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xXJSONDeruloXx dae7592788 Desktop: hand labwc's cursor to the app, so full-screen games scan out
The desktop forced a software cursor (WLR_NO_HARDWARE_CURSORS=1) because
labwc's cursor never showed when handed to the app's compositor. With a
software cursor wlroots never scans out: every frame of a full-screen game
was composited by labwc first ("Direct scan-out disabled by software
cursor", 2284 times in one Adreno 825 report).

Why the cursor never showed: wlroots' Wayland backend attaches and commits
its cursor surface before wl_pointer.set_cursor gives it the cursor role,
and sets it again with nothing new committed each time the pointer enters.
The compositor released a role-less surface's buffer on commit, so the
cursor surface had no image by the time it became the cursor.

- A role-less surface's last buffer (cursor-sized only) is held until the
  next commit; set_cursor publishes it, and a repeat set_cursor of the
  surface already shown unhides its last image.
- A dma-buf cursor is read back after the client's implicit render fence,
  as the zero-copy path waits for it.
- The desktop no longer forces a software cursor.

Device-tested on the AYN Thor (Adreno 740, 1920x1080): labwc's own cursor
is drawn, with its shapes (I-beam over a terminal); wlroots logs "Direct
scan-out enabled" for a full-screen glxgears. At the same 60 fps on screen
the GPU is 3.0 % busy against 4.6 % with the software cursor, both at
550 MHz.
2026-09-28 14:33:08 -04:00
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