Rounded corners on udev/Pixman backend, opt-in and off by default

CPU-side rounded corners for the software-only udev/Pixman renderer,
which has no shader stage to hook the existing GLES version into.
Reads a window's own committed wl_shm buffer, punches premultiplied-
alpha holes into the four corner regions, and hands the masked copy
to MemoryRenderBuffer - the same path already used for titlebar/
border/shadow bitmaps, so it composites through the ordinary unmasked
path and the corners genuinely disappear rather than being painted
over.

Cached per window, invalidated by a per-commit content_epoch counter
rather than rebuilt every frame, so an idle window costs nothing once
masked. general.rounded_corners now defaults per backend instead of
one global true: on for GLES/winit (a real GPU shader, no measurable
cost), off for udev/Pixman (an untested-on-real-hardware CPU cost for
constantly-repainting clients) - WindowManager.rounded_corners_enabled
is Option<bool> so the backend can tell "unset" from "explicitly off".

1 files changed, 6 insertions, 0 deletions

diff --git a/crates/wayland/src/protocols.rs b/crates/wayland/src/protocols.rs
index 9f23c69..f680dc3 100644
--- a/crates/wayland/src/protocols.rs
+++ b/crates/wayland/src/protocols.rs
@@ -123,6 +123,12 @@ impl CompositorHandler for CompState {
             if let Some(w) = self.id_to_window.get(&id) {
                 w.on_commit();
             }
+            // See `content_epoch`'s doc comment: this is the only per-commit
+            // signal the udev backend's rounded-corner mask cache has to
+            // invalidate itself, since content can change every frame,
+            // independent of the geometry-driven points `redraw_decoration_
+            // buffer` already runs at.
+            *self.content_epoch.entry(id).or_insert(0) += 1;
             crate::state::sync_toplevel_metadata(self, id, surface);
         }
         self.ensure_layer_initial_configure(surface);