Implement support for dual source blending in ES

src/gpu/gl/builders/GrGLFragmentShaderBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLFragmentShaderBuilder.h"
 #include "GrGLProgramBuilder.h"
 #include "gl/GrGLGpu.h"
 #include "gl/GrGLGLSL.h"
 #include "glsl/GrGLSLCaps.h"
 
 #define GL_CALL(X) GR_GL_CALL(fProgramBuilder->gpu()->glInterface(), X)
 #define GL_CALL_RET(R, X) GR_GL_CALL_RET(fProgramBuilder->gpu()->glInterface(), R, X)
 
 const char* GrGLFragmentShaderBuilder::kDstTextureColorName = "_dstColor";
 static const char* declared_color_output_name() { return "fsColorOut"; }
-static const char* dual_source_output_name() { return "dualSourceOut"; }
+static const char* declared_secondary_color_output_name() { return "fsSecondaryColorOut"; }
 
 static const char* specific_layout_qualifier_name(GrBlendEquation equation) {
     SkASSERT(GrBlendEquationIsAdvanced(equation));
 
     static const char* kLayoutQualifierNames[] = {
         "blend_support_screen",
         "blend_support_overlay",
         "blend_support_darken",
         "blend_support_lighten",
         "blend_support_colordodge",
@@ skipping 203 matching lines @@
         fCustomColorOutputIndex = fOutputs.count();
         fOutputs.push_back().set(kVec4f_GrSLType,
                                  GrGLShaderVar::kOut_TypeModifier,
                                  declared_color_output_name());
     }
 }
 
 void GrGLFragmentShaderBuilder::enableSecondaryOutput() {
     SkASSERT(!fHasSecondaryOutput);
     fHasSecondaryOutput = true;
-    fOutputs.push_back().set(kVec4f_GrSLType, GrGLShaderVar::kOut_TypeModifier,
-                             dual_source_output_name());
+    if (kGLES_GrGLStandard == fProgramBuilder->gpu()->ctxInfo().standard()) {
+        this->addFeature(1 << kBlendFuncExtended_GLSLPrivateFeature, "GL_EXT_blend_func_extended");
+    }
+
+    // If the primary output is declared, we must declare also the secondary output
+    // and vice versa, since it is not allowed to use a built-in gl_FragColor and a custom
+    // output. The condition also co-incides with the condition in whici GLES SL 2.0
+    // requires the built-in gl_SecondaryFragColorEXT, where as 3.0 requires a custom output.
+    const GrGLSLCaps& caps = *fProgramBuilder->gpu()->glCaps().glslCaps();
+    if (caps.mustDeclareFragmentShaderOutput()) {
+        fOutputs.push_back().set(kVec4f_GrSLType, GrGLShaderVar::kOut_TypeModifier,
+                                 declared_secondary_color_output_name());
+    }
 }
 
 const char* GrGLFragmentShaderBuilder::getPrimaryColorOutputName() const {
     return fHasCustomColorOutput ? declared_color_output_name() : "gl_FragColor";
 }
 
 const char* GrGLFragmentShaderBuilder::getSecondaryColorOutputName() const {
-    return dual_source_output_name();
+    const GrGLSLCaps& caps = *fProgramBuilder->gpu()->glCaps().glslCaps();
+    return caps.mustDeclareFragmentShaderOutput() ? declared_secondary_color_output_name()
+                                                  : "gl_SecondaryFragColorEXT";
 }
 
 bool GrGLFragmentShaderBuilder::compileAndAttachShaders(GrGLuint programId,
                                                         SkTDArray<GrGLuint>* shaderIds) {
     GrGLGpu* gpu = fProgramBuilder->gpu();
     this->versionDecl() = GrGLGetGLSLVersionDecl(gpu->ctxInfo());
     GrGLAppendGLSLDefaultFloatPrecisionDeclaration(kDefault_GrSLPrecision,
                                                    gpu->glStandard(),
                                                    &this->precisionQualifier());
     this->compileAndAppendLayoutQualifiers();
     fProgramBuilder->appendUniformDecls(GrGLProgramBuilder::kFragment_Visibility,
                                         &this->uniforms());
     this->appendDecls(fInputs, &this->inputs());
     // We shouldn't have declared outputs on 1.10
     SkASSERT(k110_GrGLSLGeneration != gpu->glslGeneration() || fOutputs.empty());
     this->appendDecls(fOutputs, &this->outputs());
     return this->finalize(programId, GR_GL_FRAGMENT_SHADER, shaderIds);
 }
 
 void GrGLFragmentShaderBuilder::bindFragmentShaderLocations(GrGLuint programID) {
-    if (fHasCustomColorOutput && fProgramBuilder->gpu()->glCaps().bindFragDataLocationSupport()) {
+    const GrGLCaps& caps = fProgramBuilder->gpu()->glCaps();
+    if (fHasCustomColorOutput && caps.bindFragDataLocationSupport()) {
         GL_CALL(BindFragDataLocation(programID, 0, declared_color_output_name()));
     }
-    if (fHasSecondaryOutput) {
-        GL_CALL(BindFragDataLocationIndexed(programID, 0, 1, dual_source_output_name()));
+    if (fHasSecondaryOutput && caps.glslCaps()->mustDeclareFragmentShaderOutput()) {
+        GL_CALL(BindFragDataLocationIndexed(programID, 0, 1,
+                                            declared_secondary_color_output_name()));
     }
 }
 
 void GrGLFragmentShaderBuilder::addVarying(GrGLVarying* v, GrSLPrecision fsPrec) {
     v->fFsIn = v->fVsOut;
     if (v->fGsOut) {
         v->fFsIn = v->fGsOut;
     }
     fInputs.push_back().set(v->fType, GrGLShaderVar::kVaryingIn_TypeModifier, v->fFsIn, fsPrec);
 }