gl: Add a gradient texture cache

For firefox-planet-gnome, 19135 times a gradient gets rendered using
only 10 different gradients. So we get a 100% hit rate in the cache.
Unfortunately, texture upload is not the biggest problem of this test,
as the performance increase is only moderate - at least on i965:
34.3s => 33.5s

src/cairo-gl-device.c

@@ -104,6 +104,8 @@ _gl_finish (void *device)
 
     _gl_lock (device);
 
+    _cairo_cache_fini (&ctx->gradients);
+
     _cairo_gl_context_fini_shaders (ctx);
 
     _gl_unlock (device);
@@ -201,7 +203,15 @@ _cairo_gl_context_init (cairo_gl_context_t *ctx)
 
     status = _cairo_gl_context_init_shaders (ctx);
     if (unlikely (status))
-	return status;
+        return status;
+
+    status = _cairo_cache_init (&ctx->gradients,
+                                _cairo_gl_gradient_equal,
+                                NULL,
+                                (cairo_destroy_func_t) _cairo_gl_gradient_destroy,
+                                CAIRO_GL_GRADIENT_CACHE_SIZE);
+    if (unlikely (status))
+        return status;
 
     /* Set up the dummy texture for tex_env_combine with constant color. */
     glGenTextures (1, &ctx->dummy_tex);

src/cairo-gl-gradient-private.h

@@ -41,6 +41,7 @@
 #ifndef CAIRO_GL_GRADIENT_PRIVATE_H
 #define CAIRO_GL_GRADIENT_PRIVATE_H
 
+#include "cairo-cache-private.h"
 #include "cairo-device-private.h"
 #include "cairo-reference-count-private.h"
 #include "cairo-types-private.h"
@@ -53,15 +54,19 @@
 #define GL_GLEXT_PROTOTYPES
 #include <GL/glext.h>
 
+#define CAIRO_GL_GRADIENT_CACHE_SIZE 4096
+
 /* XXX: Declare in a better place */
 typedef struct _cairo_gl_context cairo_gl_context_t;
 
 typedef struct _cairo_gl_gradient {
-    cairo_reference_count_t   ref_count;
-    cairo_device_t           *device; /* NB: we don't hold a reference */
-    GLuint                    tex;
-    unsigned int	      n_stops;
-    cairo_gradient_stop_t     stops[2];
+    cairo_cache_entry_t           cache_entry;
+    cairo_reference_count_t       ref_count;
+    cairo_device_t               *device; /* NB: we don't hold a reference */
+    GLuint                        tex;
+    unsigned int	          n_stops;
+    const cairo_gradient_stop_t  *stops;
+    cairo_gradient_stop_t         stops_embedded[2];
 } cairo_gl_gradient_t;
 
 cairo_private cairo_int_status_t
@@ -76,5 +81,8 @@ _cairo_gl_gradient_reference (cairo_gl_gradient_t *gradient);
 cairo_private void
 _cairo_gl_gradient_destroy (cairo_gl_gradient_t *gradient);
 
+cairo_private cairo_bool_t
+_cairo_gl_gradient_equal (const void *key_a, const void *key_b);
+
 
 #endif /* CAIRO_GL_GRADIENT_PRIVATE_H */

src/cairo-gl-gradient.c

@@ -149,12 +149,49 @@ _cairo_gl_gradient_render (const cairo_gl_context_t    *ctx,
     return CAIRO_STATUS_SUCCESS;
 }
 
+static unsigned long
+_cairo_gl_gradient_hash (unsigned int                  n_stops,
+                         const cairo_gradient_stop_t  *stops)
+{
+    return _cairo_hash_bytes (n_stops,
+                              stops,
+                              sizeof (cairo_gradient_stop_t) * n_stops);
+}
+
+static cairo_gl_gradient_t *
+_cairo_gl_gradient_lookup (cairo_gl_context_t           *ctx,
+                           unsigned long                 hash,
+                           unsigned int                  n_stops,
+                           const cairo_gradient_stop_t  *stops)
+{
+    cairo_gl_gradient_t lookup;
+
+    lookup.cache_entry.hash = hash,
+    lookup.n_stops = n_stops;
+    lookup.stops = stops;
+
+    return _cairo_cache_lookup (&ctx->gradients, &lookup.cache_entry);
+}
+
+cairo_bool_t
+_cairo_gl_gradient_equal (const void *key_a, const void *key_b)
+{
+    const cairo_gl_gradient_t *a = key_a;
+    const cairo_gl_gradient_t *b = key_b;
+
+    if (a->n_stops != b->n_stops)
+        return FALSE;
+
+    return memcmp (a->stops, b->stops, a->n_stops * sizeof (cairo_gradient_stop_t)) == 0;
+}
+
 cairo_int_status_t
 _cairo_gl_gradient_create (cairo_gl_context_t           *ctx,
                            unsigned int                  n_stops,
                            const cairo_gradient_stop_t  *stops,
                            cairo_gl_gradient_t         **gradient_out)
 {
+    unsigned long hash;
     cairo_gl_gradient_t *gradient;
     int tex_width;
     void *data;
@@ -163,16 +200,27 @@ _cairo_gl_gradient_create (cairo_gl_context_t           *ctx,
     if ((unsigned int) ctx->max_texture_size / 2 <= n_stops)
         return CAIRO_INT_STATUS_UNSUPPORTED;
 
+    hash = _cairo_gl_gradient_hash (n_stops, stops);
+    
+    gradient = _cairo_gl_gradient_lookup (ctx, hash, n_stops, stops);
+    if (gradient) {
+        *gradient_out = _cairo_gl_gradient_reference (gradient);
+        return CAIRO_STATUS_SUCCESS;
+    }
+
     gradient = malloc (sizeof (cairo_gl_gradient_t) + sizeof (cairo_gradient_stop_t) * (n_stops - 2));
     if (gradient == NULL)
         return _cairo_error (CAIRO_STATUS_NO_MEMORY);
 
+    tex_width = _cairo_gl_gradient_sample_width (n_stops, stops);
+
     CAIRO_REFERENCE_COUNT_INIT (&gradient->ref_count, 1);
+    gradient->cache_entry.hash = hash;
+    gradient->cache_entry.size = tex_width;
     gradient->device = &ctx->base;
     gradient->n_stops = n_stops;
-    memcpy (gradient->stops, stops, n_stops * sizeof (cairo_gradient_stop_t));
-
-    tex_width = _cairo_gl_gradient_sample_width (n_stops, stops);
+    gradient->stops = gradient->stops_embedded;
+    memcpy (gradient->stops_embedded, stops, n_stops * sizeof (cairo_gradient_stop_t));
 
     glBindBufferARB (GL_PIXEL_UNPACK_BUFFER_ARB, ctx->texture_load_pbo);
     glBufferDataARB (GL_PIXEL_UNPACK_BUFFER_ARB, tex_width * sizeof (uint32_t), 0, GL_STREAM_DRAW);
@@ -190,6 +238,10 @@ _cairo_gl_gradient_create (cairo_gl_context_t           *ctx,
 
     glBindBufferARB (GL_PIXEL_UNPACK_BUFFER_ARB, 0);
 
+    /* we ignore errors here and just return an uncached gradient */
+    if (likely (! _cairo_cache_insert (&ctx->gradients, &gradient->cache_entry)))
+        _cairo_gl_gradient_reference (gradient);
+
     *gradient_out = gradient;
     return CAIRO_STATUS_SUCCESS;
 }

src/cairo-gl-private.h

@@ -181,6 +181,8 @@ struct _cairo_gl_context {
     cairo_gl_shader_t fill_rectangles_shader;
     cairo_cache_t shaders;
 
+    cairo_cache_t gradients;
+
     cairo_gl_glyph_cache_t glyph_cache[2];
     cairo_list_t fonts;