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23680RE: [midatlanticretro] 50 years of Computer Games

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  • Bill Sudbrink
    Dec 6, 2011
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      David Gesswein wrote:
      > Vector without display lists you need to rewrite everything at 30+ Hz
      > to prevent flicker.

      I'm thinking a vector display with a display list. The SWTPc SS-30 bus
      provides a 4 byte interface per slot. I'm thinking a of programming
      interface something like:

      <low byte> vertex address
      <next byte> vertex X
      <next byte> vertex Y
      <high byte> vertex options

      vertex options would be something like:
      <low 4 bits> intensity to this vertex (0 is off)
      (do vector displays support intensity?)
      <next bit> 0 - no action
      1 - terminate (go back to vertex zero)
      <next 2 bits> unused
      <high bit> 0 - X,Y is absolute, X and Y are unsigned
      (vertex zero must be absolute?)
      1 - X,Y is relative to previous vertex, X
      and Y are 2's comp signed

      So, you poke a vertex address, then poke its three values.
      I'm not sure how "coarse" a 256x256 vector display would be.

      With relative vertexes (vertices?) moving the ships around the screen
      will require a fewer operations. Rotations will still be painful.
      I have no idea how realistic this will be to implement in hardware...
      I know it would be easy with a modern pic, but I think I want to try
      to go with a vintage design. Memory wise, it seems doable. It doesn't
      even require 1K. I could implement it with a pair of 2114 static RAMS.
      It might glitch during I/O. I could put 2K on the board and bank swap
      to commit the writes. Then I need something on the board, spinning
      through the RAM, driving three DtoA circuits? And a clock? I need to
      do some reading.

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