[gtk+] box-shadow: For top/bottom and left/right parts, repeat a single line

[Alexander Larsson <alexl src gnome org>]

commit 8e032622c864c5259786a72ca1b811603ae9ca09
Author: Alexander Larsson <alexl redhat com>
Date:   Fri Mar 20 14:56:42 2015 +0100

    box-shadow: For top/bottom and left/right parts, repeat a single line
    
    Since these part really are the same in all of the x or y direction
    and we don't blur in that direction we can just blur one line and
    repeat it during drawing.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746468

 gtk/gtkcairoblurprivate.h |    3 ++-
 gtk/gtkcssshadowvalue.c   |   29 +++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkcairoblurprivate.h b/gtk/gtkcairoblurprivate.h
index 970c082..68126d3 100644
--- a/gtk/gtkcairoblurprivate.h
+++ b/gtk/gtkcairoblurprivate.h
@@ -32,7 +32,8 @@ G_BEGIN_DECLS
 typedef enum {
   GTK_BLUR_NONE = 0,
   GTK_BLUR_X = 1<<0,
-  GTK_BLUR_Y = 1<<1
+  GTK_BLUR_Y = 1<<1,
+  GTK_BLUR_REPEAT = 1<<2
 } GtkBlurFlags;
 
 void            _gtk_cairo_blur_surface         (cairo_surface_t *surface,
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 341844f..ffdc2b6 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -328,6 +328,14 @@ gtk_css_shadow_value_start_drawing (const GtkCssValue *shadow,
   radius = _gtk_css_number_value_get (shadow->radius, 0);
   clip_radius = _gtk_cairo_blur_compute_pixels (radius);
 
+  if (blur_flags & GTK_BLUR_REPEAT)
+    {
+      if (!blur_x)
+        clip_rect.width = 1;
+      if (!blur_y)
+        clip_rect.height = 1;
+    }
+
   /* Create a larger surface to center the blur. */
   surface = cairo_surface_create_similar_image (cairo_get_target (cr),
                                                 CAIRO_FORMAT_A8,
@@ -350,6 +358,20 @@ gtk_css_shadow_value_start_drawing (const GtkCssValue *shadow,
   return blur_cr;
 }
 
+void
+mask_surface_repeat (cairo_t         *cr,
+                     cairo_surface_t *surface)
+{
+    cairo_pattern_t *pattern;
+
+    pattern = cairo_pattern_create_for_surface (surface);
+    cairo_pattern_set_extend (pattern, CAIRO_EXTEND_REPEAT);
+
+    cairo_mask (cr, pattern);
+
+    cairo_pattern_destroy (pattern);
+}
+
 static cairo_t *
 gtk_css_shadow_value_finish_drawing (const GtkCssValue *shadow,
                                      cairo_t           *cr,
@@ -370,7 +392,10 @@ gtk_css_shadow_value_finish_drawing (const GtkCssValue *shadow,
   _gtk_cairo_blur_surface (surface, radius, blur_flags);
 
   gdk_cairo_set_source_rgba (original_cr, _gtk_css_rgba_value_get_rgba (shadow->color));
-  cairo_mask_surface (original_cr, surface, 0, 0);
+  if (blur_flags & GTK_BLUR_REPEAT)
+    mask_surface_repeat (original_cr, surface);
+  else
+    cairo_mask_surface (original_cr, surface, 0, 0);
 
   cairo_destroy (cr);
 
@@ -740,7 +765,7 @@ _gtk_css_shadow_value_paint_box (const GtkCssValue   *shadow,
       /* Then the sides */
       for (i = 0; i < 4; i++)
        {
-          GtkBlurFlags blur_flags = 0;
+          GtkBlurFlags blur_flags = GTK_BLUR_REPEAT;
 
          if (i == GTK_CSS_TOP || i == GTK_CSS_BOTTOM)
            {