compositor: Update output state after mode switch

After a mode switch, the output region and transformation matrix need
to be updated. The call to weston_output_move() would do the former but
not the latter, but calling that when the output remains in the same
coordinate doesn't make much sense. Instead, update this state and the
transformation matrix in weston_output_mode_switch().

src/compositor-drm.c

@@ -1041,8 +1041,6 @@ drm_output_switch_mode(struct weston_output *output_base, struct weston_mode *mo
 
 	/*update output*/
 	output->base.current = &drm_mode->base;
-	output->base.dirty = 1;
-	weston_output_move(&output->base, output->base.x, output->base.y);
 	return 0;
 
 err_gl:

src/compositor.c

@@ -84,13 +84,31 @@ sigchld_handler(int signal_number, void *data)
 	return 1;
 }
 
+static void
+weston_output_transform_init(struct weston_output *output, uint32_t transform);
+
 WL_EXPORT int
 weston_output_switch_mode(struct weston_output *output, struct weston_mode *mode)
 {
+	int ret;
+
 	if (!output->switch_mode)
 		return -1;
 
-	return output->switch_mode(output, mode);
+	ret = output->switch_mode(output, mode);
+	if (ret < 0)
+		return ret;
+
+	/* Update output region and transformation matrix */
+	weston_output_transform_init(output, output->transform);
+
+	pixman_region32_init(&output->previous_damage);
+	pixman_region32_init_rect(&output->region, output->x, output->y,
+				  output->width, output->height);
+
+	weston_output_update_matrix(output);
+
+	return ret;
 }
 
 WL_EXPORT void