public Spring(PointMass pointmass_a, PointMass pointmass_b, float k, float damping, float length)
{
this.pointmass_a = pointmass_a;
this.pointmass_b = pointmass_b;
this.d = length;
this.k = k;
this.damping = damping;
}
public void Clear()
{
body_a = body_b = null;
pointmass_a = pointmass_b = pointmass_c = new PointMass();
edge_distance = 0f;
point = Vector2.Zero;
normal = Vector2.Zero;
penetration = 0f;
}
public Body(Shape shape, float mass)
{
this.base_shape = shape;
this.curr_shape = shape.Clone();
this.count = shape.count;
this.pointmass_list = new PointMass[shape.count];
for (int i = 0; i < shape.count; i++)
pointmass_list[i] = new PointMass(shape.points[i], mass);
this.bitmaskx = new Bitmask();
this.bitmasky = new Bitmask();
}
public Chain(PointMass from, PointMass to, int count, float k, float damping, float mass)
{
this.damping = 0.99f;
this.pointmass_list = new List<PointMass>();
this.spring_list = new List<Spring>();
float length = Vector2.Distance(from.position, to.position) / count;
Vector2 direction = to.position - from.position;
direction.Normalize();
for (int i = 0; i < count+1; i++)
pointmass_list.Add(new PointMass(new Vector2(from.position.X + direction.X * length * i, from.position.Y + direction.Y * length* i), mass));
pointmass_list[0] = from;
pointmass_list[count] = to;
for (int i = 1; i < count+1; i++)
spring_list.Add(new Spring(pointmass_list[i - 1], pointmass_list[i - 0], k, damping));
}
public Spring(PointMass pointmass_a, PointMass pointmass_b, float k, float damping)
: this(pointmass_a, pointmass_b, k, damping, 0)
{
Reset();
}
public void Update(double elapsed)
{
if (!initialized)
{
Initialize();
}
penetration_count = 0;
collision_list.Clear();
for (int i = 0; i < body_list.Count; i++)
{
body_list[i].Update(elapsed);
UpdateBitmask(body_list[i]);
}
// update chains
for (int i = 0; i < chain_list.Count; i++)
{
chain_list[i].Update(elapsed);
}
// now check for collision.
// inter-body collision!
for (int i = 0; i < body_list.Count; i++)
{
for (int j = i + 1; j < body_list.Count; j++)
{
if (body_list[i].is_static && body_list[j].is_static)
{
continue;
}
// grid-based early out.
if (((body_list[i].bitmaskx.mask & body_list[j].bitmaskx.mask) == 0) &&
((body_list[i].bitmasky.mask & body_list[j].bitmasky.mask) == 0))
{
continue;
}
// broad-phase collision via AABB.
if (!(body_list[i].aabb).Intersects(ref (body_list[j].aabb)))
{
continue;
}
if (on_aabb_collision != null)
{
this.on_aabb_collision(body_list[i], body_list[j]);
}
// okay, the AABB's of these 2 are intersecting. now check for collision of A against B.
collision_list.AddRange(Collision.Intersects(body_list[j], body_list[i]));
collision_list.AddRange(Collision.Intersects(body_list[i], body_list[j]));
}
}
// now handle all collisions found during the update at once.
// handle all collisions!
for (int i = 0; i < collision_list.Count; i++)
{
CollisionInfo info = collision_list[i];
PointMass A = info.pointmass_a;
PointMass B1 = info.pointmass_b;
PointMass B2 = info.pointmass_c;
if (on_collision != null)
{
this.on_collision(info.body_a, info.body_b, info);
}
// velocity changes as a result of collision.
Vector2 bVel = new Vector2();
bVel.X = (B1.velocity.X + B2.velocity.X) * 0.5f;
bVel.Y = (B1.velocity.Y + B2.velocity.Y) * 0.5f;
Vector2 relVel = new Vector2();
relVel.X = A.velocity.X - bVel.X;
relVel.Y = A.velocity.Y - bVel.Y;
float relDot;
Vector2.Dot(ref relVel, ref info.normal, out relDot);
if (on_penetration != null)
{
if (info.penetration > penetration_threshold)
{
this.on_penetration(info.body_a, info.body_b);
}
}
if (info.penetration > 0.3f)
{
penetration_count++;
continue;
}
float b1inf = 1.0f - info.edge_distance;
float b2inf = info.edge_distance;
float b2MassSum = ((float.IsPositiveInfinity(B1.mass)) || (float.IsPositiveInfinity(B2.mass))) ? float.PositiveInfinity : (B1.mass + B2.mass);
float massSum = A.mass + b2MassSum;
float Amove;
float Bmove;
if (float.IsPositiveInfinity(A.mass))
{
Amove = 0f;
Bmove = (info.penetration) + 0.001f;
}
else if (float.IsPositiveInfinity(b2MassSum))
{
Amove = (info.penetration) + 0.001f;
Bmove = 0f;
}
else
{
Amove = (info.penetration * (b2MassSum / massSum));
Bmove = (info.penetration * (A.mass / massSum));
}
float B1move = Bmove * b1inf;
float B2move = Bmove * b2inf;
float AinvMass = (float.IsPositiveInfinity(A.mass)) ? 0f : 1f / A.mass;
float BinvMass = (float.IsPositiveInfinity(b2MassSum)) ? 0f : 1f / b2MassSum;
float jDenom = AinvMass + BinvMass;
Vector2 numV = new Vector2();
float elas = elasticity;
numV.X = relVel.X * elas;
numV.Y = relVel.Y * elas;
float jNumerator;
Vector2.Dot(ref numV, ref info.normal, out jNumerator);
jNumerator = -jNumerator;
float j = jNumerator / jDenom;
if (!float.IsPositiveInfinity(A.mass))
{
A.position.X += info.normal.X * Amove;
A.position.Y += info.normal.Y * Amove;
}
if (!float.IsPositiveInfinity(B1.mass))
{
B1.position.X -= info.normal.X * B1move;
B1.position.Y -= info.normal.Y * B1move;
}
if (!float.IsPositiveInfinity(B2.mass))
{
B2.position.X -= info.normal.X * B2move;
B2.position.Y -= info.normal.Y * B2move;
}
Vector2 tangent = new Vector2();
VectorHelper.Perpendicular(ref info.normal, ref tangent);
float fNumerator;
Vector2.Dot(ref relVel, ref tangent, out fNumerator);
fNumerator *= friction;
float f = fNumerator / jDenom;
// adjust velocity if relative velocity is moving toward each other.
if (relDot <= 0.0001f)
{
if (!float.IsPositiveInfinity(A.mass))
{
A.velocity.X += (info.normal.X * (j / A.mass)) - (tangent.X * (f / A.mass));
A.velocity.Y += (info.normal.Y * (j / A.mass)) - (tangent.Y * (f / A.mass));
}
if (!float.IsPositiveInfinity(b2MassSum))
{
B1.velocity.X -= (info.normal.X * (j / b2MassSum) * b1inf) - (tangent.X * (f / b2MassSum) * b1inf);
B1.velocity.Y -= (info.normal.Y * (j / b2MassSum) * b1inf) - (tangent.Y * (f / b2MassSum) * b1inf);
}
if (!float.IsPositiveInfinity(b2MassSum))
{
B2.velocity.X -= (info.normal.X * (j / b2MassSum) * b2inf) - (tangent.X * (f / b2MassSum) * b2inf);
B2.velocity.Y -= (info.normal.Y * (j / b2MassSum) * b2inf) - (tangent.Y * (f / b2MassSum) * b2inf);
}
//info.body_a.UpdateBodyPositionVelocityForce(elapsed);
// info.body_b.UpdateBodyPositionVelocityForce(elapsed);
}
}
for (int i = 0; i < body_list.Count; i++)
{
body_list[i].UpdateBodyPositionVelocityForce(elapsed);
}
}
