compositor: add weston_surface bounding box

Compute a surface bounding box, especially for transformed surfaces, for
which one cannot simply use x,y,width,height.

The bounding box depends on width and height, so these are now under the
geometry.dirty flag.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

src/compositor.c

@@ -209,6 +209,7 @@ weston_surface_create(struct weston_compositor *compositor,
 	wl_list_insert(&surface->geometry.transformation_list,
 		       &surface->transform.position.link);
 	weston_matrix_init(&surface->transform.position.matrix);
+	pixman_region32_init(&surface->transform.boundingbox);
 	surface->geometry.dirty = 1;
 
 	return surface;
@@ -230,6 +231,40 @@ weston_surface_set_color(struct weston_surface *surface,
 	surface->shader = &surface->compositor->solid_shader;
 }
 
+static void
+surface_compute_bbox(struct weston_surface *surface, int32_t sx, int32_t sy,
+		     int32_t width, int32_t height,
+		     pixman_region32_t *bbox)
+{
+	int min_x = INT_MAX, min_y = INT_MAX, max_x = INT_MIN, max_y = INT_MIN;
+	int32_t s[4][2] = {
+		{ sx,         sy },
+		{ sx,         sy + height },
+		{ sx + width, sy },
+		{ sx + width, sy + height }
+	};
+	int i;
+
+	for (i = 0; i < 4; ++i) {
+		int32_t x, y;
+		weston_surface_to_global(surface, s[i][0], s[i][1], &x, &y);
+		if (x < min_x)
+			min_x = x;
+		if (x > max_x)
+			max_x = x;
+		if (y < min_y)
+			min_y = y;
+		if (y > max_y)
+			max_y = y;
+	}
+
+	/* weston_surface_to_global rounds with floor(), add the
+	 * minimum required safety margin.
+	 */
+	pixman_region32_init_rect(bbox, min_x, min_y,
+				  max_x - min_x + 1, max_y - min_y + 1);
+}
+
 WL_EXPORT void
 weston_surface_update_transform(struct weston_surface *surface)
 {
@@ -242,12 +277,19 @@ weston_surface_update_transform(struct weston_surface *surface)
 
 	surface->geometry.dirty = 0;
 
+	pixman_region32_fini(&surface->transform.boundingbox);
+
 	/* transform.position is always in transformation_list */
 	if (surface->geometry.transformation_list.next ==
 	    &surface->transform.position.link &&
 	    surface->geometry.transformation_list.prev ==
 	    &surface->transform.position.link) {
 		surface->transform.enabled = 0;
+
+		pixman_region32_init_rect(&surface->transform.boundingbox,
+					  surface->geometry.x,
+					  surface->geometry.y,
+					  surface->width, surface->height);
 		return;
 	}
 
@@ -266,6 +308,9 @@ weston_surface_update_transform(struct weston_surface *surface)
 		fprintf(stderr, "error: weston_surface %p"
 			" transformation not invertible.\n", surface);
 	}
+
+	surface_compute_bbox(surface, 0, 0, surface->width, surface->height,
+			     &surface->transform.boundingbox);
 }
 
 WL_EXPORT void
@@ -491,6 +536,7 @@ destroy_surface(struct wl_resource *resource)
 
 	wl_list_remove(&surface->buffer_link);
 
+	pixman_region32_fini(&surface->transform.boundingbox);
 	pixman_region32_fini(&surface->damage);
 	pixman_region32_fini(&surface->opaque);
 

src/compositor.h

@@ -241,6 +241,8 @@ struct weston_surface {
 	 * This is updated by weston_surface_update_transform().
 	 */
 	struct {
+		pixman_region32_t boundingbox;
+
 		/* matrix and inverse are used only if enabled = 1.
 		 * If enabled = 0, use x, y, width, height directly.
 		 */