For years now I've had this annoying little problem where the right and bottom edges of windows backed by DXGI flip model swap chains flicker during live window resizing (e.g. when grabbing the bottom right corner of a window and dragging). I've tried dozens if not hundreds of different techniques and today I finally stumbled on one that works!

TLDR:

• Step 1. Use CreateSwapChainForComposition() instead of CreateSwapChain()/CreateSwapChainForHwnd().
• Step 2. Call ResizeBuffers() in WM_NCCALCSIZE instead of WM_SIZE.
• Step 3. Render and present a new frame before returning from WM_NCCALCSIZE.

The long answer:

Grab a modern graphics-accelerated application window (e.g. Steam) by the bottom right corner and drag. You see nasty flickering with black and/or white lines, right? This flickering has haunted me for years. Every time I tried to use the DXGI flip model, no matter what I did, no matter what API's I called in what order or however careful I was with synchronization, I always encountered graphical glitches like this.

Now try the same thing with an ancient application (e.g. Notepad). It's beautiful. No glitches at all. Clearly it's possible to get this right. What the heck's going on?

I have no idea what actually causes this. I've seen it happen on AMD and NVIDIA graphics cards, so I doubt it's a driver problem. I assume it has something to do with how DWM synchronizes with DXGI-based apps, but since it's all closed source and Microsoft's documentation is light on details, it's hard to know for sure.

I recently came across this (https://docs.microsoft.com/en-us/archive/msdn-magazine/2014/june/windows-with-c-high-performance-window-layering-using-the-windows-composition-engine) little gem of an article and decided to give DirectComposition a try. I'd heard of DirectComposition before, but it's documentation makes it sound like it's meant for GUI-based applications with fancy animations, not games that just want an efficient way to get their pixels on the screen.

DirectComposition gave me similar issues at first. Instead of black and white flickering I was seeing through temporary gaps in the window to the desktop behind. And it was dragging from the top/left edges instead of the bottom/right that was causing problems. But these were totally new problems I'd never seen before, so I kept trying.

I stuck with it and, lo and behold, I found a technique that works! The trick is to resize your swap chain buffers and present a frame BEFORE the window actually resizes. In my case, that meant using WM_NCCALCSIZE instead of WM_SIZE. I've tried this before with a CreateSwapChainForHwnd() swap chain, but for some reason this technique only works when using DirectComposition. Example code below.

Be warned: I've read bug reports of capture software not working with DirectComposition. It sounds like there are workarounds, though, so it's probably just a matter of software catching up and becoming DirectComposition-aware.

#include <Windows.h>

#include <d3d11.h>
#include <dcomp.h>
#include <dxgi1_2.h>

ID3D11Device* d3d;
ID3D11DeviceContext* ctx;
IDXGISwapChain1* sc;

/// <summary>
/// Crash if hr != S_OK.
/// </summary>
void hr_check(HRESULT hr)
{
    if (hr == S_OK) return;
    while (true) __debugbreak();
}

/// <summary>
/// Passthrough (t) if truthy. Crash otherwise.
/// </summary>
template<class T> T win32_check(T t)
{
    if (t) return t;

    // Debuggers are better at displaying HRESULTs than the raw DWORD returned by GetLastError().
    HRESULT hr = HRESULT_FROM_WIN32(GetLastError());
    while (true) __debugbreak();
}

/// <summary>
/// Win32 message handler.
/// </summary>
LRESULT window_proc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
{
    switch (message)
    {
    case WM_CLOSE:
        ExitProcess(0);
        return 0;

    case WM_NCCALCSIZE:
        // Use the result of DefWindowProc's WM_NCCALCSIZE handler to get the upcoming client rect.
        // Technically, when wparam is TRUE, lparam points to NCCALCSIZE_PARAMS, but its first
        // member is a RECT with the same meaning as the one lparam points to when wparam is FALSE.
        DefWindowProc(hwnd, message, wparam, lparam);
        if (RECT* rect = (RECT*)lparam; rect->right > rect->left && rect->bottom > rect->top)
        {
            // A real app might want to compare these dimensions with the current swap chain
            // dimensions and skip all this if they're unchanged.
            UINT width = rect->right - rect->left;
            UINT height = rect->bottom - rect->top;
            hr_check(sc->ResizeBuffers(0, width, height, DXGI_FORMAT_UNKNOWN, 0));

            // Do some minimal rendering to prove this works.
            ID3D11Resource* buffer;
            ID3D11RenderTargetView* rtv;
            FLOAT color[] = { 0.0f, 0.2f, 0.4f, 1.0f };
            hr_check(sc->GetBuffer(0, IID_PPV_ARGS(&buffer)));
            hr_check(d3d->CreateRenderTargetView(buffer, NULL, &rtv));
            ctx->ClearRenderTargetView(rtv, color);
            buffer->Release();
            rtv->Release();

            // Discard outstanding queued presents and queue a frame with the new size ASAP.
            hr_check(sc->Present(0, DXGI_PRESENT_RESTART));

            // Wait for a vblank to really make sure our frame with the new size is ready before
            // the window finishes resizing.
            // TODO: Determine why this is necessary at all. Why isn't one Present() enough?
            // TODO: Determine if there's a way to wait for vblank without calling Present().
            // TODO: Determine if DO_NOT_SEQUENCE is safe to use with SWAP_EFFECT_FLIP_DISCARD.
            hr_check(sc->Present(1, DXGI_PRESENT_DO_NOT_SEQUENCE));
        }
        // We're never preserving the client area so we always return 0.
        return 0;

    default:
        return DefWindowProc(hwnd, message, wparam, lparam);
    }
}

/// <summary>
/// The app entry point.
/// </summary>
int WinMain(HINSTANCE hinstance, HINSTANCE, LPSTR, int)
{
    // Create the DXGI factory.
    IDXGIFactory2* dxgi;
    hr_check(CreateDXGIFactory1(IID_PPV_ARGS(&dxgi)));

    // Create the D3D device.
    hr_check(D3D11CreateDevice(
        NULL, D3D_DRIVER_TYPE_HARDWARE, NULL, D3D11_CREATE_DEVICE_BGRA_SUPPORT,
        NULL, 0, D3D11_SDK_VERSION, &d3d, NULL, &ctx));

    // Create the swap chain.
    DXGI_SWAP_CHAIN_DESC1 scd = {};
    // Just use a minimal size for now. WM_NCCALCSIZE will resize when necessary.
    scd.Width = 1;
    scd.Height = 1;
    scd.Format = DXGI_FORMAT_B8G8R8A8_UNORM;
    scd.SampleDesc.Count = 1;
    scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
    scd.BufferCount = 2;
    // TODO: Determine if PRESENT_DO_NOT_SEQUENCE is safe to use with SWAP_EFFECT_FLIP_DISCARD.
    scd.SwapEffect = DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL;
    scd.AlphaMode = DXGI_ALPHA_MODE_IGNORE;
    hr_check(dxgi->CreateSwapChainForComposition(d3d, &scd, NULL, &sc));

    // Register the window class.
    WNDCLASS wc = {};
    wc.lpfnWndProc = window_proc;
    wc.hInstance = hinstance;
    wc.hCursor = win32_check(LoadCursor(NULL, IDC_ARROW));
    wc.lpszClassName = TEXT("D3DWindow");
    win32_check(RegisterClass(&wc));

    // Create the window. We can use WS_EX_NOREDIRECTIONBITMAP
    // since all our presentation is happening through DirectComposition.
    HWND hwnd = win32_check(CreateWindowEx(
        WS_EX_NOREDIRECTIONBITMAP, wc.lpszClassName, TEXT("D3D Window"),
        WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hinstance, NULL));

    // Bind our swap chain to the window.
    // TODO: Determine what DCompositionCreateDevice(NULL, ...) actually does.
    // I assume it creates a minimal IDCompositionDevice for use with D3D that can't actually
    // do any adapter-specific resource allocations itself, but I'm yet to verify this.
    IDCompositionDevice* dcomp;
    IDCompositionTarget* target;
    IDCompositionVisual* visual;
    hr_check(DCompositionCreateDevice(NULL, IID_PPV_ARGS(&dcomp)));
    hr_check(dcomp->CreateTargetForHwnd(hwnd, FALSE, &target));
    hr_check(dcomp->CreateVisual(&visual));
    hr_check(target->SetRoot(visual));
    hr_check(visual->SetContent(sc));
    hr_check(dcomp->Commit());

    // Show the window and enter the message loop.
    ShowWindow(hwnd, SW_SHOWNORMAL);
    while (true)
    {
        MSG msg;
        win32_check(GetMessage(&msg, NULL, 0, 0) > 0);
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}