observer: further classify general clips

A clip with only a single path or can be reduced to a single polygon are
easier to handle than a clip containing a mixture of paths (typically
ANTIALIAS_NONE vs ANTIALIAS_DEFAULT).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/cairo-clip-polygon.c

@@ -125,3 +125,20 @@ _cairo_clip_get_polygon (const cairo_clip_t *clip,
 
     return CAIRO_STATUS_SUCCESS;
 }
+
+cairo_bool_t
+_cairo_clip_is_polygon (const cairo_clip_t *clip)
+{
+    if (_cairo_clip_is_all_clipped (clip))
+	return TRUE;
+
+    /* If there is no clip, we need an infinite polygon */
+    if (clip == NULL)
+	return FALSE;
+
+    if (clip->path == NULL)
+	return TRUE;
+
+    /* check that residual is all of the same type/tolerance */
+    return can_convert_to_polygon (clip);
+}

src/cairo-clip-private.h

@@ -204,6 +204,9 @@ _cairo_clip_copy_rectangle_list (cairo_clip_t *clip, cairo_gstate_t *gstate);
 cairo_private cairo_rectangle_list_t *
 _cairo_rectangle_list_create_in_error (cairo_status_t status);
 
+cairo_private cairo_bool_t
+_cairo_clip_is_polygon (const cairo_clip_t *clip);
+
 cairo_private cairo_int_status_t
 _cairo_clip_get_polygon (const cairo_clip_t *clip,
 			 cairo_polygon_t *polygon,

src/cairo-surface-observer-private.h

@@ -66,7 +66,7 @@ struct path {
 };
 
 struct clip {
-    unsigned int type[4]; /* none, region, boxes, general */
+    unsigned int type[6]; /* none, region, boxes, single path, polygon, general */
 };
 
 typedef struct _cairo_observation cairo_observation_t;

src/cairo-surface-observer.c

@@ -197,11 +197,14 @@ add_clip (struct clip *stats,
 	classify = 1;
     else if (clip->path == NULL)
 	classify = 2;
-    else
+    else if (clip->path->prev == NULL)
 	classify = 3;
+    else if (_cairo_clip_is_polygon (clip))
+	classify = 4;
+    else
+	classify = 5;
 
     stats->type[classify]++;
-
 }
 
 static void
@@ -1029,7 +1032,9 @@ print_clip (cairo_output_stream_t *stream, const struct clip *c)
 	"none",
 	"region",
 	"boxes",
-	"general path",
+	"single path",
+	"polygon",
+	"general",
     };
     _cairo_output_stream_printf (stream, "  clip:");
     print_array (stream, c->type, names, ARRAY_LENGTH (names));