Backends: DX12: Fix texture casting crash on 32-bit systems (introduced on 2021/05/19 and v1.83) + added comments about building on 32-bit systems. (#4225)

backends/imgui_impl_dx12.cpp

@@ -7,9 +7,13 @@
 
 // Important: to compile on 32-bit systems, this backend requires code to be compiled with '#define ImTextureID ImU64'.
 // This is because we need ImTextureID to carry a 64-bit value and by default ImTextureID is defined as void*.
-// This define is set in the example .vcxproj file and need to be replicated in your app or by adding it to your imconfig.h file.
+// To build this on 32-bit systems:
+// - [Solution 1] IDE/msbuild: in "Properties/C++/Preprocessor Definitions" add 'ImTextureID=ImU64' (this is what we do in the 'example_win32_direct12/example_win32_direct12.vcxproj' project file)
+// - [Solution 2] IDE/msbuild: in "Properties/C++/Preprocessor Definitions" add 'IMGUI_USER_CONFIG="my_imgui_config.h"' and inside 'my_imgui_config.h' add '#define ImTextureID ImU64' and as many other options as you like.
+// - [Solution 3] IDE/msbuild: edit imconfig.h and add '#define ImTextureID ImU64' (prefer solution 2 to create your own config file!)
+// - [Solution 4] command-line: add '/D ImTextureID=ImU64' to your cl.exe command-line (this is what we do in the example_win32_direct12/build_win32.bat file)
 
-// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this. 
+// You can use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
 // Prefer including the entire imgui/ repository into your project (either as a copy or as a submodule), and only build the backends you need.
 // If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
 // Read online: https://github.com/ocornut/imgui/tree/master/docs
@@ -242,7 +246,7 @@ void ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandL
                 if (r.right > r.left && r.bottom > r.top)
                 {
                     D3D12_GPU_DESCRIPTOR_HANDLE texture_handle = {};
-                    texture_handle.ptr = (UINT64)(intptr_t)pcmd->GetTexID();
+                    texture_handle.ptr = (UINT64)pcmd->GetTexID();
                     ctx->SetGraphicsRootDescriptorTable(1, texture_handle);
                     ctx->RSSetScissorRects(1, &r);
                     ctx->DrawIndexedInstanced(pcmd->ElemCount, 1, pcmd->IdxOffset + global_idx_offset, pcmd->VtxOffset + global_vtx_offset, 0);
@@ -399,6 +403,13 @@ static void ImGui_ImplDX12_CreateFontsTexture()
     }
 
     // Store our identifier
+    // READ THIS IF THE STATIC_ASSERT() TRIGGERS:
+    // - Important: to compile on 32-bit systems, this backend requires code to be compiled with '#define ImTextureID ImU64'.
+    // - This is because we need ImTextureID to carry a 64-bit value and by default ImTextureID is defined as void*.
+    // [Solution 1] IDE/msbuild: in "Properties/C++/Preprocessor Definitions" add 'ImTextureID=ImU64' (this is what we do in the 'example_win32_direct12/example_win32_direct12.vcxproj' project file)
+    // [Solution 2] IDE/msbuild: in "Properties/C++/Preprocessor Definitions" add 'IMGUI_USER_CONFIG="my_imgui_config.h"' and inside 'my_imgui_config.h' add '#define ImTextureID ImU64' and as many other options as you like.
+    // [Solution 3] IDE/msbuild: edit imconfig.h and add '#define ImTextureID ImU64' (prefer solution 2 to create your own config file!)
+    // [Solution 4] command-line: add '/D ImTextureID=ImU64' to your cl.exe command-line (this is what we do in the example_win32_direct12/build_win32.bat file)
     static_assert(sizeof(ImTextureID) >= sizeof(g_hFontSrvGpuDescHandle.ptr), "Can't pack descriptor handle into TexID, 32-bit not supported yet.");
     io.Fonts->SetTexID((ImTextureID)g_hFontSrvGpuDescHandle.ptr);
 }

docs/CHANGELOG.txt

@@ -50,6 +50,8 @@ Other Changes:
 - Backends: Win32: Rework to handle certains Windows 8.1/10 features without a manifest. (#4200, #4191)
   - ImGui_ImplWin32_GetDpiScaleForMonitor() will handle per-monitor DPI on Windows 10 without a manifest.
   - ImGui_ImplWin32_EnableDpiAwareness() will call SetProcessDpiAwareness() fallback on Windows 8.1 without a manifest.
+- Backends: DX12: Fix texture casting crash on 32-bit systems (introduced on 2021/05/19 and v1.83) + added comments
+  about building on 32-bit systems. (#4225) [@kingofthebongo2008]
 - Backends: OpenGL3: Handle GL_CLIP_ORIGIN on <4.5 contexts if "GL_ARB_clip_control" extension is detected. (#4170, #3998)
 - Examples: Updated all .vcxproj to VS2015 (toolset v140) to facilitate usage with vcpkg.
 - Examples: SDL2: Accomodate for vcpkg install having headers in SDL2/SDL.h vs SDL.h.