(TUTORIAL-INFORMATION) What Delta Movement does and How it Works.

PLEASE, READ EVERYTHING.

I want to clarify a common misunderstanding: delta movement is not itself a “speed check,” but it can be used to calculate speed. What delta movement actually represents is a 3D vector describing how much the entity moves on each axis (X, Y, Z) during the current game tick.

This means:

• The sign of each component (positive or negative) only indicates direction, not speed.

• A negative delta value does not mean “no movement” — it simply means the entity is moving toward negative coordinates.

   

During my tests, I noticed something important:
If you look only at the raw X, Y, or Z values, they can be small or negative, and therefore they are not reliable alone to determine whether the mob is “walking” or “running.”
This is why checking “if delta X > 0” or “if delta Z > 0” is not a valid method — movement can happen in the negative direction as well.

But:

Even when the components are negative, the speed can still be obtained correctly by calculating the magnitude of the vector:

speed = sqrt( dx*dx + dy*dy + dz*dz )


This gives a positive speed value, regardless of direction.

So delta movement does not fail for speed detection —
what fails is trying to check speed by inspecting the individual components separately.

What delta movement is useful for:

• Detecting the direction the entity is moving (positive or negative axis).
• Determining if the entity is moving at all (speed > 0).
• Calculating actual speed using the vector’s magnitude.
• Predicting the next position of the entity (current position + delta).
•  

Why delta Y sometimes “works” for people

When a mob jumps or falls, delta Y is large enough (positive or negative) to trigger simple conditionals like:

if deltaMovement.y > 0 

But X and Z often have very tiny values, both positive or negative, so checks like:

if deltaMovement.x > 0 

fail, because the mob may be moving but toward negative X.

Conclusion

Delta movement does not fail as a speed detection method, it only fails if someone tries to detect movement by checking individual components instead of calculating the vector’s magnitude.

That was all, i hope that this post help someone and i'll update this if i discover something new. 

Post made by: KrathK

Last Update: 13/09/25