Make GrGLShaderBuilder responsible for enabling GLSL extensions

src/gpu/gl/GrGLShaderBuilder.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 GrGLShaderBuilder_DEFINED
 #define GrGLShaderBuilder_DEFINED
 
@@ skipping 66 matching lines @@
 
     enum ShaderType {
         kVertex_ShaderType   = 0x1,
         kGeometry_ShaderType = 0x2,
         kFragment_ShaderType = 0x4,
     };
 
     GrGLShaderBuilder(const GrGLContextInfo&, GrGLUniformManager&, bool explicitLocalCoords);
 
     /**
+     * Use of these features may require a GLSL extension to be enabled. Shaders may not compile
+     * if code is added that uses one of these features without calling enableFeature()
+     */
+    enum GLSLFeature {
+        kStandardDerivatives_GLSLFeature = 0,
+
+        kLastGLSLFeature = kStandardDerivatives_GLSLFeature
+    };
+
+    /**
+     * If the feature is supported then true is returned and any necessary #extension declarations
+     * are added to the shaders. If the feature is not supported then false will be returned.
+     */
+    bool enableFeature(GLSLFeature);
+
+    /**
      * Called by GrGLEffects to add code to one of the shaders.
      */
     void vsCodeAppendf(const char format[], ...) SK_PRINTF_LIKE(2, 3) {
         va_list args;
         va_start(args, format);
         this->codeAppendf(kVertex_ShaderType, format, args);
         va_end(args);
     }
 
     void gsCodeAppendf(const char format[], ...) SK_PRINTF_LIKE(2, 3) {
@@ skipping 165 matching lines @@
 
     void appendDecls(const VarArray&, SkString*) const;
     void appendUniformDecls(ShaderType, SkString*) const;
 
     typedef GrGLUniformManager::BuilderUniform BuilderUniform;
     GrGLUniformManager::BuilderUniformArray fUniforms;
 
     // TODO: Everything below here private.
 public:
 
-    SkString    fHeader; // VS+FS, GLSL version, etc
     VarArray    fVSAttrs;
     VarArray    fVSOutputs;
     VarArray    fGSInputs;
     VarArray    fGSOutputs;
     VarArray    fFSInputs;
     SkString    fGSHeader; // layout qualifiers specific to GS
     VarArray    fFSOutputs;
     bool        fUsesGS;
 
 private:
     enum {
         kNonStageIdx = -1,
     };
 
+    /**
+     * Features that should only be enabled by GrGLShaderBuilder itself.
+     */
+    enum GLSLPrivateFeature {
+        kFragCoordConventions_GLSLPrivateFeature = kLastGLSLFeature + 1
+    };
+    bool enablePrivateFeature(GLSLPrivateFeature);
+
+    // If we ever have VS/GS features we can expand this to take a bitmask of ShaderType and track
+    // the enables separately for each shader.
+    void addFSFeature(uint32_t featureBit, const char* extensionName);
+
     const GrGLContextInfo&              fCtxInfo;
     GrGLUniformManager&                 fUniformManager;
     int                                 fCurrentStageIdx;
+    uint32_t                            fFSFeaturesAddedMask;
     SkString                            fFSFunctions;
     SkString                            fFSHeader;
 
     SkString                            fFSCode;
     SkString                            fVSCode;
     SkString                            fGSCode;
 
     bool                                fSetupFragPosition;
     GrGLUniformManager::UniformHandle   fRTHeightUniform;
 
     SkSTArray<10, AttributePair, true>  fEffectAttributes;
 
     GrGLShaderVar*                      fPositionVar;
     GrGLShaderVar*                      fLocalCoordsVar;
 
 };
 
 #endif