visible entities
                if !point_light.shadows_enabled {
                    continue;
                }

                let view_mask = maybe_view_mask.copied().unwrap_or_default();
                let light_sphere = Sphere {
                    center: Vec3A::from(transform.translation()),
                    radius: point_light.range,
                };

                for (
                    entity,
                    inherited_visibility,
                    mut view_visibility,
                    maybe_entity_mask,
                    maybe_aabb,
                    maybe_transform,
                ) in &mut visible_entity_query
                {
                    if !inherited_visibility.get() {
                        continue;
                    }

                    let entity_mask = maybe_entity_mask.copied().unwrap_or_default();
                    if !view_mask.intersects(&entity_mask) {
                        continue;
                    }

                    // If we have an aabb and transform, do frustum culling
                    if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
                        let model_to_world = transform.affine();
                        // Do a cheap sphere vs obb test to prune out most meshes outside the sphere of the light
                        if !light_sphere.intersects_obb(aabb, &model_to_world) {
                            continue;
                        }

                        for (frustum, visible_entities) in cubemap_frusta
                            .iter()
                            .zip(cubemap_visible_entities.iter_mut())
                        {
                            if frustum.intersects_obb(aabb, &model_to_world, true, true) {
                                view_visibility.set();
                                visible_entities.entities.push(entity);
                            }
                        }
                    } else {
                        view_visibility.set();
                        for visible_entities in cubemap_visible_entities.iter_mut() {
                            visible_entities.entities.push(entity);
                        }
                    }
                }

                for visible_entities in cubemap_visible_entities.iter_mut() {
                    shrink_entities(visible_entities);
                }
            }

            // Spot lights
            if let Ok((point_light, transform, frustum, mut visible_entities, maybe_view_mask)) =
                spot_lights.get_mut(light_entity)
            {
                visible_entities.entities.clear();

                // NOTE: If shadow mapping is disabled for the light then it must have no visible entities
                if !point_light.shadows_enabled {
                    continue;
                }

                let view_mask = maybe_view_mask.copied().unwrap_or_default();
                let light_sphere = Sphere {
                    center: Vec3A::from(transform.translation()),
                    radius: point_light.range,
                };

                for (
                    entity,
                    inherited_visibility,
                    mut view_visibility,
                    maybe_entity_mask,
                    maybe_aabb,
                    maybe_transform,
                ) in &mut visible_entity_query
                {
                    if !inherited_visibility.get() {
                        continue;
                    }

                    let entity_mask = maybe_entity_mask.copied().unwrap_or_default();
                    if !view_mask.intersects(&entity_mask) {
                        continue;
                    }

                    // If we have an aabb and transform, do frustum culling
                    if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
                        let model_to_world = transform.affine();
                        // Do a cheap sphere vs obb test to prune out most meshes outside the sphere of the light
                        if !light_sphere.intersects_obb(aabb, &model_to_world) {
                            continue;
                        }

                        if frustum.intersects_obb(aabb, &model_to_world, true, true) {
                            view_visibility.set();
                            visible_entities.entities.push(entity);
                        }
                    } else {
                        view_visibility.set();
                        visible_entities.entities.push(entity);
                    }
                }

                shrink_entities(&mut visible_entities);
            }
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    fn test_cluster_tiling(config: ClusterConfig, screen_size: UVec2) -> Clusters {
        let dims = config.dimensions_for_screen_size(screen_size);

        // note: near & far do not affect tiling
        let mut clusters = Clusters::default();
        clusters.update(screen_size, dims);

        // check we cover the screen
        assert!(clusters.tile_size.x * clusters.dimensions.x >= screen_size.x);
        assert!(clusters.tile_size.y * clusters.dimensions.y >= screen_size.y);
        // check a smaller number of clusters would not cover the screen
        assert!(clusters.tile_size.x * (clusters.dimensions.x - 1) < screen_size.x);
        assert!(clusters.tile_size.y * (clusters.dimensions.y - 1) < screen_size.y);
        // check a smaller tile size would not cover the screen
        assert!((clusters.tile_size.x - 1) * clusters.dimensions.x < screen_size.x);
        assert!((clusters.tile_size.y - 1) * clusters.dimensions.y < screen_size.y);
        // check we don't have more clusters than pixels
        assert!(clusters.dimensions.x <= screen_size.x);
        assert!(clusters.dimensions.y <= screen_size.y);

        clusters
    }

    #[test]
    // check tiling for small screen sizes
    fn test_default_cluster_setup_small_screensizes() {
        for x in 1..100 {
            for y in 1..100 {
                let screen_size = UVec2::new(x, y);
                let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
                assert!(
                    clusters.dimensions.x * clusters.dimensions.y * clusters.dimensions.z <= 4096
                );
            }
        }
    }

    #[test]
    // check tiling for long thin screen sizes
    fn test_default_cluster_setup_small_x() {
        for x in 1..10 {
            for y in 1..5000 {
                let screen_size = UVec2::new(x, y);
                let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
                assert!(
                    clusters.dimensions.x * clusters.dimensions.y * clusters.dimensions.z <= 4096
                );

                let screen_size = UVec2::new(y, x);
                let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
                assert!(
                    clusters.dimensions.x * clusters.dimensions.y * clusters.dimensions.z <= 4096
                );
            }
        }
    }
}