RE: [stella] acceleration and inertia

Subject: RE: [stella] acceleration and inertia
From: Manuel Rotschkar <cybergoth@xxxxxxxx>
Date: Fri, 09 Jan 2004 08:20:37 +0100
Hi there!

> Is this related in some way with this? :

> "...If the NTSC version is designed with 2 byte 
> fractional addition techniques (or anything not based
> on frames per second) to move objects, then PAL 
> conversion can be as simple as changing the fraction 
> tables, avoiding major surgery on the program." (from 
> the big book).

I think so, yes.

> I didn't really know what the author tried to say, but 
> I think I get it now. You can tell me.

It's some very simple pseudo implementation of floating 
point numbers of sorts. If you only have one byte, you 
can move a thing only in 

n pixels per frame.

With 2 bytes you can move it

n.(m/256) pixels per frame

For 1,5 pixels per frame make m = 128 for example.

Well, and for NTSC to PAL timing transfer, just ensure 
the NTSC m to be ~80% (can someone provide the correct 
value? 83,4%?) of the PAL m

That is valid at least for a NTSC to PAL50 translation. 
If you do a PAL60 conversion only, the timings match 


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