Square inside polygon results in no collision because of BiasGreaterThan. about impulseengine HOT 2 OPEN

Thanks for this post. I wrote that code ages ago... And it looks buggy. Here is what I use in my qu3e repo, which should be robust.

// Artificial axis bias to improve frame coherence
const r32 kRelTol = r32( 0.95 );
const r32 kAbsTol = r32( 0.01 );
i32 axis;
r32 sMax;
q3Vec3 n;
r32 faceMax = q3Max( aMax, bMax );
if ( kRelTol * eMax > faceMax + kAbsTol )
{
	axis = eAxis;
	sMax = eMax;
	n = nE;
}
else
{
	if ( kRelTol * bMax > aMax + kAbsTol )
	{
		axis = bAxis;
		sMax = bMax;
		n = nB;
	}
	else
	{
		axis = aAxis;
		sMax = aMax;
		n = nA;
	}
}

So then to update our function here (no edge case, just two faces), it can look like:

inline bool BiasGreaterThan( real a, real b )
{
	const real k_relative = 0.95f;
	const real k_absolute = 0.01f;
	if (k_relative * a > b + k_absolute) {
		return true;
	} else {
		return false;
	}
}

Would you like to submit a pull request? If not I can make the modification. Let me know!

from impulseengine.

Wow thanks for the quick response! Your modification also fixes the issue. No more false negative intersections. However, I'm still experimenting with the bias in my engine (currently have sequential impulse solver+feature based contacts+warm starting working) to determine what is most stable. Interestingly enough, your original bias implementation was very stable with my stacking test cases (essentially just squares stacked in different nxm configurations). But I've come to realize that it is very dependent on the order of my pairs from the broadphase as this affects the distribution of the bias on each body. For example, when I add the bodies to the world in a reverse order, then the original bias becomes more unstable.

Anyway, your change does indeed fix the bug of missing intersections, which was the most critical issue. So you can feel free to make the modification. I'm going to continue to experiment in my own engine with different biases to determine which is most stable.

from impulseengine.