import core.runtime;
import std.c.windows.windows;
import std.string;
 
extern(Windows)
LRESULT WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_PAINT:
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint( hWnd, &ps );
        enum text = "Hello, Win32 GUI(D) World!";
        TextOutA( hdc, 0, 0, text, text.length );
        EndPaint( hWnd, &ps );
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProcA(hWnd, message, wParam, lParam);
        break;
    }
 
    return 0;
}
 
extern(Windows)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    string className = "helloWindow";
    string windowName = "Hello, World!";
    HWND hWnd;
    MSG  msg;
    WNDCLASSA wc;
 
    wc.style         = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc   = &WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIconA(null, IDI_APPLICATION);
    wc.hCursor       = LoadCursorA(null, IDC_ARROW);
    wc.hbrBackground = cast(HBRUSH)(COLOR_WINDOW+1);
    wc.lpszMenuName  = null;
    wc.lpszClassName = className.toStringz;
 
    RegisterClassA(&wc);
    hWnd = CreateWindowA(className.toStringz, 
                         windowName.toStringz,
                         WS_OVERLAPPEDWINDOW,
                         CW_USEDEFAULT, CW_USEDEFAULT, 640, 480,
                         null, null, hInstance, null);
 
    ShowWindow(hWnd, SW_SHOWDEFAULT);
    UpdateWindow(hWnd);
 
    while (GetMessageA(&msg, null, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessageA(&msg);
    }
 
    return msg.wParam;
}

C:¥> dmd -L/subsystem:windows gdi32.lib hello.d

+------------------------------------------+
|Hello, World!                    [_][~][X]|
+------------------------------------------+
|Hello, Win32 GUI(D) World!                |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
|                                          |
+------------------------------------------+