在显示前台缓存内容中的一帧画面时，后台缓存正在绘制下一帧画面，当绘制完毕，则后台缓存内容便在屏幕上显示出来，而前台正好相反，又在绘制下一帧画面内容。这样循环反复，屏幕上显示的总是已经画好的图形，于是看起来所有的画面都是连续的。

-Cache contents are displayed in front of a screen, the background frame buffer is being drawn the next screen, when the rendering has finished, the cache contents of the background will be displayed on the screen, while the opposite front, but also in drawing the next frame screen content. This cycle repeated, the screen always has been drawn graphics, the screen looks all are continuous.