This demo is doing cycle counting. The top part of the screen is HGR,
the bottom is PAGE0/PAGE1 every-other-line LORES, and then the bottom
right of the screen is text mode, also interleaved PAGE0/PAGE1 as can
be seen when the text slides in.
The actual fireworks code (with the neat NTSC artifact colors) is based
on a BASIC program by FozzTexx which you can find
I had to write cycle-invariant HPLOT which was fun. The BASIC version
uses HPLOT TO (lines, rather than points) and I gave up and didn't bother
trying to make that invariant.
This has my new and improved vapor lock code that's trying to get
exact cycle-perfect vapor lock.
This works on a real Apple IIe Platinum, and in Applewin.
(Though it took a while to figure out an issue where the IIe + II+
had different results, as II+ adds $1000 to the HBLANK scan addresses).
There is still a glitch on the real-world Apple II+ though (which doesn't
happen in AppleWin), working on
tracking down why and how it can be fixed. You can see it in this picture
next to the text. Don Lancaster mentions something about the timing of
mode switches on the II vs IIe, maybe this is related.