ShaderGen: Implement pixel ubershaders

Source/Core/VideoCommon/UberShaderCommon.cpp

@@ -0,0 +1,27 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include "VideoCommon/UberShaderCommon.h"
+#include "VideoCommon/VideoConfig.h"
+
+namespace UberShader
+{
+void WriteUberShaderCommonHeader(ShaderCode& out, APIType api_type,
+                                 const ShaderHostConfig& host_config)
+{
+  // ==============================================
+  //  BitfieldExtract for APIs which don't have it
+  // ==============================================
+  if (!host_config.backend_bitfield)
+  {
+    out.Write("uint bitfieldExtract(uint val, int off, int size) {\n"
+              "	// This built-in function is only support in OpenGL 4.0+ and ES 3.1+\n"
+              "	// Microsoft's HLSL compiler automatically optimises this to a bitfield extract "
+              "instruction.\n"
+              "	uint mask = uint((1 << size) - 1);\n"
+              "	return uint(val >> off) & mask;\n"
+              "}\n\n");
+  }
+}
+}