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Editorial Team
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Asked: 2026-05-16T15:01:22+00:00

Assume I want to program a Star Field animation. Not by using OpenGL but

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Assume I want to program a Star Field animation. Not by using OpenGL but by drawing directly to the screen buffer or to off-screen buffers that can be placed on screen.

That Star Field demo running on the TRS-80 is of course just an example. Think video decoding or full-screen animations as other possibilities where rates of 20+ frames per second are needed.

What are good techniques for doing this? I am interested in both official and private API implementations.

If you can, please show some basic code.

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  1. Editorial Team

    Here’s a brief outline of one common and reasonably fast method.

    During initialization, use CGBitmapContextCreate() to create at least 2 bitmap contexts from pointers to off-screen memory buffers, and add a CALayer as a sublayer of your UIView.

    In your render loop, alternate your double buffer use, copy into and/or modify the current off-screen memory buffer, use CGBitmapContextCreateImage() to create an image from that buffer, and assign the resulting image to the CALayer contents.

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