Re: [stella] GunFight 2600: Limit broken again! Now help needed! :-)

Subject: Re: [stella] GunFight 2600: Limit broken again! Now help needed! :-)
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Fri, 16 Feb 2001 14:04:14 +0100
> And: can someone give me a crash course in clever missile programming? I
> mean, do I really have to tweak ENAMx all the time? what about just
> making the missile invisible with the background color? 

As long as there is nothing above or below the cowboy, you can disable
the missile by changing it's colour. But if you try to make the
background more interesting by adding some playfield graphics for
example, a recoloured missile would stand of against the playfield,
if you don't turn it off properly with ENAMx.

> And another question: What all is delayed with VDEL? Just STA GRPx? What
> about STA NUSIZx?

VDEL doesn't delay anything. There are actually two graphics
registers for each of the players and VDEL lets you chose
which of them to use for display.

If we call the registers GRP0-A, GRP0-B, GRP1-A and GRP1-B,
then the graphics work like this. The A registers are what
you write to when you store something to GRPx. But when you
for example do STA GRP0, not only gets the contend of the
accumulator copied to GRP0-A, also the contend of GRP1-A
gets copied to GRP1-B. With STA GRP1 you also copy the
contend GRP0-A to GRP0-B.

VDELx lets you select, if you want to display GRPx-A or

Ciao, Eckhard Stolberg

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