compositor-drm: pass ARGB fallback to gl create functions for XRGB formats

If the GL implementation doesn't provide an XRGB visual we may still be
able to proceed with an ARGB one. Since we're not changing the scanout
buffer format, and our current rendering loop always results in saturated
alpha in the frame buffer, it should be Just Fine(tm) - and probably better
than just exiting.

This is a workaround for https://bugs.freedesktop.org/show_bug.cgi?id=89689

Reviewed-By: Bryce Harrington <bryce@osg.samsung.com>
Tested-By: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-By: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>

src/compositor-drm.c

@@ -1391,14 +1391,46 @@ create_gbm_device(int fd)
 	return gbm;
 }
 
+/* When initializing EGL, if the preferred buffer format isn't availble
+ * we may be able to susbstitute an ARGB format for an XRGB one.
+ *
+ * This returns 0 if substitution isn't possible, but 0 might be a
+ * legitimate format for other EGL platforms, so the caller is
+ * responsible for checking for 0 before calling gl_renderer->create().
+ *
+ * This works around https://bugs.freedesktop.org/show_bug.cgi?id=89689
+ * but it's entirely possible we'll see this again on other implementations.
+ */
+static int
+fallback_format_for(uint32_t format)
+{
+	switch (format) {
+	case GBM_FORMAT_XRGB8888:
+		return GBM_FORMAT_ARGB8888;
+	case GBM_FORMAT_XRGB2101010:
+		return GBM_FORMAT_ARGB2101010;
+	default:
+		return 0;
+	}
+}
+
 static int
 drm_compositor_create_gl_renderer(struct drm_compositor *ec)
 {
-	EGLint format;
+	EGLint format[2] = {
+		ec->format,
+		fallback_format_for(ec->format),
+	};
+	int n_formats = 1;
 
-	format = ec->format;
-	if (gl_renderer->create(&ec->base, EGL_PLATFORM_GBM_KHR, (void *) ec->gbm,
-			       gl_renderer->opaque_attribs, &format, 1) < 0) {
+	if (format[1])
+		n_formats = 2;
+	if (gl_renderer->create(&ec->base,
+				EGL_PLATFORM_GBM_KHR,
+				(void *)ec->gbm,
+				gl_renderer->opaque_attribs,
+				format,
+				n_formats) < 0) {
 		return -1;
 	}
 
@@ -1602,13 +1634,16 @@ find_crtc_for_connector(struct drm_compositor *ec,
 static int
 drm_output_init_egl(struct drm_output *output, struct drm_compositor *ec)
 {
-	EGLint format = output->format;
-	int i, flags;
+	EGLint format[2] = {
+		output->format,
+		fallback_format_for(output->format),
+	};
+	int i, flags, n_formats = 1;
 
 	output->surface = gbm_surface_create(ec->gbm,
 					     output->base.current_mode->width,
 					     output->base.current_mode->height,
-					     format,
+					     format[0],
 					     GBM_BO_USE_SCANOUT |
 					     GBM_BO_USE_RENDERING);
 	if (!output->surface) {
@@ -1616,12 +1651,14 @@ drm_output_init_egl(struct drm_output *output, struct drm_compositor *ec)
 		return -1;
 	}
 
+	if (format[1])
+		n_formats = 2;
 	if (gl_renderer->output_create(&output->base,
 				       (EGLNativeDisplayType)output->surface,
 				       output->surface,
 				       gl_renderer->opaque_attribs,
-				       &format,
-				       1) < 0) {
+				       format,
+				       n_formats) < 0) {
 		weston_log("failed to create gl renderer output state\n");
 		gbm_surface_destroy(output->surface);
 		return -1;

src/gl-renderer.c

@@ -934,6 +934,14 @@ output_rotate_damage(struct weston_output *output,
 	go->border_damage[go->buffer_damage_index] = border_status;
 }
 
+/* NOTE: We now allow falling back to ARGB gl visuals when XRGB is
+ * unavailable, so we're assuming the background has no transparency
+ * and that everything with a blend, like drop shadows, will have something
+ * opaque (like the background) drawn underneath it.
+ *
+ * Depending on the underlying hardware, violating that assumption could
+ * result in seeing through to another display plane.
+ */
 static void
 gl_renderer_repaint_output(struct weston_output *output,
 			      pixman_region32_t *output_damage)