using System;
using System.Collections.Generic;
using FarseerPhysics.Collision;
using FarseerPhysics.Dynamics;
using Microsoft.Xna.Framework;
namespace FarseerPhysics.Common.PhysicsLogic
{
///
/// Creates a simple explosion that ignores other bodies hiding behind static bodies.
///
public sealed class SimpleExplosion : PhysicsLogic
{
public SimpleExplosion(World world)
: base(world, PhysicsLogicType.Explosion)
{
Power = 1; //linear
}
///
/// This is the power used in the power function. A value of 1 means the force
/// applied to bodies in the explosion is linear. A value of 2 means it is exponential.
///
public float Power { get; set; }
///
/// Activate the explosion at the specified position.
///
/// The position (center) of the explosion.
/// The radius of the explosion.
/// The force applied
/// A maximum amount of force. When force gets over this value, it will be equal to maxForce
/// A list of bodies and the amount of force that was applied to them.
public Dictionary Activate(Vector2 pos, float radius, float force, float maxForce = float.MaxValue)
{
HashSet affectedBodies = new HashSet();
AABB aabb;
aabb.LowerBound = pos - new Vector2(radius);
aabb.UpperBound = pos + new Vector2(radius);
// Query the world for bodies within the radius.
World.QueryAABB(fixture =>
{
if (Vector2.Distance(fixture.Body.Position, pos) <= radius)
{
if (!affectedBodies.Contains(fixture.Body))
affectedBodies.Add(fixture.Body);
}
return true;
}, ref aabb);
return ApplyImpulse(pos, radius, force, maxForce, affectedBodies);
}
private Dictionary ApplyImpulse(Vector2 pos, float radius, float force, float maxForce, HashSet overlappingBodies)
{
Dictionary forces = new Dictionary(overlappingBodies.Count);
foreach (Body overlappingBody in overlappingBodies)
{
if (IsActiveOn(overlappingBody))
{
float distance = Vector2.Distance(pos, overlappingBody.Position);
float forcePercent = GetPercent(distance, radius);
Vector2 forceVector = pos - overlappingBody.Position;
forceVector *= 1f / (float)Math.Sqrt(forceVector.X * forceVector.X + forceVector.Y * forceVector.Y);
forceVector *= MathHelper.Min(force * forcePercent, maxForce);
forceVector *= -1;
overlappingBody.ApplyLinearImpulse(forceVector);
forces.Add(overlappingBody, forceVector);
}
}
return forces;
}
private float GetPercent(float distance, float radius)
{
//(1-(distance/radius))^power-1
float percent = (float)Math.Pow(1 - ((distance - radius) / radius), Power) - 1;
if (float.IsNaN(percent))
return 0f;
return MathHelper.Clamp(percent, 0f, 1f);
}
}
}