Clover（车轴草）绘制

#include <windows.h>
#include <math.h>

#define TWO_PI (2.0*3.14159)

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

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("Clover");
    HWND          hwnd;
    MSG                msg;
    WNDCLASS   wndclass;

    wndclass.style                     =CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc      =WndProc;
    wndclass.cbClsExtra             =0;
    wndclass.cbWndExtra          =0;
    wndclass.hInstance             =hInstance;
    wndclass.hIcon                   =LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor              =LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground     =(HBRUSH) GetStockObject (WHITE_BRUSH);
    wndclass.lpszMenuName    =NULL;
    wndclass.lpszClassName      =szAppName;

    if(!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Draw a clover"),
                                         WS_OVERLAPPEDWINDOW,
                                         CW_USEDEFAULT, CW_USEDEFAULT,
                                         CW_USEDEFAULT, CW_USEDEFAULT,
                                         NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while(GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
    static HRGN        hRgnClip;
    static int            cxClient, cyClient;
    double               fAngle, fRadius;
    HCURSOR           hCursor;
    HDC                   hdc;
    HRGN              hRgnTemp[6];
    int                       i;
    PAINTSTRUCT   ps;

    switch (iMsg)
    {
    case WM_SIZE:
        cxClient = LOWORD(lParam);
        cyClient = HIWORD(lParam);

        hCursor = SetCursor (LoadCursor(NULL, IDC_WAIT));
        ShowCursor(TRUE);

        if(hRgnClip)
            DeleteObject(hRgnClip);

        hRgnTemp[0] = CreateEllipticRgn(0, cyClient/3,
                                                            cxClient/2, 2*cyClient/3);
        hRgnTemp[1] = CreateEllipticRgn(cxClient/2, cyClient/3,
                                                            cxClient, 2*cyClient/3);
        hRgnTemp[2] = CreateEllipticRgn(cxClient/3, 0,
                                                            2*cxClient/3, cyClient/2);
        hRgnTemp[3] = CreateEllipticRgn(cxClient/3, cyClient/2,
                                                            2*cxClient/3, cyClient);
        hRgnTemp[4] = CreateRectRgn(0, 0, 1, 1);
        hRgnTemp[5] = CreateRectRgn(0, 0, 1, 1);
        hRgnClip        = CreateRectRgn(0, 0, 1, 1);

        CombineRgn (hRgnTemp[4], hRgnTemp[0], hRgnTemp[1], RGN_OR);
        CombineRgn (hRgnTemp[5], hRgnTemp[2], hRgnTemp[3], RGN_OR);
        CombineRgn (hRgnClip,         hRgnTemp[4], hRgnTemp[5], RGN_XOR);

        for(i=0; i<6; i++)
            DeleteObject(hRgnTemp[i]);
        
        SetCursor(hCursor);
        ShowCursor(FALSE);
        return 0;

    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);
        
        SetViewportOrgEx(hdc, cxClient/2, cyClient/2, NULL);
        SelectClipRgn(hdc, hRgnClip);

        fRadius = hypot(cxClient/2.0, cyClient/2.0);

        for(fAngle=0.0; fAngle<TWO_PI; fAngle += TWO_PI/360)
        {
            MoveToEx(hdc, 0, 0, NULL);
            LineTo(hdc, (int)( fRadius*cos(fAngle)+0.5),
                               (int)(-fRadius*sin(fAngle)+0.5));
        }
        EndPaint(hwnd, &ps);
        return 0;

    case WM_DESTROY:
        DeleteObject(hRgnClip);
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd, iMsg, wParam, lParam);
}