[PATCH weston v2] gl-renderer: If an XRGB format is requested but unavailable, try ARGB

[Derek Foreman]

Recent versions of Mesa have stopped exposing XRGB visuals for gl on
some Intel GPUs.  While this may be changed in Mesa eventually, it's
not impossible that some other hardware in the future won't provide
XRGB visuals either.

Let's try again with an ARGB visual if XRGB is unavailable.  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.

Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
---

Dima Ryazanov called me out for fallback_format() not working on all endians,
and I've reworked the loop to be a single loop instead of two, similar to
Daniel's suggestion (but still keeping the NULL visual_id means "give me the
first match" semantic of the original)

I've also replaced calloc with aloca so I don't have to worry about freeing
the array on return, which simplifies things a little bit.  I didn't bother
zeroing out the array, since it's filled in by eglChooseConfig.

It's still an ugly function. :)

 src/gl-renderer.c | 57 +++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 43 insertions(+), 14 deletions(-)

diff --git a/src/gl-renderer.c b/src/gl-renderer.c
index ae3122f..a4fd3a0 100644
--- a/src/gl-renderer.c
+++ b/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 visual ids 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)
@@ -1897,6 +1905,15 @@ log_egl_config_info(EGLDisplay egldpy, EGLConfig eglconfig)
 		weston_log_continue(" unknown\n");
 }
 
+static EGLint
+fallback_format(EGLint format)
+{
+	if ((format & 0xFF) != 'X')
+		return 0;
+
+	return (format & 0xFFFFFF00) | 'A';
+}
+
 static int
 egl_choose_config(struct gl_renderer *gr, const EGLint *attribs,
 		  const EGLint *visual_id,
@@ -1904,41 +1921,53 @@ egl_choose_config(struct gl_renderer *gr, const EGLint *attribs,
 {
 	EGLint count = 0;
 	EGLint matched = 0;
+	EGLint fallback_id;
 	EGLConfig *configs;
+	EGLConfig fallback_config = 0;
 	int i;
 
 	if (!eglGetConfigs(gr->egl_display, NULL, 0, &count) || count < 1)
 		return -1;
 
-	configs = calloc(count, sizeof *configs);
+	configs = alloca(count * sizeof *configs);
 	if (!configs)
 		return -1;
 
 	if (!eglChooseConfig(gr->egl_display, attribs, configs,
 			      count, &matched))
-		goto out;
+		return -1;
+
+	if (!matched)
+		return -1;
 
+	if (!visual_id) {
+		*config_out = configs[0];
+		return 0;
+	}
+
+	fallback_id = fallback_format(*visual_id);
 	for (i = 0; i < matched; ++i) {
 		EGLint id;
 
-		if (visual_id) {
-			if (!eglGetConfigAttrib(gr->egl_display,
-					configs[i], EGL_NATIVE_VISUAL_ID,
-					&id))
-				continue;
+		if (!eglGetConfigAttrib(gr->egl_display,
+				configs[i], EGL_NATIVE_VISUAL_ID,
+				&id))
+			continue;
 
-			if (id != 0 && id != *visual_id)
-				continue;
+		if (id == *visual_id) {
+			*config_out = configs[i];
+			return 0;
 		}
+		if (id == fallback_id)
+			fallback_config = configs[i];
+	}
 
-		*config_out = configs[i];
-
-		free(configs);
+	if (fallback_config) {
+		weston_log("Falling back to ARGB visual\n");
+		*config_out = fallback_config;
 		return 0;
 	}
 
-out:
-	free(configs);
 	return -1;
 }
 
-- 
2.1.4