Fix various issues with framebuffer fetch

This CL does two things. First it fixes a bug of ours where when using
a custom fbFetch variable (es 3.0 and higher), we sometimes overwrite
the out color and then attempt to use it as the dst color later. This is
fixed here by using an intermediate variable.

Secondly I've added a workaround to an andreno fbFetch where reading from
the outColor always returns the original dstColor even if we've overwritten
the value.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248403003

Review-Url: https://codereview.chromium.org/2248403003

5 files changed, 26 insertions, 6 deletions

diff --git a/src/gpu/glsl/GrGLSLCaps.cpp b/src/gpu/glsl/GrGLSLCaps.cpp
index 1f4b855f5d..b33e3082ec 100755
--- a/src/gpu/glsl/GrGLSLCaps.cpp
+++ b/src/gpu/glsl/GrGLSLCaps.cpp
@@ -23,6 +23,7 @@ GrGLSLCaps::GrGLSLCaps(const GrContextOptions& options) {
     fCanUseAnyFunctionInShader = true;
     fCanUseMinAndAbsTogether = true;
     fMustForceNegatedAtanParamToFloat = false;
+    fRequiresLocalOutputColorForFBFetch = false;
     fFlatInterpolationSupport = false;
     fNoPerspectiveInterpolationSupport = false;
     fMultisampleInterpolationSupport = false;
@@ -73,6 +74,8 @@ SkString GrGLSLCaps::dump() const {
     r.appendf("Can use min() and abs() together: %s\n", (fCanUseMinAndAbsTogether ? "YES" : "NO"));
     r.appendf("Must force negated atan param to float: %s\n", (fMustForceNegatedAtanParamToFloat ?
                                                                "YES" : "NO"));
+    r.appendf("Must use local out color for FBFetch: %s\n", (fRequiresLocalOutputColorForFBFetch ?
+                                                             "YES" : "NO"));
     r.appendf("Flat interpolation support: %s\n", (fFlatInterpolationSupport ?  "YES" : "NO"));
     r.appendf("No perspective interpolation support: %s\n", (fNoPerspectiveInterpolationSupport ?
                                                              "YES" : "NO"));
diff --git a/src/gpu/glsl/GrGLSLCaps.h b/src/gpu/glsl/GrGLSLCaps.h
index 19a34620dc..d8145e729d 100755
--- a/src/gpu/glsl/GrGLSLCaps.h
+++ b/src/gpu/glsl/GrGLSLCaps.h
@@ -91,6 +91,8 @@ public:
 
     bool mustForceNegatedAtanParamToFloat() const { return fMustForceNegatedAtanParamToFloat; }
 
+    bool requiresLocalOutputColorForFBFetch() const { return fRequiresLocalOutputColorForFBFetch; }
+
     // Returns the string of an extension that must be enabled in the shader to support
     // derivatives. If nullptr is returned then no extension needs to be enabled. Before calling
     // this function, the caller should check that shaderDerivativeSupport exists.
@@ -199,6 +201,7 @@ private:
     // Used for specific driver bug work arounds
     bool fCanUseMinAndAbsTogether : 1;
     bool fMustForceNegatedAtanParamToFloat : 1;
+    bool fRequiresLocalOutputColorForFBFetch : 1;
 
     const char* fVersionDeclString;
 
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index e6ecf8c171..4513a69fc8 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -15,7 +15,7 @@
 #include "glsl/GrGLSLUniformHandler.h"
 #include "glsl/GrGLSLVarying.h"
 
-const char* GrGLSLFragmentShaderBuilder::kDstTextureColorName = "_dstColor";
+const char* GrGLSLFragmentShaderBuilder::kDstColorName = "_dstColor";
 
 static const char* sample_offset_array_name(GrGLSLFPFragmentBuilder::Coordinates coords) {
     static const char* kArrayNames[] = {
@@ -264,11 +264,11 @@ const char* GrGLSLFragmentShaderBuilder::dstColor() {
             this->enableCustomOutput();
             fOutputs[fCustomColorOutputIndex].setTypeModifier(GrShaderVar::kInOut_TypeModifier);
             fbFetchColorName = DeclaredColorOutputName();
+            // Set the dstColor to an intermediate variable so we don't override it with the output
+            this->codeAppendf("vec4 %s = %s;", kDstColorName, fbFetchColorName);
         }
-        return fbFetchColorName;
-    } else {
-        return kDstTextureColorName;
     }
+    return kDstColorName;
 }
 
 void GrGLSLFragmentShaderBuilder::enableAdvancedBlendEquationIfNeeded(GrBlendEquation equation) {
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 6845376261..55ef9db207 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -212,7 +212,7 @@ private:
     void onFinalize() override;
     void defineSampleOffsetArray(const char* name, const SkMatrix&);
 
-    static const char* kDstTextureColorName;
+    static const char* kDstColorName;
 
     /*
      * State that tracks which child proc in the proc tree is currently emitting code.  This is
diff --git a/src/gpu/glsl/GrGLSLXferProcessor.cpp b/src/gpu/glsl/GrGLSLXferProcessor.cpp
index f0f5efd37b..0f7a3db718 100644
--- a/src/gpu/glsl/GrGLSLXferProcessor.cpp
+++ b/src/gpu/glsl/GrGLSLXferProcessor.cpp
@@ -22,6 +22,8 @@ void GrGLSLXferProcessor::emitCode(const EmitArgs& args) {
     GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
     const char* dstColor = fragBuilder->dstColor();
 
+    bool needsLocalOutColor = false;
+
     if (args.fXP.getDstTexture()) {
         bool topDown = kTopLeft_GrSurfaceOrigin == args.fXP.getDstTexture()->origin();
 
@@ -59,6 +61,15 @@ void GrGLSLXferProcessor::emitCode(const EmitArgs& args) {
         fragBuilder->codeAppendf("vec4 %s = ", dstColor);
         fragBuilder->appendTextureLookup(args.fTexSamplers[0], "_dstTexCoord", kVec2f_GrSLType);
         fragBuilder->codeAppend(";");
+    } else {
+        needsLocalOutColor = args.fGLSLCaps->requiresLocalOutputColorForFBFetch();
+    }
+
+    const char* outColor = "_localColorOut";
+    if (!needsLocalOutColor) {
+        outColor = args.fOutputPrimary;
+    } else {
+        fragBuilder->codeAppendf("vec4 %s;", outColor);
     }
 
     this->emitBlendCodeForDstRead(fragBuilder,
@@ -66,9 +77,12 @@ void GrGLSLXferProcessor::emitCode(const EmitArgs& args) {
                                   args.fInputColor,
                                   args.fInputCoverage,
                                   dstColor,
-                                  args.fOutputPrimary,
+                                  outColor,
                                   args.fOutputSecondary,
                                   args.fXP);
+    if (needsLocalOutColor) {
+        fragBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, outColor);
+    }
 }
 
 void GrGLSLXferProcessor::setData(const GrGLSLProgramDataManager& pdm, const GrXferProcessor& xp) {