Re: [stella] Star Fire - Return of the Starfield ?!?

Subject: Re: [stella] Star Fire - Return of the Starfield ?!?
From: Manuel Polik <cybergoth@xxxxxxxx>
Date: Thu, 25 Jul 2002 09:59:05 +0200
Hi Thomas!

>Manuel wrote:
>> That won't work. +8 does the trick, nothing else.

>> Consider this:

>> Horizontal scrolling works with +-1 and vertical 
>> scrolling with +-8 pixels. 

>> If you shift only a single line with anything else than 
>> +8, the vertical scrolling is out of sync immediately.

>Hm, I do not understand:
>1. Why is vertical scrolling limited to 8 pixels? (your demo 
>scrolls with single pixels in both directions)

Sorry, that was unprecise.

Uhm... hm... how do I explain that...

Ok, the stars are shifted 8 pixels from one line to the next.

Looks like this for example:


Now to scroll left or right, you'd shift the starting position +-1 I
think that's clear.

Now the trick: 

To shift that picture 'up', you do nothing else than shifting the
starting position +8!

Look here, the result:


See, the middle and the right star moved up, and the leftmost reappeared
at the bottom!

>2. Why can't you correct the x-position for the first star
>*outside* the kernel and then HMOVE with every value
>you like?

That'd probably work too, I think. But why all the overhead? ;-)

That 'every value you like?' might not be so trivial to achieve, at
least not without sacrificing either RAM, ROM or cycles. And I doubt
that you really gain that much. Try looking at Solaris and EDS, it's Ok
that way I think.

>You know that there is no "Total randomness" in a computer. ;-) 

At least not in computers where the soundchip has no generator for white
noise ;-)

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