Adds filter support for offscreen canvas

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp

Index: third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
index dcc455b8659eda3ccc7c754e942228e0c205f3db..98c248c184bf90f8ef1733e6bb80347e2a4492b3 100644
--- a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2DState.cpp
@@ -272,6 +272,40 @@ void CanvasRenderingContext2DState::resetTransform() {
   m_isTransformInvertible = true;
 }
 
+sk_sp<SkImageFilter> CanvasRenderingContext2DState::getFilterForOffscreenCanvas(
+    IntSize canvasSize) const {
+  if (!m_filterValue)
+    return nullptr;
+
+  if (m_resolvedFilter)
+    return m_resolvedFilter;
+
+  FilterOperations operations =
+      FilterOperationResolver::createOffscreenFilterOperations(*m_filterValue);
+
+  // We can't reuse m_fillPaint and m_strokePaint for the filter, since these
+  // incorporate the global alpha, which isn't applicable here.
+  SkPaint fillPaintForFilter;
+  m_fillStyle->applyToPaint(fillPaintForFilter);
+  fillPaintForFilter.setColor(m_fillStyle->paintColor());
+  SkPaint strokePaintForFilter;
+  m_strokeStyle->applyToPaint(strokePaintForFilter);
+  strokePaintForFilter.setColor(m_strokeStyle->paintColor());
+
+  FilterEffectBuilder filterEffectBuilder(
+      FloatRect((FloatPoint()), FloatSize(canvasSize)),
+      1.0f,  // Deliberately ignore zoom on the canvas element.
+      &fillPaintForFilter, &strokePaintForFilter);
+
+  FilterEffect* lastEffect = filterEffectBuilder.buildFilterEffect(operations);
+  if (lastEffect) {
+    m_resolvedFilter =
+        SkiaImageFilterBuilder::build(lastEffect, ColorSpaceDeviceRGB);
+  }
+
+  return m_resolvedFilter;
+}
+
 sk_sp<SkImageFilter> CanvasRenderingContext2DState::getFilter(
     Element* styleResolutionHost,
     IntSize canvasSize,
@@ -329,6 +363,13 @@ sk_sp<SkImageFilter> CanvasRenderingContext2DState::getFilter(
   return m_resolvedFilter;
 }
 
+bool CanvasRenderingContext2DState::hasFilterForOffscreenCanvas(
+    IntSize canvasSize) const {
+  // Checking for a non-null m_filterValue isn't sufficient, since this value
+  // might refer to a non-existent filter.
+  return !!getFilterForOffscreenCanvas(canvasSize);

[esprehn, 2017/01/27 19:44:39]

This is super wasteful since you do all the work to create the filter and then
throw it away. I see the non-off screen canvas one does this too though.

[fserb, 2017/01/27 19:54:47]

The problem is there's no way to know if you actually have a proper filter
unless you try to compute it. I can create a bug to investigate this and try to
come up with a better architecture.

+}
+
 bool CanvasRenderingContext2DState::hasFilter(
     Element* styleResolutionHost,
     IntSize canvasSize,