/// <summary>
/// Verifies if a specified entity can be used in the game.
/// </summary>
/// <param name="camera">Current game camera.</param>
/// <param name="entity">The entity to be checked.</param>
/// <returns>True if the entity can be used in the game, otherwise False.</returns>
bool IsValidEntity(CameraInfo camera, GamePlayEntity entity)
{
const int maxDistanceSqr = 1000000;
// Check the entity distance from the screen.
var distance = entity.Position - camera.Position;
if (distance.LengthSquared() > maxDistanceSqr)
{
RemoveEntity(entity);
return(false);
}
return(true);
}
protected GameEntityBehavior(GamePlayEntity entity)
: base(entity)
{
}
public EntityEventArgs(GamePlayEntity entity, GameTime gameTime, GamePlay level)
: base(gameTime, level)
{
Entity = entity;
}
/// <summary>
/// Removes an entity from the game.
/// </summary>
/// <param name="entity">Entity to be removed.</param>
public void RemoveEntity(GamePlayEntity entity)
{
_entities.Remove(entity);
}
/// <summary>
/// Adds an entity to the game.
/// </summary>
/// <param name="entity">Entity to be added.</param>
public void AddEntity(GamePlayEntity entity)
{
_entities.Add(entity);
}
/// <summary>
/// Transfers energy from one entity to another.
/// </summary>
/// <param name="a">Entity A</param>
/// <param name="b">Entity B</param>
/// <param name="gameTime">Current game time.</param>
void ResolveCollision(GamePlayEntity a, GamePlayEntity b, GameTime gameTime)
{
var aDirection = Vector2.Normalize(a.Momentum);
var bDirection = Vector2.Normalize(b.Momentum);
var normal = a.Position - b.Position;
var dist = normal;
normal.Normalize();
// Calculate relative velocity
Vector2 rv = b.Momentum - a.Momentum;
// Calculate relative velocity in terms of the normal direction
float velAlongNormal = Vector2.Dot(rv, normal);
// Do not resolve if velocities are separating
if (velAlongNormal < 0)
{
return;
}
// Calculate restitution (bounciness)
float e = MathHelper.Min(a.Restitution, b.Restitution);
// Calculate impulse scalar
float j = -(1 + e) * velAlongNormal;
j /= 1 / a.Mass + 1 / b.Mass;
#region Apply impulse
Vector2 impulse = j * normal;
a.ApplyForce(-impulse, instantaneous: true);
b.ApplyForce(impulse, instantaneous: true);
#endregion
#region Apply Rotation
if (velAlongNormal > 2)
{
var collisionPlane = new Vector2(-normal.Y, normal.X);
if (a.Momentum != Vector2.Zero)
{
var angle = Vector2.Dot(aDirection, collisionPlane);
if (!b.RotateToMomentum)
{
b.ApplyRotation(angle * -j * a.Mass / b.Mass, isAcceleration: false, instantaneous: true);
}
}
if (b.Momentum != Vector2.Zero)
{
var angle = -Vector2.Dot(bDirection, collisionPlane);
if (!a.RotateToMomentum)
{
a.ApplyRotation(angle * -j * b.Mass / a.Mass, isAcceleration: false, instantaneous: true);
}
}
}
#endregion
#region Stops overlapping
var distLength = dist.Length();
if (distLength < 16)
{
a.Position += normal * (16 - distLength);
}
#endregion
a.RaiseCollision(b, gameTime, this);
b.RaiseCollision(a, gameTime, this);
}
public TouchControlBehavior(GamePlayEntity parent)
: base(parent)
{
}
public EntityCollisionEventArgs(GamePlayEntity entity, GamePlayEntity collidedWith, GameTime gameTime, GamePlay level)
: base(entity, gameTime, level)
{
CollidedWith = collidedWith;
}