Chapter 12. Drawing Offscreen
There are many reasons your application might need to draw into an offscreen graphics environment. Perhaps the most common is to create a cache containing a complex drawing. Using the cache, the complex drawing can be drawn to the screen quickly many times over. With a rasterization-based drawing library like Quartz 2D, another popular reason is to create a pixel-based representation of a drawing.
Quartz 2D includes several techniques for drawing offscreen:
You can create a graphics metafile using the PDF file format.
An application can create an offscreen pixel map and a bitmap graphics context to draw on it.
You can use a Quartz object known as a CGLayer to cache drawings offscreen.
The discussion of creating Quartz ...
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