#include <Windows.h>

#define WIDTH  400
#define HEIGHT 300

#define X_START 0
#define Y_START 0
#define X_END   399
#define Y_END   149

HINSTANCE hInst;
LPCWSTR szAppTitle = L"GDI example";
LPCWSTR szMainWindow = L"Main";

LRESULT CALLBACK MainWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    HDC hDC;
    PAINTSTRUCT ps;
    POINT pos;
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    case WM_PAINT:
        hDC = BeginPaint(hWnd, &ps);
        if (hDC)
        {
            MoveToEx(hDC, X_START, Y_START, &pos);
            LineTo(hDC, X_END, Y_END);
            EndPaint(hWnd, &ps);
        }
        break;
    default:
        return DefWindowProc(hWnd, uMsg, wParam, lParam);
    }
    return 0L;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    WNDCLASSEXW wc;
    HWND hWnd;
    MSG Msg;
    hInst = hInstance;
    ZeroMemory(&wc, sizeof(wc));
    wc.cbSize = sizeof(wc);
    wc.lpszClassName = szMainWindow;
    wc.style = CS_HREDRAW|CS_VREDRAW;
    wc.hInstance = hInst;
    wc.lpfnWndProc = (WNDPROC)MainWindowProc;
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    if (!RegisterClassExW(&wc))
    {
        MessageBoxW(0, L"Cannot register window class!", szAppTitle, MB_OK);
        return 0;
    }
    hWnd = CreateWindowExW(0,
        szMainWindow, szAppTitle,
        WS_OVERLAPPEDWINDOW,
        GetSystemMetrics(SM_CXSCREEN) / 2 - WIDTH / 2,
        GetSystemMetrics(SM_CYSCREEN) / 2 - HEIGHT / 2,
        WIDTH, HEIGHT,
        NULL, NULL, hInst, NULL);
    if (!hWnd)
    {
        MessageBoxW(0, L"Cannot create main window!", szAppTitle, MB_OK);
        return 0;
    }
    ShowWindow(hWnd, nShowCmd);
    UpdateWindow(hWnd);
    while (GetMessage(&Msg, NULL, 0, 0))
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}