Consolidate FilterOperation and FilterEffect mapRect implementations

third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp

Index: third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp b/third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp
index 1527161d5a95be30a359dca05bd8921534a50ecf..0646df1a5242d925a0fe6f5a21111d7b7d53d340 100644
--- a/third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp
+++ b/third_party/WebKit/Source/platform/graphics/filters/FEGaussianBlur.cpp
@@ -31,54 +31,44 @@
 
 #include "SkBlurImageFilter.h"
 
-static inline float gaussianKernelFactor() {
-  return 3 / 4.f * sqrtf(twoPiFloat);
-}
-
 namespace blink {
 
-FEGaussianBlur::FEGaussianBlur(Filter* filter, float x, float y)
-    : FilterEffect(filter), m_stdX(x), m_stdY(y) {}
+namespace {
 
-FEGaussianBlur* FEGaussianBlur::create(Filter* filter, float x, float y) {
-  return new FEGaussianBlur(filter, x, y);
+inline unsigned approximateBoxWidth(float s) {
+  return static_cast<unsigned>(
+      floorf(s * (3 / 4.f * sqrtf(twoPiFloat)) + 0.5f));
 }
 
-IntSize FEGaussianBlur::calculateUnscaledKernelSize(const FloatPoint& std) {
-  ASSERT(std.x() >= 0 && std.y() >= 0);
-
+IntSize calculateKernelSize(const FloatSize& std) {
+  DCHECK(std.width() >= 0 && std.height() >= 0);
   IntSize kernelSize;
   // Limit the kernel size to 1000. A bigger radius won't make a big difference
   // for the result image but inflates the absolute paint rect too much. This is
   // compatible with Firefox' behavior.

[Stephen Chennney, 2016/10/10 19:43:25]

Where do we do this limiting? It would be nice of the comment to say where the
code is (or else the comment is out of date and should be removed).

[fs, 2016/10/10 20:40:03]

It looks like this comment has outstayed its welcome. It appears to have been
added in 695f3cdf1bfd5c171556245d73d842d3bb5ba32c (back in 2010) together with a
gMaxKernelSize (set to 1000) which was clamped against.
https://codereview.chromium.org/793873002 the dropped the clamping but
supposedly forgot to remove the comment. I guess remove it then.

[fs, 2016/10/10 20:43:53]

Dropped.

-  if (std.x()) {
-    int size = std::max<unsigned>(
-        2,
-        static_cast<unsigned>(floorf(std.x() * gaussianKernelFactor() + 0.5f)));
+  if (std.width()) {
+    int size = std::max<unsigned>(2, approximateBoxWidth(std.width()));
     kernelSize.setWidth(size);
   }
-
-  if (std.y()) {
-    int size = std::max<unsigned>(
-        2,
-        static_cast<unsigned>(floorf(std.y() * gaussianKernelFactor() + 0.5f)));
+  if (std.height()) {
+    int size = std::max<unsigned>(2, approximateBoxWidth(std.height()));
     kernelSize.setHeight(size);
   }
-
   return kernelSize;
 }
 
-IntSize FEGaussianBlur::calculateKernelSize(const Filter* filter,
-                                            const FloatPoint& std) {
-  FloatPoint stdError(filter->applyHorizontalScale(std.x()),
-                      filter->applyVerticalScale(std.y()));
-  return calculateUnscaledKernelSize(stdError);
 }
 
-FloatRect FEGaussianBlur::mapEffect(const FloatRect& rect) const {
-  IntSize kernelSize =
-      calculateKernelSize(getFilter(), FloatPoint(m_stdX, m_stdY));
+FEGaussianBlur::FEGaussianBlur(Filter* filter, float x, float y)
+    : FilterEffect(filter), m_stdX(x), m_stdY(y) {}
 
+FEGaussianBlur* FEGaussianBlur::create(Filter* filter, float x, float y) {
+  return new FEGaussianBlur(filter, x, y);
+}
+
+FloatRect FEGaussianBlur::mapEffect(const FloatSize& stdDeviation,
+                                    const FloatRect& rect) {
+  IntSize kernelSize = calculateKernelSize(stdDeviation);
   // We take the half kernel size and multiply it by three, because we run box
   // blur three times.
   FloatRect result = rect;
@@ -87,6 +77,12 @@ FloatRect FEGaussianBlur::mapEffect(const FloatRect& rect) const {
   return result;
 }
 
+FloatRect FEGaussianBlur::mapEffect(const FloatRect& rect) const {
+  FloatSize stdError(getFilter()->applyHorizontalScale(m_stdX),
+                     getFilter()->applyVerticalScale(m_stdY));
+  return mapEffect(stdError, rect);
+}
+
 sk_sp<SkImageFilter> FEGaussianBlur::createImageFilter() {
   sk_sp<SkImageFilter> input(
       SkiaImageFilterBuilder::build(inputEffect(0), operatingColorSpace()));