Re: [stella] Combat REFPx mystery

Subject: Re: [stella] Combat REFPx mystery
From: Glenn Saunders <mos6507@xxxxxxxxxxx>
Date: Tue, 23 Aug 2005 04:43:28 -0400
At 12:39 AM 8/23/2005, you wrote:
>Glenn wrote:
> > But not only that, it's also still necessary to reflect the sprite, 
> like to
> > have the car point left instead of right.
>Probably they yet didn't fully understand the hardware back then?

Sure, they didn't understand what the hardware was capable of doing beyond 
the original features.  But they knew what all the built-in features were, 
and they do use the reflection, but only in a seemingly frivolous way, like 
they didn't see the obvious way it could be used to optimize things.

The number of instructions it looks like Indy 500 is having to run through 
to determine whether to turn on REFPx he could have just stored one more 
frame of graphics because it looks like he only really _has_ to turn it on 
when the car has to face left.  You'd think it would have dawned on him to 
think of the graphics in terms of left-right symmetry if he's thinking 
about the reflection feature to this extent.  That's why I wanted to know 
if anyone could figure out a reason from studying he code.

Maybe with Combat there was barely enough ROM to finish the game.  Remember 
that in those days there was a lot of latency between entering the code and 
testing it on the hardware, so despite all good intentions, some bad code 
might have stayed in there because they were not able to go through enough 
iterations to see everything they were doing that clearly.  In the very 
earliest days they actually had to write straight machine language on paper 

What they did got the job done, and in 2K, so it's not a tragedy.  I just 
don't understand the thought process.  I think similar idiosyncrasies were 
discovered in the coding style of Surround, right?

It could be that another game might have precipitated the reflection 
feature if it had already been in development while the 2600 was in 
evolution.  The very earliest games were written on prototype 
hardware.  But by early 1977 I think the hardware was fixed.  Maybe for Air 
Sea Battle?  Canyon Bomber would probably have been too late.  I would 
think that any game that has sprites that only move left and right (coinop 
titles of that era like Sea Wolf, Sky Diver, etc...) would use this feature 
so maybe it just seemed like a no-brainer to put in.

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