Backends: DX11: Expose vertex constant buffer in ImGui_ImplDX11_RenderState.

DX9 and DX12 users can already alter the projection matrix (in undocumented ways, but possible)

Author: ocornut

backends/imgui_impl_dx11.cpp

@@ -16,6 +16,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-01-06: DirectX11: Expose VertexConstantBuffer in ImGui_ImplDX11_RenderState. Reset projection matrix in ImDrawCallback_ResetRenderState handler.
 //  2024-10-07: DirectX11: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-10-07: DirectX11: Expose selected render state in ImGui_ImplDX11_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
 //  2022-10-11: Using 'nullptr' instead of 'NULL' as per our switch to C++11.
@@ -98,6 +99,27 @@ static void ImGui_ImplDX11_SetupRenderState(ImDrawData* draw_data, ID3D11DeviceC
     vp.TopLeftX = vp.TopLeftY = 0;
     device_ctx->RSSetViewports(1, &vp);
 
+    // Setup orthographic projection matrix into our constant buffer
+    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
+    D3D11_MAPPED_SUBRESOURCE mapped_resource;
+    if (device_ctx->Map(bd->pVertexConstantBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mapped_resource) == S_OK)
+    {
+        VERTEX_CONSTANT_BUFFER_DX11* constant_buffer = (VERTEX_CONSTANT_BUFFER_DX11*)mapped_resource.pData;
+        float L = draw_data->DisplayPos.x;
+        float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x;
+        float T = draw_data->DisplayPos.y;
+        float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y;
+        float mvp[4][4] =
+        {
+            { 2.0f/(R-L),   0.0f,           0.0f,       0.0f },
+            { 0.0f,         2.0f/(T-B),     0.0f,       0.0f },
+            { 0.0f,         0.0f,           0.5f,       0.0f },
+            { (R+L)/(L-R),  (T+B)/(B-T),    0.5f,       1.0f },
+        };
+        memcpy(&constant_buffer->mvp, mvp, sizeof(mvp));
+        device_ctx->Unmap(bd->pVertexConstantBuffer, 0);
+    }
+
     // Setup shader and vertex buffers
     unsigned int stride = sizeof(ImDrawVert);
     unsigned int offset = 0;
@@ -179,28 +201,6 @@ void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
     device->Unmap(bd->pVB, 0);
     device->Unmap(bd->pIB, 0);
 
-    // Setup orthographic projection matrix into our constant buffer
-    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
-    {
-        D3D11_MAPPED_SUBRESOURCE mapped_resource;
-        if (device->Map(bd->pVertexConstantBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mapped_resource) != S_OK)
-            return;
-        VERTEX_CONSTANT_BUFFER_DX11* constant_buffer = (VERTEX_CONSTANT_BUFFER_DX11*)mapped_resource.pData;
-        float L = draw_data->DisplayPos.x;
-        float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x;
-        float T = draw_data->DisplayPos.y;
-        float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y;
-        float mvp[4][4] =
-        {
-            { 2.0f/(R-L),   0.0f,           0.0f,       0.0f },
-            { 0.0f,         2.0f/(T-B),     0.0f,       0.0f },
-            { 0.0f,         0.0f,           0.5f,       0.0f },
-            { (R+L)/(L-R),  (T+B)/(B-T),    0.5f,       1.0f },
-        };
-        memcpy(&constant_buffer->mvp, mvp, sizeof(mvp));
-        device->Unmap(bd->pVertexConstantBuffer, 0);
-    }
-
     // Backup DX state that will be modified to restore it afterwards (unfortunately this is very ugly looking and verbose. Close your eyes!)
     struct BACKUP_DX11_STATE
     {
@@ -255,6 +255,7 @@ void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
     render_state.Device = bd->pd3dDevice;
     render_state.DeviceContext = bd->pd3dDeviceContext;
     render_state.SamplerDefault = bd->pFontSampler;
+    render_state.VertexConstantBuffer = bd->pVertexConstantBuffer;
     platform_io.Renderer_RenderState = &render_state;
 
     // Render command lists

backends/imgui_impl_dx11.h

@@ -21,6 +21,7 @@
 struct ID3D11Device;
 struct ID3D11DeviceContext;
 struct ID3D11SamplerState;
+struct ID3D11Buffer;
 
 // Follow "Getting Started" link and check examples/ folder to learn about using backends!
 IMGUI_IMPL_API bool     ImGui_ImplDX11_Init(ID3D11Device* device, ID3D11DeviceContext* device_context);
@@ -40,6 +41,7 @@ struct ImGui_ImplDX11_RenderState
     ID3D11Device*           Device;
     ID3D11DeviceContext*    DeviceContext;
     ID3D11SamplerState*     SamplerDefault;
+    ID3D11Buffer*           VertexConstantBuffer;
 };
 
 #endif // #ifndef IMGUI_DISABLE

docs/CHANGELOG.txt

@@ -72,6 +72,8 @@ Other changes:
   platforms not supporting VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR. (#8222) [@Zer0xFF]
 - Backends: Vulkan: Added a few more ImGui_ImplVulkanH_XXX helper functions
   primarily for the purpose of making our examples simpler.
+- Backends: DX11: Expose vertex constant buffer in ImGui_ImplDX11_RenderState.
+  Reset projection matrix in ImDrawCallback_ResetRenderState handlers. (#6969, #5834, #7468, #3590)
 - Examples: Added Win32+Vulkan example for completeness. (#8180) [@jristic]