Repaint Windows Example

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#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

// Global repaint counter
static int paintCount = 0;

int WINAPI WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                      LPSTR lpCmdLine,
                     int nCmdShow)
{
    const TCHAR CLASS_NAME[] = TEXT("WindowClass");

    WNDCLASSEX wc;
    MSG msg;

    ZeroMemory(&wc, sizeof(WNDCLASSEX));

    // Register the window class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = GetSysColorBrush(COLOR_WINDOW);
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = CLASS_NAME;
    wc.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wc))
        return 0;

    // Create the application window
    HWND hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        CLASS_NAME,
        TEXT("Repaint Demo"),
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        340,
        220,
        NULL,
        NULL,
        hInstance,
        NULL);

    if (!hwnd)
        return 0;

    // Message loop
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}


// Window procedure
LRESULT CALLBACK WndProc(HWND hwnd,
                         UINT msg,
                         WPARAM wParam,
                         LPARAM lParam)
{
    switch(msg)
    {
        case WM_SIZE:

            // Force the entire client area to be repainted whenever
            // the window is resized.
            InvalidateRect(hwnd, NULL, TRUE);
            return 0;


        case WM_PAINT:
        {
            ++paintCount;

            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            TCHAR buffer[64];

            wsprintf(buffer,
                     TEXT("WM_PAINT count: %d"),
                     paintCount);

            TextOut(hdc,
                    20,
                    20,
                    buffer,
                    lstrlen(buffer));

            EndPaint(hwnd, &ps);

            return 0;
        }


        case WM_DESTROY:

            PostQuitMessage(0);
            return 0;
    }

    return DefWindowProc(hwnd, msg, wParam, lParam);
}