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SPG:Rolling

From Sonic Retro

Revision as of 12:46, 29 August 2019 by TheGreenDeveloper (talk | contribs) (Fixed some inaccuracies I think)

Notes:

Research applies to all four of the Sega Mega Drive games, and Sonic CD.

The following only applies when Sonic is on flat, dry land with no special power-ups. Curves, water physics, Super Sonic, and Speed Shoes will be covered in separate guides.

Friction

When Sonic rolls up by pressing Down on the directional pad, he can no longer accelerate. No matter how hard or how long you press in the direction of his motion, he'll behave as if you weren't doing a thing. The only thing that happens in this case is friction, which is half of Sonic's regular friction (in Sonic 3K, Super Sonic's friction is hard-coded to always be half of the regular friction).

Deceleration

However, Sonic can decelerate while rolling. If you hold in the opposite direction of his motion, X speed will be slowed by 0.125. Additionally, unlike normal walking, friction is still in effect while rolling, even if you press in a direction. So, in effect, while decelerating, X speed slows by 0.125+0.0234375, or 0.1484375, every step.

Strangely, the same deceleration anomaly happens while rolling as while running. If absolute X speed is less than 0.1484375, when this value is subtracted, instead of just setting X speed to zero, X speed is set to .5 in the opposite direction. Thus, bizarrely, Sonic can turn around while rolling, even though he can't accelerate! This is fixed in Sonic 3 and Knuckles, so apparently the programmers themselves found this undesirable.

Top Speed

Now, just because Sonic cannot roll faster on his own, doesn't mean that a nice hill wouldn't give him some momentum every now and then. These hills and slopes can be used to roll at a very high speed. Just as with running though, Sonic has a top speed cap when rolling as well, though this one is much higher than the former, reaching a top speed of 16 pixels per step. Unlike running however, Sonic cannot surpass this speed cap by any means. If his xsp reaches a point where it reaches 16, and tries to go higher, it will automatically be set to 16 instead. Notice how I said xsp instead of gsp, that's right, it caps Sonic's global horizontal velocity, rather than his ground velocity. This can cause the angle he's moving at to be incorrect compared to the angle he's supposed to be moving. You can just cap the gsp instead, that is, if you want the cap at all.

Criteria

In Sonic 1, 2, and 3 Sonic can't roll up unless his absolute X speed is greater than or equal to 0.5.

In Sonic and Knuckles (and Sonic 3 and Knuckles), this value is increased to 1. This is because in said game, Sonic is allowed to duck while his speed is below 1, so he can perform moves such as the Spindash without needing to come to a full stop (very helpful since Sonic could get stuck weirdly sliding on slopes starting with Sonic 3).

Also in Sonic and Knuckles, probably as a way to combat the anomaly associated with turning around while rolling in the previous games, Sonic unrolls if absolute X speed falls below 0.5.

Rolling Jump

In Sonic 1, 2, 3, and Knuckles, you can't control Sonic's trajectory through the air with the directional buttons if you jump while rolling. This makes it kind of hard to Spindash to gain speed, and then make a precise jump. Though, in Sonic 3 and in Sonic & Knuckles, you can regain control of the directional keys if you perform a Insta-Shield, or any other jump ability.

However, in Sonic CD and Mania, you can control a jump made while rolling, as if it were a totally normal jump. This is probably more fair to the player.