Chapter I: ExcludeClipRect在一个剪切区域排除一个矩形,导致绘制该剪切区域时,不绘制该矩形.
ExcludeClipRect函数详情请参考MSDN,这个函数用于排除一个区域的一部分,常用于绘制图画,例如,在一个窗口的客户区绘制一幅图片,如下面代码所示:
- case WM_PAINT:
- {
- hdc = BeginPaint(hWnd, &ps);
- RECT rc = {0};
- GetClientRect (hWnd, &rc) ;
- HDC hMemDC = CreateCompatibleDC(ps.hdc);
- SelectObject(hMemDC, g_hBmpAllWstDskWallpaper);//选择位图
- //ExcludeClipRect(ps.hdc,0,0,200,100); //排除部分区域. A line
- BitBlt(ps.hdc,0,0,300,200,hMemDC,0,0,SRCCOPY);
- DeleteDC(hMemDC);
- EndPaint(hWnd,&ps);
- }
客户区,但是矩形区域{0, 0, 200, 100}显示的仍然是窗口的背景色,换句话说,位图缺了这一块.这是因为ExcludeClipRect将{0, 0, 200, 100}矩形从窗口剪切区域
Chaper II: ExcludeClipRect函数不释放排除的矩形区域
将Chapter I代码中的A行改为:
- BOOL g_bCall = TRUE;//全局变量.
- if (g_bCall)
- {
- g_bCall = FALSE;
- ExcludeClipRect(ps.hdc,0,0,200,100); //排除部分区域,仅调用一次. A line
- }
该DC上绘制,那么有没有什么办法恢复该区域呢? 其实很简单,将那块被"Exclude"掉的矩形区域再"找回来"就行了.办法就是程序再创建一个剪切区域,使其大小和位置
- #define RECT_WIDTH(rt) (rt.right-rt.left)
- #define RECT_HEIGHT(rt) (rt.bottom-rt.top)
- RECT g_rcExclud = {0};
- BOOL g_bCancelExcludeRect = FALSE;
- case WM_PAINT:
- {
- hdc = BeginPaint(hWnd, &ps);
- RECT rc = {0};
- GetClientRect (hWnd, &rc) ;
- HDC hMemDC = CreateCompatibleDC(ps.hdc);
- SelectObject(hMemDC, g_hBmpAllWstDskWallpaper);//选择位图
- // "exclud"掉的区域在右下角.
- g_rcExclud.left = rc.right-200;
- g_rcExclud.top = rc.bottom-100;
- g_rcExclud.right = rc.right;
- g_rcExclud.bottom = rc.bottom;
- HRGN hrgn = NULL; // 将上次"exclud"掉的区域填补回来.
- if (g_bCancelExcludeRect && RECT_WIDTH(g_rcExclud) && RECT_HEIGHT(g_rcExclud))
- {
- hrgn = CreateRectRgn(g_rcExclud.left, g_rcExclud.top, g_rcExclud.right, g_rcExclud.bottom);
- ExtSelectClipRgn(ps.hdc, hrgn, RGN_OR);
- FillRect(ps.hdc,&g_rcExclud,(HBRUSH)GetStockObject(COLOR_WINDOW));//擦除上次绘制的图片区域.
- }
- (!g_bCancelExcludeRect) //"exclud"掉窗口右下角区域.
- ExcludeClipRect(ps.hdc,g_rcExclud.left, g_rcExclud.top, RECT_WIDTH(g_rcExclud), RECT_HEIGHT(g_rcExclud));
- BitBlt(ps.hdc,0,0,400,300,hMemDC,0,0,SRCCOPY);//在右下角绘制一个位图.
- DeleteDC(hMemDC);
- if (hrgn != NULL) DeleteObject(hrgn);
- EndPaint(hWnd,&ps);
- }
Chapter III: 使用ExcludeClipRect实现无闪烁图像
有网友写过相关文章:http://dev.10086.cn/cmdn/wiki/index.php?edition-view-6349-1.html
而"exclude"掉的区域是不会被背景擦除的.
而且这篇文章还有一个地方没有说清楚,那就是解决图像闪烁的办法其实是不用擦除窗口背景,而绘制窗口前景色,图像区域用位图绘制,其它区域用窗口背景色绘制,
- case WM_PAINT:
- {
- hdc = BeginPaint(hWnd, &ps);
- RECT rc = {0};
- GetClientRect (hWnd, &rc) ;
- HDC hMemDC = CreateCompatibleDC(ps.hdc);
- SelectObject(hMemDC, g_hBmpAllWstDskWallpaper);
- HRGN hrgn = NULL;
- if (RECT_WIDTH(g_rcExclud) && RECT_HEIGHT(g_rcExclud))
- {
- hrgn = CreateRectRgn(g_rcExclud.left, g_rcExclud.top, g_rcExclud.right, g_rcExclud.bottom);
- ExtSelectClipRgn(ps.hdc, hrgn, RGN_OR);//恢复上次被"excude"掉的区域,必须的,否则这一部分不会被绘制.
- FillRect(ps.hdc,&g_rcExclud,(HBRUSH)GetStockObject(COLOR_WINDOW));//擦除上次绘制的图片区域.
- }
- g_rcExclud.left = rc.right-300;
- g_rcExclud.top = rc.bottom-200;
- g_rcExclud.right = rc.right;
- g_rcExclud.bottom = rc.bottom;
- BitBlt(ps.hdc,g_rcExclud.left,g_rcExclud.top,g_rcExclud.right-g_rcExclud.left,g_rcExclud.bottom-g_rcExclud.top,hMemDC,0,0,SRCCOPY);
- ExcludeClipRect(ps.hdc,g_rcExclud.left,g_rcExclud.top, g_rcExclud.right, g_rcExclud.bottom);//排除掉图像所占据的区域
- FillRect(ps.hdc,&rc,(HBRUSH)GetStockObject(COLOR_WINDOW));// 用窗口背景色绘制其余区域.
- DeleteObject(hrgn);
- DeleteDC (hMemDC) ; //释放内存设备环境
- EndPaint(hWnd, &ps);
- return 0;
- }
- break;
- case WM_SIZE:
- InvalidateRect(hWnd, NULL, FALSE);//最后一个参数为FALSE,表示不用擦除背景.
- break;
最后,改变窗口的大小,观察一下这幅图片,始终在窗口右下角,而且图片的确不再闪烁.
本文转自jetyi51CTO博客，原文链接：http://blog.51cto.com/jetyi/642401
，如需转载请自行联系原作者
