Examples: DX12: Fixed compilation of imgui_impl_dx12.cpp in viewport branch. Multi-viewport is still not functional.

examples/example_win32_directx12/main.cpp

@@ -38,9 +38,9 @@ static D3D12_CPU_DESCRIPTOR_HANDLE  g_mainRenderTargetDescriptor[NUM_BACK_BUFFER
 
 void CreateRenderTarget()
 {
-    ID3D12Resource* pBackBuffer;
     for (UINT i = 0; i < NUM_BACK_BUFFERS; i++)
     {
+        ID3D12Resource* pBackBuffer = NULL;
         g_pSwapChain->GetBuffer(i, IID_PPV_ARGS(&pBackBuffer));
         g_pd3dDevice->CreateRenderTargetView(pBackBuffer, NULL, g_mainRenderTargetDescriptor[i]);
         g_mainRenderTargetResource[i] = pBackBuffer;
@@ -415,7 +415,7 @@ int main(int, char**)
         if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
         {
             ImGui::UpdatePlatformWindows();
-            ImGui::RenderPlatformWindowsDefault();
+            ImGui::RenderPlatformWindowsDefault(NULL, (void*)g_pd3dCommandList);
         }
 
         g_pSwapChain->Present(1, 0); // Present with vsync

examples/imgui_impl_dx12.cpp

@@ -731,18 +731,22 @@ static void ImGui_ImplDX12_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
     */
 }
 
-static void ImGui_ImplDX12_RenderWindow(ImGuiViewport* viewport, void*)
+// arg = ID3D12GraphicsCommandList*
+static void ImGui_ImplDX12_RenderWindow(ImGuiViewport* viewport, void* renderer_arg)
 {
     ImGuiViewportDataDx12* data = (ImGuiViewportDataDx12*)viewport->RendererUserData;
     IM_ASSERT(0);
     (void)data;
+
+    ID3D12GraphicsCommandList* command_list = (ID3D12GraphicsCommandList*)renderer_arg;
+
     /*
     ImVec4 clear_color = ImVec4(0.0f, 0.0f, 0.0f, 1.0f);
     g_pd3dDeviceContext->OMSetRenderTargets(1, &data->RTView, NULL);
     if (!(viewport->Flags & ImGuiViewportFlags_NoRendererClear))
         g_pd3dDeviceContext->ClearRenderTargetView(data->RTView, (float*)&clear_color);
     */
-    ImGui_ImplDX12_RenderDrawData(viewport->DrawData);
+    ImGui_ImplDX12_RenderDrawData(viewport->DrawData, command_list);
 }
 
 static void ImGui_ImplDX12_SwapBuffers(ImGuiViewport* viewport, void*)