/// <summary>
/// Sphere / Sphere Collision
/// </summary>
/// <param name="first"></param>
/// <param name="second"></param>
public void TestCollision(RigidObject first, RigidObject second)
{
// Simple sphere / sphere collision
Vector3 direction = first.Position - second.Position;
if (direction.LengthSquared() < Math.Pow(first.Scale.X + second.Scale.X, 2))
{
float diff = direction.Length() - first.Scale.X - second.Scale.X;
// First, normalize the direction vector
direction.Normalize();
// If the spheres are overlapping, push them out a little so they just touch
first.Position -= diff / 2 * direction;
second.Position += diff / 2 * direction;
// Next, find the relative velocity between the two bodies
Vector3 relativeVelocity = first.Velocity - second.Velocity;
// Find the velocity in the direction of contact - use dot product
float relativeVelocityPerp = -Vector3.Dot(relativeVelocity, direction);
// Esoteric: Finally, the impulse is determined using this relationship
float impulse = relativeVelocityPerp / (1 / first.Mass + 1 / second.Mass);
// Add the impulses in the correct direction to both bodies
first.AddForce = 2 * impulse * direction;
second.AddForce = -2 * impulse * direction;
collisions[secondIndex]++;
}
}
private void AddSphere()
{
RigidObject sphere = new RigidObject();
sphere.Model = sphereModel;
sphere.Texture = sphereTexture;
sphere.Position = new Vector3(
(float)(random.NextDouble()*20 - 10),
(float)(random.NextDouble()*20 - 10),
(float)(random.NextDouble()*20 - 10));
sphere.Velocity = new Vector3(
(float)(random.NextDouble()*4 - 2),
(float)(random.NextDouble()*4 - 2),
(float)(random.NextDouble()*4 - 2));
sphere.Mass = (float)(1 + random.NextDouble() * 4);
sphere.Scale *= (float)(0.5 + random.NextDouble());
sphere.BallColor = RigidObject.ColorBank[random.Next(0, 6)];
spheres.Add(sphere);
}
/// <summary>
/// Sphere / Triangle Collision
/// </summary>
/// <param name="first"></param>
/// <param name="A"></param>
/// <param name="B"></param>
/// <param name="C"></param>
public void TestCollision(RigidObject first, Vector3 A, Vector3 B, Vector3 C)
{
// First, make the sphere center our origin
A = A - first.Position;
B = B - first.Position;
C = C - first.Position;
// Find the surface normal for the triangle (using a cross product)
Vector3 normal = Vector3.Cross(C - A, B - A);
normal.Normalize();
// Find how far away the sphere is from the triangle
// We use a dot prouct to "project" Vector A on the normal
float separation = (float)Math.Abs(Vector3.Dot(A, normal));
// If the sphere is too far away, then quit
if (separation > first.Scale.X)
return;
// Good, so now it is in range! Find the contact point on the plane of the triangle
Vector3 P = separation * normal;
// Esoteric: Determine if the point is actually in the triangle
if (Vector3.Dot(Vector3.Cross(B - A, P - A), Vector3.Cross(C - A, P - A)) > 0 ||
Vector3.Dot(Vector3.Cross(B - C, P - C), Vector3.Cross(A - C, P - C)) > 0)
return;
// If the sphere is actually moving away, then don't bother (dot product here
if (Vector3.Dot(first.Velocity, normal) > 0)
return;
// Finally, add the impulse force to the sphere
first.AddForce = -2 * Vector3.Dot(first.Velocity, normal) * normal * first.Mass;
}
