[stella] single line kernels and horizontal position calculation

Subject: [stella] single line kernels and horizontal position calculation
From: Glenn Saunders <cybpunks@xxxxxxxxxxxx>
Date: Mon, 12 Feb 2001 00:34:41 -0800
I was wondering, in single-line kernels and sprites which have different horizontal positions on the same screen, how is horizontal motion typically calculated?

It looks like no matter how fast the horizontal calculation routine that it winds up consuming too much time on the scanline to scan out the results on the same line, hence the traditional 2-line kernel utilizing VDEL.

Take a game like Atlantis, for instance. It only draws one sprite going across the screen on any given scanline, right? And it enforces vertical separation so that there is time to calculate new horizontal positions between ships. But other games have more free-form displays which would have objects moving vertically through the "compute scanlines".

I am thinking that the only way to solve this is to use tables to precalculate everything.

Does anyone have any tables handy for this purpose?

I may need to do something because I am going to have to adjust the missile positions on every line AND rewrite the playfield. I could precalculate the missile offsets during VBLANK but I may be short on the RAM needed to store these values.

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