FeaturePair.value not set correctly?

[huweiATgithub]

Hi Erin, Thank you for your great illustrative code, it is very good for learning rigid body dynamics.

From Arbiter::Update,

box2d-lite/src/Arbiter.cpp

Lines 40 to 50 in 227b71b

	Contact* cNew = newContacts + i;
	int k = -1;
	for (int j = 0; j < numContacts; ++j)
	{
	Contact* cOld = contacts + j;
	if (cNew->feature.value == cOld->feature.value)
	{
	k = j;
	break;
	}
	}

I think FeaturePair.value is used to distinguish contacts. While in Collide.cpp where contacts are computed, the only place to set value is in ClipVertex's constructor which set value=0.

box2d-lite/src/Collide.cpp

Lines 44 to 49 in 227b71b

	struct ClipVertex
	{
	ClipVertex() { fp.value = 0; }
	Vec2 v;
	FeaturePair fp;
	};

Does it seem like this value is not correctly assigned for its purpose?

Thank you.

[bit-hack]

I have been doing some work on Box2D-Lite and your ticket caught my attention.

It also looked to me that fp.value is only ever set to 0 but thats not the case.
If you look at the definition of FeaturePair we can see that its actually a union type so setting inEdge1, etc will also affect value. This seems like just a way to speed up comparisons between all of these char members using type punning.

union FeaturePair
{
  struct Edges
  {
    char inEdge1;
    char outEdge1;
    char inEdge2;
    char outEdge2;
  } e;
  int value;
};

[huweiATgithub]

Oh, I see. Thank you!