//Code from Simple Dynamics framework - Minsi Chen
public void AddCollisionPair(CollisionPair pair)
{
Object A = pair.BodyA;
Object B = pair.BodyB;
//Check if the pair already exists
foreach (var p in mCollisionPairs)
{
if (
(Object.ReferenceEquals(A, p.BodyA) && Object.ReferenceEquals(B, p.BodyB)) ||
(Object.ReferenceEquals(A, p.BodyB) && Object.ReferenceEquals(B, p.BodyA))
)
{
return;
}
}
mCollisionPairs.Add(pair);
}
//AABB Box to AABB box collision
//Creates a collision pair with appropriate info
public CollisionPair Collision(Box b)
{
Box a = this;
Vector2 collisionNormal = Vector2.Zero;
float collisionDepth = 1000;
Vector2[] normalsAABB = new Vector2[4]
{
new Vector2(1, 0),
new Vector2(-1, 0),
new Vector2(0, 1),
new Vector2(0, -1)
};
float[] distances = new float[4]
{
b.Max().X - a.Min().X,
a.Max().X - b.Min().X,
b.Max().Y - a.Min().Y,
a.Max().Y - b.Min().Y
};
for (int i = 0; i < 4; i++)
{
if (i == 0 || (distances[i] < collisionDepth))
{
collisionNormal = normalsAABB[i];
collisionDepth = distances[i];
}
}
CollisionPair p = new CollisionPair();
p.BodyA = a.parent;
p.BodyB = b.parent;
p.CollisionDepth = collisionDepth;
p.ContactNormal = collisionNormal;
p.ContactPoint = (a.Center() + (collisionNormal * (1 / collisionDepth)));
return(p);
}
public void Resolve(CollisionPair data)
{
Object a = data.BodyA;
Object b = data.BodyB;
if (a.Name == "Button" || b.Name == "Button")
{
return;
}
if (a == null || b == null)
{
return;
}
//perform the displacement using the collision depth and normal
#region Displacement
//data.ContactNormal.Normalize();
Vector2 displacement = (data.ContactNormal * data.CollisionDepth);
if (!a.IsStatic && b.IsStatic && !b.IsParticle)
{
a.Position += displacement * 1f;
}
else if (!a.IsStatic && !b.IsParticle)
{
a.Position += displacement / 1f;
}
if (!b.IsStatic && a.IsStatic && !a.IsParticle)
{
b.Position -= displacement * 1f;
}
else if (!b.IsStatic && !a.IsParticle)
{
b.Position -= displacement / 1f;
}
(a.HitBox).UpdatePos(a.Position);
(b.HitBox).UpdatePos(b.Position);
#endregion
//perform the impulse response
#region Impulse Collision
Vector2 relativeVelocity = b.RigidBody.LinearVelocity - a.RigidBody.LinearVelocity;
float rVN = Vector2.Dot(relativeVelocity, data.ContactNormal);
float elasticity = (a.Bounciness + b.Bounciness) / 2;
float mass;
if (a.IsStatic || b.IsParticle)
{
mass = b.RigidBody.InvMass;
}
else if (b.IsStatic || a.IsParticle)
{
mass = a.RigidBody.InvMass;
}
else
{
mass = (a.RigidBody.InvMass + b.RigidBody.InvMass);
}
float impulse = (-1 * (1 + elasticity) * rVN) / mass;
if (!a.IsStatic && !b.IsParticle)
{
data.BodyA.RigidBody.LinearVelocity -= (data.ContactNormal * (impulse / a.RigidBody.Mass));
}
if (!b.IsStatic && !a.IsParticle)
{
data.BodyB.RigidBody.LinearVelocity += (data.ContactNormal * (impulse / b.RigidBody.Mass));
}
//Console.WriteLine("Friction impulse" + frictionImpulse + " Linear velocity" + a.RigidBody.LinearVelocity);
#endregion
relativeVelocity = b.RigidBody.LinearVelocity - a.RigidBody.LinearVelocity;
rVN = Vector2.Dot(relativeVelocity, data.ContactNormal);
//perform the friction response
#region Friction Collision
//Referenced - https://gamedevelopment.tutsplus.com/tutorials/how-to-create-a-custom-2d-physics-engine-friction-scene-and-jump-table--gamedev-7756
float frictionImpulse;
float dynamicFriction;
Vector2 tangent = relativeVelocity - (rVN * data.ContactNormal);
if (tangent != Vector2.Zero)
{
tangent.Normalize();
}
else
{
tangent = Vector2.Zero;
}
float magnitude = -Vector2.Dot(relativeVelocity, tangent);
magnitude = magnitude / (a.RigidBody.InvMass + b.RigidBody.InvMass);
float totalFriction = MathHelper.Clamp((float)Math.Sqrt(a.StaticFriction * a.StaticFriction + b.StaticFriction * b.StaticFriction), 0, 1f);
float impulse2 = (-1 * (1 + elasticity) * Vector2.Dot(relativeVelocity, tangent));
if (Math.Abs(magnitude) < impulse2 * totalFriction)
{
frictionImpulse = (magnitude);
}
else
{
dynamicFriction = MathHelper.Clamp((float)Math.Sqrt(a.DynamicFriction * a.DynamicFriction + b.DynamicFriction * b.DynamicFriction), 0f, 1f);
frictionImpulse = (dynamicFriction);
}
if (!a.IsStatic && !b.IsParticle)
{
data.BodyA.RigidBody.LinearVelocity -= tangent / (1 - frictionImpulse) * impulse2 / a.RigidBody.Mass;
}
if (!b.IsStatic && !a.IsParticle)
{
data.BodyB.RigidBody.LinearVelocity += tangent / (1 - frictionImpulse) * impulse2 / b.RigidBody.Mass;
}
#endregion
}