How to set up a clipping rectangle or area

问题

How does one set up, modify, and clear a clipping rectangle inside a iOS drawRect for clipping generic CG drawing of lines, text, images, etc. to a small portion of a view?

Is it possible to use a more complex clipping region that is a composite of a bunch of rectangles and circles?

回答1:

You can set a clipping area with arbitrary paths, not restricted to rectangles. The followings are some ways of doing it:

1. You can draw an arbitrary path and set a clipping area with it. For example:

   CGContextBeginPath(context);
   //draw a path here
   CGContextClosePath(context);
   CGContextClip(context);
   //following drawing on the context will be clipped
   

2. If you want to use a mask image to set a clipping area, use CGContextClipToMask method.

See Apple's 'QuartzDemo' sample project for more usages.

回答2:

If you just want to clip to a rect you can use:

CGContextClipToRect(context, clipRect);

来源：https://stackoverflow.com/questions/5451838/how-to-set-up-a-clipping-rectangle-or-area