Real-Time Physics Simulation Forum

I haven't tried it myself, so I don't know. Given the enormous particle counts in the example, I guess that some thousands of particles should be possible in real-time -- but that's just my guess. Would be interesting to consider for Bullet once we have its OpenCL-version. With the current version y...

It's some days old now, but maybe some of you haven't seen it yet: http://vimeo.com/13457383

Lagoa Multiphysics is a quite impressive plug-in for Softimage XSI's node system ICE.

Well, it is not PD only for large time steps and large stiffness/damping constants, but as their paper is entitled "large steps in cloth simulation", they should have realized this :wink: I realized it already with my second test of my implementation where the simulation just exploded. Aft...

The formulas are the same for a uv-aligned triangle. Let (x0, x1, x2) be such a triangle with the uv-coordinates (0, 0), (L1, 0), (0, L2). L1 and L2 are the rest lengths of the edges x0-x1 and x0-x2, respectively. This fulfills the requirement of the paper that |dw/du| = |dw/dv| = 1 if w is the rest...

Yes, they only use stretch/bend/shear-terms, but the stretch-term is a spring. They have a more general setting with triangles and uv-coordinates so that the behaviour is not so dependent on the tesselation, but for a triangle with one u- and one v-parallel edge, the formula for the stretch-term is ...

They state: "The matrices we ultimately hand to our CG method are positive definite." and "Let us define the symmetric positive definite matrix A by A = M - h df/dv - h^2 df/dx." If you read mathematical papers on the CG method, there is the requirement of positivity. Maybe that ...

if you read the cloth papers people always state that the matrix is PD. Yes, this is also my impression. These papers seem to be a bit optimistic. The case of non-PD is not academic, it occurs already for typical time steps together with stiff cloth. For positive definiteness, you get the condition...

Thanks for the reply, Dirk. In your second post, the derivation is wrong (check the physical units). I also get del_E/del_x = k * ( |x| - L ) * x / |x| Then write this as: del_E/del_x = k * ( 1 - L/|x| ) * x With del_(1/|x|)/del_x = -1/|x|^3 * x I get del_2E/del_x2 = k * ( 1 - L/|x| ) * E3 + (k * L ...

I implemented the algorithm described by Baraff and Witkin in "Large Steps in Cloth Simulation" (SIGGRAPH 98) and encountered severe instabilities with large stiffness and damping values. I found out the reason, namely that the system matrix used by the implicit integration is NOT positive...

OK, that high number of iterations is due to a very large (and thus not recommended) mass ratio: the mass of the sphere is 300 times larger than that of the mounted cylinder. Nevertheless, my question remains if an adaptive number of iterations is a good or bad idea.

The constraint solver uses a constant number of iterations (m_numIterations) with a default value of 10. While this works fine in most cases, there are situations where you need a lot more iterations. For example, I have a cylinder which is mounted on a horizontal hinge with fixed position in the wo...

Thanks for the explanation! But still the question remains why I cannot get a bouncing behaviour with the current implementation, and why it works fine when I remove the conditions?

I am testing the slider constraint, and I would like to have a bouncing behaviour. I played with the parameters, but couldn't find a satisfying set-up. Then I played with the code, and I can get a bouncing behaviour if I remove the conditions (vel < 0) and (newc > info->m_constraintError[srow]) when...

The second term seems to be OK even if the angular velocities differ. If you take my equation p * (vA - vB) + ((wB_t - wA_t) x p) * omegaA + ((wB_R * fB_t) x p) * (omegaA - omegaB) = 0 and the corresponding equation seen from B p * (vA - vB) + ((wB_t - wA_t) x p) * omegaB + ((wA_R * fA_t) x p) * (om...

Thanks for the explanation of the mass weighting. The existing code does mot mean that angular velocities of BodyA and BodyB are equal. It uses to vectors p and q perpendicular to the slider axis and assumes that projections of angular velocities to these axes are equal. Hmm, is this really true? If...