Struct egui::Id

pub struct Id(/* private fields */);

egui tracks widgets frame-to-frame using Ids.

For instance, if you start dragging a slider one frame, egui stores the sliders Id as the current active id so that next frame when you move the mouse the same slider changes, even if the mouse has moved outside the slider.

For some widgets Ids are also used to persist some state about the widgets, such as Window position or whether not a collapsing header region is open.

This implies that the Ids must be unique.

For simple things like sliders and buttons that don’t have any memory and doesn’t move we can use the location of the widget as a source of identity. For instance, a slider only needs a unique and persistent ID while you are dragging the slider. As long as it is still while moving, that is fine.

For things that need to persist state even after moving (windows, collapsing headers) the location of the widgets is obviously not good enough. For instance, a collapsing region needs to remember whether or not it is open even if the layout next frame is different and the collapsing is not lower down on the screen.

Then there are widgets that need no identifiers at all, like labels, because they have no state nor are interacted with.

This is niche-optimized to that Option<Id> is the same size as Id.

Implementations

impl Id

pub const NULL: Self = _

A special Id, in particular as a key to crate::Memory::data for when there is no particular widget to attach the data.

The null Id is still a valid id to use in all circumstances, though obviously it will lead to a lot of collisions if you do use it!

pub fn new(source: impl Hash) -> Self

Generate a new Id by hashing some source (e.g. a string or integer).

pub fn with(self, child: impl Hash) -> Self

Generate a new Id by hashing the parent Id and the given argument.

pub fn short_debug_format(&self) -> String

Short and readable summary

pub fn value(&self) -> u64

The inner value of the Id.

This is a high-entropy hash, or Self::NULL.

Trait Implementations

impl Clone for Id

fn clone(&self) -> Id

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Id

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl From<&'static str> for Id

Convenience

fn from(string: &'static str) -> Self

Converts to this type from the input type.

impl From<String> for Id

fn from(string: String) -> Self

Converts to this type from the input type.

impl From<ViewportId> for Id

fn from(id: ViewportId) -> Self

Converts to this type from the input type.

impl Hash for Id

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Id

fn eq(&self, other: &Id) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Id

impl Eq for Id

impl StructuralEq for Id

impl StructuralPartialEq for Id