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>

D3D11: Fix provoking vertex for flat triangle strips.
c7a92fdb · Jamie Madill · 31e60cf2 · c7a92fdb · c7a92fdb
Commit c7a92fdb authored Oct 29, 2015 by Jamie Madill
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Showing with 19 additions and 13 deletions

DynamicHLSL.cpp src/libANGLE/renderer/d3d/DynamicHLSL.cpp +19 -6

ProvokingVertexTest.cpp src/tests/gl_tests/ProvokingVertexTest.cpp +0 -7

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--- a/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
+++ b/src/libANGLE/renderer/d3d/DynamicHLSL.cpp
@@ -1436,17 +1436,30 @@ std::string DynamicHLSL::generateGeometryShaderHLSL(gl::PrimitiveType primitiveT
    shaderStream << preambleString << "\n"
                 << "[maxvertexcount(" << maxVertexOutput << ")]\n"
-                 << "void main(" << inputPT << " GS_INPUT input[" << inputSize << "],"
+                 << "void main(" << inputPT << " GS_INPUT input[" << inputSize << "], ";
-                                                                                  " inout "
-                 << outputPT << "Stream<GS_OUTPUT> outStream)\n"
+    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["
+        shaderStream << "    copyVertex(output, input[" << vertexIndex
-                     << flatVertexIndex << "]);\n";
+                     << "], input[lastVertexIndex]);\n";
        if (!pointSprites)
        {

--- a/src/tests/gl_tests/ProvokingVertexTest.cpp
+++ b/src/tests/gl_tests/ProvokingVertexTest.cpp
@@ -200,13 +200,6 @@ TEST_P(ProvokingVertexTest, FlatLine)
 // Test drawing a simple triangle strip with flat shading, and different valued vertices.
 TEST_P(ProvokingVertexTest, FlatTriStrip)
 {
-    // TODO(jmadill): Implement on the D3D back-end.
-    if (isD3D11())
-    {
-        std::cout << "Test disabled on D3D11." << std::endl;
-        return;
-    }
    GLint vertexData[]     = {1, 2, 3, 4, 5, 6};
    GLfloat positionData[] = {-1.0f, -1.0f, -1.0f, 1.0f,  0.0f, -1.0f,
                              0.0f,  1.0f,  1.0f,  -1.0f, 1.0f, 1.0f};