Dynamic circle effect from Contra 3 / Probotector

[RexyDallas]

As for the big scaling keyhole/circle transition, it should be interesting to load into an emulator and see what's happening. It acts as a vector layer, but I guess it's not the case, just what it looks like.

Perhaps they use some background priority trickery. IE: Step 1: keyhole, and other backgrounds, are behind Mario. Step 2: Other backgrounds are set above Mario, with a Keyhole-shaped cutout. Is this possible on an SNES?

Also, I have noticed a few quirks:
1. The enemies disappear when it shrinks.
2. The item at the top of the screen is also sucked into the keyhole.
3. It is rendered above the menu.

EDIT: I just reached a keyhole. When I disable all layers, including sprites, there is a blue color, and then the keyhole is there.



When I disable transparency effects, the color in the background disappears, or BG#2 disappears if it is enabled. When I disable clipping windows, the hidden sprites reappear.

Also, I found an article on SNES transparency, and another on windows.