Fix filter primitive bounds computations.

include/core/SkImageFilter.h

Index: include/core/SkImageFilter.h
diff --git a/include/core/SkImageFilter.h b/include/core/SkImageFilter.h
index 909a2f82840e93c2c6842a3407ef3b67ec3eb893..08ebaf2696a2eed1f73f40326dfa538077700b17 100644
--- a/include/core/SkImageFilter.h
+++ b/include/core/SkImageFilter.h
@@ -346,6 +346,24 @@ protected:
     // implementation recursively unions all input bounds, or returns false if
     // no inputs.
     virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*) const;
+    enum MapDirection {
+        kForward_MapDirection,
+        kReverse_MapDirection
+    };
+
+    // Performs a forwards or reverse mapping of the given rect to accommodate

[reed1, 2015/12/09 16:11:41]

nit: can we use /** comment style here? Partly for consistency, and partly for
doxygen.

[Stephen White, 2015/12/09 17:02:57]

Done.

+    // this filter's margin requirements. kForward_MapDirection is used to
+    // determine the destination pixels which would be touched by filtering
+    // the given given source rect (e.g., given source bitmap bounds,
+    // determine the optimal bounds of the filtered offscreen bitmap).
+    // kReverse_MapDirection is used to determine which pixels of the
+    // input(s) would be required to fill the given destination rect
+    // (e.g., clip bounds). NOTE: these operations may not be the
+    // inverse of the other. For example, blurring expands the given rect
+    // in both forward and reverse directions. Unlike
+    // onFilterBounds(), this function is non-recursive.
+    virtual void onFilterNodeBounds(const SkIRect&, const SkMatrix&, SkIRect*,
+                                    MapDirection direction) const;
 
     // Helper function which invokes filter processing on the input at the
     // specified "index". If the input is null, it leaves "result" and
@@ -405,6 +423,14 @@ protected:
     virtual bool asFragmentProcessor(GrFragmentProcessor**, GrTexture*, const SkMatrix&,
                                      const SkIRect& bounds) const;
 
+    /**
+     *  Creates a modified Context for use when recursing up the image filter DAG.
+     *  The clip bounds are adjusted to accommodate any margins that this
+     *  filter requires by calling this node's
+     *  onFilterNodeBounds(..., kReverse_MapDirection).
+     */
+    Context mapContext(const Context& ctx) const;
+
 private:
     friend class SkGraphics;
     static void PurgeCache();