我在看PtRaw控件时，其中有这样一句话，一直没有很好的理解，现求教各位，望给予指点！
这句话是这样的：
You must refresh the contents of the canvas whenever they become damaged. This is necessary because Photon doesn’t keep track of the widget’s raw contents for you. It’s more efficient to have you, as application programmer, maintain the original data structure and redraw the contents of the canvas. If it takes a long time to render the contents of the canvas, consider rendering them into an image and copying the image into the canvas when it’s damaged.
请问红色粗体字这句话如何理解？How to render them into an image?
望指教！谢谢！