CosmicR (./4):Do you know how the official Neo Geo games do this kind of horizontal scroll?

there is no simple answer because it depends on the game and the requirements (number of sprites to use etc.). It also sometimes changes from level to level or layers are switched on and off.

- metal slug games use one or two background layers of 32 unlinked sprites in most level games.
- zedblade mostly uses one layer of 32 linked sprites and create the paralaxscrolling via linescroll
- blazing star uses up to 3 layers consisting of 21 unlinked sprites each
- pulstar uses 23 not linked sprites per layer
- spinmaster is very interesting, originally a layer consisted of 32 sprites, but later this was changed to 21sprites... looks a bit strange in VRAM.

if you don't want to use too many sprites then the solution with 32 linked sprites is probably the easiest but if you want to be on the safe side then you should work with 21 sprites even if it means a little more work for you.

by the way, if you use the neogeo typical black border (right and left 8 black pixels) then 20 sprites per layer are enough!