Unwritten shader output variables should not crash.

src/libANGLE/renderer/d3d/DynamicHLSL.cpp

@@ -72,19 +72,18 @@ std::string HLSLTypeString(GLenum type)
     return HLSLComponentTypeString(gl::VariableComponentType(type), gl::VariableComponentCount(type));
 }
 
-const PixelShaderOutputVariable &GetOutputAtLocation(const std::vector<PixelShaderOutputVariable> &outputVariables,
+const PixelShaderOutputVariable *FindOutputAtLocation(const std::vector<PixelShaderOutputVariable> &outputVariables,
                                                         unsigned int location)
 {
     for (size_t variableIndex = 0; variableIndex < outputVariables.size(); ++variableIndex)
     {
         if (outputVariables[variableIndex].outputIndex == location)
         {
-            return outputVariables[variableIndex];
+            return &outputVariables[variableIndex];
         }
     }
 
-    UNREACHABLE();
-    return outputVariables[0];
+    return NULL;
 }
 
 const std::string VERTEX_ATTRIBUTE_STUB_STRING = "@@ VERTEX ATTRIBUTES @@";
@@ -457,12 +456,18 @@ std::string DynamicHLSL::generatePixelShaderForOutputSignature(const std::string
         {
             unsigned int location = (binding - GL_COLOR_ATTACHMENT0);
 
-            const PixelShaderOutputVariable &outputVariable = GetOutputAtLocation(outputVariables, location);
+            const PixelShaderOutputVariable *outputVariable = FindOutputAtLocation(outputVariables, location);
 
-            declarationHLSL += "    " + HLSLTypeString(outputVariable.type) + " " + outputVariable.name +
-                               " : " + targetSemantic + Str(layoutIndex) + ";\n";
+            // OpenGL ES 3.0 spec $4.2.1
+            // If [...] not all user-defined output variables are written, the values of fragment colors
+            // corresponding to unwritten variables are similarly undefined.
+            if (outputVariable)
+            {
+                declarationHLSL += "    " + HLSLTypeString(outputVariable->type) + " " + outputVariable->name +
+                                   " : " + targetSemantic + Str(layoutIndex) + ";\n";
 
-            copyHLSL += "    output." + outputVariable.name + " = " + outputVariable.source + ";\n";
+                copyHLSL += "    output." + outputVariable->name + " = " + outputVariable->source + ";\n";
+            }
         }
     }
 

tests/angle_tests/DrawBuffersTest.cpp

@@ -287,3 +287,38 @@ TYPED_TEST(DrawBuffersTest, FirstHalfNULL)
 
     glDeleteProgram(program);
 }
+
+TYPED_TEST(DrawBuffersTest, UnwrittenOutputVariablesShouldNotCrash)
+{
+    // Bind two render targets but use a shader which writes only to the first one.
+    glBindTexture(GL_TEXTURE_2D, mTextures[0]);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, mTextures[0], 0);
+
+    glBindTexture(GL_TEXTURE_2D, mTextures[1]);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, mTextures[1], 0);
+
+    bool flags[8] = { true, false };
+
+    GLuint program;
+    setupMRTProgram(flags, &program);
+
+    const GLenum bufs[] =
+    {
+        GL_COLOR_ATTACHMENT0,
+        GL_COLOR_ATTACHMENT1,
+        GL_NONE,
+        GL_NONE,
+    };
+
+    glUseProgram(program);
+    glDrawBuffersEXT(4, bufs);
+
+    // This call should not crash when we dynamically generate the HLSL code.
+    glDrawArrays(GL_TRIANGLES, 0, 3);
+
+    verifyAttachment(0, mTextures[0]);
+
+    EXPECT_GL_NO_ERROR();
+
+    glDeleteProgram(program);
+}