public bool Intersects(Box2d box)
{
// there are eight possible separating axis between two
// boxes:
// four from the first box,
// four from the second box.
// foreach such axis, we create a "ray" outgoing from the
// corresponding edge, in the normal direction.
// projecting the other boxes four corners onto that ray,
// and finding out that all projections are positive,
// means we have found a separating axis and can return
// 'false', no intersection.
// helpers:
// project points on rays
// creating rays from box
//
// what is a ray in our case? it is simply a start point,
// and a direction vector. vector2 times two will be nice for this.
// to compute the starting points of rays for one box, we
// need to rotate around the anchor point and use the range information
// available. ortho simply!
// to compute the direction of the rays, is just a rotation of
// either v(1,0) or v(0,1) vector
bool one = SeparatingAxis(this, box);
bool two = SeparatingAxis(box, this);
bool foundSepAxis = one || two;
return !foundSepAxis;
}
static bool SeparatingAxis(Box2d b1, Box2d b2)
{
// If i can find a projection minima that is positive,
// I've found a separating axis.
for (int i = 0; i < 4; i++)
{
Vector2 rayStart, rayDir;
b1.GetRay(i, out rayStart, out rayDir);
double projectionMin = 1;
for (int j = 0; j < 4; j++)
{
Vector2 corner;
b2.GetCorner(j, out corner);
double projection = Project(rayStart, rayDir, corner);
if (projection <= projectionMin)
projectionMin = projection;
}
if (projectionMin > 0)
return true;
}
return false;
}
public TopBox(Box2d box)
{
this.box = box;
}
public SideBox(Box2d box, double planeOffset)
{
this.box = box;
this.planeOffset = planeOffset;
}
public BottomBox(Box2d box)
{
this.box = box;
}
void RenderBox(IRenderer renderer, Box2d box)
{
renderer.PushMatrix();
renderer.Translate(Logic2World(box.X, box.Y));
renderer.Rotate(-Vector3.UnitY, box.Rotation);
float amin = (float)box.Amin;
float amax = (float)box.Amax;
float bmin = (float)box.Bmin;
float bmax = (float)box.Bmax;
renderer.DrawLine(new Vector3(amin, 0, bmin), new Vector3(amin, 0, bmax));
renderer.DrawLine(new Vector3(amax, 0, bmin), new Vector3(amax, 0, bmax));
renderer.DrawLine(new Vector3(amin, 0, bmin), new Vector3(amax, 0, bmin));
renderer.DrawLine(new Vector3(amin, 0, bmax), new Vector3(amax, 0, bmax));
renderer.PopMatrix();
}
