Under the Surface of Classic Sonic

@Conradd72371258 Pretty much.

@SCDDeconstruct I was going to ask for the other 2D games like Mania, Superstars, or even Advance 1 but I imagine they also use different engines compared to the classics, correct?

There exists a collision bug where the check used to prevent Sonic from clipping on top of a surface he's too far below from isn't done if he's moving horizontally in the air. This can easily be seen if you put a solid object on a top solid surface and hit it from the bottom.

@Conradd72371258 Hard to say. Chaotix uses a different engine from the mainline games, and it's not nearly as documented as them.

@SCDDeconstruct What about Knuckles' Chaotix?

...and Sonic 3 & Knuckles.

...and Sonic CD...

@LittlePlanetCD If anyone is curious about how this jump works, check out this explanation. Note that the 2011 remake actually can't do this without modding it. x.com/SCDDeconstruct…

if you thought that was insane, watch this

@mothnaman @Needlen0se @ParapastaCD @LittlePlanetCD It should, yes. It's a direct port of the original assembly code, unlike the 2011 remake.

@Needlen0se @ParapastaCD @LittlePlanetCD Does this work on gems collection/96 pc port?

12800 = 50 * 0x100

Here's a silly difference between the 510 and 0.28A (512) prototypes of Sonic CD. Special stage rings always appear in 510, but never in 0.28A. 0.28A added a ring count check, but only checked the top byte. As a result, they can only appear if the player has at least 12800 rings.

(You can find the hack here: sonicresearch.org/community/inde…)

There's a ROM hack of Chaotix called Knuckles' Clackers by GenesisDoes that reimplements loops, and even uses the masking sprite... but it still illustrates the problematic nature of loops with the tethering mechanic.

Loops were planned on being implemented in Chaotix, even being present in prototypes... yeah, I can see why they were removed (footage provided by @MDTravisYT)

Here's the highlighted line from the decompilation: #L437" target="_blank" rel="nofollow noopener">git.sr.ht/~benoitren/son…

I looked into this and saw from the decompilation that the stage ID check is messed up. The original Sega CD version checks if the stage is Palmtree Panic act 1 (zone ID 0, act ID 0), but the 90s PC port checks if the zone ID is 255 and if the act ID is 1...

@chrisprice @Mellon_Nova I actually might look deeper into this. I did notice that the 712 prototype had the same bugged special stage 1 background palette cycling as in the PC version...

@Mellon_Nova @SCDDeconstruct It does show why at least. Suspect at some point they were hitting death barrier and coded in the block. I've always suspected PC96 is branched off a little before final copy, back when Intel was pushing Dino in 1993. Like, around Ver 1.05.

There's a hidden tunnel that can be found right towards the end of the 3D loop section at the beginning of Palmtree Panic act 1 that I'm not sure is even accessible via normal means. Anyone have any ideas?

@SCDDeconstruct Can also get to them utilizing the moving peelout glitch Obviously still not intended, but still interesting