void EPAHandle(const Collider &collider_a, const Collider &collider_b,
const Simplex &simplex, Contacts &contacts)
{
std::vector<Simplex::Vert> epa_simplex
= { simplex.vertices[0], simplex.vertices[1], simplex.vertices[2] };
// 100 is for security purposes, preventing an infinite loop
for (int i = 0; i < 100; ++i)
{
// find the edge closest to the origin in the simplex
SimplexEdge edge = EPAFindClosestEdge(epa_simplex);
// find the furthest minkowski difference point in the direction of the normal
Vector2 support, support_A, support_B;
Support(collider_a, collider_b, edge.normal,
support, support_A, support_B);
// find the distance between the point and the edge
float dist = Vector2::Dot(support, edge.normal);
// if we've hit the border of the minkowski difference
if (dist - edge.distance < 0.01f)
{
contacts.push_back(Contact());
auto &contact = contacts.back();
contact.normal = edge.normal;
contact.pen_depth = dist;
// For contact points
// Find the repeating point, if there is no repeating point,
// project onto the edge, and use the homogenous coords to find the contact point.
Simplex::Vert &vert_0 = epa_simplex[edge.index_0],
&vert_1 = epa_simplex[edge.index_1];
// if there are no repitions, we project the origin onto the edge
// to find the contact point
float t;
// get the interval from the x coordinates
if (vert_0.vert.x > 0 && vert_1.vert.x < 0 ||
vert_0.vert.x < 0 && vert_1.vert.x > 0)
{
t = (-vert_0.vert.x) / (vert_1.vert.x - vert_0.vert.x);
}
// get the interval from the y coordinates
else
{
t = (-vert_0.vert.y) / (vert_1.vert.y - vert_0.vert.y);
}
contact.point = vert_0.parent_p0 + t * (vert_1.parent_p0 - vert_0.parent_p0);
return;
}
else
{
// add the point inbetween the points where it was found
epa_simplex.insert(epa_simplex.begin() + edge.index_1,
{ support_A, support_B, support });
}
}
}
bool IsColliding(const Collider &collider_a, const Collider &collider_b, Contacts &contacts)
{
// quick check with the individual collider AABBs for a quick out
if (!collider_a.aabb.Overlap(collider_b.aabb))
return false;
// our simplex for this collision test
Simplex simplex;
// Set initial search direction to the difference of centers
Vector2 d = Vector2(1, -1);//Vector2(collider_b.root_trans.PositionWC() - collider_a.root_trans.PositionWC());
// get the first minkowski difference point
simplex.Add(Support(collider_a, collider_b, d));
// negate the support point, giving us a vector in the direction of the origin
d = -simplex.A().vert;
int count = 0;
// start looping
while (count < 100)
{
// add a new point to the simplex because we haven't terminated yet
simplex.Add(Support(collider_a, collider_b, d));
// see if the simplex is on the correct side of the origin
if (Vector2::OppositeDirection(simplex.A().vert, d))
{
// if the point added last was not past the origin in the direction of d
// then the Minkowski Sum cannot possibly contain the origin since
// the last point added is on the edge of the Minkowski Difference
return false;
}
else
{
// oterwise we need to determine if the origin is in the current simplex
// this function will set the next search direction for us if it fails.
if (simplex.ContainsOrigin(d))
{
// if it does then we know there is a collision
// handle the collision with the EPA algorithm
EPAHandle(collider_a, collider_b, simplex, contacts);
// find the incident edge.
if (contacts.size())
{
auto &it = contacts.back();
it.info.e.edge_a = collider_a.FindIndex(it.normal);
it.info.e.edge_b = collider_b.FindIndex(-it.normal);
}
return true;
}
}
++count;
}
return false;
}
