Search found 698 matches

by drleviathan
Fri Mar 19, 2021 10:23 pm
Forum: General Bullet Physics Support and Feedback
Topic: "multiple mesh parts" with btBvhTriangleMeshShape?
Replies: 4
Views: 1639

Re: "multiple mesh parts" with btBvhTriangleMeshShape?

My interpretation of the manual (although I wasn't able to find a copy with the section you describe) is: if you have multiple distinct mesh "parts"... then you could store them in single btBvhTriangleMeshShape instance in one RigidBody... and the collision behavior would be identical to w...
by drleviathan
Tue Mar 16, 2021 4:23 pm
Forum: General Bullet Physics Support and Feedback
Topic: Object falling when turning
Replies: 1
Views: 1415

Re: Object falling when turning

The ball easily falls out of the pipe because when the pipe is "teleported" to a new transform the two objects interpenetrate and the "interpenetration logic" is happy to push the ball to the outside. It doesn't know inside from outside: it just tries to resolve the overlap. You ...
by drleviathan
Tue Mar 09, 2021 10:58 pm
Forum: General Bullet Physics Support and Feedback
Topic: Hinge vehicle balance
Replies: 3
Views: 1688

Re: Hinge vehicle balance

Car race-em games often require very tuned "game physics" (as opposed to "accurate physics") in order to make them fun. The example for this I usually give is: crashes. Accurate car crashes happen quite fast: you're in control when suddenly the vehicle is tumbling faster than you...
by drleviathan
Wed Mar 03, 2021 4:17 pm
Forum: General Bullet Physics Support and Feedback
Topic: [HELP] Explosiveness and stretching of physical object connections
Replies: 3
Views: 1542

Re: [HELP] Explosiveness and stretching of physical object connections

Because of bug, sword when attached to hand was always falling, increasing it's velocity higher and higher so everything it touches would fly away. Sword was separate object that was moving as their own as attachment to hand bone, so it wasn't physical movement. Ah I see: you were slamming the swor...
by drleviathan
Wed Mar 03, 2021 3:02 pm
Forum: General Bullet Physics Support and Feedback
Topic: [HELP] Explosiveness and stretching of physical object connections
Replies: 3
Views: 1542

Re: [HELP] Explosiveness and stretching of physical object connections

I watched the video. I believe what is happening is: the objects get into a state of interpenetration and the penetration resolution logic separates them but does so in a non-physical way. The penetration resolution logic is pretty good at getting the objects out of overlap while not pumping too muc...
by drleviathan
Tue Feb 23, 2021 11:12 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1819

Re: rotation format in bullet physics

is there a way to efficiently integrate the rotation with this vector? Do you mean: "Given some initial rotation Q0 and a non-zero angular velocity W ... is it possible to compute the rotation Q(t) as time progresses forward?" If so then: yes. In fact, that is what Bullet does: RigidBody ...
by drleviathan
Tue Feb 23, 2021 7:03 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1819

Re: rotation format in bullet physics

AngularVelocity is indeed a btVector3, however its units are radians/second. It represents the rate of change of the rotation... not the rotation. Perhaps you had a question about AngularVelocity?
by drleviathan
Tue Feb 23, 2021 4:53 pm
Forum: General Bullet Physics Support and Feedback
Topic: rotation format in bullet physics
Replies: 5
Views: 1819

Re: rotation format in bullet physics

Bullet stores both position and rotation in a btTransform which is a 4x4 matrix under the hood. You can extract just the rotation part into a normalized btQuaternion which is a 4D "vector". The components of a Quaternion are NOT the normalized_axis + angle, however with some practice you c...
by drleviathan
Thu Feb 18, 2021 7:48 pm
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2169

Re: Food Simulation

I'm guessing your container walls are thin, and the scoop part of your spoon might also be relatively thin. Thin convex parts of a btCompoundShape could very well penetrate with those of another. A likely simple solution would be to change your container model to have thick walls: at least twice as ...
by drleviathan
Wed Feb 17, 2021 9:04 pm
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2169

Re: Food Simulation

I would expect hacd to use btCompoundShape under the hood. Maybe try also using hacd on the container.
by drleviathan
Wed Feb 17, 2021 5:55 am
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2169

Re: Food Simulation

Bullet is tuned for meters and seconds. There are hard-coded thresholds in the details of shapes and collisions which makes Bullet not work well for tiny objects. However, you could "pretend" Bullet's units are centimeters instead of meters, and thereby simulate smaller physics. So a 0.01m...
by drleviathan
Tue Feb 16, 2021 6:39 am
Forum: General Bullet Physics Support and Feedback
Topic: Food Simulation
Replies: 7
Views: 2169

Re: Food Simulation

To avoid tunneling of convex grains through a concave container in Bullet you should use btCompoundShape (collection of convex sub-shapes) for the container rather than a convex mesh shape like btBvhTriangleMeshShape . The penetration resolution logic works much better for convex-vs-convex than conv...
by drleviathan
Sun Feb 14, 2021 8:47 pm
Forum: General Bullet Physics Support and Feedback
Topic: Collisions between static object and rigidbody ignored?
Replies: 5
Views: 1814

Re: Collisions between static object and rigidbody ignored?

Dunno quite what is going wrong but: In the first case: (a) World gravity is <0,0,0> (b) Both RigidBodies are dynamic (non-zero mass) (c) It looks to me like you create the two objects in an overlapping state so penetration resolution pushes them apart and one moves up while the other moves down. In...
by drleviathan
Fri Feb 12, 2021 2:55 pm
Forum: General Bullet Physics Support and Feedback
Topic: The wire stretched out very long,how to control it!Help! PLS!!!
Replies: 1
Views: 1295

Re: The wire stretched out very long,how to control it!Help! PLS!!!

To summarize your problem (and correct me if I'm wrong): you have a spring constraint that is not stiff enough for your purposes. Weak springs are easy and stiff springs are hard (they can go unstable). Here's some advice without knowing more about what you're really trying to do: (1) Maybe you want...
by drleviathan
Thu Jan 28, 2021 8:02 pm
Forum: General Bullet Physics Support and Feedback
Topic: [Solved]If I want hard constraints is featherstone and multibody the only effective solution?
Replies: 5
Views: 2596

Re: If I want hard constraints is featherstone and multibody the only effective solution?

Years ago (2014) I tried using FixedConstraints (with dynamic transforms) to drive a ragdoll character. I tried a range of numbers of constraints and body-parts. As I recall: with the mass ratios and timesteps I was using: above 15 constraints it was pseudo unstable and with 9 constraints (and fewer...