Road-drawing techniques

[Wrathchild]

Hi,

 

Are there any sites that detail the techniques/algorithms

behind drawing roads/tracks in old 8-bit games such as

Pole Position, Outrun, Overlander, Elektragilde etc?

 

I'm interested in how these evolved, e.g. adding hills,

and how different display architectures, e.g. raster,

tile based or (Atari) display-lists can be exploited.

 

Thanks,

Mark

[Nukey Shay]

GFX on the horizon:

One simple way is just to change the display list pointer for the starting memory location of that line...that way you can have larger strings of memory devoted to that scanline than what is visible on the screen. An example of using pointers is just to look at the existing display list right at the top (by setting bit 6 in the display code IIRC...and then following with a two-byte address). That two-byte address is dynamic, and can be changed at any time in the running program.

 

Another (more attractive) way is to scroll the scanline...by using the fine-scrolling technique for the first 7 pixels and then performing a coarse scroll. This can be combined with the above method so that there is more area than can be seen.

 

No algorithms required.

 

For the road itself, the fine scrolling can be used with graphics that are set up with one-point perspective /...and scrolling to a higher degree as you move towards the center of the screen when curves are to be displayed. By using a seperate color for the edges of the "road", a DLI can be used to change the color register of that color every x scanlines to give the illusion of movement.