Jump Cancel is a mechanic that involves using a step or ceiling to cancel a jump's vertical speed.
This can be useful to gain more momentum that normally possible.
- The jump motion (0.42m) is the height of the first tick of a jump.
- The step height (0.6m) is the highest step the Player can move onto while on ground.
Both values are hard-coded into the game, but they aren't always used correctly.
This makes it possible to use Stepping mechanics in unintended ways.
This is also called "Slab Boost".
This variant only works if the step height difference Δ is between 0.42m and 0.6m.
- If Δ < 0.42m, the Player jumps above the step before the collision can be detected.
- If Δ > 0.60m, there is a collision, but the step is too high to apply stepping mechanics.
When walking up a step, the game attempts to place the Player correctly by:
- Setting their Y speed to 0.
- Setting their Y coordinate above the step.
In the process, the jump's vertical speed is lost, but horizontal speed is conserved. This makes it possible to jump again 2 ticks later.
Jump Cancel can be used to build momentum on stairs, amongst other blocks.
This variant is unintended, and was patched in recent versions of the game.
This variant only works if the ceiling height Δ is between 1.8m and 2.22m.
- If Δ < 1.80m, the ceiling is too low for the Player to fit, and the collision is registered as a wall.
- If Δ > 2.22m, there is no first-tick collision.
Ceiling jump-cancel is performed by jumping "into" a ceiling:
- The Player must previously be on ground and jump on the next tick.
- There must be no obstacle above the Player's current position (if there is, it must be taller than the ceiling).
- The Player's next intended position must collide with the ceiling.
From the game engine's perspective, everything happened as if the Player walked up a step, so the Player's speed and position are (mistakenly) changed to reflect that. This makes it possible to jump again 2 ticks later.
It is possible to chain multiple jump-cancels under a ceiling. In that case, it's referred to as grinding, and makes it possible to use 2-tick momentum under any kind of ceiling (as long as it satisfies the conditions above).
Unfortunately, it requires extremely precise mouse movement, so it's unlikely to be used outside of Tool-Assisted Parkour.
For example, a 1bm hh 5b is possible by using grinding:
- The Y coordinate stays the same throughout the momentum. This indicates the use of jump-cancel.
- To perform grinding under a 2b ceiling, the Player must repeatedly move inside and outside of the 2bc.
- The momentum gained is essentially the same as for a 1bm tdhh 5b, but done with 2bc instead.