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    I’d like to hear more about what the starfield layers do.

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      Funny thing, if the sources I’ve found online (including MAME source) are to be believed, there were only ever two games that used the starfield generator for its intended purpose. Everyone else, if they used it at all, just used it as a no-memory-cost way to get flat backgrounds, by setting all the palette entries equal.

      From what I’ve been able to tell by sourcediving jtcps1 and this doc:

      • Each starfield layer had an X and Y scroll coordinate; those and the 15-color palette used by the starfields were all the CPU had control over.
      • The starfield data was burned into ROM.
      • The starfields were always at the back of the layer stack.

      So really just a pattern of dots (presumably enough bigger than one screen that the player wouldn’t get distracted by repetition) that you could palette how you chose and scroll on demand. And two of them so that you could scroll them at different rates and create a 3D-ish effect.

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        Thank you! I’d imagined it was probably something like that. What an unusual feature.