[cairo-polygon] Add a cache of eight edges to cairo_polygon_t

Many, if not most, of polygons have very few edges.  This avoids
calling malloc() for those cases.

2 files changed, 24 insertions, 7 deletions

diff --git a/src/cairo-polygon.c b/src/cairo-polygon.c
index 99c42981..6ed0165e 100644
--- a/src/cairo-polygon.c
+++ b/src/cairo-polygon.c
@@ -56,26 +56,42 @@ _cairo_polygon_init (cairo_polygon_t *polygon)
 void
 _cairo_polygon_fini (cairo_polygon_t *polygon)
 {
-    if (polygon->edges_size) {
+    if (polygon->edges != polygon->edges_embedded)
 	free (polygon->edges);
-	polygon->edges = NULL;
-	polygon->edges_size = 0;
-	polygon->num_edges = 0;
-    }
+
+    polygon->edges = NULL;
+    polygon->edges_size = 0;
+    polygon->num_edges = 0;
 
     polygon->has_current_point = FALSE;
 }
 
+/* make room for at least one more edge */
 static cairo_status_t
 _cairo_polygon_grow (cairo_polygon_t *polygon)
 {
     cairo_edge_t *new_edges;
     int old_size = polygon->edges_size;
-    int new_size = old_size ? 2 * old_size : 16;
+    int embedded_size = sizeof (polygon->edges_embedded) / sizeof (polygon->edges_embedded[0]);
+    int new_size = 2 * MAX (old_size, 16);
+
+    /* we have a local buffer at polygon->edges_embedded.  try to fulfill the request
+     * from there. */
+    if (old_size < embedded_size) {
+	polygon->edges = polygon->edges_embedded;
+	polygon->edges_size = embedded_size;
+	return CAIRO_STATUS_SUCCESS;
+    }
 
     assert (polygon->num_edges <= polygon->edges_size);
 
-    new_edges = realloc (polygon->edges, new_size * sizeof (cairo_edge_t));
+    if (polygon->edges == polygon->edges_embedded) {
+	new_edges = malloc (new_size * sizeof (cairo_edge_t));
+	if (new_edges)
+	    memcpy (new_edges, polygon->edges, old_size * sizeof (cairo_edge_t));
+    } else {
+	new_edges = realloc (polygon->edges, new_size * sizeof (cairo_edge_t));
+    }
 
     if (new_edges == NULL) {
 	return CAIRO_STATUS_NO_MEMORY;
diff --git a/src/cairoint.h b/src/cairoint.h
index 7a4c9d57..32519509 100755
--- a/src/cairoint.h
+++ b/src/cairoint.h
@@ -428,6 +428,7 @@ typedef struct _cairo_polygon {
     int num_edges;
     int edges_size;
     cairo_edge_t *edges;
+    cairo_edge_t  edges_embedded[8];
 } cairo_polygon_t;
 
 typedef struct _cairo_spline {