Jump to content
  • Advertisement
Sign in to follow this  

Need EPA assistance

This topic is 1016 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Shape *s1,*s2;

void epa()
	static std::vector<Vec2D> s;

        //a,b,c are points from gjk simplex

	for (int i = 0; i < 32; i++)
		Vec2D norm = Vec2D::Zero();
		float dist = 0;
		int index = -1;

		epaClosestEdge(s, index, norm, dist);

		Vec2D p = support(norm);

		float d = p * norm;

		if (d - dist < 1e-6)
			collisionNormal = norm;
			penetration = d;
			s.insert(s.begin() + index, p);

void epaClosestEdge(std::vector<Vec2D>& s, int& edgeIndex, Vec2D& normal, float& dist)
	dist = INFINITY;

	for (int i = 0; i < s.size(); i++)
		int j = i + 1 == s.size()? 0 : i + 1;

		Vec2D a = s[i];
		Vec2D b = s[j];

		Vec2D e = b - a;

		Vec2D oa = a;

		Vec2D n = tripleProduct(e, oa, e);


		float d = n * a;

		if (d < dist)
			dist = d;
			normal = n;
			edgeIndex = j;

Vec2D support(Vec2D& n)
	Vec2D a = getfar(s1, n);
	Vec2D b = getfar(s2, -n);

	return a-b;

Vec2D getfar(Shape* s, Vec2D& n)
	float maxDot = -INFINITY;
	Vec2D best;

	for (int i = 0; i < s->vsCount(); i++)
		Vec2D v = s->vs(i);

		float d = v * n;

		if (d > maxDot)
			maxDot = d;
			best = v;

	return best;

Plain copy-paste-adaptation to cpp from dyn4j.


1. What about simplex' winding? Should it be CW, CCW or arbitrary given?

2. Any mistakes in my implementation? Any situations when this implementation fails? 

3. How can I get contatct points? Why is it said that EPA gives only one contact point? All i get are penetration and normal.


Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!