commit b8af5ad73abb17bca0b385949715f6f10ff9b6da
author Chris Dalton <csmartdalton@google.com> Mon Feb 25 14:54:21 2019 -0700
committer Skia Commit-Bot <skia-commit-bot@chromium.org> Mon Feb 25 23:32:23 2019 +0000
tree d023953bfb0daa36a243c5681ab833d50921f00e
parent 35a3abe7655ad24410f3d32dbf3111ee592ea69b

sksl: Negate dFdy when the Y axis is flipped

Bug: skia:
Change-Id: Icbdaa6b1ebbe00168f57ebb888c2345d4f7a5e7d
Reviewed-on: https://skia-review.googlesource.com/c/195160
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

src/sksl/SkSLGLSLCodeGenerator.cpp

diff --git a/src/sksl/SkSLGLSLCodeGenerator.cpp b/src/sksl/SkSLGLSLCodeGenerator.cpp
index 9f8a185..285a94c 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.cpp
+++ b/src/sksl/SkSLGLSLCodeGenerator.cpp
@@ -460,9 +460,9 @@
         (*fFunctionClasses)["abs"]         = FunctionClass::kAbs;
         (*fFunctionClasses)["atan"]        = FunctionClass::kAtan;
         (*fFunctionClasses)["determinant"] = FunctionClass::kDeterminant;
-        (*fFunctionClasses)["dFdx"]        = FunctionClass::kDerivative;
-        (*fFunctionClasses)["dFdy"]        = FunctionClass::kDerivative;
-        (*fFunctionClasses)["fwidth"]      = FunctionClass::kDerivative;
+        (*fFunctionClasses)["dFdx"]        = FunctionClass::kDFdx;
+        (*fFunctionClasses)["dFdy"]        = FunctionClass::kDFdy;
+        (*fFunctionClasses)["fwidth"]      = FunctionClass::kFwidth;
         (*fFunctionClasses)["fma"]         = FunctionClass::kFMA;
         (*fFunctionClasses)["fract"]       = FunctionClass::kFract;
         (*fFunctionClasses)["inverse"]     = FunctionClass::kInverse;
@@ -517,7 +517,15 @@
                     }
                 }
                 break;
-            case FunctionClass::kDerivative:
+            case FunctionClass::kDFdy:
+                if (fProgram.fSettings.fFlipY) {
+                    // Flipping Y also negates the Y derivatives.
+                    this->write("-dFdy");
+                    nameWritten = true;
+                }
+                // fallthru
+            case FunctionClass::kDFdx:
+            case FunctionClass::kFwidth:
                 if (!fFoundDerivatives &&
                     fProgram.fSettings.fCaps->shaderDerivativeExtensionString()) {
                     SkASSERT(fProgram.fSettings.fCaps->shaderDerivativeSupport());

src/sksl/SkSLGLSLCodeGenerator.h

diff --git a/src/sksl/SkSLGLSLCodeGenerator.h b/src/sksl/SkSLGLSLCodeGenerator.h
index 99e7d47..2a743ea 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.h
+++ b/src/sksl/SkSLGLSLCodeGenerator.h
@@ -227,7 +227,9 @@
         kAbs,
         kAtan,
         kDeterminant,
-        kDerivative,
+        kDFdx,
+        kDFdy,
+        kFwidth,
         kFMA,
         kFract,
         kInverse,

src/sksl/SkSLMetalCodeGenerator.cpp

diff --git a/src/sksl/SkSLMetalCodeGenerator.cpp b/src/sksl/SkSLMetalCodeGenerator.cpp
index da206b4..c457d35 100644
--- a/src/sksl/SkSLMetalCodeGenerator.cpp
+++ b/src/sksl/SkSLMetalCodeGenerator.cpp
@@ -218,7 +218,8 @@
     } else if (c.fFunction.fBuiltin && "dFdx" == c.fFunction.fName) {
         this->write("dfdx");
     } else if (c.fFunction.fBuiltin && "dFdy" == c.fFunction.fName) {
-        this->write("dfdy");
+        // Flipping Y also negates the Y derivatives.
+        this->write((fProgram.fSettings.fFlipY) ? "-dfdy" : "dfdy");
     } else {
         this->writeName(c.fFunction.fName);
     }

src/sksl/SkSLSPIRVCodeGenerator.cpp

diff --git a/src/sksl/SkSLSPIRVCodeGenerator.cpp b/src/sksl/SkSLSPIRVCodeGenerator.cpp
index 77d8805..1804ecb 100644
--- a/src/sksl/SkSLSPIRVCodeGenerator.cpp
+++ b/src/sksl/SkSLSPIRVCodeGenerator.cpp
@@ -98,8 +98,7 @@
     fIntrinsicMap[String("findMSB")]     = BY_TYPE_GLSL(FindSMsb, FindSMsb, FindUMsb);
     fIntrinsicMap[String("dFdx")]        = std::make_tuple(kSPIRV_IntrinsicKind, SpvOpDPdx,
                                                            SpvOpUndef, SpvOpUndef, SpvOpUndef);
-    fIntrinsicMap[String("dFdy")]        = std::make_tuple(kSPIRV_IntrinsicKind, SpvOpDPdy,
-                                                           SpvOpUndef, SpvOpUndef, SpvOpUndef);
+    fIntrinsicMap[String("dFdy")]        = SPECIAL(DFdy);
     fIntrinsicMap[String("fwidth")]      = std::make_tuple(kSPIRV_IntrinsicKind, SpvOpFwidth,
                                                            SpvOpUndef, SpvOpUndef, SpvOpUndef);
     fIntrinsicMap[String("texture")]     = SPECIAL(Texture);
@@ -917,6 +916,20 @@
             this->writeWord(args[1], out);
             break;
         }
+        case kDFdy_SpecialIntrinsic: {
+            SpvId fn = this->writeExpression(*c.fArguments[0], out);
+            this->writeOpCode(SpvOpDPdy, 4, out);
+            this->writeWord(this->getType(c.fType), out);
+            this->writeWord(result, out);
+            this->writeWord(fn, out);
+            if (fProgram.fSettings.fFlipY) {
+                // Flipping Y also negates the Y derivatives.
+                SpvId flipped = this->nextId();
+                this->writeInstruction(SpvOpFNegate, this->getType(c.fType), flipped, result, out);
+                return flipped;
+            }
+            break;
+        }
         case kClamp_SpecialIntrinsic: {
             std::vector<SpvId> args = this->vectorize(c.fArguments, out);
             SkASSERT(args.size() == 3);

src/sksl/SkSLSPIRVCodeGenerator.h

diff --git a/src/sksl/SkSLSPIRVCodeGenerator.h b/src/sksl/SkSLSPIRVCodeGenerator.h
index ef96e57..02adfa5 100644
--- a/src/sksl/SkSLSPIRVCodeGenerator.h
+++ b/src/sksl/SkSLSPIRVCodeGenerator.h
@@ -95,6 +95,7 @@
         kMin_SpecialIntrinsic,
         kMix_SpecialIntrinsic,
         kMod_SpecialIntrinsic,
+        kDFdy_SpecialIntrinsic,
         kSaturate_SpecialIntrinsic,
         kSubpassLoad_SpecialIntrinsic,
         kTexture_SpecialIntrinsic,