The question is worded pretty bad but what I want to do is pretty simple, I just can't figure it out. I have a vehicle entity and I want to spawn its wheels. I have 4 offset vec3 to tell me where to spawn the wheel, previously I was just spawning the wheel at the vehicles translation plus the offset rotation. But this doesn't account for the vehicle's rotation. I can't make the wheels children of the vehicle because it would mess with the physics. How can I achieve this?
#How to spawn another entity as if it were a child on another entity without making it a child
iron bluff
bitter kindle
This isn't currently achievable atm, transform propagation is mandatory for parent/child. This will be solved more with relations 🌈 in the future but for now I just use a separate component to mark Attach::Translation(Entity) personally
iron bluff
The physics joints handle moving the wheel with the vehicle I just can't figure out the math behind where to spawn the wheel relative to the vehicle when there is a rotation invloved
bitter kindle
if you are using rapier the joints should be relative to the collider you are attaching to
so you shouldn't need to worry about rotation in that case
like in my project I have
let mut hand_joint = SphericalJointBuilder::new()
.local_anchor2(Vec3::new(0.0, arm_radius, 0.0))
you specify the anchors on each physics objects own local orientation
iron bluff
If the wheels aren't where they are ment to be the joint launches them into place making all the vehicles get launched
wooden parcel
Is the vehicle already existing? Or is the entire thing spawned at once?
If it's spawned at once, you could spawn it as a child with inactive physics and a marker, and then remove the parent-child relationship the next frame along with removing the marker and activating physics
If it exists already, you can use the global transform on the vehicle to transform a point in "vehicle" space to world space
(note that if the vehicle doesn't have a parent, you can do the same with a normal transform component, and then you can spawn them together using a clone of the original transform)
iron bluff
This works but if there is a better way let me know
transform.right() * wheel.position.x
+ transform.up() * wheel.position.y
+ transform.back() * wheel.position.z
+ transform.translation,
The resulting transform is what I assign to the wheel entity and the transform variable in the code belongs to the vehicle
Would this method work for my case?
https://docs.rs/bevy/latest/bevy/prelude/struct.Transform.html#method.transform_point
wooden parcel
That method is the inverse of what you need - it takes something from global space to local space