one player at two positions Vbi

Grevle · October 11, 2014

I have learned some assembler and can put players on screen in the vbi with assembler. Is it possible in the vbi to have lets say player 1 appear to be at two different positions at one time ? As a example using player 1 appear at the left side and the put it at the right side of the screen appearing as another object, all this happening inside the vertical blank intertupt. ? Thus looking like 2 different objects ? is it a name for it ? "sprite multiplexing" ?

snicklin · October 11, 2014

You're sort of on the right lines. Yes, you can have sprite multiplexing for extra sprites.

However, you would use DLI's (display list interrupts) and not vertical blank interrupts.

If you use the VBIs, you would have one player being shown in one frame and one in the next, therefore you would have flickering as it alternated position per frame.

However, if you use DLI's (when the electron beam hits the right of the screen), you can then shift the position of the player.

If you wanted 1 player to be on the left and right of the screen, you'd have to time the DLI to take place half way through the raster line being displayed.

If you wanted 1 player to be in two different vertical positions, you could use a normal DLI (this is the more normal and less complex way of doing it).

If you do a search through AA, you should find some examples of people doing this in their code.