Bug 1042327. Use a more narrow workaround for pixman bug. r=jrmuizel

--HG--
extra : rebase_source : 4631ea06598c681a5729e225d4e2f495fbb2622b

gfx/src/nsRegion.h

@@ -103,7 +103,15 @@ public:
   }
   nsRegion& And(const nsRegion& aRegion, const nsRect& aRect)
   {
-    pixman_region32_intersect_rect(&mImpl, aRegion.Impl(), aRect.x, aRect.y, aRect.width, aRect.height);
+    // pixman has a bug where it doesn't validate the input to intersect_rect
+    // and can end up with regions with empty rects, so take the more round about route
+    // if we're passing in an empty rect.
+    if (aRect.IsEmpty()) {
+      SetEmpty();
+    } else {
+      pixman_region32_intersect_rect(&mImpl, aRegion.Impl(),
+                                     aRect.x, aRect.y, aRect.width, aRect.height);
+    }
     return *this;
   }
   nsRegion& And(const nsRect& aRect1, const nsRect& aRect2)
@@ -262,13 +270,7 @@ public:
   {
     return pixman_region32_equal(Impl(), aRegion.Impl());
   }
-  uint32_t GetNumRects () const
-  {
-    // Work around pixman bug. Sometimes pixman creates regions with 1 rect
-    // that's empty.
-    uint32_t result = pixman_region32_n_rects(Impl());
-    return (result == 1 && GetBounds().IsEmpty()) ? 0 : result;
-  }
+  uint32_t GetNumRects () const { return pixman_region32_n_rects(Impl()); }
   const nsRect GetBounds () const { return BoxToRect(mImpl.extents); }
   uint64_t Area () const;
   // Converts this region from aFromAPP, an appunits per pixel ratio, to
@@ -409,11 +411,6 @@ public:
     mRegion = &aRegion;
     i = 0;
     boxes = pixman_region32_rectangles(aRegion.Impl(), &n);
-    // Work around pixman bug. Sometimes pixman creates regions with 1 rect
-    // that's empty.
-    if (n == 1 && nsRegion::BoxToRect(boxes[0]).IsEmpty()) {
-      n = 0;
-    }
   }
 
   const nsRect* Next ()