Minecraft's collision physics is very simplistic: instead of ray-tracing the collisions, the game simply moves the player sequentially along each axis.
As a reminder, Minecraft's physics is updated 20 ticks per second. The player's movement and collisions are updated once per tick.
A collision box consists of one or multiple bounding boxes, which are simple cuboids define by minimum and maximum X/Y/Z coordinates.
Collisions usually involve an Entity and a Block: entities and blocks typically don't collide among themselves.
- The player only has one bounding box, of dimensions 0.6×1.8×0.6 m3. Their position (as shown in F3) is located at the bottom center
- Blocks have more complicated collision boxes (see this list).
Note: a "hitbox" is what the player can click on (e.g. attack an entity, press a button, open a door). It may or may not overlap with the collision box.
Every tick, after the player's velocity has been updated, the game does these steps to check collisions:
- Move the player along the Y axis. If a vertical collision is detected while moving downward, the player is now considered to be on ground.
- Move the player along the X axis.
- Move the player along the Z axis.
- If the player is on ground and collided with a wall, they are able to step over it if it's less than 0.6m tall.
Vertical Collisions (Y)
Vertical movement is processed before horizontal movement. Due to this:
- The player is able to jump one tick after running off a block. In particular, this is why headhitter timing works.
- To land on a block, the player's bounding box must overlap its surface on the final tick of the jump.
When the player hits a floor or ceiling, their vertical speed is reset to 0.
Horizontal Collisions (X/Z)
Due to the X axis being processed before the Z axis, corner collisions don't behave the same depending on the direction.
This phenomenon is especially noticeable with more speed.
It's important to distinguish "X-facing" jumps from "Z-facing" ones:
- X-facing refers to jumps that point towards East/West. The corner is difficult to avoid, and the player may have to start jumping further back than expected.
- Z-facing refers to jumps that point towards North/South. The corner is easier to avoid, and in particular it's possible to do a hh-timing from the front.
The axis of a jump can be checked with F3.
Players tend to find Z-facing neos more intuitive, but X-facing neos can actually be more lenient:
- Z-facing neos are very similar to linear jumps (assuming optimal movement). To convert a neo, simply add 1.2 to its distance and increase its tier by one. For example, a triple neo is equivalent to a "4.2+0.25" (which cannot be built, but this sort of comparison is useful for analysis)
- X-facing neos don't have a linear equivalent. Compared to Z-facing neos, they are "shifted" by 1 tick (wall collision begins and ends 1 tick earlier). This shift reduces the momentum, but makes it more efficient as the player typically has more speed at the end of a jump than at the start.
Some jumps are only possible when facing one axis or the other (for example, a 2bm triple neo is only possible X-facing)
In 1.14, the collision physics were updated. The collision order now depends on the player's velocity:
- If the player has more Z speed than X speed (in absolute value), the collision order is Y-X-Z.
- Otherwise, the collision order is Y-Z-X.
In most cases, all collisions now resemble X-facing. Some jumps which involve cutting corners may be very different compared to pre-1.14.