ImDrawCallback_ResetRenderState, Examples: Added support for reset render state callback. (#2037, #1639, #2452)

docs/CHANGELOG.txt

@@ -45,6 +45,11 @@ Breaking Changes:
   on them but it is possible you have!).
 
 Other Changes:
+- ImDrawList: Added ImDrawCallback_ResetRenderState, a special ImDrawList::AddCallback() value
+  to request the renderer back-end to reset its render state. (#2037, #1639, #2452)
+- Examples: Added support for ImDrawCallback_ResetRenderState in all renderer back-ends.
+  Each renderer code setting up initial render state has been moved to a function so it could
+  be called at the start of rendering and when a ResetRenderState is requested. (#2037, #1639, #2452)
 - InputText: Fixed selection background starts rendering one frame after the cursor movement
   when first transitioning from no-selection to has-selection. (Bug in 1.69) (#2436) [@Nazg-Gul]
 - InputText: Work-around for buggy standard libraries where isprint('\t') returns true. (#2467, #1336)

examples/imgui_impl_allegro5.cpp

@@ -60,23 +60,9 @@ struct ImDrawVertAllegro
     ALLEGRO_COLOR col;
 };
 
-// Render function.
-// (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
-void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
+static void ImGui_ImplAllegro5_SetupRenderState(ImDrawData* draw_data)
 {
-    // Avoid rendering when minimized
-    if (draw_data->DisplaySize.x <= 0.0f || draw_data->DisplaySize.y <= 0.0f)
-        return;
-
-    // Backup Allegro state that will be modified
-    ALLEGRO_TRANSFORM last_transform = *al_get_current_transform();
-    ALLEGRO_TRANSFORM last_projection_transform = *al_get_current_projection_transform();
-    int last_clip_x, last_clip_y, last_clip_w, last_clip_h;
-    al_get_clipping_rectangle(&last_clip_x, &last_clip_y, &last_clip_w, &last_clip_h);
-    int last_blender_op, last_blender_src, last_blender_dst;
-    al_get_blender(&last_blender_op, &last_blender_src, &last_blender_dst);
-
-    // Setup render state
+    // Setup blending
     al_set_blender(ALLEGRO_ADD, ALLEGRO_ALPHA, ALLEGRO_INVERSE_ALPHA);
 
     // Setup orthographic projection matrix
@@ -92,7 +78,28 @@ void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
         al_orthographic_transform(&transform, L, T, 1.0f, R, B, -1.0f);
         al_use_projection_transform(&transform);
     }
+}
+
+// Render function.
+// (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
+void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
+{
+    // Avoid rendering when minimized
+    if (draw_data->DisplaySize.x <= 0.0f || draw_data->DisplaySize.y <= 0.0f)
+        return;
+
+    // Backup Allegro state that will be modified
+    ALLEGRO_TRANSFORM last_transform = *al_get_current_transform();
+    ALLEGRO_TRANSFORM last_projection_transform = *al_get_current_projection_transform();
+    int last_clip_x, last_clip_y, last_clip_w, last_clip_h;
+    al_get_clipping_rectangle(&last_clip_x, &last_clip_y, &last_clip_w, &last_clip_h);
+    int last_blender_op, last_blender_src, last_blender_dst;
+    al_get_blender(&last_blender_op, &last_blender_src, &last_blender_dst);
+
+    // Setup desired render state
+    ImGui_ImplAllegro5_SetupRenderState(draw_data);
 
+    // Render command lists
     for (int n = 0; n < draw_data->CmdListsCount; n++)
     {
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
@@ -135,10 +142,16 @@ void ImGui_ImplAllegro5_RenderDrawData(ImDrawData* draw_data)
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
             if (pcmd->UserCallback)
             {
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplAllegro5_SetupRenderState(draw_data);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {
+                // Draw
                 ALLEGRO_BITMAP* texture = (ALLEGRO_BITMAP*)pcmd->TextureId;
                 al_set_clipping_rectangle(pcmd->ClipRect.x - clip_off.x, pcmd->ClipRect.y - clip_off.y, pcmd->ClipRect.z - pcmd->ClipRect.x, pcmd->ClipRect.w - pcmd->ClipRect.y);
                 al_draw_prim(&vertices[0], g_VertexDecl, texture, idx_offset, idx_offset + pcmd->ElemCount, ALLEGRO_PRIM_TRIANGLE_LIST);

examples/imgui_impl_dx10.cpp

@@ -55,6 +55,37 @@ struct VERTEX_CONSTANT_BUFFER
     float   mvp[4][4];
 };
 
+static void ImGui_ImplDX10_SetupRenderState(ImDrawData* draw_data, ID3D10Device* ctx)
+{
+    // Setup viewport
+    D3D10_VIEWPORT vp;
+    memset(&vp, 0, sizeof(D3D10_VIEWPORT));
+    vp.Width = (UINT)draw_data->DisplaySize.x;
+    vp.Height = (UINT)draw_data->DisplaySize.y;
+    vp.MinDepth = 0.0f;
+    vp.MaxDepth = 1.0f;
+    vp.TopLeftX = vp.TopLeftY = 0;
+    ctx->RSSetViewports(1, &vp);
+
+    // Bind shader and vertex buffers
+    unsigned int stride = sizeof(ImDrawVert);
+    unsigned int offset = 0;
+    ctx->IASetInputLayout(g_pInputLayout);
+    ctx->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
+    ctx->IASetIndexBuffer(g_pIB, sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT, 0);
+    ctx->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
+    ctx->VSSetShader(g_pVertexShader);
+    ctx->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
+    ctx->PSSetShader(g_pPixelShader);
+    ctx->PSSetSamplers(0, 1, &g_pFontSampler);
+
+    // Setup render state
+    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
+    ctx->OMSetBlendState(g_pBlendState, blend_factor, 0xffffffff);
+    ctx->OMSetDepthStencilState(g_pDepthStencilState, 0);
+    ctx->RSSetState(g_pRasterizerState);
+}
+
 // Render function
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 void ImGui_ImplDX10_RenderDrawData(ImDrawData* draw_data)
@@ -172,33 +203,8 @@ void ImGui_ImplDX10_RenderDrawData(ImDrawData* draw_data)
     ctx->IAGetVertexBuffers(0, 1, &old.VertexBuffer, &old.VertexBufferStride, &old.VertexBufferOffset);
     ctx->IAGetInputLayout(&old.InputLayout);
 
-    // Setup viewport
-    D3D10_VIEWPORT vp;
-    memset(&vp, 0, sizeof(D3D10_VIEWPORT));
-    vp.Width = (UINT)draw_data->DisplaySize.x;
-    vp.Height = (UINT)draw_data->DisplaySize.y;
-    vp.MinDepth = 0.0f;
-    vp.MaxDepth = 1.0f;
-    vp.TopLeftX = vp.TopLeftY = 0;
-    ctx->RSSetViewports(1, &vp);
-
-    // Bind shader and vertex buffers
-    unsigned int stride = sizeof(ImDrawVert);
-    unsigned int offset = 0;
-    ctx->IASetInputLayout(g_pInputLayout);
-    ctx->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
-    ctx->IASetIndexBuffer(g_pIB, sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT, 0);
-    ctx->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
-    ctx->VSSetShader(g_pVertexShader);
-    ctx->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
-    ctx->PSSetShader(g_pPixelShader);
-    ctx->PSSetSamplers(0, 1, &g_pFontSampler);
-
-    // Setup render state
-    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
-    ctx->OMSetBlendState(g_pBlendState, blend_factor, 0xffffffff);
-    ctx->OMSetDepthStencilState(g_pDepthStencilState, 0);
-    ctx->RSSetState(g_pRasterizerState);
+    // Setup desired DX state
+    ImGui_ImplDX10_SetupRenderState(draw_data, ctx);
 
     // Render command lists
     int vtx_offset = 0;
@@ -212,8 +218,12 @@ void ImGui_ImplDX10_RenderDrawData(ImDrawData* draw_data)
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
             if (pcmd->UserCallback)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplDX10_SetupRenderState(draw_data, ctx);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

examples/imgui_impl_dx11.cpp

@@ -55,6 +55,37 @@ struct VERTEX_CONSTANT_BUFFER
     float   mvp[4][4];
 };
 
+static void ImGui_ImplDX11_SetupRenderState(ImDrawData* draw_data, ID3D11DeviceContext* ctx)
+{
+    // Setup viewport
+    D3D11_VIEWPORT vp;
+    memset(&vp, 0, sizeof(D3D11_VIEWPORT));
+    vp.Width = draw_data->DisplaySize.x;
+    vp.Height = draw_data->DisplaySize.y;
+    vp.MinDepth = 0.0f;
+    vp.MaxDepth = 1.0f;
+    vp.TopLeftX = vp.TopLeftY = 0;
+    ctx->RSSetViewports(1, &vp);
+
+    // Setup shader and vertex buffers
+    unsigned int stride = sizeof(ImDrawVert);
+    unsigned int offset = 0;
+    ctx->IASetInputLayout(g_pInputLayout);
+    ctx->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
+    ctx->IASetIndexBuffer(g_pIB, sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT, 0);
+    ctx->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
+    ctx->VSSetShader(g_pVertexShader, NULL, 0);
+    ctx->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
+    ctx->PSSetShader(g_pPixelShader, NULL, 0);
+    ctx->PSSetSamplers(0, 1, &g_pFontSampler);
+
+    // Setup blend state
+    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
+    ctx->OMSetBlendState(g_pBlendState, blend_factor, 0xffffffff);
+    ctx->OMSetDepthStencilState(g_pDepthStencilState, 0);
+    ctx->RSSetState(g_pRasterizerState);
+}
+
 // Render function
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
@@ -177,33 +208,8 @@ void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
     ctx->IAGetVertexBuffers(0, 1, &old.VertexBuffer, &old.VertexBufferStride, &old.VertexBufferOffset);
     ctx->IAGetInputLayout(&old.InputLayout);
 
-    // Setup viewport
-    D3D11_VIEWPORT vp;
-    memset(&vp, 0, sizeof(D3D11_VIEWPORT));
-    vp.Width =  draw_data->DisplaySize.x;
-    vp.Height = draw_data->DisplaySize.y;
-    vp.MinDepth = 0.0f;
-    vp.MaxDepth = 1.0f;
-    vp.TopLeftX = vp.TopLeftY = 0;
-    ctx->RSSetViewports(1, &vp);
-
-    // Bind shader and vertex buffers
-    unsigned int stride = sizeof(ImDrawVert);
-    unsigned int offset = 0;
-    ctx->IASetInputLayout(g_pInputLayout);
-    ctx->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
-    ctx->IASetIndexBuffer(g_pIB, sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT, 0);
-    ctx->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
-    ctx->VSSetShader(g_pVertexShader, NULL, 0);
-    ctx->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
-    ctx->PSSetShader(g_pPixelShader, NULL, 0);
-    ctx->PSSetSamplers(0, 1, &g_pFontSampler);
-
-    // Setup render state
-    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
-    ctx->OMSetBlendState(g_pBlendState, blend_factor, 0xffffffff);
-    ctx->OMSetDepthStencilState(g_pDepthStencilState, 0);
-    ctx->RSSetState(g_pRasterizerState);
+    // Setup desired DX state
+    ImGui_ImplDX11_SetupRenderState(draw_data, ctx);
 
     // Render command lists
     int vtx_offset = 0;
@@ -215,10 +221,14 @@ void ImGui_ImplDX11_RenderDrawData(ImDrawData* draw_data)
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
-            if (pcmd->UserCallback)
+            if (pcmd->UserCallback != NULL)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplDX11_SetupRenderState(draw_data, ctx);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

examples/imgui_impl_dx12.cpp

@@ -58,6 +58,61 @@ struct VERTEX_CONSTANT_BUFFER
     float   mvp[4][4];
 };
 
+static void ImGui_ImplDX12_SetupRenderState(ImDrawData* draw_data, ID3D12GraphicsCommandList* ctx, FrameResources* fr)
+{
+    // 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).
+    VERTEX_CONSTANT_BUFFER vertex_constant_buffer;
+    {
+        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(&vertex_constant_buffer.mvp, mvp, sizeof(mvp));
+    }
+
+    // Setup viewport
+    D3D12_VIEWPORT vp;
+    memset(&vp, 0, sizeof(D3D12_VIEWPORT));
+    vp.Width = draw_data->DisplaySize.x;
+    vp.Height = draw_data->DisplaySize.y;
+    vp.MinDepth = 0.0f;
+    vp.MaxDepth = 1.0f;
+    vp.TopLeftX = vp.TopLeftY = 0.0f;
+    ctx->RSSetViewports(1, &vp);
+
+    // Bind shader and vertex buffers
+    unsigned int stride = sizeof(ImDrawVert);
+    unsigned int offset = 0;
+    D3D12_VERTEX_BUFFER_VIEW vbv;
+    memset(&vbv, 0, sizeof(D3D12_VERTEX_BUFFER_VIEW));
+    vbv.BufferLocation = fr->VertexBuffer->GetGPUVirtualAddress() + offset;
+    vbv.SizeInBytes = fr->VertexBufferSize * stride;
+    vbv.StrideInBytes = stride;
+    ctx->IASetVertexBuffers(0, 1, &vbv);
+    D3D12_INDEX_BUFFER_VIEW ibv;
+    memset(&ibv, 0, sizeof(D3D12_INDEX_BUFFER_VIEW));
+    ibv.BufferLocation = fr->IndexBuffer->GetGPUVirtualAddress();
+    ibv.SizeInBytes = fr->IndexBufferSize * sizeof(ImDrawIdx);
+    ibv.Format = sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT;
+    ctx->IASetIndexBuffer(&ibv);
+    ctx->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
+    ctx->SetPipelineState(g_pPipelineState);
+    ctx->SetGraphicsRootSignature(g_pRootSignature);
+    ctx->SetGraphicsRoot32BitConstants(0, 16, &vertex_constant_buffer, 0);
+
+    // Setup blend factor
+    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
+    ctx->OMSetBlendFactor(blend_factor);
+}
+
 // Render function
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 void ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandList* ctx)
@@ -140,57 +195,8 @@ void ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandL
     fr->VertexBuffer->Unmap(0, &range);
     fr->IndexBuffer->Unmap(0, &range);
 
-    // 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).
-    VERTEX_CONSTANT_BUFFER vertex_constant_buffer;
-    {
-        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(&vertex_constant_buffer.mvp, mvp, sizeof(mvp));
-    }
-
-    // Setup viewport
-    D3D12_VIEWPORT vp;
-    memset(&vp, 0, sizeof(D3D12_VIEWPORT));
-    vp.Width = draw_data->DisplaySize.x;
-    vp.Height = draw_data->DisplaySize.y;
-    vp.MinDepth = 0.0f;
-    vp.MaxDepth = 1.0f;
-    vp.TopLeftX = vp.TopLeftY = 0.0f;
-    ctx->RSSetViewports(1, &vp);
-
-    // Bind shader and vertex buffers
-    unsigned int stride = sizeof(ImDrawVert);
-    unsigned int offset = 0;
-    D3D12_VERTEX_BUFFER_VIEW vbv;
-    memset(&vbv, 0, sizeof(D3D12_VERTEX_BUFFER_VIEW));
-    vbv.BufferLocation = fr->VertexBuffer->GetGPUVirtualAddress() + offset;
-    vbv.SizeInBytes = fr->VertexBufferSize * stride;
-    vbv.StrideInBytes = stride;
-    ctx->IASetVertexBuffers(0, 1, &vbv);
-    D3D12_INDEX_BUFFER_VIEW ibv;
-    memset(&ibv, 0, sizeof(D3D12_INDEX_BUFFER_VIEW));
-    ibv.BufferLocation = fr->IndexBuffer->GetGPUVirtualAddress();
-    ibv.SizeInBytes = fr->IndexBufferSize * sizeof(ImDrawIdx);
-    ibv.Format = sizeof(ImDrawIdx) == 2 ? DXGI_FORMAT_R16_UINT : DXGI_FORMAT_R32_UINT;
-    ctx->IASetIndexBuffer(&ibv);
-    ctx->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
-    ctx->SetPipelineState(g_pPipelineState);
-    ctx->SetGraphicsRootSignature(g_pRootSignature);
-    ctx->SetGraphicsRoot32BitConstants(0, 16, &vertex_constant_buffer, 0);
-
-    // Setup blend factor
-    const float blend_factor[4] = { 0.f, 0.f, 0.f, 0.f };
-    ctx->OMSetBlendFactor(blend_factor);
+    // Setup desired DX state
+    ImGui_ImplDX12_SetupRenderState(draw_data, ctx, fr);
 
     // Render command lists
     int vtx_offset = 0;
@@ -202,10 +208,14 @@ void ImGui_ImplDX12_RenderDrawData(ImDrawData* draw_data, ID3D12GraphicsCommandL
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
-            if (pcmd->UserCallback)
+            if (pcmd->UserCallback != NULL)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplDX12_SetupRenderState(draw_data, ctx, fr);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

examples/imgui_impl_dx9.cpp

@@ -42,6 +42,62 @@ struct CUSTOMVERTEX
 };
 #define D3DFVF_CUSTOMVERTEX (D3DFVF_XYZ|D3DFVF_DIFFUSE|D3DFVF_TEX1)
 
+static void ImGui_ImplDX9_SetupRenderState(ImDrawData* draw_data)
+{
+    // Setup viewport
+    D3DVIEWPORT9 vp;
+    vp.X = vp.Y = 0;
+    vp.Width = (DWORD)draw_data->DisplaySize.x;
+    vp.Height = (DWORD)draw_data->DisplaySize.y;
+    vp.MinZ = 0.0f;
+    vp.MaxZ = 1.0f;
+    g_pd3dDevice->SetViewport(&vp);
+
+    // Setup render state: fixed-pipeline, alpha-blending, no face culling, no depth testing, shade mode (for gradient)
+    g_pd3dDevice->SetPixelShader(NULL);
+    g_pd3dDevice->SetVertexShader(NULL);
+    g_pd3dDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);
+    g_pd3dDevice->SetRenderState(D3DRS_LIGHTING, false);
+    g_pd3dDevice->SetRenderState(D3DRS_ZENABLE, false);
+    g_pd3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
+    g_pd3dDevice->SetRenderState(D3DRS_ALPHATESTENABLE, false);
+    g_pd3dDevice->SetRenderState(D3DRS_BLENDOP, D3DBLENDOP_ADD);
+    g_pd3dDevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA);
+    g_pd3dDevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);
+    g_pd3dDevice->SetRenderState(D3DRS_SCISSORTESTENABLE, true);
+    g_pd3dDevice->SetRenderState(D3DRS_SHADEMODE, D3DSHADE_GOURAUD);
+    g_pd3dDevice->SetRenderState(D3DRS_FOGENABLE, false);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_MODULATE);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
+    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
+    g_pd3dDevice->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
+    g_pd3dDevice->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
+
+    // Setup orthographic projection matrix
+    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right).
+    // Being agnostic of whether <d3dx9.h> or <DirectXMath.h> can be used, we aren't relying on D3DXMatrixIdentity()/D3DXMatrixOrthoOffCenterLH() or DirectX::XMMatrixIdentity()/DirectX::XMMatrixOrthographicOffCenterLH()
+    {
+        float L = draw_data->DisplayPos.x + 0.5f;
+        float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x + 0.5f;
+        float T = draw_data->DisplayPos.y + 0.5f;
+        float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y + 0.5f;
+        D3DMATRIX mat_identity = { { { 1.0f, 0.0f, 0.0f, 0.0f,  0.0f, 1.0f, 0.0f, 0.0f,  0.0f, 0.0f, 1.0f, 0.0f,  0.0f, 0.0f, 0.0f, 1.0f } } };
+        D3DMATRIX mat_projection =
+        { { {
+            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,
+            (L+R)/(L-R),  (T+B)/(B-T),  0.5f,  1.0f
+        } } };
+        g_pd3dDevice->SetTransform(D3DTS_WORLD, &mat_identity);
+        g_pd3dDevice->SetTransform(D3DTS_VIEW, &mat_identity);
+        g_pd3dDevice->SetTransform(D3DTS_PROJECTION, &mat_projection);
+    }
+}
+
 // Render function.
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 void ImGui_ImplDX9_RenderDrawData(ImDrawData* draw_data)
@@ -111,58 +167,8 @@ void ImGui_ImplDX9_RenderDrawData(ImDrawData* draw_data)
     g_pd3dDevice->SetIndices(g_pIB);
     g_pd3dDevice->SetFVF(D3DFVF_CUSTOMVERTEX);
 
-    // Setup viewport
-    D3DVIEWPORT9 vp;
-    vp.X = vp.Y = 0;
-    vp.Width = (DWORD)draw_data->DisplaySize.x;
-    vp.Height = (DWORD)draw_data->DisplaySize.y;
-    vp.MinZ = 0.0f;
-    vp.MaxZ = 1.0f;
-    g_pd3dDevice->SetViewport(&vp);
-
-    // Setup render state: fixed-pipeline, alpha-blending, no face culling, no depth testing, shade mode (for gradient)
-    g_pd3dDevice->SetPixelShader(NULL);
-    g_pd3dDevice->SetVertexShader(NULL);
-    g_pd3dDevice->SetRenderState(D3DRS_CULLMODE, D3DCULL_NONE);
-    g_pd3dDevice->SetRenderState(D3DRS_LIGHTING, false);
-    g_pd3dDevice->SetRenderState(D3DRS_ZENABLE, false);
-    g_pd3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
-    g_pd3dDevice->SetRenderState(D3DRS_ALPHATESTENABLE, false);
-    g_pd3dDevice->SetRenderState(D3DRS_BLENDOP, D3DBLENDOP_ADD);
-    g_pd3dDevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA);
-    g_pd3dDevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);
-    g_pd3dDevice->SetRenderState(D3DRS_SCISSORTESTENABLE, true);
-    g_pd3dDevice->SetRenderState(D3DRS_SHADEMODE, D3DSHADE_GOURAUD);
-    g_pd3dDevice->SetRenderState(D3DRS_FOGENABLE, false);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_MODULATE);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
-    g_pd3dDevice->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
-    g_pd3dDevice->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
-    g_pd3dDevice->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
-
-    // Setup orthographic projection matrix
-    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right).
-    // Being agnostic of whether <d3dx9.h> or <DirectXMath.h> can be used, we aren't relying on D3DXMatrixIdentity()/D3DXMatrixOrthoOffCenterLH() or DirectX::XMMatrixIdentity()/DirectX::XMMatrixOrthographicOffCenterLH()
-    {
-        float L = draw_data->DisplayPos.x + 0.5f;
-        float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x + 0.5f;
-        float T = draw_data->DisplayPos.y + 0.5f;
-        float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y + 0.5f;
-        D3DMATRIX mat_identity = { { { 1.0f, 0.0f, 0.0f, 0.0f,  0.0f, 1.0f, 0.0f, 0.0f,  0.0f, 0.0f, 1.0f, 0.0f,  0.0f, 0.0f, 0.0f, 1.0f } } };
-        D3DMATRIX mat_projection =
-        { { {
-            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,
-            (L+R)/(L-R),  (T+B)/(B-T),  0.5f,  1.0f
-        } } };
-        g_pd3dDevice->SetTransform(D3DTS_WORLD, &mat_identity);
-        g_pd3dDevice->SetTransform(D3DTS_VIEW, &mat_identity);
-        g_pd3dDevice->SetTransform(D3DTS_PROJECTION, &mat_projection);
-    }
+    // Setup desired DX state
+    ImGui_ImplDX9_SetupRenderState(draw_data);
 
     // Render command lists
     int vtx_offset = 0;
@@ -174,9 +180,14 @@ void ImGui_ImplDX9_RenderDrawData(ImDrawData* draw_data)
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
-            if (pcmd->UserCallback)
+            if (pcmd->UserCallback != NULL)
             {
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplDX9_SetupRenderState(draw_data);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

examples/imgui_impl_opengl2.cpp

@@ -72,24 +72,9 @@ void    ImGui_ImplOpenGL2_NewFrame()
         ImGui_ImplOpenGL2_CreateDeviceObjects();
 }
 
-// OpenGL2 Render function.
-// (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
-// Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly, in order to be able to run within any OpenGL engine that doesn't do so.
-void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
+static void ImGui_ImplOpenGL2_SetupRenderState(ImDrawData* draw_data, int fb_width, int fb_height)
 {
-    // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
-    int fb_width = (int)(draw_data->DisplaySize.x * draw_data->FramebufferScale.x);
-    int fb_height = (int)(draw_data->DisplaySize.y * draw_data->FramebufferScale.y);
-    if (fb_width == 0 || fb_height == 0)
-        return;
-
-    // We are using the OpenGL fixed pipeline to make the example code simpler to read!
     // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, vertex/texcoord/color pointers, polygon fill.
-    GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
-    GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
-    GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
-    GLint last_scissor_box[4]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);
-    glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
     glDisable(GL_CULL_FACE);
@@ -121,6 +106,28 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
     glMatrixMode(GL_MODELVIEW);
     glPushMatrix();
     glLoadIdentity();
+}
+
+// OpenGL2 Render function.
+// (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
+// Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly, in order to be able to run within any OpenGL engine that doesn't do so.
+void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
+{
+    // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
+    int fb_width = (int)(draw_data->DisplaySize.x * draw_data->FramebufferScale.x);
+    int fb_height = (int)(draw_data->DisplaySize.y * draw_data->FramebufferScale.y);
+    if (fb_width == 0 || fb_height == 0)
+        return;
+
+    // Backup GL state
+    GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
+    GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
+    GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
+    GLint last_scissor_box[4]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);
+    glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
+
+    // Setup desired GL state
+    ImGui_ImplOpenGL2_SetupRenderState(draw_data, fb_width, fb_height);
 
     // Will project scissor/clipping rectangles into framebuffer space
     ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
@@ -141,8 +148,12 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
             if (pcmd->UserCallback)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplOpenGL2_SetupRenderState(draw_data, fb_width, fb_height);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {
@@ -167,7 +178,7 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
         }
     }
 
-    // Restore modified state
+    // Restore modified GL state
     glDisableClientState(GL_COLOR_ARRAY);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
     glDisableClientState(GL_VERTEX_ARRAY);

examples/imgui_impl_opengl3.cpp

@@ -150,6 +150,56 @@ void    ImGui_ImplOpenGL3_NewFrame()
         ImGui_ImplOpenGL3_CreateDeviceObjects();
 }
 
+static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_width, int fb_height, GLuint vertex_array_object)
+{
+    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
+    glEnable(GL_BLEND);
+    glBlendEquation(GL_FUNC_ADD);
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+    glDisable(GL_CULL_FACE);
+    glDisable(GL_DEPTH_TEST);
+    glEnable(GL_SCISSOR_TEST);
+#ifdef GL_POLYGON_MODE
+    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+#endif
+
+    // Setup viewport, orthographic projection matrix
+    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayMin is typically (0,0) for single viewport apps.
+    glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
+    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;
+    const float ortho_projection[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,        -1.0f,   0.0f },
+        { (R+L)/(L-R),  (T+B)/(B-T),  0.0f,   1.0f },
+    };
+    glUseProgram(g_ShaderHandle);
+    glUniform1i(g_AttribLocationTex, 0);
+    glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
+#ifdef GL_SAMPLER_BINDING
+    glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
+#endif
+
+    (void)vertex_array_object;
+#ifndef IMGUI_IMPL_OPENGL_ES2
+    glBindVertexArray(vertex_array_object);
+#endif
+
+    // Bind vertex/index buffers and setup attributes for ImDrawVert
+    glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
+    glEnableVertexAttribArray(g_AttribLocationVtxPos);
+    glEnableVertexAttribArray(g_AttribLocationVtxUV);
+    glEnableVertexAttribArray(g_AttribLocationVtxColor);
+    glVertexAttribPointer(g_AttribLocationVtxPos,   2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
+    glVertexAttribPointer(g_AttribLocationVtxUV,    2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
+    glVertexAttribPointer(g_AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE,  sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
+}
+
 // OpenGL3 Render function.
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 // Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly, in order to be able to run within any OpenGL engine that doesn't do so.
@@ -195,55 +245,14 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
         clip_origin_lower_left = false;
 #endif
 
-    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
-    glEnable(GL_BLEND);
-    glBlendEquation(GL_FUNC_ADD);
-    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
-    glDisable(GL_CULL_FACE);
-    glDisable(GL_DEPTH_TEST);
-    glEnable(GL_SCISSOR_TEST);
-#ifdef GL_POLYGON_MODE
-    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
-#endif
-
-    // Setup viewport, orthographic projection matrix
-    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayMin is typically (0,0) for single viewport apps.
-    glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
-    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;
-    const float ortho_projection[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,        -1.0f,   0.0f },
-        { (R+L)/(L-R),  (T+B)/(B-T),  0.0f,   1.0f },
-    };
-    glUseProgram(g_ShaderHandle);
-    glUniform1i(g_AttribLocationTex, 0);
-    glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-#ifdef GL_SAMPLER_BINDING
-    glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
-#endif
-
+    // Setup desired GL state
     // Recreate the VAO every time (this is to easily allow multiple GL contexts to be rendered to. VAO are not shared among GL contexts)
     // The renderer would actually work without any VAO bound, but then our VertexAttrib calls would overwrite the default one currently bound.
-#ifndef IMGUI_IMPL_OPENGL_ES2
     GLuint vertex_array_object = 0;
+#ifndef IMGUI_IMPL_OPENGL_ES2
     glGenVertexArrays(1, &vertex_array_object);
-    glBindVertexArray(vertex_array_object);
 #endif
-
-    // Bind vertex/index buffers and setup attributes for ImDrawVert
-    glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
-    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
-    glEnableVertexAttribArray(g_AttribLocationVtxPos);
-    glEnableVertexAttribArray(g_AttribLocationVtxUV);
-    glEnableVertexAttribArray(g_AttribLocationVtxColor);
-    glVertexAttribPointer(g_AttribLocationVtxPos,   2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
-    glVertexAttribPointer(g_AttribLocationVtxUV,    2, GL_FLOAT,         GL_FALSE, sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
-    glVertexAttribPointer(g_AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE,  sizeof(ImDrawVert), (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
+    ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);
 
     // Will project scissor/clipping rectangles into framebuffer space
     ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
@@ -262,10 +271,14 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
-            if (pcmd->UserCallback)
+            if (pcmd->UserCallback != NULL)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplOpenGL3_SetupRenderState(draw_data, fb_width, fb_height, vertex_array_object);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

examples/imgui_impl_vulkan.cpp

@@ -259,6 +259,49 @@ static void CreateOrResizeBuffer(VkBuffer& buffer, VkDeviceMemory& buffer_memory
     p_buffer_size = new_size;
 }
 
+static void ImGui_ImplVulkan_SetupRenderState(ImDrawData* draw_data, VkCommandBuffer command_buffer, ImGui_ImplVulkanH_FrameRenderBuffers* rb, int fb_width, int fb_height)
+{
+    // Bind pipeline and descriptor sets:
+    {
+        vkCmdBindPipeline(command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, g_Pipeline);
+        VkDescriptorSet desc_set[1] = { g_DescriptorSet };
+        vkCmdBindDescriptorSets(command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, g_PipelineLayout, 0, 1, desc_set, 0, NULL);
+    }
+
+    // Bind Vertex And Index Buffer:
+    {
+        VkBuffer vertex_buffers[1] = { rb->VertexBuffer };
+        VkDeviceSize vertex_offset[1] = { 0 };
+        vkCmdBindVertexBuffers(command_buffer, 0, 1, vertex_buffers, vertex_offset);
+        vkCmdBindIndexBuffer(command_buffer, rb->IndexBuffer, 0, sizeof(ImDrawIdx) == 2 ? VK_INDEX_TYPE_UINT16 : VK_INDEX_TYPE_UINT32);
+    }
+
+    // Setup viewport:
+    {
+        VkViewport viewport;
+        viewport.x = 0;
+        viewport.y = 0;
+        viewport.width = (float)fb_width;
+        viewport.height = (float)fb_height;
+        viewport.minDepth = 0.0f;
+        viewport.maxDepth = 1.0f;
+        vkCmdSetViewport(command_buffer, 0, 1, &viewport);
+    }
+
+    // Setup scale and translation:
+    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayMin is typically (0,0) for single viewport apps.
+    {
+        float scale[2];
+        scale[0] = 2.0f / draw_data->DisplaySize.x;
+        scale[1] = 2.0f / draw_data->DisplaySize.y;
+        float translate[2];
+        translate[0] = -1.0f - draw_data->DisplayPos.x * scale[0];
+        translate[1] = -1.0f - draw_data->DisplayPos.y * scale[1];
+        vkCmdPushConstants(command_buffer, g_PipelineLayout, VK_SHADER_STAGE_VERTEX_BIT, sizeof(float) * 0, sizeof(float) * 2, scale);
+        vkCmdPushConstants(command_buffer, g_PipelineLayout, VK_SHADER_STAGE_VERTEX_BIT, sizeof(float) * 2, sizeof(float) * 2, translate);
+    }
+}
+
 // Render function
 // (this used to be set in io.RenderDrawListsFn and called by ImGui::Render(), but you can now call this directly from your main loop)
 void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer command_buffer)
@@ -323,45 +366,8 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
         vkUnmapMemory(v->Device, rb->IndexBufferMemory);
     }
 
-    // Bind pipeline and descriptor sets:
-    {
-        vkCmdBindPipeline(command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, g_Pipeline);
-        VkDescriptorSet desc_set[1] = { g_DescriptorSet };
-        vkCmdBindDescriptorSets(command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, g_PipelineLayout, 0, 1, desc_set, 0, NULL);
-    }
-
-    // Bind Vertex And Index Buffer:
-    {
-        VkBuffer vertex_buffers[1] = { rb->VertexBuffer };
-        VkDeviceSize vertex_offset[1] = { 0 };
-        vkCmdBindVertexBuffers(command_buffer, 0, 1, vertex_buffers, vertex_offset);
-        vkCmdBindIndexBuffer(command_buffer, rb->IndexBuffer, 0, sizeof(ImDrawIdx) == 2 ? VK_INDEX_TYPE_UINT16 : VK_INDEX_TYPE_UINT32);
-    }
-
-    // Setup viewport:
-    {
-        VkViewport viewport;
-        viewport.x = 0;
-        viewport.y = 0;
-        viewport.width = (float)fb_width;
-        viewport.height = (float)fb_height;
-        viewport.minDepth = 0.0f;
-        viewport.maxDepth = 1.0f;
-        vkCmdSetViewport(command_buffer, 0, 1, &viewport);
-    }
-
-    // Setup scale and translation:
-    // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayMin is typically (0,0) for single viewport apps.
-    {
-        float scale[2];
-        scale[0] = 2.0f / draw_data->DisplaySize.x;
-        scale[1] = 2.0f / draw_data->DisplaySize.y;
-        float translate[2];
-        translate[0] = -1.0f - draw_data->DisplayPos.x * scale[0];
-        translate[1] = -1.0f - draw_data->DisplayPos.y * scale[1];
-        vkCmdPushConstants(command_buffer, g_PipelineLayout, VK_SHADER_STAGE_VERTEX_BIT, sizeof(float) * 0, sizeof(float) * 2, scale);
-        vkCmdPushConstants(command_buffer, g_PipelineLayout, VK_SHADER_STAGE_VERTEX_BIT, sizeof(float) * 2, sizeof(float) * 2, translate);
-    }
+    // Setup desired Vulkan state
+    ImGui_ImplVulkan_SetupRenderState(draw_data, command_buffer, rb, fb_width, fb_height);
 
     // Will project scissor/clipping rectangles into framebuffer space
     ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
@@ -376,10 +382,14 @@ void ImGui_ImplVulkan_RenderDrawData(ImDrawData* draw_data, VkCommandBuffer comm
         for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
         {
             const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
-            if (pcmd->UserCallback)
+            if (pcmd->UserCallback != NULL)
             {
-                // User callback (registered via ImDrawList::AddCallback)
-                pcmd->UserCallback(cmd_list, pcmd);
+                // User callback, registered via ImDrawList::AddCallback()
+                // (ImDrawCallback_ResetRenderState is a special callback value used by the user to request the renderer to reset render state.)
+                if (pcmd->UserCallback == ImDrawCallback_ResetRenderState)
+                    ImGui_ImplVulkan_SetupRenderState(draw_data, command_buffer, rb, fb_width, fb_height);
+                else
+                    pcmd->UserCallback(cmd_list, pcmd);
             }
             else
             {

imgui.h

@@ -1759,11 +1759,18 @@ struct ImColor
 
 // Draw callbacks for advanced uses.
 // NB: You most likely do NOT need to use draw callbacks just to create your own widget or customized UI rendering,
-// you can poke into the draw list for that! Draw callback may be useful for example to: A) Change your GPU render state,
-// B) render a complex 3D scene inside a UI element without an intermediate texture/render target, etc.
+// you can poke into the draw list for that! Draw callback may be useful for example to: 
+//  A) Change your GPU render state,
+//  B) render a complex 3D scene inside a UI element without an intermediate texture/render target, etc.
 // The expected behavior from your rendering function is 'if (cmd.UserCallback != NULL) { cmd.UserCallback(parent_list, cmd); } else { RenderTriangles() }'
 typedef void (*ImDrawCallback)(const ImDrawList* parent_list, const ImDrawCmd* cmd);
 
+// Special Draw Callback value to request renderer back-end to reset the graphics/render state.
+// The renderer back-end needs to handle this special value, otherwise it will crash trying to call a function at this address.
+// This is useful for example if you submitted callbacks which you know have altered the render state and you want it to be restored.
+// It is not done by default because they are many perfectly useful way of altering render state for imgui contents (e.g. changing shader/blending settings before an Image call).
+#define ImDrawCallback_ResetRenderState     (ImDrawCallback)(-1)
+
 // Typically, 1 command = 1 GPU draw call (unless command is a callback)
 struct ImDrawCmd
 {