Implement cc::FilterOperations::MapRect.

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 1b2cca70060d2868caae9c49701f49ee8fa692e5..37ff8711c2b6a2c628747d5defb18395f4d6301f 100644
--- a/cc/output/filter_operation.cc
+++ b/cc/output/filter_operation.cc
@@ -11,6 +11,9 @@
 #include "cc/base/math_util.h"
 #include "cc/output/filter_operation.h"
 #include "ui/gfx/animation/tween.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/rect_conversions.h"
+#include "ui/gfx/skia_util.h"
 
 namespace cc {
 
@@ -317,4 +320,41 @@ void FilterOperation::AsValueInto(base::trace_event::TracedValue* value) const {
   }
 }
 
+static int SpreadForStdDeviation(float std_deviation) {
+  // https://dvcs.w3.org/hg/FXTF/raw-file/tip/filters/index.html#feGaussianBlurElement
+  // provides this approximation for evaluating a gaussian blur by a triple box
+  // filter.
+  float d = floorf(std_deviation * 3.f * sqrt(8.f * atan(1.f)) / 4.f + 0.5f);
+  return static_cast<int>(ceilf(d * 3.f / 2.f));
+}
+
+gfx::Rect FilterOperation::MapRect(const gfx::Rect& rect) const {
+  switch (type_) {
+    case FilterOperation::BLUR: {
+      int spread = SpreadForStdDeviation(amount());
+      gfx::Rect result = rect;
+      result.Inset(-spread, -spread, -spread, -spread);
+      return result;
+    }
+    case FilterOperation::DROP_SHADOW: {
+      int spread = SpreadForStdDeviation(amount());
+      gfx::Rect result = rect;
+      result.Inset(-spread, -spread, -spread, -spread);
+      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, SkMatrix::I(), SkImageFilter::kForward_MapDirection);
+      return gfx::SkIRectToRect(out_rect);
+    }
+    default:
+      return rect;
+  }
+}
+
 }  // namespace cc