Re: [stella] Sea Wolf type score w/ independent colors

Subject: Re: [stella] Sea Wolf type score w/ independent colors
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Mon, 17 May 2004 10:14:47 +0200
Glenn wrote:
> Thomas, could you please explain the code?  I've already looked at it and 
> have a good idea how it works but it would be nice if you explained it 
> yourself.

Actually the code is not very complex and just combining some already 
known tricks.

To reduce the number of writes to a color register I am using the same 
trick as in the score display for Jammed. Instead of changing the colors 
of the two sprites, I am setting them to black and invert the graphics data. 
Then I am putting playfield graphics behind the sprites (which are static 
during the display loop) and change their color instead. 

So what you see on screen is the color of the underlying playfield which is 
masked by the black sprites lying ahead. 

The timing is very critcal, so I had to remove WSYNC and to use VDELP0/1, 
illegal opcodes (lax) and the stackpointer for temporarily storing values.

The colors are hardcoded (one could be loaded from zp), but that should 
work in the majority of cases.


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