Revert "Remove interpolants are inaccurate workaround for Adreno 3xx."

This reverts commit a7a278205bb040061cb4ba46839efe18635c7edc.

Reason for revert: Chrome change had to be reverted because of new failures on Nexus 9 and 6P.

Original change's description:
> Remove interpolants are inaccurate workaround for Adreno 3xx.
> 
> The chrome screenshot unit test that led to adding this workaround has
> been adjusted to avoid testing AA edges of rendered rectangles. We're
> accepting the inaccuracy in favor of increased performance.
> 
> Chrome change: https://chromium-review.googlesource.com/c/chromium/src/+/1129041
> 
> Bug: chromium:847984
> Change-Id: I9b714ade2a67e956ebb2773ebe3b8632dc3a50c6
> Reviewed-on: https://skia-review.googlesource.com/140180
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

TBR=bsalomon@google.com,brianosman@google.com

Change-Id: Ic6b0e5a343556e59d144852f9fa5b561302f9781
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:847984
Reviewed-on: https://skia-review.googlesource.com/140380
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

4 files changed, 68 insertions, 28 deletions

diff --git a/src/gpu/GrShaderCaps.cpp b/src/gpu/GrShaderCaps.cpp
index 70c7388f29..486909e028 100644
--- a/src/gpu/GrShaderCaps.cpp
+++ b/src/gpu/GrShaderCaps.cpp
@@ -38,6 +38,7 @@ GrShaderCaps::GrShaderCaps(const GrContextOptions& options) {
     fMustObfuscateUniformColor = false;
     fMustGuardDivisionEvenAfterExplicitZeroCheck = false;
     fCanUseFragCoord = true;
+    fInterpolantsAreInaccurate = false;
     fIncompleteShortIntPrecision = false;
     fFlatInterpolationSupport = false;
     fPreferFlatInterpolation = false;
@@ -111,6 +112,7 @@ void GrShaderCaps::dumpJSON(SkJSONWriter* writer) const {
     writer->appendBool("Must guard division even after explicit zero check",
                        fMustGuardDivisionEvenAfterExplicitZeroCheck);
     writer->appendBool("Can use gl_FragCoord", fCanUseFragCoord);
+    writer->appendBool("Interpolants are inaccurate", fInterpolantsAreInaccurate);
     writer->appendBool("Incomplete short int precision", fIncompleteShortIntPrecision);
     writer->appendBool("Flat interpolation support", fFlatInterpolationSupport);
     writer->appendBool("Prefer flat interpolation", fPreferFlatInterpolation);
@@ -146,6 +148,7 @@ void GrShaderCaps::applyOptionsOverrides(const GrContextOptions& options) {
         SkASSERT(!fMustObfuscateUniformColor);
         SkASSERT(!fMustGuardDivisionEvenAfterExplicitZeroCheck);
         SkASSERT(fCanUseFragCoord);
+        SkASSERT(!fInterpolantsAreInaccurate);
         SkASSERT(!fIncompleteShortIntPrecision);
     }
 #if GR_TEST_UTILS
diff --git a/src/gpu/GrShaderCaps.h b/src/gpu/GrShaderCaps.h
index 66c75dfebb..e16c9f6d5b 100644
--- a/src/gpu/GrShaderCaps.h
+++ b/src/gpu/GrShaderCaps.h
@@ -121,6 +121,9 @@ public:
     // If false, SkSL uses a workaround so that sk_FragCoord doesn't actually query gl_FragCoord
     bool canUseFragCoord() const { return fCanUseFragCoord; }
 
+    // If true interpolated vertex shader outputs are inaccurate.
+    bool interpolantsAreInaccurate() const { return fInterpolantsAreInaccurate; }
+
     // If true, short ints can't represent every integer in the 16-bit two's complement range as
     // required by the spec. SKSL will always emit full ints.
     bool incompleteShortIntPrecision() const { return fIncompleteShortIntPrecision; }
@@ -274,6 +277,7 @@ private:
     bool fMustObfuscateUniformColor                   : 1;
     bool fMustGuardDivisionEvenAfterExplicitZeroCheck : 1;
     bool fCanUseFragCoord                             : 1;
+    bool fInterpolantsAreInaccurate                   : 1;
     bool fIncompleteShortIntPrecision                 : 1;
 
     const char* fVersionDeclString;
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 2b923fa4ac..5cb23427c5 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -2608,9 +2608,11 @@ void GrGLCaps::applyDriverCorrectnessWorkarounds(const GrGLContextInfo& ctxInfo,
 #endif
 
     // We've seen Adreno 3xx devices produce incorrect (flipped) values for gl_FragCoord, in some
-    // (rare) situations. It's sporadic, and mostly on older drivers.
+    // (rare) situations. It's sporadic, and mostly on older drivers. It also seems to be the case
+    // that the interpolation of vertex shader outputs is quite inaccurate.
     if (kAdreno3xx_GrGLRenderer == ctxInfo.renderer()) {
         shaderCaps->fCanUseFragCoord = false;
+        shaderCaps->fInterpolantsAreInaccurate = true;
     }
 
     // gl_FragCoord has an incorrect subpixel offset on legacy Tegra hardware.
diff --git a/src/gpu/ops/GrTextureOp.cpp b/src/gpu/ops/GrTextureOp.cpp
index 2fe8bb0ab4..bced31dbc5 100644
--- a/src/gpu/ops/GrTextureOp.cpp
+++ b/src/gpu/ops/GrTextureOp.cpp
@@ -203,38 +203,69 @@ public:
                 }
                 args.fFragBuilder->codeAppend(";");
                 if (textureGP.usesCoverageEdgeAA()) {
+                    const char* aaDistName = nullptr;
                     bool mulByFragCoordW = false;
-                    GrGLSLVarying aaDistVarying(kFloat4_GrSLType,
-                                                GrGLSLVarying::Scope::kVertToFrag);
-                    if (kFloat3_GrVertexAttribType == textureGP.fPositions.type()) {
-                        args.fVaryingHandler->addVarying("aaDists", &aaDistVarying);
-                        // The distance from edge equation e to homogenous point p=sk_Position
-                        // is e.x*p.x/p.wx + e.y*p.y/p.w + e.z. However, we want screen space
-                        // interpolation of this distance. We can do this by multiplying the
-                        // varying in the VS by p.w and then multiplying by sk_FragCoord.w in
-                        // the FS. So we output e.x*p.x + e.y*p.y + e.z * p.w
-                        args.fVertBuilder->codeAppendf(
-                                R"(%s = float4(dot(aaEdge0, %s), dot(aaEdge1, %s),
-                                               dot(aaEdge2, %s), dot(aaEdge3, %s));)",
-                                aaDistVarying.vsOut(), textureGP.fPositions.name(),
-                                textureGP.fPositions.name(), textureGP.fPositions.name(),
-                                textureGP.fPositions.name());
-                        mulByFragCoordW = true;
+                    // When interpolation is inaccurate we perform the evaluation of the edge
+                    // equations in the fragment shader rather than interpolating values computed
+                    // in the vertex shader.
+                    if (!args.fShaderCaps->interpolantsAreInaccurate()) {
+                        GrGLSLVarying aaDistVarying(kFloat4_GrSLType,
+                                                    GrGLSLVarying::Scope::kVertToFrag);
+                        if (kFloat3_GrVertexAttribType == textureGP.fPositions.type()) {
+                            args.fVaryingHandler->addVarying("aaDists", &aaDistVarying);
+                            // The distance from edge equation e to homogenous point p=sk_Position
+                            // is e.x*p.x/p.wx + e.y*p.y/p.w + e.z. However, we want screen space
+                            // interpolation of this distance. We can do this by multiplying the
+                            // varying in the VS by p.w and then multiplying by sk_FragCoord.w in
+                            // the FS. So we output e.x*p.x + e.y*p.y + e.z * p.w
+                            args.fVertBuilder->codeAppendf(
+                                    R"(%s = float4(dot(aaEdge0, %s), dot(aaEdge1, %s),
+                                                   dot(aaEdge2, %s), dot(aaEdge3, %s));)",
+                                    aaDistVarying.vsOut(), textureGP.fPositions.name(),
+                                    textureGP.fPositions.name(), textureGP.fPositions.name(),
+                                    textureGP.fPositions.name());
+                            mulByFragCoordW = true;
+                        } else {
+                            args.fVaryingHandler->addVarying("aaDists", &aaDistVarying);
+                            args.fVertBuilder->codeAppendf(
+                                    R"(%s = float4(dot(aaEdge0.xy, %s.xy) + aaEdge0.z,
+                                                   dot(aaEdge1.xy, %s.xy) + aaEdge1.z,
+                                                   dot(aaEdge2.xy, %s.xy) + aaEdge2.z,
+                                                   dot(aaEdge3.xy, %s.xy) + aaEdge3.z);)",
+                                    aaDistVarying.vsOut(), textureGP.fPositions.name(),
+                                    textureGP.fPositions.name(), textureGP.fPositions.name(),
+                                    textureGP.fPositions.name());
+                        }
+                        aaDistName = aaDistVarying.fsIn();
                     } else {
-                        args.fVaryingHandler->addVarying("aaDists", &aaDistVarying);
-                        args.fVertBuilder->codeAppendf(
-                                R"(%s = float4(dot(aaEdge0.xy, %s.xy) + aaEdge0.z,
-                                               dot(aaEdge1.xy, %s.xy) + aaEdge1.z,
-                                               dot(aaEdge2.xy, %s.xy) + aaEdge2.z,
-                                               dot(aaEdge3.xy, %s.xy) + aaEdge3.z);)",
-                                aaDistVarying.vsOut(), textureGP.fPositions.name(),
-                                textureGP.fPositions.name(), textureGP.fPositions.name(),
-                                textureGP.fPositions.name());
+                        GrGLSLVarying aaEdgeVarying[4]{
+                                {kFloat3_GrSLType, GrGLSLVarying::Scope::kVertToFrag},
+                                {kFloat3_GrSLType, GrGLSLVarying::Scope::kVertToFrag},
+                                {kFloat3_GrSLType, GrGLSLVarying::Scope::kVertToFrag},
+                                {kFloat3_GrSLType, GrGLSLVarying::Scope::kVertToFrag}
+                        };
+                        for (int i = 0; i < 4; ++i) {
+                            SkString name;
+                            name.printf("aaEdge%d", i);
+                            args.fVaryingHandler->addVarying(name.c_str(), &aaEdgeVarying[i],
+                                                             Interpolation::kCanBeFlat);
+                            args.fVertBuilder->codeAppendf(
+                                    "%s = aaEdge%d;", aaEdgeVarying[i].vsOut(), i);
+                        }
+                        args.fFragBuilder->codeAppendf(
+                                R"(float4 aaDists = float4(dot(%s.xy, sk_FragCoord.xy) + %s.z,
+                                                           dot(%s.xy, sk_FragCoord.xy) + %s.z,
+                                                           dot(%s.xy, sk_FragCoord.xy) + %s.z,
+                                                           dot(%s.xy, sk_FragCoord.xy) + %s.z);)",
+                        aaEdgeVarying[0].fsIn(), aaEdgeVarying[0].fsIn(),
+                        aaEdgeVarying[1].fsIn(), aaEdgeVarying[1].fsIn(),
+                        aaEdgeVarying[2].fsIn(), aaEdgeVarying[2].fsIn(),
+                        aaEdgeVarying[3].fsIn(), aaEdgeVarying[3].fsIn());
+                        aaDistName = "aaDists";
                     }
                     args.fFragBuilder->codeAppendf(
                             "float mindist = min(min(%s.x, %s.y), min(%s.z, %s.w));",
-                            aaDistVarying.fsIn(), aaDistVarying.fsIn(), aaDistVarying.fsIn(),
-                            aaDistVarying.fsIn());
+                            aaDistName, aaDistName, aaDistName, aaDistName);
                     if (mulByFragCoordW) {
                         args.fFragBuilder->codeAppend("mindist *= sk_FragCoord.w;");
                     }