Implement color filter as GrGLEffect

include/gpu/GrEffect.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrEffect_DEFINED
 #define GrEffect_DEFINED
 
@@ skipping 77 matching lines @@
 
     /**
      * This function is used to perform optimizations. When called the color and validFlags params
      * indicate whether the input components to this effect in the FS will have known values.
      * validFlags is a bitfield of GrColorComponentFlags. The function updates both params to
      * indicate known values of its output. A component of the color param only has meaning if the
      * corresponding bit in validFlags is set.
      */
     virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const = 0;
 
+    /** Will this effect read the source color value? */
+    bool willUseInputColor() const { return fWillUseInputColor; }
+
     /** This object, besides creating back-end-specific helper objects, is used for run-time-type-
         identification. The factory should be an instance of templated class,
         GrTBackendEffectFactory. It is templated on the subclass of GrEffect. The subclass must have
         a nested type (or typedef) named GLEffect which will be the subclass of GrGLEffect created
         by the factory.
 
         Example:
         class MyCustomEffect : public GrEffect {
         ...
             virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE {
@@ skipping 106 matching lines @@
      * Subclasses call this from their constructor to register GrTextureAccesses. The effect
      * subclass manages the lifetime of the accesses (this function only stores a pointer). The
      * GrTextureAccess is typically a member field of the GrEffect subclass. This must only be
      * called from the constructor because GrEffects are immutable.
      */
     void addTextureAccess(const GrTextureAccess* textureAccess);
 
     GrEffect()
         : fWillReadDstColor(false)
         , fWillReadFragmentPosition(false)
+        , fWillUseInputColor(true)
         , fHasVertexCode(false)
         , fEffectRef(NULL) {}
 
     /** This should be called by GrEffect subclass factories. See the comment on AutoEffectUnref for
         an example factory function. */
     static GrEffectRef* CreateEffectRef(GrEffect* effect) {
         if (NULL == effect->fEffectRef) {
             effect->fEffectRef = SkNEW_ARGS(GrEffectRef, (effect));
         } else {
             effect->fEffectRef->ref();
@@ skipping 46 matching lines @@
      */
     void setWillReadDstColor() { fWillReadDstColor = true; }
 
     /**
      * If the effect will generate a backend-specific effect that will read the fragment position
      * in the FS then it must call this method from its constructor. Otherwise, the request to
      * access the fragment position will be denied.
      */
     void setWillReadFragmentPosition() { fWillReadFragmentPosition = true; }
 
+    /**
+     * If the effect will generate a result that does not depend on the input color value then it must
+     * call this function from its constructor. Otherwise, when its generated backend-specific code
+     * might fail during variable binding due to unused variables.
+     */
+    void setWillNotUseInputColor() { fWillUseInputColor = false; }
+
 private:
     bool isEqual(const GrEffect& other) const {
         if (&this->getFactory() != &other.getFactory()) {
             return false;
         }
         bool result = this->onIsEqual(other);
 #ifdef SK_DEBUG
         if (result) {
             this->assertEquality(other);
         }
@@ skipping 14 matching lines @@
     friend class GrEffectStage;  // to rewrap GrEffect in GrEffectRef when restoring an effect-stage
                                  // from deferred state, to call isEqual on naked GrEffects, and
                                  // to inc/dec deferred ref counts.
     friend class GrVertexEffect; // to set fHasVertexCode and build fVertexAttribTypes.
 
     SkSTArray<4, const GrCoordTransform*, true>  fCoordTransforms;
     SkSTArray<4, const GrTextureAccess*, true>   fTextureAccesses;
     SkSTArray<kMaxVertexAttribs, GrSLType, true> fVertexAttribTypes;
     bool                                         fWillReadDstColor;
     bool                                         fWillReadFragmentPosition;
+    bool                                         fWillUseInputColor;
     bool                                         fHasVertexCode;
     GrEffectRef*                                 fEffectRef;
 
     typedef SkRefCnt INHERITED;
 };
 
 inline GrEffectRef::GrEffectRef(GrEffect* effect) {
     SkASSERT(NULL != effect);
     effect->ref();
     fEffect = effect;
@@ skipping 10 matching lines @@
 };                                                                                                \
 static SkAlignedSStorage<k_##NAME##_StorageSize> g_##NAME##_Storage;                              \
 static void* NAME##_RefLocation = (char*)g_##NAME##_Storage.get() + k_##NAME##_EffectRefOffset;   \
 static GrEffect* NAME##_Effect SkNEW_PLACEMENT_ARGS(g_##NAME##_Storage.get(), EFFECT_CLASS, ARGS);\
 static SkAutoTDestroy<GrEffect> NAME##_ad(NAME##_Effect);                                         \
 static GrEffectRef* NAME(GrEffect::CreateStaticEffectRef(NAME##_RefLocation, NAME##_Effect));     \
 static SkAutoTDestroy<GrEffectRef> NAME##_Ref_ad(NAME)
 
 
 #endif