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, 8 insertions, 1 deletions

diff --git a/crates/wayland/src/winit.rs b/crates/wayland/src/winit.rs
index 5f072b6..f50d095 100644
--- a/crates/wayland/src/winit.rs
+++ b/crates/wayland/src/winit.rs
@@ -242,6 +242,8 @@ impl WaylandPlatform {
             border_top_decorations: HashMap::new(),
             shadow_buffers: HashMap::new(),
             rounded_corners_program,
+            content_epoch: HashMap::new(),
+            rounded_content_buffers: HashMap::new(),
             border_side_buffers: HashMap::new(),
             last_synced_size: HashMap::new(),
             pending: pending.clone(),
@@ -406,7 +408,12 @@ impl WaylandPlatform {
         // The bar/dock/launcher, skipped entirely for a fullscreen window --
         // see `udev.rs`'s matching push for the full reasoning.
         let hide_top_layers = self.wm.borrow().visible_windows_front_to_back().any(|w| w.fullscreen);
-        let rounded_corners_enabled = self.wm.borrow().rounded_corners_enabled;
+        // `None` (the user's config never touched `general.rounded_corners`)
+        // defaults to *on* here - this backend has an actual GPU shader
+        // behind the feature (see `rounded_corners.rs`), no untested
+        // per-frame CPU cost to weigh the way the udev backend's own
+        // default has to.
+        let rounded_corners_enabled = self.wm.borrow().rounded_corners_enabled.unwrap_or(true);
         if !hide_top_layers {
             custom_elements.extend(
                 crate::elements::output_layer_elements(renderer, &self.output, (0, 0), |layer| matches!(layer, Layer::Top | Layer::Overlay))