[stella] Gunfight 2600: Design thoughts

Subject: [stella] Gunfight 2600: Design thoughts
From: Manuel Polik <cybergoth@xxxxxxxx>
Date: Thu, 19 Apr 2001 00:06:55 +0200
Hi there, hope you had Happy Easter Weekends!
     (At least happier than me, as I was very sad about the 
      death of Joey Ramone...)

Ok, as for Gunfight, I maybe tell you about some thoughts I spent on it
lately. When I was implementing the reload/sixshooter mode (Not finished
yet, I'm still tweaking it) I discovered some major misunderstanding of
a certain VCS issue on my side, which I wasn't aware until then. 
Until then I thought I could do shootable 12 blocks wide obstacles with
a reflected playfield, using PF2 twice. But this just isn't possible
with my kernel, if at all. 

First thing is that you'd have to rewrite PF2 two times on both lines of
the 2LK, which I just don't have the cycles to. 
Second is that you'd have to time the second write to PF2 so exactly,
that it's value changes at the very pixel both PF2s touch. (Has anyone
ever tried that?)

Next thought I had was using a reflected playfield, using the higher
nibble of PF2 on the left side and PF0 on the right. But that'd render
the problem even worse: Now you'd have to write not only two PF bytes
per line, but you'd additionally have to clear 'em both again for the
next line!

Now, the only way I've made up to cope with all these limitations, is
using a reflected playfield and draw symetric obstacles. There's no
problem to display these, I'm already doing the river like that. 
The Problem is making them shootable, which I think wouldn't work too
good. The reason is simple. Let's say I'd write the data of a half coach
into PF2 - it makes a complete one on the screen. Now if one cowboy
shoots at the left side of the coach and I'd remove a pixel there, it'd
automatically remove the same pixel on the right side.

The only thing I can think of to solve this problem is *slicing* the
obstacles, i.e. you can only shoot of whole lines of an obstacle at
once. Could make sense on some obstacles and be stupid on others. I'm
thinking for example of a continous moving train, where you'd have to
shoot out some slices *first* to get your bullets through to the other

The only other way I can think of ATM is to skip shootable obstacles
completely, but offer lots of different obstacle layouts instead, like
the river, some rocky/fency areas, a train, a coach, a tree and a cactus
for example...

Hm... hm... we'll see... suggestions/thoughts welcome... 


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