Real-Time Physics Simulation Forum

what is rel_pos? relative position? the center of mass/object's origin? just leave it 0? I didn't use Bullet, but it seems obvious that rel_pos is a point where the force is applied. Likely it's coordinated in the body frame, likely with an origin in the center of mass. So applyForce with 0 rel_pos...

Thanks for the answer! Ahh, I see, we indeed treat pseudo impulses in a different ways: in velocity solver we compute them and then clamp impulses associated with active inequality constraints, which leads to necessity of correction of other pseudo impulses; in position solver we first clamp constra...

Thanks!

No. That would require some history of a mutual movement, not just body states. So it would be not so natural. Though, it's definitely doable, but there would the same issues both in quaternion based approach and local frames based one.

I figured out what the problem was. It was... an error in the basic matrix class from which everything linear algebra stuff like vectors inherited. The error was in access to a matrix element function. But it did not show because almost always I worked with whether vectors (matrices with 1 width) or...

Please help me understand the correct way to treat inequality constraints in an NGS numerical scheme. Life is easy if we have only one such constraint: we just clamp the whole accumulated impulse in the velocity correction phase and just clamp every incremental impulse in the position coppection pha...

I have a fully working constraint model and that's what I have for the Jacobian for a hinge. That's because you use another constraints. Of course it's possible to use kind of (for the first body) a * e3A = 0, b * e3A = 0, where e3A is the unit vector rigidly connected with body A. In a body A fram...

Nope. Jacobians are coordinate expressions of differentials of maps from "coordinate space" to "constraint space". In simple words, if we have n constraints C_i and m coordinates x_j, ij-th matrix element J_{ij} is dC_i/dt |_{v_j = 1}, where v_j = dx_j/dt. It's written in the pre...

I'm stuck. Even for just one body which I want to constraint in rotation about one axis it doesn't work, though the problem seems obvious. Let V = (Vx, Vy, Vz) be a vector coordinates in a world frame, and q is a unit orientation quaternion of a body (so that if u is a column of coordinates in a bod...

I still not implemented this but I'm pretty sure that a reasonable way is to treat this contacts in a way you treat any other constraint. I.e. you can just iteratively solve corresponding (inequality) constraints. Or (a better way) you solve them simultaneously. Look at the end of Erin's presentatio...

He computed effective mass matrix (inverse of it) in the usual way. If you have a constraint C on your (generalized) coordinates you can deduce a velocity constraint by differentiation so Cdot = JV, where V is a colums of (generalized) velocities (velocities components and angular velocities in this...

Hi! I'm trying to understand joints implementation based on Lagnange multipliers. Now I'm thinking about a hinge joint between two rigid bodies. Here's how I think it should be done. Please tell me if I'm missing something or if something could be done better. Let us talk about just angular movement...

Thanks for the answer! If I understood you correctly, no. What I want to do is to forbid some body orientations. So there would be some allowed rotations and some forbidden. In 2d a rotation can be described by knowledge where some particular vector, (1, 0) for example, goes. So 2d rotations can be ...

Hello. I'm implementing a physics engine with rigid bodies with constraints using Baltman and Radeztsky's article: http://twvideo01.ubm-us.net/o1/vault/gdc04/slides/using_verlet_integration.pdf I want to speak about angle constraint between two bodies (section 8 ). The idea is as follows. We determi...