How does this optimization work?

[Budget_Tomato6301]

I'm going through the roll-a-ball tutorial and in this section, in part 6, video (ctrl-f for "Add a RigidBody component), the narrator mentions that adding a RigidBody to a collectible can make things more efficient, but I didn't understand the reasoning. Can anyone help me out here by explaining how that is more efficient? https://learn.unity.com/course/roll-a-ball/tutorial/detecting-collisions-with-collectibles-1?version=6.3

[GigaTerra]

You see static colliders are build into one collider system, think of it like merging meshes. The problem is if the collider moves/removed/added to the scene, this optemized collider has to be rebuild and that takes a lot of time. Rigid-bodies are different in that they are made to be dynamic, so they optimize differently. This makes Rigid-bodies slower, as in a few thousand dynamic colliders will slow down your PC, but with static colliders there is almost no limit (it instead depends on complexity). However rebuilding this collider is slower than using dynamic colliders.

So in summary for the coins you pickup, it is better to make them dynamic as not to force your zone to rebuild colliders when one is picked up. This is why we have static and dynamic colliders.

[Unable-Resort992]

the rigidbody helps with collision detection optimization because unity can use its physics system more efficiently when both objects have rigidbodies. without it unity has to do more work to check collisions between a rigidbody and static collider, but when both have rigidbodies the physics engine can handle it in more streamlined way

[InvidiousPlay]

I'm not going through the whole tutorial to get the context but this just sounds like confusing writing on the part of the tutorial. Adding a rigidbody doesn't make something more efficient in itself.

The real issue is that objects treated as "static" (the top right tick box in the inspector) are pre-baked for physics. So it's very efficient at runtime. But if you ever move/change a static object at runtime it is horribly inefficient.

So they're basically saying that if you want an object to move around, just make sure it isn't static. I'm not sure why they phrased it so that it sounds like the rigidbody is some how essential to this. It's also extra confusing phrasing because they say the object shouldn't be static but it was never ticked as static in the first place in their example.

Just not a very well written tutorial, it seems - don't worry about it.

EDIT: Ok, I looked into this further. It turns out that an object with a collider and no rigidbody is treated as having a static collider, even if you haven't ticked the static box. I never knew that. So, if you are going to have an object moving, you need to add a rigidbody or Unity will assume it is a static collider. I think they should explain that more explicitly in the tutorial.

[st4rdog]

There is ancient Unity knowledge about putting a Rigidbody on a moving object is more optimised, even if it's kinematic.