CLOVER程式

要用常規的方法畫出這個圖形，就必須根據橢圓的邊線公式計算出每條直線的端點。利用複雜的剪裁區域，可以直接畫出這些線條，而讓Windows確定其端點。CLOVER如程式5-8所示。

程式5-8 CLOVER

CLOVER.C

/*--------------------------------------------------------------------------

CLOVER.C -- Clover Drawing Program Using Regions

(c) Charles Petzold, 1998

----------------------------------------------------------------------*/

#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) ;

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) ;

}