Revert "Revert "Make SkSL GLSL generator declare sk_FragColor inout when EXT fb fetch is used.""

This reverts commit d40133092a.

Bug: skia:
Change-Id: I236505da047d5ad29e4952d8955eb7aa1bfb870b
Reviewed-on: https://skia-review.googlesource.com/118621
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

src/gpu/gl/builders/GrGLProgramBuilder.cpp

@@ -154,6 +154,8 @@ GrGLProgram* GrGLProgramBuilder::finalize() {
     settings.fCaps = this->gpu()->glCaps().shaderCaps();
     settings.fFlipY = this->pipeline().proxy()->origin() != kTopLeft_GrSurfaceOrigin;
     settings.fSharpenTextures = this->gpu()->getContext()->contextPriv().sharpenMipmappedTextures();
+    settings.fFragColorIsInOut = this->fragColorIsInOut();
+
     SkSL::Program::Inputs inputs;
     SkTDArray<GrGLuint> shadersToDelete;
     bool cached = fGpu->glCaps().programBinarySupport() && nullptr != fCached.get();

src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp

@@ -170,6 +170,11 @@ const char* GrGLSLFragmentShaderBuilder::getPrimaryColorOutputName() const {
     return fHasCustomColorOutput ? DeclaredColorOutputName() : "sk_FragColor";
 }
 
+bool GrGLSLFragmentShaderBuilder::primaryColorOutputIsInOut() const {
+    return fHasCustomColorOutput &&
+           fOutputs[fCustomColorOutputIndex].getTypeModifier() == GrShaderVar::kInOut_TypeModifier;
+}
+
 void GrGLSLFragmentBuilder::declAppendf(const char* fmt, ...) {
     va_list argp;
     va_start(argp, fmt);

src/gpu/glsl/GrGLSLFragmentShaderBuilder.h

@@ -119,6 +119,7 @@ private:
     void enableSecondaryOutput();
     const char* getPrimaryColorOutputName() const;
     const char* getSecondaryColorOutputName() const;
+    bool primaryColorOutputIsInOut() const;
 
 #ifdef SK_DEBUG
     // As GLSLProcessors emit code, there are some conditions we need to verify.  We use the below

src/gpu/glsl/GrGLSLProgramBuilder.h

@@ -115,6 +115,8 @@ protected:
 
     void finalizeShaders();
 
+    bool fragColorIsInOut() const { return fFS.primaryColorOutputIsInOut(); }
+
 private:
     // reset is called by program creator between each processor's emit code.  It increments the
     // stage offset for variable name mangling, and also ensures verfication variables in the

src/gpu/vk/GrVkPipelineStateBuilder.cpp

@@ -144,6 +144,7 @@ GrVkPipelineState* GrVkPipelineStateBuilder::finalize(const GrStencilSettings& s
     settings.fCaps = this->caps()->shaderCaps();
     settings.fFlipY = this->pipeline().proxy()->origin() != kTopLeft_GrSurfaceOrigin;
     settings.fSharpenTextures = this->gpu()->getContext()->contextPriv().sharpenMipmappedTextures();
+    SkASSERT(!this->fragColorIsInOut());
     SkAssertResult(this->createVkShaderModule(VK_SHADER_STAGE_VERTEX_BIT,
                                               fVS,
                                               &vertShaderModule,

src/sksl/SkSLGLSLCodeGenerator.cpp

@@ -1270,7 +1270,11 @@ void GLSLCodeGenerator::writeProgramElement(const ProgramElement& e) {
                     this->writeLine();
                 } else if (builtin == SK_FRAGCOLOR_BUILTIN &&
                            fProgram.fSettings.fCaps->mustDeclareFragmentShaderOutput()) {
-                    this->write("out ");
+                    if (fProgram.fSettings.fFragColorIsInOut) {
+                        this->write("inout ");
+                    } else {
+                        this->write("out ");
+                    }
                     if (usesPrecisionModifiers()) {
                         this->write("mediump ");
                     }

src/sksl/SkSLMetalCodeGenerator.cpp

@@ -451,6 +451,8 @@ void MetalCodeGenerator::writeFunction(const FunctionDefinition& f) {
     }
     this->writeLine(") {");
 
+    ASSERT(!fProgram.fSettings.fFragColorIsInOut);
+
     if ("main" == f.fDeclaration.fName) {
         switch (fProgram.fKind) {
             case Program::kFragment_Kind:

src/sksl/SkSLSPIRVCodeGenerator.cpp

@@ -2545,6 +2545,7 @@ void SPIRVCodeGenerator::writeGlobalVars(Program::Kind kind, const VarDeclaratio
         }
         if (var->fModifiers.fLayout.fBuiltin == SK_FRAGCOLOR_BUILTIN &&
             kind != Program::kFragment_Kind) {
+            ASSERT(!fProgram.fSettings.fFragColorIsInOut);
             continue;
         }
         if (!var->fReadCount && !var->fWriteCount &&

src/sksl/ir/SkSLProgram.h

@@ -71,6 +71,8 @@ struct Program {
         // if false, sk_FragCoord is exactly the same as gl_FragCoord. If true, the y coordinate
         // must be flipped.
         bool fFlipY = false;
+        // If true the destination fragment color is read sk_FragColor. It must be declared inout.
+        bool fFragColorIsInOut = false;
         // if true, Setting objects (e.g. sk_Caps.fbFetchSupport) should be replaced with their
         // constant equivalents during compilation
         bool fReplaceSettings = true;