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Moving Bits to the Screen

The Quartz imaging model does not provide the same sort of bit-copying functionality as QuickDraw because Quartz is not based on bitmap graphics. Most of the time you’ll want to adopt strategies that are not bit-based. However if you really need to draw bits, Quartz has the capability. To draw bits, create a bitmap graphics context and draw into it. You can then create an image from the bitmap graphics context by calling the function CGBitmapContextCreateImage (available starting in Mac OS X v10.4). To draw the image to screen, call CGContextDrawImage, supplying the appropriate windows graphics context.

Drawing to a bitmap graphics context, caching the drawing to a CGImage, and then drawing the image to a window graphics context is faster than copying the bits back from the backing store. (Note that you can no longer assume that window back buffers are in main memory.) Keep in mind that the source pixels of a CGImage are immutable.

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