compositor-drm: Support scan out of transformed buffers

If a client renders its buffers with the same transform as the output,
we can scan out them when fullscreen.

src/compositor-drm.c

@@ -316,10 +316,11 @@ drm_output_prepare_scanout_surface(struct weston_output *_output,
 
 	if (es->geometry.x != output->base.x ||
 	    es->geometry.y != output->base.y ||
-	    es->geometry.width != output->base.current->width ||
+	    es->buffer == NULL ||
-	    es->geometry.height != output->base.current->height ||
+	    es->buffer->width != output->base.current->width ||
-	    es->transform.enabled ||
+	    es->buffer->height != output->base.current->height ||
-	    es->buffer == NULL)
+	    output->base.transform != es->buffer_transform ||
+	    es->transform.enabled)
 		return NULL;
 
 	bo = gbm_bo_import(c->gbm, GBM_BO_IMPORT_WL_BUFFER,
@@ -566,6 +567,9 @@ drm_output_prepare_overlay_surface(struct weston_output *output_base,
 	uint32_t format;
 	wl_fixed_t sx1, sy1, sx2, sy2;
 
+	if (output_base->transform != WL_OUTPUT_TRANSFORM_NORMAL)
+		return NULL;
+
 	if (c->sprites_are_broken)
 		return NULL;
 
@@ -678,6 +682,8 @@ drm_output_prepare_cursor_surface(struct weston_output *output_base,
 		(struct drm_compositor *) output_base->compositor;
 	struct drm_output *output = (struct drm_output *) output_base;
 
+	if (output->base.transform != WL_OUTPUT_TRANSFORM_NORMAL)
+		return NULL;
 	if (output->cursor_surface)
 		return NULL;
 	if (es->output_mask != (1u << output_base->id))

src/compositor.c

@@ -2793,9 +2793,6 @@ weston_output_init(struct weston_output *output, struct weston_compositor *c,
 	output->mm_height = height;
 	output->dirty = 1;
 
-	if (transform != WL_OUTPUT_TRANSFORM_NORMAL)
-		output->disable_planes++;
-
 	weston_output_transform_init(output, transform);
 	weston_output_init_zoom(output);