Use child processors to implement compose color filter.

include/core/SkColorFilter.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkColorFilter_DEFINED
 #define SkColorFilter_DEFINED
 
@@ skipping 106 matching lines @@
     /** Construct a colorfilter whose effect is to first apply the inner filter and then apply
      *  the outer filter to the result of the inner's.
      *  The reference counts for outer and inner are incremented.
      *
      *  Due to internal limits, it is possible that this will return NULL, so the caller must
      *  always check.
      */
     static SkColorFilter* CreateComposeFilter(SkColorFilter* outer, SkColorFilter* inner);
 
     /**
-     *  A subclass may implement this factory function to work with the GPU backend.
-     *  If it returns true, then 1 or more fragment processors will have been appended to the
-     *  array, each of which has been ref'd, so that the caller is responsible for calling unref()
-     *  on them when they are finished. If more than one processor is appended, they will be
-     *  applied in FIFO order.
+     *  A subclass may implement this factory function to work with the GPU backend. It returns
+     *  a GrFragmentProcessor that implemets the color filter in GPU shader code.
      *
-     *  The fragment processor(s) must each return their color as a premul normalized value
-     *  e.g. each component between [0..1] and each color component <= alpha.
+     *  The fragment processor receives a premultiplied input color and produces a premultiplied
+     *  output color.
      *
-     *  If the subclass returns false, then it should not modify the array at all.
+     *  A null return indicates that the color filter isn't implemented for the GPU backend.
      */
-    virtual bool asFragmentProcessors(GrContext*, GrProcessorDataManager*,
-                                      SkTDArray<const GrFragmentProcessor*>*) const {
-        return false;
+    virtual const GrFragmentProcessor* asFragmentProcessor(GrContext*,
+                                                           GrProcessorDataManager*) const {
+        return nullptr;
     }
 
     bool affectsTransparentBlack() const {
         return this->filterColor(0) != 0;
     }
 
     SK_TO_STRING_PUREVIRT()
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
     SK_DEFINE_FLATTENABLE_TYPE(SkColorFilter)
 
 protected:
     SkColorFilter() {}
 
 private:
     /*
      *  Returns 1 if this is a single filter (not a composition of other filters), otherwise it
      *  reutrns the number of leaf-node filters in a composition. This should be the same value
      *  as the number of GrFragmentProcessors returned by asFragmentProcessors's array parameter.
      *
      *  e.g. compose(filter, compose(compose(filter, filter), filter)) --> 4
      */
     virtual int privateComposedFilterCount() const { return 1; }
     friend class SkComposeColorFilter;
 
     typedef SkFlattenable INHERITED;
 };
 
 #endif