Apidya Effect

[mcgeezer]

I was watching a video of Apidya and noticed an effect that I can't quite get my head around how they've done it.

[ Show youtube player ]

I know this has probably been discussed before but... wow, that looks wacky.

Geezer

Edit - effect is at 19.40 in the video

[saimon69]

If you mean the trippy entrails special stage @19:40 ,that is the (in)famous wobbling that danscott was describing in the power drift thread; i think playfields are oscillated horizontally by the blitter AND vertically by the copper plus sprites for the collision pillars - that or there are animation frames for the horizontal wobble

[Tigerskunk]

Timestamp to see that effect?

[mcgeezer]

[ Show youtube player ]

[ross]

hmm, it's probably a lot simpler than you think.
In practice, nothing happens on the screen that is not preset.

I would do it like this:
Dual playfield, copper per line for separate scroll and color gradients, vertical sprite multiplexing.
Bee, bubbles and pillars with sprites (so they are not affected by the wobbling effects).
Background playfield divided into columns of 16 pixels, blitter in copy mode for each column (to change y-position) and horizontal screen shift in the meantime (per line or quasi).
Same thing for the foreground playfield but with less use of the blitter because the columns are of limited height or absent
(in this case you can also split columns in vertical slices for separate wobbling).
In the meantime you change the position of the pointers of the screens (so could be that in some cases the columns are not to be blitted because the y is pre-set by screen position).

The final effect is really nice (and the use of colors makes it psychedelic, which is was the initial intention).