This is just some more Apple II Xdraw (firmware vector drawing).
In this case I wanted to draw short lines, the value for the
shapetable was $04 $00. I tried various ways to point to this
value in a short manner, but even putting it at address $0101 (an
easy pointer to load into X/Y/A) didn't help with the size.
Eventually I found $0400 in ROM and point to that instead.
I really liked the effect but despite all the effort was not able
to get it down to the 16-byte category. If you're lucky you can
remove the HPOSN call to save 3 bytes, but that depends on random
RAM contents at boot.
So anyway, in agony after weeks I just kept it at 17 bytes and
submitted it as a 32-byte demo.
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