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
STA PF0
LDA Variable1
STA PF1
LDA Variable2
STA PF2
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).
Chris...
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