Re: Screen memory mapping VIC-20

From: Anders Carlsson <>
Date: Fri, 7 Jul 2017 15:06:24 +0200
Message-ID: <A40AD4858C9D42CEB81EEB8A52F06E1B@ryds>
Pasi 'A1bert' Ojala wrote:

>> That would easily use all of the color RAM even with a smaller picture 
>> area.
> I don't think I have changed the location of the color memory on the fly 
> though.

I think it would require double buffering of the screen matrix, as those two 
go hand in hand. In multi colour mode, the four colours basically are:

1. Colour memory, individual for each character
2. Background colour, normally static for the entire screen
3. Border colour, ditto
4. High nybble of the volume register, ditto

In Pasi's picture viewer, at least the background, border and high nybble 
would be updated on each raster line instead of being static for the entire 
screen. I suppose if you have enough CPU time you could update the colour 
memory too, or double buffer the screen matrix and switch the colour memory 
for at least one more colour.

I think in the very latest VIC-20 graphics modes, tricks like these and more 
have already been taken. It is a matter of how much expansion RAM and CPU 
time one wants to invest on an effect like that.

Best regards

Anders Carlsson

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Received on 2017-07-07 14:00:06

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