transparent window using Windows Composition engine in c++

Question

First, I want to say that I am a newbie in direct2d usage.

My final purpose is to have per pixel transparent window. I have found this nice article :

https://learn.microsoft.com/en-us/archive/msdn-magazine/2014/june/windows-with-c-high-performance-window-layering-using-the-windows-composition-engine

and it seems that it answers my question. Before writing my per-pixel transparent window, I just tried to test the code in that link. But when I run the program, the disk that should be displayed in the window is not displayed at all.

Here is the complete code that I have written, using just C++ win api, without the COM stuff added by the author Kenny Kerr. There are few functions in it, mainly :

• d2d_init() : it sets up Direct2D
• render() : it displays the scene
• main() : it creates and display the window, calls d2d_init()
• the window procedure which calls render() in WM_PAINT

#include <iostream>

#ifdef _WIN32_WINNT
# undef _WIN32_WINNT
#endif
#define _WIN32_WINNT 0x0A00

#include <guiddef.h>
#include <d2d1_1.h>
#include <d3d11.h>
#include <dxgi1_3.h>
#include <dcomp.h>

static HINSTANCE instance = NULL;
static HWND win = NULL;

LRESULT CALLBACK _window_procedure(HWND   window,
                                   UINT   message,
                                   WPARAM window_param,
                                   LPARAM data_param);

typedef struct
{
    ID3D11Device *d3d_device;
    IDXGIDevice *dxgi_device;
    IDXGIFactory2 *dxgi_factory;
    ID2D1Factory1 *d2d_factory;
    ID2D1Device *d2d_device;
    ID2D1DeviceContext *d2d_device_ctx;
    IDCompositionDevice *dcomp_device;
    IDCompositionVisual *dcomp_visual;
    IDCompositionTarget *dcomp_target;
    IDXGISwapChain1 *dxgi_swapchain;
} D2d;

int d2d_init(HWND win, D2d *d2d)
{
    const D3D_FEATURE_LEVEL levels[] =
    {
        D3D_FEATURE_LEVEL_12_1,
        D3D_FEATURE_LEVEL_12_0,
        D3D_FEATURE_LEVEL_11_1,
        D3D_FEATURE_LEVEL_11_0,
        D3D_FEATURE_LEVEL_10_1,
        D3D_FEATURE_LEVEL_10_0
    };
    D2D1_FACTORY_OPTIONS opt;
    DXGI_SWAP_CHAIN_DESC1 desc;
    RECT r;
    HRESULT res;

    /* direct3d device */
    res = D3D11CreateDevice(NULL, D3D_DRIVER_TYPE_HARDWARE, NULL,
                            D3D11_CREATE_DEVICE_BGRA_SUPPORT |
                            D3D11_CREATE_DEVICE_DEBUG,
                            levels, sizeof(levels) / sizeof(D3D_FEATURE_LEVEL),
                            D3D11_SDK_VERSION, &d2d->d3d_device, NULL, NULL);
    if (FAILED(res))
        return 0;

    /* dxgi device */
    res = d2d->d3d_device->QueryInterface(&d2d->dxgi_device);
    if (FAILED(res))
        goto release_d3d_device;

    /* dxgi factory */
    res = CreateDXGIFactory2(DXGI_CREATE_FACTORY_DEBUG,
                             __uuidof(d2d->dxgi_factory),
                             (void **)&d2d->dxgi_factory);
    if (FAILED(res))
        goto release_dxgi_device;

    /* d2d factory */
    opt.debugLevel = D2D1_DEBUG_LEVEL_INFORMATION;
    res = D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED,
                            __uuidof(d2d->d2d_factory), &opt,
                            (void **)&d2d->d2d_factory);
    if (FAILED(res))
        goto release_dxgi_factory;

    /* d2d device */

    res = d2d->d2d_factory->CreateDevice(d2d->dxgi_device, &d2d->d2d_device);
    if (FAILED(res))
        goto release_d2d_factory;

    /* d2d device context */

    // FIXME : D2D1_DEVICE_CONTEXT_OPTIONS_ENABLE_MULTITHREADED_OPTIMIZATIONS
    res = d2d->d2d_device->CreateDeviceContext(D2D1_DEVICE_CONTEXT_OPTIONS_NONE,
                                               &d2d->d2d_device_ctx);
    if (FAILED(res))
        goto release_d2d_device;

    /* dcomp device */
    res = DCompositionCreateDevice(d2d->dxgi_device,
                                   __uuidof(d2d->dcomp_device),
                                   (void **)&d2d->dcomp_device);
    if (FAILED(res))
        goto release_d2d_device_ctx;

    /* dcomp visual */
    res = d2d->dcomp_device->CreateVisual(&d2d->dcomp_visual);
    if (FAILED(res))
        goto release_dcomp_device;

    /* dcomp target */
    res = d2d->dcomp_device->CreateTargetForHwnd(win, TRUE,
                                                 &d2d->dcomp_target);
    if (FAILED(res))
        goto release_dcomp_visual;

    /* dxgi swapchain */
    if (!GetClientRect(win, &r))
        goto release_dcomp_target;

    desc.Width = r.right - r.left; /* width of client area */
    desc.Height = r.bottom - r.top; /* height of client area */
    desc.Format = DXGI_FORMAT_B8G8R8A8_UNORM;
    desc.Stereo = FALSE;
    desc.SampleDesc.Count = 1;
    desc.SampleDesc.Quality = 0;
    desc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
    desc.BufferCount = 2;
    desc.Scaling = DXGI_SCALING_STRETCH;
    desc.SwapEffect= DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL;
    desc.AlphaMode = DXGI_ALPHA_MODE_PREMULTIPLIED;
    desc.Flags = 0;

    res = d2d->dxgi_factory->CreateSwapChainForComposition(d2d->dxgi_device,
                                                           &desc,
                                                           NULL,
                                                           &d2d->dxgi_swapchain);
    if (FAILED(res))
        goto release_dcomp_target;

    return 1;

  release_dcomp_target:
    d2d->dcomp_target->Release();
  release_dcomp_visual:
    d2d->dcomp_visual->Release();
  release_dcomp_device:
    d2d->dcomp_device->Release();
  release_d2d_device_ctx:
    d2d->d2d_device_ctx->Release();
  release_d2d_device:
    d2d->d2d_device->Release();
  release_d2d_factory:
    d2d->d2d_factory->Release();
  release_dxgi_factory:
    d2d->dxgi_factory->Release();
  release_dxgi_device:
    d2d->dxgi_device->Release();
  release_d3d_device:
    d2d->d3d_device->Release();

    return 0;
}

void d2d_shutdown(D2d *d2d)
{
    d2d->dxgi_swapchain->Release();
    d2d->dcomp_target->Release();
    d2d->dcomp_visual->Release();
    d2d->dcomp_device->Release();
    d2d->d2d_device_ctx->Release();
    d2d->d2d_device->Release();
    d2d->d2d_factory->Release();
    d2d->dxgi_factory->Release();
    d2d->dxgi_device->Release();
    d2d->d3d_device->Release();
}

void render(D2d *d2d)
{
    IDXGISurface *surface;
    ID2D1Bitmap1 *bitmap;
    D2D1_BITMAP_PROPERTIES1 properties;
    D2D1_COLOR_F c;
    HRESULT res;

    std::cout << "render" << std::endl;

    /* swapchain buffer in a IDXGISurface */
    res = d2d->dxgi_swapchain->GetBuffer(0, __uuidof(surface),
                                         (void **)&surface);
    if (FAILED(res))
        return;

    properties.pixelFormat.alphaMode = D2D1_ALPHA_MODE_PREMULTIPLIED;
    properties.pixelFormat.format = DXGI_FORMAT_B8G8R8A8_UNORM;
    properties.dpiX = 0;
    properties.dpiY = 0;
    properties.bitmapOptions = (D2D1_BITMAP_OPTIONS)(D2D1_BITMAP_OPTIONS_TARGET | D2D1_BITMAP_OPTIONS_CANNOT_DRAW);
    properties.colorContext = NULL;

    res = d2d->d2d_device_ctx->CreateBitmapFromDxgiSurface(surface,
                                                           &properties,
                                                           &bitmap);
    if (FAILED(res))
        goto release_surface;

    d2d->d2d_device_ctx->SetTarget(bitmap);
    d2d->d2d_device_ctx->BeginDraw();

    c.r = 0.0f;
    c.g = 0.0f;
    c.b = 0.0f;
    c.a = 0.0f;
    d2d->d2d_device_ctx->Clear(&c);

    ID2D1SolidColorBrush *brush;
    D2D1_COLOR_F brushColor;
    D2D1_BRUSH_PROPERTIES bp;

    brushColor.r = 0.18f;
    brushColor.g = 0.55f;
    brushColor.b = 0.340f;
    brushColor.a = 0.75f;

    bp.opacity = 0.0f;
    bp.transform.m11 = 1.0f;
    bp.transform.m12 = 0.0f;
    bp.transform.m21 = 0.0f;
    bp.transform.m22 = 1.0f;
    bp.transform.dx = 0.0f;
    bp.transform.dy = 0.0f;
    res = d2d->d2d_device_ctx->CreateSolidColorBrush(&brushColor, &bp, &brush);
    if (FAILED(res))
    {
          std::cout << "CreateSolidColorBrush failed" << std::endl;
          goto release_bitmap;
    }

    D2D1_ELLIPSE ellipse;
    ellipse.point.x = 320.0f;
    ellipse.point.y = 240.0f;
    ellipse.radiusX = 100.0f;
    ellipse.radiusY = 100.0f;
    d2d->d2d_device_ctx->FillEllipse(ellipse, brush);
    brush->Release();

    d2d->d2d_device_ctx->EndDraw(NULL, NULL);

    d2d->dxgi_swapchain->Present(1, 0);
    d2d->dcomp_visual->SetContent(d2d->dxgi_swapchain);
    d2d->dcomp_target->SetRoot(d2d->dcomp_visual);
    d2d->dcomp_device->Commit();

  release_bitmap:
    bitmap->Release();
  release_surface:
    surface->Release();
}


LRESULT CALLBACK
_window_procedure(HWND   window,
                  UINT   message,
                  WPARAM window_param,
                  LPARAM data_param)
{
  switch (message)
    {
    case WM_CLOSE:
      PostQuitMessage(0);
      return 0;
    case WM_KEYUP:
      if (window_param == 'Q')
        {
          PostQuitMessage(0);
        }
      if (window_param == 'T')
        {
            std::cout << "transp" << std::endl;
        }
      return 0;
      /* GDI notifications */
    case WM_CREATE:
        return 0;
    case WM_PAINT:
      {
        RECT rect;
        D2d *d2d;

        d2d = (D2d *)GetWindowLongPtr(window, GWLP_USERDATA);

        std::cout << "paint" << std::endl;

        if (GetUpdateRect(window, &rect, FALSE))
          {
            PAINTSTRUCT ps;
            BeginPaint(window, &ps);

            render(d2d);

            EndPaint(window, &ps);
          }
        return 0;
      }
    default:
      return DefWindowProc(window, message, window_param, data_param);
    }
}

int main()
{
    /* class */
    WNDCLASS wc;

    instance = GetModuleHandle(NULL);
    if (!instance)
        return 1;

    memset (&wc, 0, sizeof (WNDCLASS));
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = _window_procedure;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = instance;
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(1 + COLOR_BTNFACE);
    wc.lpszMenuName =  NULL;
    wc.lpszClassName = "D2D";

    if(!RegisterClass(&wc))
        goto free_library;

    /* Window */
    int w;
    int h;
    RECT r;
    DWORD style;
    DWORD exstyle;

    w = 640;
    h = 480;

    style = WS_OVERLAPPEDWINDOW | WS_SIZEBOX;
    exstyle = WS_EX_NOREDIRECTIONBITMAP;

    r.left = 0;
    r.top = 0;
    r.right = w;
    r.bottom = h;
    if (!AdjustWindowRectEx(&r, style, FALSE, exstyle))
        goto unregister_class;

    win = CreateWindowEx(exstyle,
                         "D2D", "Test",
                         style,
                         100, 100,
                         r.right - r.left,
                         r.bottom - r.top,
                         NULL,
                         NULL, instance, NULL);
    if (!win)
        goto unregister_class;

    /* d2d init */
    D2d d2d;

    if (!d2d_init(win, &d2d))
    {
        std::cout << "d2d init failed" << std::endl;
        goto destroy_win;
    }

    SetWindowLongPtr(win, GWLP_USERDATA, (LONG_PTR)&d2d);
    ShowWindow(win, SW_SHOWNORMAL);
    UpdateWindow(win);

    /* msg loop */
    while(1)
    {
        MSG msg;
        BOOL ret;

        ret = PeekMessage(&msg, NULL, 0, 0, PM_REMOVE);
        if (ret)
        {
            do
            {
                if (msg.message == WM_QUIT)
                  goto beach;
                TranslateMessage(&msg);
                DispatchMessageW(&msg);
            } while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE));
        }
    }

 beach:
    d2d_shutdown(&d2d);
    DestroyWindow(win);
    UnregisterClass("D2D", instance);
    FreeLibrary(instance);

    std::cout << "exiting..." << std::endl;

    return 0;

  destroy_win:
    DestroyWindow(win);
  unregister_class:
    UnregisterClass("D2D", instance);
  free_library:
    FreeLibrary(instance);

    std::cout << "exiting 2..." << std::endl;

    return 1;
}

Now, I am blocked. I've searched a lot on Internet the last week, but i have not seen any code tha could help me.

Does someone see where my error is ?

thank you

Answer 1

Just set a non zero opacity for the ellipse brush, for example:

bp.opacity = 1.0f;