Palm OS/C/离屏窗口编程

请确保在所有启动应用程序的事件传递完毕后，将焦点设置到您的离屏窗口上。

创建离屏窗口

(并记住您的应用程序最初启动的原始窗口)

 WinHandle  offWin;
 WinHandle  sysWin;

 Coord             width  = 160;
 Coord             height = 160;
 WindowFormatType  format = screenFormat;
 UInt16            error;
 offWin = WinCreateOffscreenWindow( width, height, format, &error);
 sysWin = WinGetDrawWindow();

释放离屏窗口

 Boolean  eraseIt = false;
 if ( offWin != NULL)
 {
   WinDeleteWindow( offWin, eraseIt);
 }

将焦点设置到离屏窗口

 WinSetDrawWindow( offWin);

在调用此函数之后，诸如WinEraseRectangle, WinDrawLine等等函数将绘制到离屏窗口上。

将您的离屏绘制内容转存到原始窗口

 WinHandle         srcWin;
 WinHandle         destWin;
 RectangleType     r;
 Coord             destX;
 Coord             destY;
 WinDrawOperation  mode;
 
 srcWin = offWin;
 destWin = sysWin;
 r.topLeft.x = 0;
 r.topLeft.y = 0;
 r.extent.x = 160;
 r.extent.y = 160;
 destX = 0;
 destY = 0;
 mode = winPaint;
 WinCopyRectangle( srcWin, destWin, &r, destX, destY, mode);