Is something wrong in btSubsimplexConvexCast

[fishboy82]

Hi:
When I read btSubsimplexConvexCast that implement Gino's GJK convex sweep algo. I found something confused me the code Line is:

lambda = lambda - VdotW / VdotR;
//interpolate to next lambda
// x = s + lambda * r;
interpolatedTransA.getOrigin().setInterpolate3(fromA.getOrigin(),toA.getOrigin(),lambda);
interpolatedTransB.getOrigin().setInterpolate3(fromB.getOrigin(),toB.getOrigin(),lambda);
//m_simplexSolver->reset();
//check next line
w = supVertexA-supVertexB;
lastLambda = lambda;
n = v;
hasResult = true;
}

It seems strange because this is advanced the configration space's origin,but why w is still in the old configration space. Should we need to translate w in to the new configration space's that is w = w+(lambda * (lina-linb) something like this?

[Vroonsh]

Hi,

You're right, I've had some weird Raytest Results due to this issue (Hit results outside the colliding shape)

Just after it you have this call :

Code: Select all

m_simplexSolver->addVertex( w, supVertexA , supVertexB);

So, you'll have to recalculate supVertexA and supVertexB before the w calculation :

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		if ( VdotW > btScalar(0.))
		{
			VdotR = v.dot(r);

			if (VdotR >= -(SIMD_EPSILON*SIMD_EPSILON))
				return false;
			else
			{
				lambda = lambda - VdotW / VdotR;
				//interpolate to next lambda
				//	x = s + lambda * r;
				interpolatedTransA.getOrigin().setInterpolate3(fromA.getOrigin(),toA.getOrigin(),lambda);
				interpolatedTransB.getOrigin().setInterpolate3(fromB.getOrigin(),toB.getOrigin(),lambda);
				//m_simplexSolver->reset();
				//check next line

Code: Select all

supVertexA = interpolatedTransA(m_convexA->localGetSupportingVertex(-v*interpolatedTransA.getBasis()));
supVertexB = interpolatedTransB(m_convexB->localGetSupportingVertex(v*interpolatedTransB.getBasis()));

Code: Select all

				w = supVertexA-supVertexB;
				lastLambda = lambda;
				n = v;
				hasResult = true;
			}
		} 
		m_simplexSolver->addVertex( w, supVertexA , supVertexB);

It solved my Raytest bug.

[Erwin Coumans]

It would be very helpful if you have a patch (using svn) and reproduction case for this (preferably filed in the issue tracker)

Could you help with this?
Thanks a lot,
Erwin

[Vroonsh]

Hi Erwin,

Sorry for the delay, didn't saw your answer.

Please find the svn patch attached.

Based on the 2156 version

We Didn't test all the samples with this patch, seems to work properly with our game code.

Regards

Boris