Examples: DirectX12: Fixed Alt+Enter fullscreen in DirectX12 example. (#4346, #4348)

This also removes unnecessary recreation of backend-owned device objects when the window is resized.
+ amend original PR with a g_pSwapChain->SetFullscreenState(false, NULL); call.

docs/CHANGELOG.txt

@@ -96,6 +96,8 @@ Other Changes:
 - Backends: OpenGL3: Use OES_vertex_array extension on Emscripten + backup/restore current state. (#4266, #4267) [@harry75369]
 - Backends: GLFW: Installing and exposed ImGui_ImplGlfw_MonitorCallback() for forward compatibility with docking branch.
 - Backends: OSX: Added a fix for shortcuts using CTRL key instead of CMD key. (#4253) [@rokups]
+- Examples: DX12: Fixed handling of Alt+Enter in example app (using swapchain's ResizeBuffers). (#4346) [@PathogenDavid]
+- Examples: DX12: Removed unecessary recreation of backend-owned device objects when window is resized. (#4347) [@PathogenDavid]
 - Examples: OSX+OpenGL2: Fix event forwarding (fix key remaining stuck when using shortcuts with Cmd/Super key).
   Other OSX examples were not affected. (#4253, #1873) [@rokups]
 - Examples: Updated all .vcxproj to VS2015 (toolset v140) to facilitate usage with vcpkg.

examples/example_win32_directx12/main.cpp

@@ -54,7 +54,6 @@ void CreateRenderTarget();
 void CleanupRenderTarget();
 void WaitForLastSubmittedFrame();
 FrameContext* WaitForNextFrameResources();
-void ResizeSwapChain(HWND hWnd, int width, int height);
 LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
 
 // Main code
@@ -352,7 +351,7 @@ bool CreateDeviceD3D(HWND hWnd)
 void CleanupDeviceD3D()
 {
     CleanupRenderTarget();
-    if (g_pSwapChain) { g_pSwapChain->Release(); g_pSwapChain = NULL; }
+    if (g_pSwapChain) { g_pSwapChain->SetFullscreenState(false, NULL); g_pSwapChain->Release(); g_pSwapChain = NULL; }
     if (g_hSwapChainWaitableObject != NULL) { CloseHandle(g_hSwapChainWaitableObject); }
     for (UINT i = 0; i < NUM_FRAMES_IN_FLIGHT; i++)
         if (g_frameContext[i].CommandAllocator) { g_frameContext[i].CommandAllocator->Release(); g_frameContext[i].CommandAllocator = NULL; }
@@ -432,31 +431,6 @@ FrameContext* WaitForNextFrameResources()
     return frameCtx;
 }
 
-void ResizeSwapChain(HWND hWnd, int width, int height)
-{
-    DXGI_SWAP_CHAIN_DESC1 sd;
-    g_pSwapChain->GetDesc1(&sd);
-    sd.Width = width;
-    sd.Height = height;
-
-    IDXGIFactory4* dxgiFactory = NULL;
-    g_pSwapChain->GetParent(IID_PPV_ARGS(&dxgiFactory));
-
-    g_pSwapChain->Release();
-    CloseHandle(g_hSwapChainWaitableObject);
-
-    IDXGISwapChain1* swapChain1 = NULL;
-    dxgiFactory->CreateSwapChainForHwnd(g_pd3dCommandQueue, hWnd, &sd, NULL, NULL, &swapChain1);
-    swapChain1->QueryInterface(IID_PPV_ARGS(&g_pSwapChain));
-    swapChain1->Release();
-    dxgiFactory->Release();
-
-    g_pSwapChain->SetMaximumFrameLatency(NUM_BACK_BUFFERS);
-
-    g_hSwapChainWaitableObject = g_pSwapChain->GetFrameLatencyWaitableObject();
-    assert(g_hSwapChainWaitableObject != NULL);
-}
-
 // Forward declare message handler from imgui_impl_win32.cpp
 extern IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);
 
@@ -472,11 +446,10 @@ LRESULT WINAPI WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
         if (g_pd3dDevice != NULL && wParam != SIZE_MINIMIZED)
         {
             WaitForLastSubmittedFrame();
-            ImGui_ImplDX12_InvalidateDeviceObjects();
             CleanupRenderTarget();
-            ResizeSwapChain(hWnd, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam));
+            HRESULT result = g_pSwapChain->ResizeBuffers(0, (UINT)LOWORD(lParam), (UINT)HIWORD(lParam), DXGI_FORMAT_UNKNOWN, DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT);
+            assert(SUCCEEDED(result) && "Failed to resize swapchain.");
             CreateRenderTarget();
-            ImGui_ImplDX12_CreateDeviceObjects();
         }
         return 0;
     case WM_SYSCOMMAND: