Change BitfieldExtract to use a pointer to the bitfield member

Source/Core/Common/BitField.h

@@ -155,8 +155,8 @@ struct BitField
 
   constexpr T Value() const { return Value(std::is_signed<T>()); }
   constexpr operator T() const { return Value(); }
-  constexpr std::size_t StartBit() const { return position; }
-  constexpr std::size_t NumBits() const { return bits; }
+  static constexpr std::size_t StartBit() { return position; }
+  static constexpr std::size_t NumBits() { return bits; }
 
 private:
   // Unsigned version of StorageType

Source/Core/Common/CMakeLists.txt

@@ -125,6 +125,7 @@ add_library(common
   TraversalClient.cpp
   TraversalClient.h
   TraversalProto.h
+  TypeUtils.h
   UPnP.cpp
   UPnP.h
   VariantUtil.h

Source/Core/Common/TypeUtils.h

@@ -0,0 +1,70 @@
+// Copyright 2021 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <type_traits>
+
+namespace Common
+{
+template <typename>
+struct MemberPointerInfo;
+// Helper to get information about a pointer to a data member.
+// See https://en.cppreference.com/w/cpp/language/pointer#Pointers_to_members
+// This template takes the type for a member pointer.
+template <typename M, typename O>
+struct MemberPointerInfo<M O::*>
+{
+  using MemberType = M;
+  using ObjectType = O;
+};
+
+// This template takes a specific member pointer.
+template <auto member_pointer>
+using MemberType = typename MemberPointerInfo<decltype(member_pointer)>::MemberType;
+
+// This template takes a specific member pointer.
+template <auto member_pointer>
+using ObjectType = typename MemberPointerInfo<decltype(member_pointer)>::ObjectType;
+
+namespace detail
+{
+template <int x>
+struct Data
+{
+  static constexpr int GetX() { return x; }
+};
+struct Foo
+{
+  Data<1> a;
+  Data<2> b;
+  int c;
+};
+struct Bar : Foo
+{
+  int d;
+};
+
+static_assert(std::is_same_v<MemberType<&Foo::a>, Data<1>>);
+static_assert(MemberType<&Foo::a>::GetX() == 1);
+static_assert(std::is_same_v<MemberType<&Foo::b>, Data<2>>);
+static_assert(MemberType<&Foo::b>::GetX() == 2);
+static_assert(std::is_same_v<MemberType<&Foo::c>, int>);
+
+static_assert(std::is_same_v<ObjectType<&Foo::a>, Foo>);
+static_assert(std::is_same_v<ObjectType<&Foo::b>, Foo>);
+static_assert(std::is_same_v<ObjectType<&Foo::c>, Foo>);
+
+static_assert(std::is_same_v<MemberType<&Foo::c>, MemberPointerInfo<int Foo::*>::MemberType>);
+static_assert(std::is_same_v<ObjectType<&Foo::c>, MemberPointerInfo<int Foo::*>::ObjectType>);
+
+static_assert(std::is_same_v<MemberType<&Bar::c>, int>);
+static_assert(std::is_same_v<MemberType<&Bar::d>, int>);
+
+static_assert(std::is_same_v<ObjectType<&Bar::d>, Bar>);
+// Somewhat unexpected behavior:
+static_assert(std::is_same_v<ObjectType<&Bar::c>, Foo>);
+static_assert(!std::is_same_v<ObjectType<&Bar::c>, Bar>);
+}  // namespace detail
+}  // namespace Common

Source/Core/DolphinLib.props

@@ -152,6 +152,7 @@
     <ClInclude Include="Common\Timer.h" />
     <ClInclude Include="Common\TraversalClient.h" />
     <ClInclude Include="Common\TraversalProto.h" />
+    <ClInclude Include="Common\TypeUtils.h" />
     <ClInclude Include="Common\UPnP.h" />
     <ClInclude Include="Common\VariantUtil.h" />
     <ClInclude Include="Common\Version.h" />

Source/Core/VideoCommon/UberShaderCommon.cpp

@@ -103,29 +103,29 @@ void WriteVertexLighting(ShaderCode& out, APIType api_type, std::string_view wor
             "  int4 lacc = int4(255, 255, 255, 255);\n"
             "\n");
 
-  out.Write("  if ({} != 0u)\n", BitfieldExtract("colorreg", LitChannel().matsource));
+  out.Write("  if ({} != 0u)\n", BitfieldExtract<&LitChannel::matsource>("colorreg"));
   out.Write("    mat.xyz = int3(round(((chan == 0u) ? {}.xyz : {}.xyz) * 255.0));\n",
             in_color_0_var, in_color_1_var);
 
-  out.Write("  if ({} != 0u)\n", BitfieldExtract("alphareg", LitChannel().matsource));
+  out.Write("  if ({} != 0u)\n", BitfieldExtract<&LitChannel::matsource>("alphareg"));
   out.Write("    mat.w = int(round(((chan == 0u) ? {}.w : {}.w) * 255.0));\n", in_color_0_var,
             in_color_1_var);
   out.Write("  else\n"
             "    mat.w = " I_MATERIALS " [chan + 2u].w;\n"
             "\n");
 
-  out.Write("  if ({} != 0u) {{\n", BitfieldExtract("colorreg", LitChannel().enablelighting));
-  out.Write("    if ({} != 0u)\n", BitfieldExtract("colorreg", LitChannel().ambsource));
+  out.Write("  if ({} != 0u) {{\n", BitfieldExtract<&LitChannel::enablelighting>("colorreg"));
+  out.Write("    if ({} != 0u)\n", BitfieldExtract<&LitChannel::ambsource>("colorreg"));
   out.Write("      lacc.xyz = int3(round(((chan == 0u) ? {}.xyz : {}.xyz) * 255.0));\n",
             in_color_0_var, in_color_1_var);
   out.Write("    else\n"
             "      lacc.xyz = " I_MATERIALS " [chan].xyz;\n"
             "\n");
   out.Write("    uint light_mask = {} | ({} << 4u);\n",
-            BitfieldExtract("colorreg", LitChannel().lightMask0_3),
-            BitfieldExtract("colorreg", LitChannel().lightMask4_7));
-  out.Write("    uint attnfunc = {};\n", BitfieldExtract("colorreg", LitChannel().attnfunc));
-  out.Write("    uint diffusefunc = {};\n", BitfieldExtract("colorreg", LitChannel().diffusefunc));
+            BitfieldExtract<&LitChannel::lightMask0_3>("colorreg"),
+            BitfieldExtract<&LitChannel::lightMask4_7>("colorreg"));
+  out.Write("    uint attnfunc = {};\n", BitfieldExtract<&LitChannel::attnfunc>("colorreg"));
+  out.Write("    uint diffusefunc = {};\n", BitfieldExtract<&LitChannel::diffusefunc>("colorreg"));
   out.Write(
       "    for (uint light_index = 0u; light_index < 8u; light_index++) {{\n"
       "      if ((light_mask & (1u << light_index)) != 0u)\n"
@@ -135,8 +135,8 @@ void WriteVertexLighting(ShaderCode& out, APIType api_type, std::string_view wor
             "  }}\n"
             "\n");
 
-  out.Write("  if ({} != 0u) {{\n", BitfieldExtract("alphareg", LitChannel().enablelighting));
-  out.Write("    if ({} != 0u) {{\n", BitfieldExtract("alphareg", LitChannel().ambsource));
+  out.Write("  if ({} != 0u) {{\n", BitfieldExtract<&LitChannel::enablelighting>("alphareg"));
+  out.Write("    if ({} != 0u) {{\n", BitfieldExtract<&LitChannel::ambsource>("alphareg"));
   out.Write("      if ((components & ({}u << chan)) != 0u) // VB_HAS_COL0\n", VB_HAS_COL0);
   out.Write("        lacc.w = int(round(((chan == 0u) ? {}.w : {}.w) * 255.0));\n", in_color_0_var,
             in_color_1_var);
@@ -149,10 +149,10 @@ void WriteVertexLighting(ShaderCode& out, APIType api_type, std::string_view wor
             "    }}\n"
             "\n");
   out.Write("    uint light_mask = {} | ({} << 4u);\n",
-            BitfieldExtract("alphareg", LitChannel().lightMask0_3),
-            BitfieldExtract("alphareg", LitChannel().lightMask4_7));
-  out.Write("    uint attnfunc = {};\n", BitfieldExtract("alphareg", LitChannel().attnfunc));
-  out.Write("    uint diffusefunc = {};\n", BitfieldExtract("alphareg", LitChannel().diffusefunc));
+            BitfieldExtract<&LitChannel::lightMask0_3>("alphareg"),
+            BitfieldExtract<&LitChannel::lightMask4_7>("alphareg"));
+  out.Write("    uint attnfunc = {};\n", BitfieldExtract<&LitChannel::attnfunc>("alphareg"));
+  out.Write("    uint diffusefunc = {};\n", BitfieldExtract<&LitChannel::diffusefunc>("alphareg"));
   out.Write("    for (uint light_index = 0u; light_index < 8u; light_index++) {{\n\n"
             "      if ((light_mask & (1u << light_index)) != 0u)\n\n"
             "        lacc.w += CalculateLighting(light_index, attnfunc, diffusefunc, {}, {}).w;\n",

Source/Core/VideoCommon/UberShaderCommon.h

@@ -10,6 +10,7 @@
 #include <fmt/format.h>
 
 #include "Common/CommonTypes.h"
+#include "Common/TypeUtils.h"
 
 class ShaderCode;
 enum class APIType;
@@ -29,10 +30,11 @@ void WriteVertexLighting(ShaderCode& out, APIType api_type, std::string_view wor
                          std::string_view out_color_1_var);
 
 // bitfieldExtract generator for BitField types
-template <typename T>
-std::string BitfieldExtract(std::string_view source, T type)
+template <auto ptr_to_bitfield_member>
+std::string BitfieldExtract(std::string_view source)
 {
-  return fmt::format("bitfieldExtract({}, {}, {})", source, static_cast<u32>(type.StartBit()),
-                     static_cast<u32>(type.NumBits()));
+  using BitFieldT = Common::MemberType<ptr_to_bitfield_member>;
+  return fmt::format("bitfieldExtract({}, {}, {})", source, static_cast<u32>(BitFieldT::StartBit()),
+                     static_cast<u32>(BitFieldT::NumBits()));
 }
 }  // namespace UberShader