Revert "Revert "Allow FPs to elevate default precision for the entire fragment program""

This reverts commit 903c3f70400462e191ccbca63393b2df3fe2dd11.

Reason for revert: Vulkan issue fixed in compiler.

Original change's description:
> Revert "Allow FPs to elevate default precision for the entire fragment program"
> 
> This reverts commit 92d7ccafdf896cf19764e025873d13315a76842d.
> 
> Reason for revert: Vulkan errors.
> 
> Original change's description:
> > Allow FPs to elevate default precision for the entire fragment program
> > 
> > Currently, GrConfigConversionEffect is able to round-trip on many mobile
> > GPUs because it uses highp for all intermediate variables (including the
> > texture fetch result). Separating the texture sample into a different
> > processor breaks that.
> > 
> > This is a blunt instrument, not to be used lightly.
> > 
> > Bug: skia:
> > Change-Id: I2ab365e3da79628069e2eb727c43c2bf45bfd789
> > Reviewed-on: https://skia-review.googlesource.com/10162
> > Reviewed-by: Brian Salomon <bsalomon@google.com>
> > Commit-Queue: Brian Osman <brianosman@google.com>
> > 
> 
> TBR=bsalomon@google.com,robertphillips@google.com,brianosman@google.com,ethannicholas@google.com,reviews@skia.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> 
> Change-Id: Iee5bb409f86a9cabecc76bd1273a5b3cef6af179
> Reviewed-on: https://skia-review.googlesource.com/10967
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
> 

TBR=bsalomon@google.com,robertphillips@google.com,reviews@skia.org,brianosman@google.com,ethannicholas@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I733a0ecc40b58d8727f0259b5498c8e6610cedce
Reviewed-on: https://skia-review.googlesource.com/11010
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

3 files changed, 24 insertions, 10 deletions

diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index a1f5173436..484bd78211 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -85,7 +85,8 @@ GrGLSLFragmentShaderBuilder::GrGLSLFragmentShaderBuilder(GrGLSLProgramBuilder* p
     , fCustomColorOutputIndex(-1)
     , fHasSecondaryOutput(false)
     , fUsedSampleOffsetArrays(0)
-    , fHasInitializedSampleMask(false) {
+    , fHasInitializedSampleMask(false)
+    , fDefaultPrecision(kMedium_GrSLPrecision) {
     fSubstageIndices.push_back(0);
 #ifdef SK_DEBUG
     fUsedProcessorFeatures = GrProcessor::kNone_RequiredFeatures;
@@ -178,6 +179,10 @@ void GrGLSLFragmentShaderBuilder::overrideSampleCoverage(const char* mask) {
     fHasInitializedSampleMask = true;
 }
 
+void GrGLSLFragmentShaderBuilder::elevateDefaultPrecision(GrSLPrecision precision) {
+    fDefaultPrecision = SkTMax(fDefaultPrecision, precision);
+}
+
 const char* GrGLSLFragmentShaderBuilder::dstColor() {
     SkDEBUGCODE(fHasReadDstColor = true;)
 
@@ -279,7 +284,7 @@ GrSurfaceOrigin GrGLSLFragmentShaderBuilder::getSurfaceOrigin() const {
 
 void GrGLSLFragmentShaderBuilder::onFinalize() {
     fProgramBuilder->varyingHandler()->getFragDecls(&this->inputs(), &this->outputs());
-    GrGLSLAppendDefaultFloatPrecisionDeclaration(kDefault_GrSLPrecision,
+    GrGLSLAppendDefaultFloatPrecisionDeclaration(fDefaultPrecision,
                                                  *fProgramBuilder->shaderCaps(),
                                                  &this->precisionQualifier());
     if (fUsedSampleOffsetArrays & (1 << kSkiaDevice_Coordinates)) {
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 764f3bd812..65bcb8dae6 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -94,6 +94,13 @@ public:
     virtual const char* distanceVectorName() const = 0;
 
     /**
+     * Overrides the default precision for the entire fragment program. Processors that require
+     * high precision input (eg from incoming texture samples) may use this. For calculations that
+     * are limited to a single processor's code, it is better to annotate individual declarations.
+     */
+    virtual void elevateDefaultPrecision(GrSLPrecision) = 0;
+
+    /**
      * Fragment procs with child procs should call these functions before/after calling emitCode
      * on a child proc.
      */
@@ -167,6 +174,7 @@ public:
     void appendOffsetToSample(const char* sampleIdx, Coordinates) override;
     void maskSampleCoverage(const char* mask, bool invert = false) override;
     void overrideSampleCoverage(const char* mask) override;
+    void elevateDefaultPrecision(GrSLPrecision) override;
     const SkString& getMangleString() const override { return fMangleString; }
     void onBeforeChildProcEmitCode() override;
     void onAfterChildProcEmitCode() override;
@@ -225,13 +233,14 @@ private:
      */
     SkString fMangleString;
 
-    bool       fSetupFragPosition;
-    bool       fHasCustomColorOutput;
-    int        fCustomColorOutputIndex;
-    bool       fHasSecondaryOutput;
-    uint8_t    fUsedSampleOffsetArrays;
-    bool       fHasInitializedSampleMask;
-    SkString   fDistanceVectorOutput;
+    bool          fSetupFragPosition;
+    bool          fHasCustomColorOutput;
+    int           fCustomColorOutputIndex;
+    bool          fHasSecondaryOutput;
+    uint8_t       fUsedSampleOffsetArrays;
+    bool          fHasInitializedSampleMask;
+    SkString      fDistanceVectorOutput;
+    GrSLPrecision fDefaultPrecision;
 
 #ifdef SK_DEBUG
     // some state to verify shaders and effects are consistent, this is reset between effects by
diff --git a/src/gpu/glsl/GrGLSLVarying.cpp b/src/gpu/glsl/GrGLSLVarying.cpp
index 7d841f5417..ef3fe8af23 100644
--- a/src/gpu/glsl/GrGLSLVarying.cpp
+++ b/src/gpu/glsl/GrGLSLVarying.cpp
@@ -42,7 +42,7 @@ void GrGLSLVaryingHandler::internalAddVarying(const char* name,
 
     SkASSERT(varying);
     v.fType = varying->fType;
-    v.fPrecision = precision;
+    v.fPrecision = (kDefault_GrSLPrecision == precision) ? kMedium_GrSLPrecision : precision;
     v.fIsFlat = flat;
     fProgramBuilder->nameVariable(&v.fVsOut, 'v', name);
     v.fVisibility = kNone_GrShaderFlags;