[gtk+] gtkcssshadowvalue: Use cairo_surface_create_similar_image

[Jasper St. Pierre <jstpierre src gnome org>]

commit e6a0378289909a5ac6f7824560147565eb01737e
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Sep 2 11:21:02 2014 -0700

    gtkcssshadowvalue: Use cairo_surface_create_similar_image
    
    Calling this on an Xlib surface allows us to keep this in SHM memory,
    giving it a potential speedup so we don't have to copy it to SHM memory
    for the Composite when we mask later.

 gtk/gtkcssshadowvalue.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 671f4f0..7f72698 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -331,9 +331,10 @@ gtk_css_shadow_value_start_drawing (const GtkCssValue *shadow,
   clip_radius = _gtk_cairo_blur_compute_pixels (radius);
 
   /* Create a larger surface to center the blur. */
-  surface = cairo_image_surface_create (CAIRO_FORMAT_A8,
-                                        clip_rect.width + 2 * clip_radius,
-                                        clip_rect.height + 2 * clip_radius);
+  surface = cairo_surface_create_similar_image (cairo_get_target (cr),
+                                                CAIRO_FORMAT_A8,
+                                                clip_rect.width + 2 * clip_radius,
+                                                clip_rect.height + 2 * clip_radius);
   cairo_surface_set_device_offset (surface, clip_radius - clip_rect.x, clip_radius - clip_rect.y);
   blur_cr = cairo_create (surface);
   cairo_set_user_data (blur_cr, &shadow_key, cairo_reference (cr), (cairo_destroy_func_t) cairo_destroy);