Fix CONSTANT_ALPHA and ONE_MINUS_CONSTANT_ALPHA blend modes in the D3D11 path.

src/libGLESv2/renderer/Renderer11.cpp

@@ -676,7 +676,23 @@ void Renderer11::setBlendState(const gl::BlendState &blendState, const gl::Color
                 "blend state.");
         }
 
-        const float blendColors[] = { blendColor.red, blendColor.green, blendColor.blue, blendColor.alpha };
+        float blendColors[4] = {0.0f};
+        if (blendState.sourceBlendRGB != GL_CONSTANT_ALPHA && blendState.sourceBlendRGB != GL_ONE_MINUS_CONSTANT_ALPHA &&
+            blendState.destBlendRGB != GL_CONSTANT_ALPHA && blendState.destBlendRGB != GL_ONE_MINUS_CONSTANT_ALPHA)
+        {
+            blendColors[0] = blendColor.red;
+            blendColors[1] = blendColor.green;
+            blendColors[2] = blendColor.blue;
+            blendColors[3] = blendColor.alpha;
+        }
+        else
+        {
+            blendColors[0] = blendColor.alpha;
+            blendColors[1] = blendColor.alpha;
+            blendColors[2] = blendColor.alpha;
+            blendColors[3] = blendColor.alpha;
+        }
+
         mDeviceContext->OMSetBlendState(dxBlendState, blendColors, sampleMask);
 
         mCurBlendState = blendState;