Implement -webkit-box-reflect as a filter.

third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h

Index: third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h
diff --git a/third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h b/third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h
index f7a2668cc3c5c6ca15bce8ed64c8e48e1dd2f21e..157b9373b30f618bae7fa8813feb21a07c569693 100644
--- a/third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h
+++ b/third_party/WebKit/Source/platform/graphics/filters/FilterOperation.h
@@ -29,6 +29,7 @@
 #include "platform/Length.h"
 #include "platform/PlatformExport.h"
 #include "platform/graphics/Color.h"
+#include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/filters/Filter.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Noncopyable.h"
@@ -56,6 +57,7 @@ public:
         CONTRAST,
         BLUR,
         DROP_SHADOW,
+        BOX_REFLECT,

[pdr., 2016/03/29 18:36:55]

Can you add a very short comment describing this and mentioning that it isn't a
web exposed filter type?

I like the way this is implemented. WDYT about suggesting "filter:
box-reflect(...)" to the specs group as a way to spec reflection?

[Stephen White, 2016/03/30 14:41:35]

+1

[jbroman, 2016/04/05 15:51:56]

I'd think that specifying something more similar to what developers actually use
today
would be more practical. I'm not sure there actually is demand for arbitrarily
interleaving
these. It's also a little funny in that it's sensitive to the border box (it
uses it to position
itself), which seems a little stranger in the general case.

I think I'd envision specifying (or at least internally thinking of it as)
something like this:

  Name: box-reflect
  Value: none | [ above | below | right | left ]? <length>? <image>?
  Initial: none
  Applies to: all elements
  Inherited: no
  (etc)

  If the value of the 'box-reflect' property is not 'none', then it renders
  as though there were an additional filter function at the end of the 'filter'
  property, which behaves as follows: <details of reflection, alignment, etc.
here>

I could imagine going further and adding it as an explicit filter function, but
that seems
like more work that I'm not sure would be valued.

         NONE
     };
 
@@ -74,6 +76,7 @@ public:
         case DROP_SHADOW:
             return true;
         case REFERENCE:
+        case BOX_REFLECT:
             return false;
         case NONE:
             break;
@@ -314,7 +317,35 @@ private:
 
 DEFINE_FILTER_OPERATION_TYPE_CASTS(DropShadowFilterOperation, DROP_SHADOW);
 
-} // namespace blink
+class PLATFORM_EXPORT BoxReflectFilterOperation : public FilterOperation {
+public:
+    static PassRefPtrWillBeRawPtr<BoxReflectFilterOperation> create(ReflectionDirection direction, float offset)
+    {
+        return adoptRefWillBeNoop(new BoxReflectFilterOperation(direction, offset));
+    }
+
+    ReflectionDirection direction() const { return m_direction; }
+    float offset() const { return m_offset; }
 
+    bool affectsOpacity() const override { return true; }
+    bool movesPixels() const override { return true; }
+
+private:
+    PassRefPtrWillBeRawPtr<FilterOperation> blend(const FilterOperation* from, double progress) const override;
+    bool operator==(const FilterOperation&) const override;
+
+    BoxReflectFilterOperation(ReflectionDirection direction, float offset)
+        : FilterOperation(BOX_REFLECT)
+        , m_direction(direction)
+        , m_offset(offset)
+    {
+    }
+
+    ReflectionDirection m_direction;
+    float m_offset;
+};
+DEFINE_FILTER_OPERATION_TYPE_CASTS(BoxReflectFilterOperation, BOX_REFLECT);
+
+} // namespace blink
 
 #endif // FilterOperation_h