象图映射
Delete the selected item's pixmap. 14删除选择项目的点阵图。
To show a rotating object, we can scan-convert into the pixmap successive views from slightly different locations, one after another. 比如要显示一个旋转的物体，我们需要在前后连贯，变化不大的视点上一次接一次地进行扫描转换。
To display animations with raster systems, animated objects (which may consist of graphical primitives such as lines, polygons, and so on) must be scan-converted into their pixmap in the frame buffer. 为了在光栅系统中显示动画，必须将运动物体(由如线，多边形这样的图元组成)经扫描转换变为可在帧缓存放的位图。
/* free the pixmap with the given ID. */XFreePixmap(display, pixmap); 在释放一个pixmap之后 - 我们绝对不能再访问它。
