You can get the sourcecode
here in the demos/outline2021/128b/ directory of
my dos33fsprogs github repository: git clone https://github.com/deater/dos33fsprogs/
Vote for this at Pouet
Run-through of the Effects
This code takes advantage of Apple II shapetables.
This is a neat feature of the Apple II: in-ROM scaled/rotated vector drawing
routines. You can point to a nul-terminated list of numbers and it is
interpreted as a series of vector drawing commands.
You can DRAW the pattern at a location on the screen with SCALE and
ROTation. You can also XDRAW (exclusive-or) which is handy if you want
to also erase something you previously drew.
Normally you'd pain-stakingly plot out the vector you want to draw, but
if you're doing size-coding you can just point to random parts of RAM/ROM
and hope for the best and maybe find some interesting results.
This first result was one I accidentally made when trying to make a compact
lovebyte entry. It's almost a circle, but as you can see on real hardware
with aspect ratio it's more of an oval.
I also found this one by accident, it's what you get if you treat
the ROM at $D004, $D104, $D204, etc, as shapetables with rotation.
This one was the basis for my 16-byte Lovebyte entry, it's a nice pattern
you can find by using $F001 in ROM as your shape table.
Finally I wanted to find some other interesting patterns. I methodically
searched starting from $D000 at the beginning of the Applesoft ROM.
The first nice set of patterns was around $D34D for about 32 patterns or so.
So this demo shows them, then does them again with rotation. In theory
it will do this for 64 angles before repeating, but for time reasons
the demo version is cut off after only 1 angle.
There might be further better patterns, I've only searched through about 1000
of the ROM locations and there are many more left unexplored.
Some people watching the demoparty stream enjoyed the wipe "effect" between
scenes. I always find that amusing, as long-time Apple II people would
recognize that as the stock "HGR" screen clearing that ends up looking like
a fancy venetian-blinds thing due to Woz's bizzarre memory layout.
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