VR Weapon

[Timtaran]

I have Kinematic-Dynamic bodies system for player controlled bodies and my grabbing system works by mounting objects to dynamic body using FixedConstraint.

My gun consists of 3 parts - frame, slide, magazine. I'm trying to mount slide and magazine to frame using FixedConstraints (I plan to replace it with SliderConstraint for slide later). However I couldn't find is there any way to make Jolt treat them as single object, so when applying forces or colliding with static terrain my gun splits up into multiple parts.
While I can remove magazine because it became part of frame while being inside, I'm not sure what I can do with slide, because it should be possible to grab it and move.

Is it possible to make this purely with Jolt, or it would be better to look for some workarounds?

output.mp4

[jrouwe]

However I couldn't find is there any way to make Jolt treat them as single object

With constraints there's always a bit of slack because the simulation is not perfect, but it looks like there is a lot of slack in your movie. I have some questions:

• Which of the bodies (arm/gun/slide/magazine) are dynamic and which of them are kinematic?
• Are you disabling collision between the gun/slide/magazine? (i.e. do you use CollisionGoup?)
• Are you controlling kinematic bodies by using BodyInterface::MoveKinematic? If you're using a different function (e.g. SetPosition) then what you see in this movie is what typically happens.

[Timtaran]

The only kinematic body there is white wireframed body that doesn't collide with anything and it is controlled via MoveKinematic. Collisions are disabled by rejecting them via ContactListener.
"Explosion" at end happens when I'm applying impulse to frame (main part).

Yellow wireframed body is dynamic player body with 6DOF constraint with [-0.5; 0.5] axis limits to kinematic body.

[jrouwe]

I still don't understand your setup. Can you spell it out for me. Which bodies are there and how are they connected and which bodies do you drive?

[Timtaran]

My bodies:

1. Kinematic player body (white body)
   Use non-colliding with anything object layer
2. Dynamic player body (yellow body)
   6DOF constraint to body 1
3. Gun frame
   FixedConstraint to body 2
4. Gun slide
   FixedConstraint to body 3
5. Gun magazine
   Fixed Constraint to body 3

Other bodies are dynamic and use object layer that collides with everything else (except non-colliding layer).
If I change magazine and slide bodies object layer to non-colliding, nothing changes.

Before every physics tick I'm using MoveKinematic on body 1 with player's controller position and rotation.

At the end I'm applying impluse (angular and linear) to body 3 after gunshot, maybe too big, but it well demonstrates that bodies "splits"

[jrouwe]

I'm not sure what the purpose of body 2 is, but I would get rid of it (if you need some smoothing of the player input, then do that in your code). In general it's good to not move your kinematic body too abrubtly.

Other things to try:

• Make sure body 1 is the heaviest body and body 5 the lightest. Lower mass bodies follow heavier mass bodies more easily (e.g. divide the mass by 2 for every step from body 1 to 5).
• Use FixedConstraintSettings::mAutoDetectPoint to determine the best attachment points between the bodies
• Play around with the update frequency. You want at least 60Hz but higher values result in stiffer constraints.
• Play around with PhysicsSettings::mBaumgarte, higher values correct the error faster.
• Play around with PhysicsSettings::mNumPositionSteps, higher values correct the error faster (but cause the sim to take more time)
• Play around with PhysicsSettings::mNumVelocitySteps, higher values make the constraints stiffer (but cause the sim to take more time)

[Timtaran]

Thanks, I will try this.

Regarding me using dynamic and kinematic body, my idea was in having physical player body (like in Bonelab). To make body 2 be able to react to forces, I have [-0.5; 0.5] limit axis on constraint instead of [0; 0].
I didn't find other way of achieving this, so this is what I came with.

[Timtaran]

Worked without changing masses but I increased values too high, but I will play with it.