fix(playback): stop forcing legacy OpenGL renderer on X11 mpv backend (#188)

src/shared/mpv-x11-backend.test.ts

@@ -99,9 +99,10 @@ test('applyX11EnvOverrides strips Wayland hints and pins session type to x11', (
   assert.equal(result.XDG_SESSION_TYPE, 'x11');
 });
 
-test('MPV_X11_BACKEND_ARGS pins the GPU stack to X11', () => {
-  assert.deepEqual(
-    [...MPV_X11_BACKEND_ARGS],
-    ['--vo=gpu', '--gpu-api=opengl', '--gpu-context=x11egl,x11'],
+test('MPV_X11_BACKEND_ARGS pins the window context to X11 without overriding the renderer', () => {
+  assert.deepEqual([...MPV_X11_BACKEND_ARGS], ['--gpu-context=x11vk,x11egl,x11']);
+  assert.equal(
+    MPV_X11_BACKEND_ARGS.some((arg) => arg.startsWith('--vo=') || arg.startsWith('--gpu-api=')),
+    false,
   );
 });

src/shared/mpv-x11-backend.ts

@@ -12,12 +12,18 @@
   so the gate and the mpv backend args stay in one place.
 */
 
-/** mpv args that pin the GPU/windowing stack to X11/XWayland (libGL via EGL on X11). */
-export const MPV_X11_BACKEND_ARGS = [
-  '--vo=gpu',
-  '--gpu-api=opengl',
-  '--gpu-context=x11egl,x11',
-] as const;
+/**
+ * mpv args that pin the *windowing* stack to X11/XWayland, in Vulkan-then-OpenGL order.
+ * mpv walks the list and skips contexts that do not match the configured `--gpu-api`,
+ * so this works for both a Vulkan and an OpenGL config.
+ *
+ * Deliberately does NOT set `--vo`/`--gpu-api`: forcing `--vo=gpu --gpu-api=opengl` here
+ * used to drop configs off `vo=gpu-next` onto the legacy renderer, where user shaders
+ * written for gpu-next (e.g. ArtCNN, `//!COMPONENTS 4` LUMA hooks) abort mpv with
+ * `copy_image: Assertion '*offset + count < sizeof(dst)' failed` as soon as their
+ * upscale-only `//!WHEN` condition turns on, i.e. on the first fullscreen toggle.
+ */
+export const MPV_X11_BACKEND_ARGS = ['--gpu-context=x11vk,x11egl,x11'] as const;
 
 export type LinuxDesktopEnv = {
   xdgCurrentDesktop: string;