[stella] single line kernels and horizontal position calculation

[Glenn Saunders <cybpunks@xxxxxxxxxxxx>]

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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