Julian Orth b60b57c407 protocol: add wl_surface.discard_constraints request ... This commit defines a new discard_constraints request. This request is intended to be used by clients that use the wp-fifo and wp-commit-timing protocols for frame pacing but want to be able to respond immediately to resize requests. Consider a client using wp-fifo presenting to a display with refresh rate 1 (unitless). The client has allocated 3 buffers O1, O2, and O3. The client receives a resize request at time T+2. The client allocates new buffers N1, N2, and N3 with the new size. The following sequence of requests and events can be observed in WAYLAND_DEBUG output: T+0: release(O1) T+0: -> attach(O1) T+1: release(O2) T+1: -> attach(O2) T+2: release(O3) T+2: -> attach(O3) T+2: resize request T+2: -> attach(N1) T+2: -> attach(N2) T+2: -> attach(N3) T+3: release(O1) T+4: release(O2) T+5: release(O3) T+6: release(N1) T+6: -> attach(N1) Due to the lack of backpressure, all newly created buffers are attached immediately at T+2. Since O1, O2, and O3 are still equeued, the content update containing N1 will only be applied at T+5 and therefore cannot be released any earlier than T+6, creating a presentation bubble between T+3 and T+6. Furthermore, even if the client did not attach N2 immediately at T+2, N1 would not become visible until T+5, which means that the client effectively does not respond to the resize request until T+5. This effect can be observed with the following command: vkcube --present_mode 2 Resizing the application window causes easily visible stutters on displays with low refresh rates. Note that the queue can grow unbounded if the client receives an unbounded number of resize requests between refresh cycles. To remedy this, this commit allows the client to hint to the compositor that it should discard all existing constraints, if able. Since compositor architectures might impose limitations on which constraints the compositor is able to discard, this is left to compositor policy. It is expected that most compositors should be able to discard wp-fifo and wp-commit-timing constraints. Some compositors might be able to discard buffer constraints if the buffer in question is superseded by another buffer in a later content update. I had considered creating per-interface requests, such as wp_fifo_v1.discard_constraints, however, such constraints are often created by WSI layers and an update of the WSI layer could introduce new constraints that the client would not be aware of. To discard all constraints, the WSI layer would have to invoke these requests and there are no APIs for the client to communicate to the WSI layer which behavior is desired. Signed-off-by: Julian Orth <ju.orth@gmail.com>		2025-10-26 01:06:10 +02:00
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.gitignore	Update .gitignore for protocol/	2013-11-19 13:26:04 -08:00
generate-shm-formats.py	Add an automated script to update wl_shm.format	2019-09-06 12:09:22 +00:00
tests.xml	Replace initial 8 spaces with a tab for all xml files	2020-04-29 12:21:33 +00:00
wayland.dtd	Add support for the deprecated-since XML attribute	2024-04-24 16:18:28 +00:00
wayland.xml	protocol: add wl_surface.discard_constraints request	2025-10-26 01:06:10 +02:00