backend-wayland: use DRM formats for EGLConfig

Define a specific DRM format for the GL-renderer to render in. It goes through
fuzzy matching in egl-glue.c which ensures we get exactly the number of bits
for each channel, but does not require an exact format match.

This ensures we get the bit depth we expect instead of the first arbitrary
EGLConfig.

This should not change the current behaviour, because Mesa EGL takes care to
order the configs as apps expect.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/backend-wayland/wayland.c

@@ -38,6 +38,7 @@
 #include <sys/mman.h>
 #include <linux/input.h>
 
+#include <drm_fourcc.h>
 #include <wayland-client.h>
 #include <wayland-cursor.h>
 
@@ -63,6 +64,10 @@
 
 #define WINDOW_TITLE "Weston Compositor"
 
+static const uint32_t wayland_formats[] = {
+	DRM_FORMAT_ARGB8888,
+};
+
 struct wayland_backend {
 	struct weston_backend base;
 	struct weston_compositor *compositor;
@@ -775,8 +780,8 @@ wayland_output_init_gl_renderer(struct wayland_output *output)
 					      output->gl.egl_window,
 					      output->gl.egl_window,
 					      gl_renderer->alpha_attribs,
-					      NULL,
-					      0) < 0)
+					      wayland_formats,
+					      ARRAY_LENGTH(wayland_formats)) < 0)
 		goto cleanup_window;
 
 	return 0;
@@ -2770,8 +2775,8 @@ wayland_backend_create(struct weston_compositor *compositor,
 						EGL_PLATFORM_WAYLAND_KHR,
 						b->parent.wl_display,
 						gl_renderer->alpha_attribs,
-						NULL,
-						0) < 0) {
+						wayland_formats,
+						ARRAY_LENGTH(wayland_formats)) < 0) {
 			weston_log("Failed to initialize the GL renderer; "
 				   "falling back to pixman.\n");
 			b->use_pixman = true;