Bullet softbody cloth was stretched away

[ericking]

I am new one for bullet softbody simulation, I get a cloth mesh with its local space vertexs and indices from other graphic engine, and then I used createFromTrimesh(...) to create a softbody successfully, and then I create a rigidbody in body for soft cloth to attached, some details as follow image. and then add into dynamic world to step simulate.

QQ图片20190723154642.png

for attached to rigid body , I set three anchor points from soft cloth skirt mesh with setMass 0,and then get rigid body transform matrix4x4(called wmat) at every frame .when get a new frame simulation cloth vertexs from bullet, I will transform these new simulated vertexs by wmat, and covered the cloth mesh vertexs ,and give it back to my grapic engine to draw .
But the reslut is very strange like this :

res.png

Can anyone help me ,what is wrong with it?

[steven]

very interesting! have you found the rootcause?