[gtk+] blur: Use recording surface for capturing things to blur

[Benjamin Otte <otte src gnome org>]

commit f2cb8f12705ab3a36767df3430f8868ed7b29536
Author: Benjamin Otte <otte redhat com>
Date:   Thu Sep 20 02:39:35 2012 +0200

    blur: Use recording surface for capturing things to blur
    
    This gets around clipping issues quite nicely and provides us with a
    (mostly theoretical) performance boost.

 gtk/gtkcssshadowvalue.c |   45 +++++++++++++++++++++++++++++++++------------
 1 files changed, 33 insertions(+), 12 deletions(-)
---
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 56ebe3a..7d4acbc 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -21,6 +21,8 @@
 
 #include "gtkcssshadowvalueprivate.h"
 
+#include <math.h>
+
 #include "gtkcairoblurprivate.h"
 #include "gtkcssnumbervalueprivate.h"
 #include "gtkcssrgbavalueprivate.h"
@@ -309,7 +311,7 @@ static cairo_t *
 gtk_css_shadow_value_start_drawing (const GtkCssValue *shadow,
                                     cairo_t           *cr)
 {
-  cairo_rectangle_int_t clip_rect;
+  cairo_rectangle_t clip;
   cairo_surface_t *surface;
   cairo_t *blur_cr;
   gdouble radius;
@@ -318,13 +320,16 @@ gtk_css_shadow_value_start_drawing (const GtkCssValue *shadow,
   if (radius == 0.0)
     return cr;
 
-  gdk_cairo_get_clip_rectangle (cr, &clip_rect);
+  radius = ceil (radius);
+  cairo_clip_extents (cr, &clip.x, &clip.y, &clip.width, &clip.height);
+  clip.x -= radius;
+  clip.y -= radius;
+  clip.width += 2 * radius;
+  clip.height += 2 * radius;
 
   /* Create a larger surface to center the blur. */
-  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
-                                        clip_rect.width + 2 * radius,
-                                        clip_rect.height + 2 * radius);
-  cairo_surface_set_device_offset (surface, radius - clip_rect.x, radius - clip_rect.y);
+  surface = cairo_recording_surface_create (CAIRO_CONTENT_COLOR_ALPHA, &clip);
+  cairo_surface_set_device_offset (surface, - clip.x, - clip.y);
   blur_cr = cairo_create (surface);
   cairo_set_user_data (blur_cr, &shadow_key, cairo_reference (cr), (cairo_destroy_func_t) cairo_destroy);
 
@@ -344,23 +349,39 @@ gtk_css_shadow_value_finish_drawing (const GtkCssValue *shadow,
                                      cairo_t           *cr)
 {
   gdouble radius;
-  cairo_t *original_cr;
-  cairo_surface_t *surface;
+  cairo_t *original_cr, *image_cr;
+  cairo_surface_t *recording_surface, *image_surface;
+  cairo_rectangle_t ink;
 
   radius = _gtk_css_number_value_get (shadow->radius, 0);
   if (radius == 0.0)
     return cr;
 
-  surface = cairo_get_target (cr);
+  recording_surface = cairo_get_target (cr);
   original_cr = cairo_get_user_data (cr, &shadow_key);
 
   /* Blur the surface. */
-  _gtk_cairo_blur_surface (surface, radius);
-
-  cairo_set_source_surface (original_cr, surface, 0, 0);
+  cairo_recording_surface_ink_extents (recording_surface, &ink.x, &ink.y, &ink.width, &ink.height);
+  ink.width = ceil (ink.width + ink.x - floor (ink.x)) + 2 * ceil (radius);
+  ink.height = ceil (ink.height + ink.y - floor (ink.y)) + 2 * ceil (radius);
+  ink.x = floor (ink.x) + ceil (radius);
+  ink.y = floor (ink.y) + ceil (radius);
+
+  image_surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, ink.width, ink.height);
+  cairo_surface_set_device_offset (image_surface, - ink.x, - ink.y);
+  
+  image_cr = cairo_create (image_surface);
+  cairo_set_source_surface (image_cr, recording_surface, 0, 0);
+  cairo_paint (image_cr);
+  cairo_destroy (image_cr);
+
+  _gtk_cairo_blur_surface (image_surface, radius);
+
+  cairo_set_source_surface (original_cr, image_surface, 0, 0);
   cairo_paint (original_cr);
 
   cairo_destroy (cr);
+  cairo_surface_destroy (image_surface);
 
   return original_cr;
 }