[atari7800] Re: Please help me understand display lists and display list lists

  • From: "Eric Ball" <ek-ball@xxxxxxxxxx>
  • To: <atari7800@xxxxxxxxxxxxx>
  • Date: Thu, 20 Nov 2003 20:47:52 -0500

The source for Spacewar http://www.atariage.com/users/ericball/spacewar.zip
has a routine to take a list of sprite positions and develop a the display
lists.   It's a little strange because SPRDL2 has to create the 16x16 ship
sprites from the 16x8 graphics.  SPRDL1 handles the 8x8 sprites and may be
easier to understand.  It also handles top to bottom and side to side wrap
around.

There are two ways to determine which display lists a sprite belongs in.
Either have the Y position map to a memory address directly (which restricts
the size of the display lists), or use a lookup table (see Spacewar).  Then
you will need to have an index pointer to the end of the list, again either
a separate table or embeded in the list (again see Spacewar).

As you can guess, one of the objectives for Spacewar is to fill that sample
code gap.  So if there is something in there which needs to be explained
better, let me know so I can update the comments.


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