How to set up a clipping rectangle or area

How doe开发者_高级运维s 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?

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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.

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

CGContextClipToRect(context, clipRect);