cc: Implement and use FilterOperations::MapRectReverse for mapping backdrop bounding box.

cc/output/filter_operation.cc

Index: cc/output/filter_operation.cc
diff --git a/cc/output/filter_operation.cc b/cc/output/filter_operation.cc
index 78588748ba59d63c5d68bd35e1df56cba76f0d22..efa91b4347f46a78d53082eda67f60861e2f5bf4 100644
--- a/cc/output/filter_operation.cc
+++ b/cc/output/filter_operation.cc
@@ -327,14 +327,18 @@ gfx::Rect FilterOperation::MapRect(const gfx::Rect& rect,
   switch (type_) {
     case FilterOperation::BLUR: {
       SkVector spread = MapStdDeviation(amount(), matrix);
+      float spreadX = std::abs(spread.x());
+      float spreadY = std::abs(spread.y());
       gfx::Rect result = rect;
-      result.Inset(-spread.x(), -spread.y(), -spread.x(), -spread.y());
+      result.Inset(-spreadX, -spreadY, -spreadX, -spreadY);
       return result;
     }
     case FilterOperation::DROP_SHADOW: {
       SkVector spread = MapStdDeviation(amount(), matrix);
+      float spreadX = std::abs(spread.x());
+      float spreadY = std::abs(spread.y());
       gfx::Rect result = rect;
-      result.Inset(-spread.x(), -spread.y(), -spread.x(), -spread.y());
+      result.Inset(-spreadX, -spreadY, -spreadX, -spreadY);
       result += drop_shadow_offset().OffsetFromOrigin();
       result.Union(rect);
       return result;
@@ -352,4 +356,38 @@ gfx::Rect FilterOperation::MapRect(const gfx::Rect& rect,
   }
 }
 
+gfx::Rect FilterOperation::MapRectReverse(const gfx::Rect& rect,

[Stephen White, 2016/06/07 16:00:34]

This looks awfully similar to the existing flavour above. Could we instead have
MapRect() take an (optional) MapDirection, and just have this one call it?

[jbroman, 2016/06/08 15:17:37]

Done.

+                                          const SkMatrix& matrix) const {
+  switch (type_) {
+    case FilterOperation::BLUR: {
+      SkVector spread = MapStdDeviation(amount(), matrix);
+      float spreadX = std::abs(spread.x());

[Stephen White, 2016/06/07 16:00:34]

If this needs to be abs'ed to handle negative scale, chances we'll need to check
the SkBlurImageFilter's version too (for reference filters). Might want to add a
reference filter FEGaussianBlur + reflection test.

[jbroman, 2016/06/08 15:17:37]

SkBlurImageFilter does apply abs:

sigma.fX = SkMinScalar(SkScalarAbs(sigma.fX), MAX_SIGMA);
sigma.fY = SkMinScalar(SkScalarAbs(sigma.fY), MAX_SIGMA);

[Stephen White, 2016/06/08 22:05:23]

So it does. Thanks!

+      float spreadY = std::abs(spread.y());
+      gfx::Rect result = rect;
+      result.Inset(-spreadX, -spreadY, -spreadX, -spreadY);
+      return result;
+    }
+    case FilterOperation::DROP_SHADOW: {
+      SkVector spread = MapStdDeviation(amount(), matrix);
+      float spreadX = std::abs(spread.x());
+      float spreadY = std::abs(spread.y());
+      gfx::Rect result = rect;
+      result.Inset(-spreadX, -spreadY, -spreadX, -spreadY);
+      result -= drop_shadow_offset().OffsetFromOrigin();
+      result.Union(rect);
+      return result;
+    }
+    case FilterOperation::REFERENCE: {
+      if (!image_filter())
+        return rect;
+      SkIRect in_rect = gfx::RectToSkIRect(rect);
+      SkIRect out_rect = image_filter()->filterBounds(
+          in_rect, matrix, SkImageFilter::kReverse_MapDirection);
+      return gfx::SkIRectToRect(out_rect);
+    }
+    default:
+      return rect;
+  }
+}
+
 }  // namespace cc