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per-surface explicit synchronization support

This object implements per-surface explicit synchronization.

Synchronization refers to co-ordination of pipelined operations performed on buffers. Most GPU clients will schedule an asynchronous operation to render to the buffer, then immediately send the buffer to the compositor to be attached to a surface.

In implicit synchronization, ensuring that the rendering operation is complete before the compositor displays the buffer is an implementation detail handled by either the kernel or userspace graphics driver.

By contrast, in explicit synchronization, dma_fence objects mark when the asynchronous operations are complete. When submitting a buffer, the client provides an acquire fence which will be waited on before the compositor accesses the buffer. The Wayland server, through a zwp_linux_buffer_release_v1 object, will inform the client with an event which may be accompanied by a release fence, when the compositor will no longer access the buffer contents due to the specific commit that requested the release event.

Each surface can be associated with only one object of this interface at any time.

In version 1 of this interface, explicit synchronization is only guaranteed to be supported for buffers created with any version of the wp_linux_dmabuf buffer factory. Version 2 additionally guarantees explicit synchronization support for opaque EGL buffers, which is a type of platform specific buffers described in the EGL_WL_bind_wayland_display extension. Compositors are free to support explicit synchronization for additional buffer types.

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