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());