[clip] Intersect to region extents.

When querying the intersection of a rectangle with the clip region, the
result only depends upon the region extents so we do not need to perform
an expensive region-region intersection computation.

src/cairo-clip.c

@@ -179,20 +179,12 @@ _cairo_clip_intersect_to_rectangle (cairo_clip_t            *clip,
     }
 
     if (clip->has_region) {
-	cairo_region_t intersection;
+	cairo_rectangle_int_t extents;
 
-	_cairo_region_init_rect (&intersection, rectangle);
-
-	status = _cairo_region_intersect (&intersection, &clip->region,
-					  &intersection);
-
-	if (!status)
-	    _cairo_region_get_extents (&intersection, rectangle);
-
-        _cairo_region_fini (&intersection);
-
-        if (unlikely (status))
-            return status;
+	_cairo_region_get_extents (&clip->region, &extents);
+	is_empty = _cairo_rectangle_intersect (rectangle, &extents);
+	if (is_empty)
+	    return CAIRO_STATUS_SUCCESS;
     }
 
     if (clip->surface)

src/cairo-surface-fallback.c

@@ -578,7 +578,6 @@ _clip_and_composite_trapezoids (const cairo_pattern_t *src,
 
             has_clear_region = TRUE;
             status = _cairo_clip_intersect_to_region (clip, &clear_region);
-
             if (unlikely (status))
                 goto out;