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### Do Not Assume Support for Double Scanned Modes

If you are developing a game or application that wishes to support 320x200, 320x240 or 400x300 modes (in any color depth), be prepared for situtations where these modes do not exist. To be able to initialize these modes on today’s hardware requires support for double scanning, and there are some controllers in the field that do not support this. On these controllers these modes can never be supported, so your application or game must be able to deal with the situation if these modes do not exist.

In lieu of these modes not being available, the controller may provide support for 320x400, 320x480 and 400x600 modes which do not require double scanning. One neat solution is to support these modes by rendering your frames to a system memory buffer with a resolution 320x200, 320x240 or 400x300, and then do a copy to display memory with a 2x vertical stretch (just duplicate every scanline twice in software). The end result will look identical to a real 320x200, 320x240 or 400x300 mode, and you will only lose a small amount in overall performance.

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