PhysicsBone of KineticBody has no effect in collision

jdoohen52

I have this dog of KineticBody class, and it has a capsule shaped CollisionShape which only covers its body:

I also have PhysicalBone attached to its head and leg bones.:

The reason of doing this is to track its leg/head movement in animation and still keep the physics correct - for example, it can hit things with its leg in a lifting-leg animation. If these were not add as PhysicalBone of BoneAttachment but just CollisionShape of the KineticBody, it does not move when bones moved by animation.

However, these physics bones (dog's head & leg) seems not been considered by physics system, only the CollisionShape of the KineticBody (dog's body) does:

Is there a way to fix it? Thank you!

TwistedTwigleg

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newmodels

I think the shape only works when it's a child of the physics node. So if it's a child of something that is not a physics node, it will just be a shape sitting there.

Maybe you can make it a child of a kinematic body, and make the kinematic body the child of the bone.

newmodels

I have not tried this thing with Godot.

dotted

My experience has been that a KinematicBody must be moved directly by gd-script operating on the KinematicBody node. In other words, a parent node transform change is not propagated to the KinematicBody's transform nor to the physics engine.

Since i haven't used physics-bone I can't give direct advice, but in looking at the tutorial, I have the impression that the physics-bones should be arranged in a hierarchy of these bones. Mixing and matching to bone-attachment prolly isn't meant to work. The bones are designed to simulate rag-doll physics; their movement is designed for control by the physics engine.

I expect you would have to name each bone for physics simulation since they are not in a heirarchy, per a comment made near the end of the tutorial below.

https://docs.godotengine.org/en/stable/tutorials/physics/ragdoll_system.html

If you want to try kinematic bodies, you will need to slave a kinematic shape to the animation in some way and update its transform on each animation frame. You might want to try having the kinematic 'bound' to the relevant limb/head and simply copy over the global transform of the body part in your KinematicBody _physics_process call

jdoohen52

I> @newmodels said:

I think the shape only works when it's a child of the physics node. So if it's a child of something that is not a physics node, it will just be a shape sitting there.

Maybe you can make it a child of a kinematic body, and make the kinematic body the child of the bone.

Thanks! I tried to change bones to kinematic body but doesn't work. And physics bone seems also a type of a PhysicsNode:

I suspect it's because shape is the grandchild, not direct child of the root Kinematic Body node. But I cannot make it a direct child of the root, because it has to be a bone attachment otherwise it doesn't move with the bone

cybereality

Can you just make the body collision shape bigger? Does it need exact collision on the head or would the fixed collision shape be good enough?

jdoohen52

@cybereality said: Can you just make the body collision shape bigger? Does it need exact collision on the head or would the fixed collision shape be good enough?

Head probably can be covered by body's shape too, above screenshots are not for easier to observe the collision doesn't work. For legs I do need them to have separately because I have a few animations that the dog move its legs. I'd like things to be pushed and moved only when its leg hit the object

jdoohen52

@dotted said: My experience has been that a KinematicBody must be moved directly by gd-script operating on the KinematicBody node. In other words, a parent node transform change is not propagated to the KinematicBody's transform nor to the physics engine.

Since i haven't used physics-bone I can't give direct advice, but in looking at the tutorial, I have the impression that the physics-bones should be arranged in a hierarchy of these bones. Mixing and matching to bone-attachment prolly isn't meant to work. The bones are designed to simulate rag-doll physics; their movement is designed for control by the physics engine.

That could be the reason. I'll give a try arranged in a hierarchy of the bones with the ragdoll system tutorial, without intermediate BoneAttachment nodes

I expect you would have to name each bone for physics simulation since they are not in a heirarchy, per a comment made near the end of the tutorial below.

https://docs.godotengine.org/en/stable/tutorials/physics/ragdoll_system.html

If you want to try kinematic bodies, you will need to slave a kinematic shape to the animation in some way and update its transform on each animation frame. You might want to try having the kinematic 'bound' to the relevant limb/head and simply copy over the global transform of the body part in your KinematicBody _physics_process call

:+1: Have limb/head as separate body and update its transformation in _physics_process sounds very intelligent and likely works. I'll try if physics bone in hierarchy of bones doesn't work.

newmodels

There is a way to get godot to show an attachment of a bone. In blender I attach an object to the bone. Exporting to .glb then importing into godot, I am able to get a node to that bone. Godot team is working on way for bone mounting.

jdoohen52

@dotted I tried both approach but unfortunately both of them not working. The first approach is follow the ragdoll tutorial, add Physics bone to the skeleton, and adjust them. I intentionally made head larger than the real one, but it still doesn't collide. The second approach is turn each bone attachment (my original hierarchy) or physics bones (approach 1) into kinemetic bodies. I didn't write code for them yet but I expect them to collide but it doesn't. I wonder how people are creating 3D fighting games? that would require fists and feet to be accurately attached to related bones and collision shape also moves with body animations. However I didn't find any made open source projects of this kind.

jdoohen52

@newmodels said: There is a way to get godot to show an attachment of a bone. In blender I attach an object to the bone. Exporting to .glb then importing into godot, I am able to get a node to that bone. Godot team is working on way for bone mounting.

My model is also exported from blender. It has bones and bone animations as an AnimationPlayer node. In this case can you attach some "CollisionShape" equivalent thing to bones in blender, so they move with bone animations, and import it into godot as collision shape?

newmodels

You might be able to attach an empty, then inside godot attach your physics object. I don't know if it would work. I know this works for unity3d, i've done this type of animating for it. Making the player feet have collision objects. I have not tried to get this working in Godot, because I've been using a different method. Based on my use of the other game engine.

newmodels

Well I do remember. I was creating area's this way. It might work. But it would probably have to be a rigidbody, not a kinematic body.

dotted

I didn't write code for them yet but I expect them to collide but it doesn't. I wonder how people are creating 3D fighting games?

If you are trying for that, I might suggest finding some sample or tutorial project that demonstrates 3d model interactions like that. You may save yourself a lot of time experimenting.

note: There is a debug option to turn on display of collision shapes. Use that and you might get a better idea of what is or is not happening.

Kinematic bodies can effect other bodies (rigid bodies), but don't respond to physics (ie the engine doesn't simulate collision reactions on them; that is their purpose; collisions are calculated with them but 'physics' must be implemented by you). You must write your own code for them to react to collisions . Conversely if you have rigid bodies in scene and a kinematic hits it, the rigid body will react.

Note: Until you move a kinematic body to match the skeleton or model transform in code, it will simply sit where it is spawned. Don't expect hierarchies of kinematic bodies to work, because generally my experience has been you need to control each directly and can't expect a scene hierarchy to do so.

So in this case I would try to collect a model part's (head or leg) transform and apply it to a kinematic in the kinematic's _physics_process(). Generally don't make a kinematic the child of any other kinematic or scene node being moved, instead use a spatial to organize the assembly, keeping kinematics and your model separate under your organizing node. This node should not transformed except for initial placement.

jdoohen52

Thanks for everyone's help, I took the idea from your replies and finally make it! So my original project still need some cleanup, but for future comers that interested to this topic, you can view this branch of this fork: https://github.com/ailisp/godot-3d-mannequin/tree/fight Basically the upstream repo has a human, it can run but head would overlap with the wall (no collision is detected there). My branch: - Head doesn't overlap with the wall, and it's for every animation, head collision moves together with the head bone - Add an attack, by pressing "J", and if the right hand fist hit the wall, player will be bounce back

For a high level overview on how this is made: - Add bone attachment to Skeleton, select bone attachment property to attach to head/hand bone, this will move attached objects as animation moves - Add Area as sub node of bone attachment, add CollisionShape to Area that roughly match head and fist's shape - Connect Area enter body / leave body to set / clear a flag variable to indicate collision happening - In physics process check that flag variable and if collide, move_and_slide player accordingly

Some caveat i run into: - must set Collision Layer/Mask of Player to not collide with player, because area is attached to player body, if not set it's always considered as colliding - must set physics fps to 120, otherwise head area still overlap with wall than bounce back.