Re: [stella] Turbo?

Subject: Re: [stella] Turbo?
From: Christopher Tumber <christophertumber@xxxxxxxxxx>
Date: Tue, 01 Apr 2003 17:35:26 -0500
Manuel wrote:

>The background color changes must happen _timed_ and on 
>_every_ scanline, so a real repositioning scanline can't 
>be executed. 
>So the sprite needs to be shifted in the gaps between 
>cars, which'd require a certain minimum vertical 
>distance from one car to another, since it can only be 
>shifted 7/8 pixels per scannline.

Looking at the screen shot - The bottom two cars (red and green) are P0/P1, the other cars (blue and white) however could be M0/M1/Ball. So presumably cars in the distance are M0/M1/Ball and only when they become close enough to show detail they become P1/P0. 

So no sprites are shared and all sprites can be positioned just below the score (&etc). (The M0/M1/Ball is presumably moved for the second, wider line but that's no problem except eliminating the "HMOVE comb") 

The scanlines just below the T58 are relatively simple - White/Green/White and mirrored. Even when this is presumably moving outwards, the most complicated it gets is Green/White/Green/White/Green and still mirrored. On these two coloured scanlines all you'd need to draw the buildings/sky is 

LDA Variable0
LDA Variable1
LDA Variable2

Which can easily fit into Horizontal Blank. Also consider that the sprites do not need full left/right movement on a scanline, they only need to be positioned in about the middle third of the screen (any further left/right and they crash into a building). So the positioning routine doesn't not have to be all that flexible and any calcs can extend a little beyond the HBLANK.

Actually, it makes sense why that furthest car would be white if it's the Ball and thereforing sharing colour with PF (The buildings).


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