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, 9 insertions, 1 deletions

diff --git a/crates/config/src/lib.rs b/crates/config/src/lib.rs
index 43577f8..2c57b0a 100644
--- a/crates/config/src/lib.rs
+++ b/crates/config/src/lib.rs
@@ -1008,7 +1008,15 @@ fn default_config() -> HashMap<String, ConfigValue> {
     set("general.animation_duration", Number(200.0));
     set("general.shadows", Bool(true));
     set("general.resize_margin", Number(6.0));
-    set("general.rounded_corners", Bool(true));
+    // Deliberately *not* seeded here, unlike every other `general.*` key --
+    // its actual default differs by backend (GLES/winit: on; udev/Pixman:
+    // off, an untested-on-real-hardware CPU cost too real to default to on
+    // - see `crates/wayland/src/rounded_corners.rs`), and neither backend
+    // is known yet at the point `default_config` runs. Leaving the key
+    // genuinely absent (rather than pre-seeded `true`/`false`) is what lets
+    // `main.rs`'s `apply_general_settings` tell "user never touched this"
+    // apart from "user explicitly chose a value" and hand the *unset* case
+    // to whichever backend ends up connecting instead of deciding for it.
     set("general.focus_follows_mouse", Bool(false));
     set("general.mouse_follows_focus", Bool(true));
     set("general.auto_raise", Bool(false));