Re: [stella] single line res

Subject: Re: [stella] single line res
From: Mark De Smet <de-smet@xxxxxxxxxxxxxxx>
Date: Tue, 20 Jun 2000 22:42:25 -0500 (CDT)
> Could someone explain to me how single line res sprites are generated?  In 
> all my readings I've never seen a really good explanation for this.  Maybe 
> if Greg Troutman still actively reads the list?

Um, I'm not sure what you mean by single line sprites.  As a programmer
you have the perogative to change all the graphics sprites every line.

> This is done through VDEL tricks, correct?  From reading the Stella 

As I understood it, the VDEL was implemented to solve an issue when you do
a double line resolution display.  If you are doing a double line display,
you only update all the registers every other line(and do
something/nothing else on the other line).  The issue arose, although it
is fine for your playfield to only change everyother line, what about
objects that move vertically(like missles, or tanks)?  If you only do
screen stuff everyother line, the moving object would jump every other
line when moving.  Using vdel, you can do your graphics updates on every
other line, yet still be able to place players and missles on any line.

> documentation it makes it seem as though you can't write single line 
> kernels due to timing constraints.  I know that's not true, but it may have 
> seemed that way in 1979.

I think this is correct.  I think they didn't know that they were able to
update graphics everyline.  Hence they put in the vdel.


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