commit c7a92fdb774f1f4f8defa54c5b4562b6c8e03571
author Jamie Madill <jmadill@chromium.org> Thu Oct 29 10:08:09 2015 -0400
committer Jamie Madill <jmadill@chromium.org> Mon Nov 02 22:31:56 2015 +0000
tree d30b6d7abdefdf76014f15d8c2d8d60cf072bf6e
parent 31e60cf221801a60c052112b5a0bbcfad9b5f705

D3D11: Fix provoking vertex for flat triangle strips.

Triangle strips alternate the provoking vertex based on the
primitive, so use the primitive ID in the GS to determine this.
This might interact poorly with primitive restart, so we might have
to use a slow path for that.

BUG=angleproject:754

Change-Id: I4f6f520887d4c4c52d2ad020e6db148607f68325
Reviewed-on: https://chromium-review.googlesource.com/309156
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>

src/libANGLE/renderer/d3d/DynamicHLSL.cpp

diff --git a/src/libANGLE/renderer/d3d/DynamicHLSL.cpp b/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
index 32791b2..fa684f4 100644
--- a/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
+++ b/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
@@ -1436,17 +1436,30 @@
 
     shaderStream << preambleString << "\n"
                  << "[maxvertexcount(" << maxVertexOutput << ")]\n"
-                 << "void main(" << inputPT << " GS_INPUT input[" << inputSize << "],"
-                                                                                  " inout "
-                 << outputPT << "Stream<GS_OUTPUT> outStream)\n"
+                 << "void main(" << inputPT << " GS_INPUT input[" << inputSize << "], ";
+
+    if (primitiveType == PRIMITIVE_TRIANGLE_STRIP)
+    {
+        shaderStream << "uint primitiveID : SV_PrimitiveID, ";
+    }
+
+    shaderStream << " inout " << outputPT << "Stream<GS_OUTPUT> outStream)\n"
                  << "{\n"
                  << "    GS_OUTPUT output = (GS_OUTPUT)0;\n";
 
-    int flatVertexIndex = inputSize - 1;
+    if (primitiveType == PRIMITIVE_TRIANGLE_STRIP)
+    {
+        shaderStream << "    uint lastVertexIndex = (primitiveID % 2 == 0 ? 2 : 1);\n";
+    }
+    else
+    {
+        shaderStream << "    uint lastVertexIndex = " << (inputSize - 1) << ";\n";
+    }
+
     for (int vertexIndex = 0; vertexIndex < inputSize; ++vertexIndex)
     {
-        shaderStream << "    copyVertex(output, input[" << vertexIndex << "], input["
-                     << flatVertexIndex << "]);\n";
+        shaderStream << "    copyVertex(output, input[" << vertexIndex
+                     << "], input[lastVertexIndex]);\n";
 
         if (!pointSprites)
         {