Make GrGLShaderBuilder check whether GrEffect advertised that it would require the dst color or frag

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 135 matching lines @@
     int numTextures() const { return fTextureAccesses.count(); }
 
     /** Returns the access pattern for the texture at index. index must be valid according to
         numTextures(). */
     const GrTextureAccess& textureAccess(int index) const { return *fTextureAccesses[index]; }
 
     /** Shortcut for textureAccess(index).texture(); */
     GrTexture* texture(int index) const { return this->textureAccess(index).getTexture(); }
 
     /** Will this effect read the destination pixel value? */
-    bool willReadDst() const { return fWillReadDst; }
+    bool willReadDstColor() const { return fWillReadDstColor; }
+
+    /** Will this effect read the fragment position? */
+    bool willReadFragmentPosition() const { return fWillReadFragmentPosition; }
 
     int numVertexAttribs() const { return fVertexAttribTypes.count(); }
 
     GrSLType vertexAttribType(int index) const { return fVertexAttribTypes[index]; }
 
     static const int kMaxVertexAttribs = 2;
 
     /** Useful for effects that want to insert a texture matrix that is implied by the texture
         dimensions */
     static inline SkMatrix MakeDivByTextureWHMatrix(const GrTexture* texture) {
@@ skipping 39 matching lines @@
      */
     void addTextureAccess(const GrTextureAccess* textureAccess);
 
     /**
      * Subclasses call this from their constructor to register vertex attributes (at most
      * kMaxVertexAttribs). This must only be called from the constructor because GrEffects are
      * immutable.
      */
     void addVertexAttrib(GrSLType type);
 
-    GrEffect() : fWillReadDst(false), fEffectRef(NULL) {}
+    GrEffect() : fWillReadDstColor(false), fWillReadFragmentPosition(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();
         }
         return effect->fEffectRef;
@@ skipping 35 matching lines @@
     template <typename T>
     static const T& CastEffect(const GrEffect& effectRef) {
         return *static_cast<const T*>(&effectRef);
     }
 
     /**
      * If the effect subclass will read the destination pixel value then it must call this function
      * from its constructor. Otherwise, when its generated backend-specific effect class attempts
      * to generate code that reads the destination pixel it will fail.
      */
-    void setWillReadDst() { fWillReadDst = true; }
+    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; }
 
 private:
     bool isEqual(const GrEffect& other) const {
         if (&this->getFactory() != &other.getFactory()) {
             return false;
         }
         bool result = this->onIsEqual(other);
 #if GR_DEBUG
         if (result) {
             GrAssert(this->numTextures() == other.numTextures());
@@ skipping 12 matching lines @@
 
     void EffectRefDestroyed() { fEffectRef = NULL; }
 
     friend class GrEffectRef;   // to call EffectRefDestroyed()
     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.
 
     SkSTArray<4, const GrTextureAccess*, true>   fTextureAccesses;
     SkSTArray<kMaxVertexAttribs, GrSLType, true> fVertexAttribTypes;
-    bool                                         fWillReadDst;
+    bool                                         fWillReadDstColor;
+    bool                                         fWillReadFragmentPosition;
     GrEffectRef*                                 fEffectRef;
 
     typedef GrRefCnt INHERITED;
 };
 
 inline GrEffectRef::GrEffectRef(GrEffect* effect) {
     GrAssert(NULL != effect);
     effect->ref();
     fEffect = effect;
 }
 
 /**
  * This creates an effect outside of the effect memory pool. The effect's destructor will be called
  * at global destruction time. NAME will be the name of the created GrEffectRef.
  */
 #define GR_CREATE_STATIC_EFFECT(NAME, EFFECT_CLASS, ARGS)                                         \
 enum {                                                                                            \
     k_##NAME##_EffectRefOffset = GR_CT_ALIGN_UP(sizeof(EFFECT_CLASS), 8),                         \
     k_##NAME##_StorageSize = k_##NAME##_EffectRefOffset + sizeof(GrEffectRef)                     \
 };                                                                                                \
 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