Coders, how was [this] done in [this] game?

[lionagony]

Playing so many Amiga games these days I often have technical questions about them and thought maybe this could be a good thread for me or any others that have questions about how certain things were done in certain games. I'll start with these 3:

Elfmania - how are they able to do line scrolling on the floors when it's not in dual playfield mode? [ Show youtube player ] If that was always possible why wasn't it used more? Maybe the first level of T-Racer is also done that way. [ Show youtube player ]

Apocalypse - at 8:02 in this video [ Show youtube player ] how were they able to get so many colors on screen if it was in 7+8 color dual playfield mode? Or maybe it wasn't. In the Youtube comments the developer says "I think for that game we managed to exploit a Denise-chip hack where an extra parallax layer was achieved by redefining sprites in the split-second that the raster scan goes from the right of the screen to the left. It was actually a small set of sprites that were continually redefined ahead of the raster scan to create the illusion of a parallax layer." Someone comments on that "so the skyline layer were achieved with sprites.. I always though it were using another bitplane.." and he responds "Yes, I think so. It's hard to remember now if it was that game or another. There was a maximum number of bitplanes and it was possible to squeeze one more out of the system with a sprite hack. I feel pretty sure I used it on Apocalypse, but it was a million years ago." Can someone explain that Denise hack he's mentioning?

Cool Spot - the backgrounds in Cool Spot have always mystified me, I think it's in dual playfield mode but then why are the backgrounds in only one color like at 48:34 here [ Show youtube player ] with the shelves just done by the copper? Or do they somehow have the dual playfield using 3 bitplanes in the foreground and just one bitplane in the background for more speed? Is that possible and would it be faster? Also how in the same video above at 16:16 do they make the boat appear to go up and down in the background?

Thanks for any explanations.

[AestheticDebris]

I think Apocalypse is just a case of using repeating sprites to create the background layer rather than Dual Playfield.

For Cool Spot, no you can't choose the distribution of playfield layers on the Amiga. The backgrounds do just look like a single bitplanes with some copper colours though. My guess is that layer is just being scrolled manually with the blitter. The boat going up and down is just scrolling that layer, you just have to keep track of the fact you want it to move independently as well as relative to the player so you're moving things the correct amount depending on on-screen action.