[gtk+] css: Avoid excessive shadow rendering

[Matthias Clasen <matthiasc src gnome org>]

commit cb3393f001b432cf863dc3d2e8eba63b5a8a6647
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Dec 2 08:29:24 2014 -0500

    css: Avoid excessive shadow rendering
    
    The shadow rendering code had code to exit early if we determine
    that the shadow is entirely clipped away. Unfortunately, the check
    based on cairo clip extents fails for any clip regions that are
    more complicated than axis-aligned rectangles, and we are using
    a hollow rounded rectangle here. So, instead, do the check manually,
    using the just-introduced API in GtkRoundedBox.

 gtk/gtkcssshadowvalue.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)
---
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index d3847ba..4ea2f76 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -638,9 +638,15 @@ _gtk_css_shadow_value_paint_box (const GtkCssValue   *shadow,
 {
   GtkRoundedBox box, clip_box;
   double spread, radius, clip_radius, x, y, outside;
+  double x1, y1, x2, y2;
 
   g_return_if_fail (shadow->class == &GTK_CSS_VALUE_SHADOW);
 
+  cairo_clip_extents (cr, &x1, &y1, &x2, &y2);
+  if ((shadow->inset && !_gtk_rounded_box_intersects_rectangle (padding_box, x1, y1, x2, y2)) ||
+      (!shadow->inset && _gtk_rounded_box_contains_rectangle (padding_box, x1, y1, x2, y2)))
+    return;
+
   cairo_save (cr);
 
   spread = _gtk_css_number_value_get (shadow->spread, 0);
@@ -658,7 +664,6 @@ _gtk_css_shadow_value_paint_box (const GtkCssValue   *shadow,
     {
       cairo_set_fill_rule (cr, CAIRO_FILL_RULE_EVEN_ODD);
       _gtk_rounded_box_path (padding_box, cr);
-
       outside = spread + clip_radius + MAX (fabs (x), fabs (y));
       clip_box = *padding_box;
       _gtk_rounded_box_grow (&clip_box, outside, outside, outside, outside);
@@ -667,12 +672,6 @@ _gtk_css_shadow_value_paint_box (const GtkCssValue   *shadow,
       cairo_clip (cr);
     }
 
-  if (has_empty_clip (cr))
-    {
-      cairo_restore (cr);
-      return;
-    }
-
   box = *padding_box;
   _gtk_rounded_box_move (&box, x, y);