Fix ImGui rendering on HDR swap chains

dependencies/imgui/imgui_impl_dx11.cpp

@@ -63,6 +63,7 @@ struct ImGui_ImplDX11_Data
     ID3D11RasterizerState*      pRasterizerState;
     ID3D11BlendState*           pBlendState;
     ID3D11DepthStencilState*    pDepthStencilState;
+    ImGui_ImplDXGI_ColorSpace   ColorSpace;
     int                         VertexBufferSize;
     int                         IndexBufferSize;
 
@@ -456,24 +457,14 @@ bool    ImGui_ImplDX11_CreateDeviceObjects()
 
     // Create the pixel shader
     {
-        static const char* pixelShader =
-            "struct PS_INPUT\
-            {\
-            float4 pos : SV_POSITION;\
-            float4 col : COLOR0;\
-            float2 uv  : TEXCOORD0;\
-            };\
-            sampler sampler0;\
-            Texture2D texture0;\
-            \
-            float4 main(PS_INPUT input) : SV_Target\
-            {\
-            float4 out_col = input.col * texture0.Sample(sampler0, input.uv); \
-            return out_col; \
-            }";
+        const D3D_SHADER_MACRO shaderDefines[] =
+        {
+            { "IMGUI_COLOR_SPACE", ImGui_ImplDXGI_GetColorSpaceShaderDefine(bd->ColorSpace) },
+            { nullptr, nullptr },
+        };
 
         ID3DBlob* pixelShaderBlob;
-        if (FAILED(D3DCompile(pixelShader, strlen(pixelShader), nullptr, nullptr, nullptr, "main", "ps_4_0", 0, 0, &pixelShaderBlob, nullptr)))
+        if (FAILED(D3DCompile(ImGui_ImplDXGI_PixelShader, strlen(ImGui_ImplDXGI_PixelShader), nullptr, shaderDefines, nullptr, "main", "ps_4_0", 0, 0, &pixelShaderBlob, nullptr)))
             return false; // NB: Pass ID3DBlob* pErrorBlob to D3DCompile() to get error showing in (const char*)pErrorBlob->GetBufferPointer(). Make sure to Release() the blob!
         if (bd->pd3dDevice->CreatePixelShader(pixelShaderBlob->GetBufferPointer(), pixelShaderBlob->GetBufferSize(), nullptr, &bd->pPixelShader) != S_OK)
         {
@@ -548,13 +539,14 @@ void    ImGui_ImplDX11_InvalidateDeviceObjects()
     if (bd->pVertexShader)          { bd->pVertexShader->Release(); bd->pVertexShader = nullptr; }
 }
 
-bool    ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context)
+bool    ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context, ImGui_ImplDXGI_ColorSpace color_space)
 {
     ImGuiIO& io = *igGetIO();
     IM_ASSERT(io.BackendRendererUserData == nullptr && "Already initialized a renderer backend!");
 
     // Setup backend capabilities flags
     ImGui_ImplDX11_Data* bd = IM_NEW(ImGui_ImplDX11_Data)();
+    bd->ColorSpace = color_space;
     io.BackendRendererUserData = (void*)bd;
     io.BackendRendererName = "imgui_impl_dx11";
     io.BackendFlags |= ImGuiBackendFlags_RendererHasVtxOffset;  // We can honor the ImDrawCmd::VtxOffset field, allowing for large meshes.

dependencies/imgui/imgui_impl_dx11.h

@@ -16,12 +16,13 @@
 
 #pragma once
 #include <imgui_impl.h>
+#include <imgui_impl_dxgi_hdr.h>
 #ifndef IMGUI_DISABLE
 
 struct ID3D11Device;
 struct ID3D11DeviceContext;
 
-IMGUI_IMPL_API bool     ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context);
+IMGUI_IMPL_API bool     ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context, ImGui_ImplDXGI_ColorSpace color_space = ImGui_ImplDXGI_ColorSpace_SDR);
 IMGUI_IMPL_API void     ImGui_ImplDX11_Shutdown();
 IMGUI_IMPL_API void     ImGui_ImplDX11_NewFrame();
 IMGUI_IMPL_API void     ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data);

dependencies/imgui/imgui_impl_dx12.cpp

@@ -67,6 +67,7 @@ struct ImGui_ImplDX12_Data
     D3D12_GPU_DESCRIPTOR_HANDLE hFontSrvGpuDescHandle;
     ID3D12DescriptorHeap*       pd3dSrvDescHeap;
     UINT                        numFramesInFlight;
+    ImGui_ImplDXGI_ColorSpace   ColorSpace;
 
     ImGui_ImplDX12_Data()       { memset((void*)this, 0, sizeof(*this)); }
 };
@@ -676,23 +677,13 @@ bool    ImGui_ImplDX12_CreateDeviceObjects()
 
     // Create the pixel shader
     {
-        static const char* pixelShader =
-            "struct PS_INPUT\
-            {\
-              float4 pos : SV_POSITION;\
-              float4 col : COLOR0;\
-              float2 uv  : TEXCOORD0;\
-            };\
-            SamplerState sampler0 : register(s0);\
-            Texture2D texture0 : register(t0);\
-            \
-            float4 main(PS_INPUT input) : SV_Target\
-            {\
-              float4 out_col = input.col * texture0.Sample(sampler0, input.uv); \
-              return out_col; \
-            }";
+        const D3D_SHADER_MACRO shaderDefines[] =
+        {
+            { "IMGUI_COLOR_SPACE", ImGui_ImplDXGI_GetColorSpaceShaderDefine(bd->ColorSpace) },
+            { nullptr, nullptr },
+        };
 
-        if (FAILED(D3DCompile(pixelShader, strlen(pixelShader), nullptr, nullptr, nullptr, "main", "ps_5_0", 0, 0, &pixelShaderBlob, nullptr)))
+        if (FAILED(D3DCompile(ImGui_ImplDXGI_PixelShader, strlen(ImGui_ImplDXGI_PixelShader), nullptr, shaderDefines, nullptr, "main", "ps_5_0", 0, 0, &pixelShaderBlob, nullptr)))
         {
             vertexShaderBlob->Release();
             return false; // NB: Pass ID3DBlob* pErrorBlob to D3DCompile() to get error showing in (const char*)pErrorBlob->GetBufferPointer(). Make sure to Release() the blob!
@@ -774,7 +765,8 @@ void    ImGui_ImplDX12_InvalidateDeviceObjects()
 }
 
 bool ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* cbv_srv_heap,
-                         D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle)
+                         D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle,
+                         ImGui_ImplDXGI_ColorSpace color_space)
 {
     ImGuiIO& io = *igGetIO();
     IM_ASSERT(io.BackendRendererUserData == nullptr && "Already initialized a renderer backend!");
@@ -790,6 +782,7 @@ bool ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FO
 
     bd->pd3dDevice = device;
     bd->RTVFormat = rtv_format;
+    bd->ColorSpace = color_space;
     bd->hFontSrvCpuDescHandle = font_srv_cpu_desc_handle;
     bd->hFontSrvGpuDescHandle = font_srv_gpu_desc_handle;
     bd->numFramesInFlight = num_frames_in_flight;

dependencies/imgui/imgui_impl_dx12.h

@@ -19,6 +19,7 @@
 
 #pragma once
 #include <imgui_impl.h>
+#include <imgui_impl_dxgi_hdr.h>
 #ifndef IMGUI_DISABLE
 #include <dxgiformat.h> // DXGI_FORMAT
 
@@ -33,7 +34,8 @@ struct D3D12_GPU_DESCRIPTOR_HANDLE;
 // render target and descriptor heap that contains font_srv_cpu_desc_handle/font_srv_gpu_desc_handle.
 // font_srv_cpu_desc_handle and font_srv_gpu_desc_handle are handles to a single SRV descriptor to use for the internal font texture.
 IMGUI_IMPL_API bool     ImGui_ImplDX12_Init(ID3D12Device* device, int num_frames_in_flight, DXGI_FORMAT rtv_format, ID3D12DescriptorHeap* cbv_srv_heap,
-                                            D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle);
+                                            D3D12_CPU_DESCRIPTOR_HANDLE font_srv_cpu_desc_handle, D3D12_GPU_DESCRIPTOR_HANDLE font_srv_gpu_desc_handle,
+                                            ImGui_ImplDXGI_ColorSpace color_space = ImGui_ImplDXGI_ColorSpace_SDR);
 IMGUI_IMPL_API void     ImGui_ImplDX12_Shutdown();
 IMGUI_IMPL_API void     ImGui_ImplDX12_NewFrame();
 IMGUI_IMPL_API void     ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandList* graphics_command_list);

dependencies/imgui/imgui_impl_dxgi_hdr.h

@@ -0,0 +1,89 @@
+#pragma once
+
+enum ImGui_ImplDXGI_ColorSpace
+{
+    ImGui_ImplDXGI_ColorSpace_SDR = 0,
+    ImGui_ImplDXGI_ColorSpace_scRGB,
+    ImGui_ImplDXGI_ColorSpace_HDR10,
+};
+
+inline const char* ImGui_ImplDXGI_GetColorSpaceShaderDefine(ImGui_ImplDXGI_ColorSpace color_space)
+{
+    switch (color_space)
+    {
+    case ImGui_ImplDXGI_ColorSpace_scRGB:
+        return "1";
+    case ImGui_ImplDXGI_ColorSpace_HDR10:
+        return "2";
+    default:
+        return "0";
+    }
+}
+
+// ImGui colors and textures are treated as sRGB/Rec.709. HDR output uses a
+// 203-nit graphics white, as recommended by BT.2408, while SDR output remains
+// byte-for-byte compatible with the stock Dear ImGui renderer backend.
+inline constexpr const char* ImGui_ImplDXGI_PixelShader = R"(
+#ifndef IMGUI_COLOR_SPACE
+#define IMGUI_COLOR_SPACE 0
+#endif
+
+struct PS_INPUT
+{
+    float4 pos : SV_POSITION;
+    float4 col : COLOR0;
+    float2 uv  : TEXCOORD0;
+};
+
+SamplerState sampler0 : register(s0);
+Texture2D texture0 : register(t0);
+
+static const float GRAPHICS_WHITE_NITS = 203.0;
+
+float3 SrgbToLinear(float3 color)
+{
+    float3 low = color / 12.92;
+    float3 high = pow((color + 0.055) / 1.055, 2.4);
+    return lerp(low, high, step(0.04045, color));
+}
+
+float3 Rec709ToRec2020(float3 color)
+{
+    const float3x3 transform =
+    {
+        0.6274040, 0.3292820, 0.0433136,
+        0.0690970, 0.9195400, 0.0113612,
+        0.0163916, 0.0880132, 0.8955950
+    };
+    return mul(transform, color);
+}
+
+float3 LinearToPq(float3 color)
+{
+    const float m1 = 2610.0 / 16384.0;
+    const float m2 = 2523.0 / 32.0;
+    const float c1 = 3424.0 / 4096.0;
+    const float c2 = 2413.0 / 128.0;
+    const float c3 = 2392.0 / 128.0;
+
+    float3 p = pow(max(color, 0.0), m1);
+    return pow((c1 + c2 * p) / (1.0 + c3 * p), m2);
+}
+
+float4 main(PS_INPUT input) : SV_Target
+{
+    float4 out_col = input.col * texture0.Sample(sampler0, input.uv);
+
+#if IMGUI_COLOR_SPACE == 1
+    // scRGB is linear Rec.709 and defines 1.0 as 80 nits.
+    out_col.rgb = SrgbToLinear(saturate(out_col.rgb)) * (GRAPHICS_WHITE_NITS / 80.0);
+#elif IMGUI_COLOR_SPACE == 2
+    // HDR10 uses Rec.2020 primaries and the absolute ST.2084/PQ transfer curve.
+    float3 linear_rec709 = SrgbToLinear(saturate(out_col.rgb));
+    float3 linear_rec2020 = Rec709ToRec2020(linear_rec709);
+    out_col.rgb = LinearToPq(linear_rec2020 * (GRAPHICS_WHITE_NITS / 10000.0));
+#endif
+
+    return out_col;
+}
+)";

mhw-cs-plugin-loader/D3DModule.cpp

@@ -25,6 +25,28 @@
 // DirectXTK12 References SerializeRootSignature so we need to link this
 #pragma comment(lib, "d3d12.lib")
 
+namespace {
+
+// DXGI exposes methods to set a swap-chain color space, but not to query the
+// active one. MHW uses these back-buffer formats for its two HDR output paths.
+ImGui_ImplDXGI_ColorSpace infer_imgui_color_space(DXGI_FORMAT back_buffer_format) {
+    switch (back_buffer_format) {
+    case DXGI_FORMAT_R16G16B16A16_FLOAT:
+        dlog::debug("Using scRGB color management for ImGui");
+        return ImGui_ImplDXGI_ColorSpace_scRGB;
+
+    case DXGI_FORMAT_R10G10B10A2_UNORM:
+        dlog::debug("Using HDR10 color management for ImGui");
+        return ImGui_ImplDXGI_ColorSpace_HDR10;
+
+    default:
+        dlog::debug("Using SDR color management for ImGui");
+        return ImGui_ImplDXGI_ColorSpace_SDR;
+    }
+}
+
+}
+
 void D3DModule::initialize(CoreClr* coreclr) {
     if (!preloader::LoaderConfig::get().get_imgui_rendering_enabled()) {
         dlog::debug("Skipping D3D module initialization because imgui rendering is disabled");
@@ -558,6 +580,8 @@ void D3DModule::d3d12_initialize_imgui(IDXGISwapChain* swap_chain) {
     const auto rtv_descriptor_size = m_d3d12_device->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE_RTV);
     D3D12_CPU_DESCRIPTOR_HANDLE rtv_handle = m_d3d12_back_buffers->GetCPUDescriptorHandleForHeapStart();
 
+    DXGI_FORMAT back_buffer_format = DXGI_FORMAT_UNKNOWN;
+
     for (auto i = 0u; i < desc.BufferCount; ++i) {
         ComPtr<ID3D12Resource> back_buffer;
         if (FAILED(swap_chain->GetBuffer(i, IID_PPV_ARGS(back_buffer.GetAddressOf())))) {
@@ -566,7 +590,17 @@ void D3DModule::d3d12_initialize_imgui(IDXGISwapChain* swap_chain) {
         }
 
         const auto buffer_desc = back_buffer->GetDesc();
-        dlog::debug("Creating RTV for back buffer {}, with size {}x{}", i, buffer_desc.Width, buffer_desc.Height);
+        if (i == 0) {
+            back_buffer_format = buffer_desc.Format;
+        }
+
+        dlog::debug(
+            "Creating RTV for back buffer {}, with size {}x{} and format {}",
+            i,
+            buffer_desc.Width,
+            buffer_desc.Height,
+            static_cast<u32>(buffer_desc.Format)
+        );
 
         m_d3d12_device->CreateRenderTargetView(back_buffer.Get(), nullptr, rtv_handle);
         m_d3d12_frame_contexts[i].RenderTargetDescriptor = rtv_handle;
@@ -575,6 +609,8 @@ void D3DModule::d3d12_initialize_imgui(IDXGISwapChain* swap_chain) {
         rtv_handle.ptr += rtv_descriptor_size;
     }
 
+    const auto imgui_color_space = infer_imgui_color_space(back_buffer_format);
+
     if (!ImGui_ImplWin32_Init(m_game_window)) {
         dlog::error("Failed to initialize ImGui Win32");
         return;
@@ -583,9 +619,10 @@ void D3DModule::d3d12_initialize_imgui(IDXGISwapChain* swap_chain) {
     ImGui_ImplWin32_EnableDpiAwareness();
 
     if (!ImGui_ImplDX12_Init(m_d3d12_device, desc.BufferCount,
-        DXGI_FORMAT_R8G8B8A8_UNORM, m_d3d12_srv_heap.Get(),
+        back_buffer_format, m_d3d12_srv_heap.Get(),
         m_d3d12_srv_heap->GetCPUDescriptorHandleForHeapStart(),
-        m_d3d12_srv_heap->GetGPUDescriptorHandleForHeapStart())) {
+        m_d3d12_srv_heap->GetGPUDescriptorHandleForHeapStart(),
+        imgui_color_space)) {
         dlog::error("Failed to initialize ImGui D3D12");
         return;
     }
@@ -618,6 +655,16 @@ void D3DModule::d3d11_initialize_imgui(IDXGISwapChain* swap_chain) {
         return;
     }
 
+    DXGI_FORMAT back_buffer_format = desc.BufferDesc.Format;
+    ComPtr<ID3D11Texture2D> back_buffer;
+    if (SUCCEEDED(swap_chain->GetBuffer(0, IID_PPV_ARGS(back_buffer.GetAddressOf())))) {
+        D3D11_TEXTURE2D_DESC back_buffer_desc;
+        back_buffer->GetDesc(&back_buffer_desc);
+        back_buffer_format = back_buffer_desc.Format;
+    }
+
+    const auto imgui_color_space = infer_imgui_color_space(back_buffer_format);
+
     RECT client_rect;
     GetClientRect(desc.OutputWindow, &client_rect);
 
@@ -638,7 +685,7 @@ void D3DModule::d3d11_initialize_imgui(IDXGISwapChain* swap_chain) {
         return;
     }
 
-    if (!ImGui_ImplDX11_Init(m_d3d11_device, m_d3d11_device_context)) {
+    if (!ImGui_ImplDX11_Init(m_d3d11_device, m_d3d11_device_context, imgui_color_space)) {
         dlog::error("Failed to initialize ImGui D3D11");
         return;
     }

mhw-cs-plugin-loader/mhw-cs-plugin-loader.vcxproj

@@ -135,6 +135,7 @@
     <ClInclude Include="..\dependencies\imgui\imgui_impl.h" />
     <ClInclude Include="..\dependencies\imgui\imgui_impl_dx11.h" />
     <ClInclude Include="..\dependencies\imgui\imgui_impl_dx12.h" />
+    <ClInclude Include="..\dependencies\imgui\imgui_impl_dxgi_hdr.h" />
     <ClInclude Include="..\dependencies\imgui\imgui_impl_win32.h" />
     <ClInclude Include="AddressRepository.h" />
     <ClInclude Include="Bitfield.h" />
@@ -206,4 +207,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>

mhw-cs-plugin-loader/mhw-cs-plugin-loader.vcxproj.filters

@@ -143,6 +143,9 @@
     <ClInclude Include="..\dependencies\imgui\imgui_impl_dx12.h">
       <Filter>Header Files\ImGui</Filter>
     </ClInclude>
+    <ClInclude Include="..\dependencies\imgui\imgui_impl_dxgi_hdr.h">
+      <Filter>Header Files\ImGui</Filter>
+    </ClInclude>
     <ClInclude Include="..\dependencies\imgui\imgui_impl_win32.h">
       <Filter>Header Files\ImGui</Filter>
     </ClInclude>
@@ -246,4 +249,4 @@
       <Filter>Resource Files</Filter>
     </None>
   </ItemGroup>
-</Project>
+</Project>