Apple II 2k 40x96 Lores Demo FAQ FAQ

1. Can you do useful calculations during the display part of the code?
   
   Yes, every other scanline (so every 130 cycles) you have to flip pages with a 4-cycle long instruction. As long as you can flip in time, you can do whatever you want in the remaining 126 cycles.
   
   The demo is lazy and just does busy waits in there.
   
   
2. Why is the rasterbar so small?
   
   It's as big as I could easily animate in the 4550 cycles available during VBLANK
   
   
3. Why is the music so awful?
   
   For Hackfest you are supposed to do everything in 4 days, presumably coding the music too. I had sheet music for this song (from SuperMarioLand) so I could transcribe it easily.
   
   I'm only using 2 channels so it doesn't sound great, but it does mean the sound only takes 500 cycles every 30Hz to write out to the Mockingboard.
4. Are you the first person to use this graphics mode?
   
   Maybe? Flipping Apple II modes with cycle counting (sometimes called "vapor lock") is an old technique, dating back to the early 1980s. Both Bob Bishop and Don Lancaster have articles about it from that timeframe.
   
   It's possible someone else thought of using this exact mode, but I have not seen any examples of its use.