Re: [stella] Polar to Cartesian Co-Ordinate Converter

Subject: Re: [stella] Polar to Cartesian Co-Ordinate Converter
From: "Roger Williams" <mer02@xxxxxxxxxxxxx>
Date: Sun, 21 Oct 2001 17:41:01 -0700
> Can you do your demos with single scanline accurate movement?
These demos were thrown together to provide a platform for demonstrating
the pol2cart routine.  My eventual plans involve using pol2cart in the
which means that Y cannot be preserved.  The single scanline vertical
resolution is also so much finer than the horizontal that it seemed
to go for it when something "almost as good" could be realized much more

That said, there is no reason one couldn't use Y as the counter for a more
normal kernal where VDEL would work, giving 1-scanline resolution.
I didn't do that because you have to write both GRPx all the way down
the screen.  (If you turn on VDEL for a player in this kernal, it doesn't
appear at all if it's not positioned within the other player 's and it
bleeds down
to the bottom of the screen if its bottom is below that of the other

With an appropriate kernal all three demos should work nicely at 192
vertical, and the polar routine can even correct the aspect ratio.  But
my main focus was on the polar routine and with rotation, and to my
eye it looks better to have nearly-square pixels, and they're more
compatible with 2's complement 8-bit math anyway.

The kernal I wrote for this sucks on many levels, but it did the job of
demonstrating my polar coordinate routine.   I expect anyone who studies
the sprite movement demos to quickly figure out how to clean them up
for more general-purpose work.  The hard stuff is there, and the lazy
stuff is obvious.

--Roger Williams

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