gl-renderer: Don't use swap_buffers_with_damage with fan debug

Fan debug mode repaints the whole surface in order to clear any 'trails'
left over from previous fan paints. If this happens, fall back to using
regular eglSwapBuffers rather than eglSwapBuffersWithDamageEXT, since
the damage region we would pass will be too small.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/renderer-gl/gl-renderer.c

@@ -1411,9 +1411,10 @@ gl_renderer_repaint_output(struct weston_output *output,
 			    2.0 / output->current_mode->width,
 			    -2.0 / output->current_mode->height, 1);
 
-	/* if debugging, redraw everything outside the damage to clean up
-	 * debug lines from the previous draw on this buffer:
-	 */
+	/* In fan debug mode, redraw everything to make sure that we clear any
+	 * fans left over from previous draws on this buffer.
+	 * This precludes the use of EGL_EXT_swap_buffers_with_damage, since
+	 * we damage the whole area. */
 	if (gr->fan_debug) {
 		pixman_region32_t undamaged;
 		pixman_region32_init(&undamaged);
@@ -1446,7 +1447,7 @@ gl_renderer_repaint_output(struct weston_output *output,
 
 	go->end_render_sync = create_render_sync(gr);
 
-	if (gr->swap_buffers_with_damage) {
+	if (gr->swap_buffers_with_damage && !gr->fan_debug) {
 		pixman_region32_init(&buffer_damage);
 		weston_transformed_region(output->width, output->height,
 					  output->transform,