using System;
using System.Collections.Generic;
using System.Linq;
using FarseerPhysics.Collision;
using FarseerPhysics.Collision.Shapes;
using FarseerPhysics.Dynamics;
using Microsoft.Xna.Framework;
namespace FarseerPhysics.Common.PhysicsLogic
{
internal struct ShapeData
{
public Body Body;
public float Max;
public float Min; // absolute angles
}
/// <summary>
/// This is a comprarer used for
/// detecting angle difference between rays
/// </summary>
internal class RayDataComparer : IComparer<float>
{
#region IComparer<float> Members
int IComparer<float>.Compare(float a, float b)
{
float diff = (a - b);
if (diff > 0)
return 1;
if (diff < 0)
return -1;
return 0;
}
#endregion
}
/* Methodology:
* Force applied at a ray is inversely proportional to the square of distance from source
* AABB is used to query for shapes that may be affected
* For each RIGID BODY (not shape -- this is an optimization) that is matched, loop through its vertices to determine
* the extreme points -- if there is structure that contains outlining polygon, use that as an additional optimization
* Evenly cast a number of rays against the shape - number roughly proportional to the arc coverage
* -Something like every 3 degrees should do the trick although this can be altered depending on the distance (if really close don't need such a high density of rays)
* -There should be a minimum number of rays (3-5?) applied to each body so that small bodies far away are still accurately modeled
* -Be sure to have the forces of each ray be proportional to the average arc length covered by each.
* For each ray that actually intersects with the shape (non intersections indicate something blocking the path of explosion):
* > apply the appropriate force dotted with the negative of the collision normal at the collision point
* > optionally apply linear interpolation between aforementioned Normal force and the original explosion force in the direction of ray to simulate "surface friction" of sorts
*/
/// <summary>
/// This is an explosive... it explodes.
/// </summary>
/// <remarks>
/// Original Code by Steven Lu - see http://www.box2d.org/forum/viewtopic.php?f=3&t=1688
/// Ported to Farseer 3.0 by Nicol�s Hormaz�bal
/// </remarks>
public sealed class Explosion : PhysicsLogic
{
/// <summary>
/// Two degrees: maximum angle from edges to first ray tested
/// </summary>
private const float MaxEdgeOffset = MathHelper.Pi / 90;
/// <summary>
/// Ratio of arc length to angle from edges to first ray tested.
/// Defaults to 1/40.
/// </summary>
public float EdgeRatio = 1.0f / 40.0f;
/// <summary>
/// Ignore Explosion if it happens inside a shape.
/// Default value is false.
/// </summary>
public bool IgnoreWhenInsideShape = false;
/// <summary>
/// Max angle between rays (used when segment is large).
/// Defaults to 15 degrees
/// </summary>
public float MaxAngle = MathHelper.Pi / 15;
/// <summary>
/// Maximum number of shapes involved in the explosion.
/// Defaults to 100
/// </summary>
public int MaxShapes = 100;
/// <summary>
/// How many rays per shape/body/segment.
/// Defaults to 5
/// </summary>
public int MinRays = 5;
private List<ShapeData> _data = new List<ShapeData>();
private Dictionary<Fixture, List<Vector2>> _exploded;
private RayDataComparer _rdc;
public Explosion(World world)
: base(world, PhysicsLogicType.Explosion)
{
_exploded = new Dictionary<Fixture, List<Vector2>>();
_rdc = new RayDataComparer();
_data = new List<ShapeData>();
}
/// <summary>
/// This makes the explosive explode
/// </summary>
/// <param name="pos">
/// The position where the explosion happens
/// </param>
/// <param name="radius">
/// The explosion radius
/// </param>
/// <param name="maxForce">
/// The explosion force at the explosion point
/// (then is inversely proportional to the square of the distance)
/// </param>
/// <returns>
/// A dictionnary containing all the "exploded" fixtures
/// with a list of the applied impulses
/// </returns>
public Dictionary<Fixture, List<Vector2>> Activate(Vector2 pos, float radius, float maxForce)
{
_exploded.Clear();
AABB aabb;
aabb.LowerBound = pos + new Vector2(-radius, -radius);
aabb.UpperBound = pos + new Vector2(radius, radius);
Fixture[] shapes = new Fixture[MaxShapes];
// More than 5 shapes in an explosion could be possible, but still strange.
Fixture[] containedShapes = new Fixture[5];
bool exit = false;
int shapeCount = 0;
int containedShapeCount = 0;
// Query the world for overlapping shapes.
World.QueryAABB(
fixture =>
{
if (fixture.TestPoint(ref pos))
{
if (IgnoreWhenInsideShape)
exit = true;
else
containedShapes[containedShapeCount++] = fixture;
}
else
{
shapes[shapeCount++] = fixture;
}
// Continue the query.
return true;
}, ref aabb);
if (exit)
{
return _exploded;
}
// Per shape max/min angles for now.
float[] vals = new float[shapeCount * 2];
int valIndex = 0;
for (int i = 0; i < shapeCount; ++i)
{
PolygonShape ps;
CircleShape cs = shapes[i].Shape as CircleShape;
if (cs != null)
{
// We create a "diamond" approximation of the circle
Vertices v = new Vertices();
Vector2 vec = Vector2.Zero + new Vector2(cs.Radius, 0);
v.Add(vec);
vec = Vector2.Zero + new Vector2(0, cs.Radius);
v.Add(vec);
vec = Vector2.Zero + new Vector2(-cs.Radius, cs.Radius);
v.Add(vec);
vec = Vector2.Zero + new Vector2(0, -cs.Radius);
v.Add(vec);
ps = new PolygonShape(v, 0);
}
else
ps = shapes[i].Shape as PolygonShape;
if ((shapes[i].Body.BodyType == BodyType.Dynamic) && ps != null)
{
Vector2 toCentroid = shapes[i].Body.GetWorldPoint(ps.MassData.Centroid) - pos;
float angleToCentroid = (float)Math.Atan2(toCentroid.Y, toCentroid.X);
float min = float.MaxValue;
float max = float.MinValue;
float minAbsolute = 0.0f;
float maxAbsolute = 0.0f;
for (int j = 0; j < (ps.Vertices.Count()); ++j)
{
Vector2 toVertex = (shapes[i].Body.GetWorldPoint(ps.Vertices[j]) - pos);
float newAngle = (float)Math.Atan2(toVertex.Y, toVertex.X);
float diff = (newAngle - angleToCentroid);
diff = (diff - MathHelper.Pi) % (2 * MathHelper.Pi);
// the minus pi is important. It means cutoff for going other direction is at 180 deg where it needs to be
if (diff < 0.0f)
diff += 2 * MathHelper.Pi; // correction for not handling negs
diff -= MathHelper.Pi;
if (Math.Abs(diff) > MathHelper.Pi)
throw new ArgumentException("OMG!");
// Something's wrong, point not in shape but exists angle diff > 180
if (diff > max)
{
max = diff;
maxAbsolute = newAngle;
}
if (diff < min)
{
min = diff;
minAbsolute = newAngle;
}
}
vals[valIndex] = minAbsolute;
++valIndex;
vals[valIndex] = maxAbsolute;
++valIndex;
}
}
Array.Sort(vals, 0, valIndex, _rdc);
_data.Clear();
bool rayMissed = true;
for (int i = 0; i < valIndex; ++i)
{
Fixture shape = null;
float midpt;
int iplus = (i == valIndex - 1 ? 0 : i + 1);
if (vals[i] == vals[iplus])
continue;
if (i == valIndex - 1)
{
// the single edgecase
midpt = (vals[0] + MathHelper.Pi * 2 + vals[i]);
}
else
{
midpt = (vals[i + 1] + vals[i]);
}
midpt = midpt / 2;
Vector2 p1 = pos;
Vector2 p2 = radius * new Vector2((float)Math.Cos(midpt),
(float)Math.Sin(midpt)) + pos;
// RaycastOne
bool hitClosest = false;
World.RayCast((f, p, n, fr) =>
{
Body body = f.Body;
if (!IsActiveOn(body))
return 0;
if (body.UserData != null)
{
int index = (int)body.UserData;
if (index == 0)
{
// filter
return -1.0f;
}
}
hitClosest = true;
shape = f;
return fr;
}, p1, p2);
//draws radius points
if ((hitClosest) && (shape.Body.BodyType == BodyType.Dynamic))
{
if ((_data.Count() > 0) && (_data.Last().Body == shape.Body) && (!rayMissed))
{
int laPos = _data.Count - 1;
ShapeData la = _data[laPos];
la.Max = vals[iplus];
_data[laPos] = la;
}
else
{
// make new
ShapeData d;
d.Body = shape.Body;
d.Min = vals[i];
d.Max = vals[iplus];
_data.Add(d);
}
if ((_data.Count() > 1)
&& (i == valIndex - 1)
&& (_data.Last().Body == _data.First().Body)
&& (_data.Last().Max == _data.First().Min))
{
ShapeData fi = _data[0];
fi.Min = _data.Last().Min;
_data.RemoveAt(_data.Count() - 1);
_data[0] = fi;
while (_data.First().Min >= _data.First().Max)
{
fi.Min -= MathHelper.Pi * 2;
_data[0] = fi;
}
}
int lastPos = _data.Count - 1;
ShapeData last = _data[lastPos];
while ((_data.Count() > 0)
&& (_data.Last().Min >= _data.Last().Max)) // just making sure min<max
{
last.Min = _data.Last().Min - 2 * MathHelper.Pi;
_data[lastPos] = last;
}
rayMissed = false;
}
else
{
rayMissed = true; // raycast did not find a shape
}
}
for (int i = 0; i < _data.Count(); ++i)
{
if (!IsActiveOn(_data[i].Body))
continue;
float arclen = _data[i].Max - _data[i].Min;
float first = MathHelper.Min(MaxEdgeOffset, EdgeRatio * arclen);
int insertedRays = (int)Math.Ceiling(((arclen - 2.0f * first) - (MinRays - 1) * MaxAngle) / MaxAngle);
if (insertedRays < 0)
insertedRays = 0;
float offset = (arclen - first * 2.0f) / ((float)MinRays + insertedRays - 1);
//Note: This loop can go into infinite as it operates on floats.
//Added FloatEquals with a large epsilon.
for (float j = _data[i].Min + first;
j < _data[i].Max || MathUtils.FloatEquals(j, _data[i].Max, 0.0001f);
j += offset)
{
Vector2 p1 = pos;
Vector2 p2 = pos + radius * new Vector2((float)Math.Cos(j), (float)Math.Sin(j));
Vector2 hitpoint = Vector2.Zero;
float minlambda = float.MaxValue;
List<Fixture> fl = _data[i].Body.FixtureList;
for (int x = 0; x < fl.Count; x++)
{
Fixture f = fl[x];
RayCastInput ri;
ri.Point1 = p1;
ri.Point2 = p2;
ri.MaxFraction = 50f;
RayCastOutput ro;
if (f.RayCast(out ro, ref ri, 0))
{
if (minlambda > ro.Fraction)
{
minlambda = ro.Fraction;
hitpoint = ro.Fraction * p2 + (1 - ro.Fraction) * p1;
}
}
// the force that is to be applied for this particular ray.
// offset is angular coverage. lambda*length of segment is distance.
float impulse = (arclen / (MinRays + insertedRays)) * maxForce * 180.0f / MathHelper.Pi *
(1.0f - Math.Min(1.0f, minlambda));
// We Apply the impulse!!!
Vector2 vectImp = Vector2.Dot(impulse * new Vector2((float)Math.Cos(j),
(float)Math.Sin(j)), -ro.Normal) *
new Vector2((float)Math.Cos(j),
(float)Math.Sin(j));
_data[i].Body.ApplyLinearImpulse(ref vectImp, ref hitpoint);
// We gather the fixtures for returning them
Vector2 val = Vector2.Zero;
List<Vector2> vectorList;
if (_exploded.TryGetValue(f, out vectorList))
{
val.X += Math.Abs(vectImp.X);
val.Y += Math.Abs(vectImp.Y);
vectorList.Add(val);
}
else
{
vectorList = new List<Vector2>();
val.X = Math.Abs(vectImp.X);
val.Y = Math.Abs(vectImp.Y);
vectorList.Add(val);
_exploded.Add(f, vectorList);
}
if (minlambda > 1.0f)
{
hitpoint = p2;
}
}
}
}
// We check contained shapes
for (int i = 0; i < containedShapeCount; ++i)
{
Fixture fix = containedShapes[i];
if (!IsActiveOn(fix.Body))
continue;
float impulse = MinRays * maxForce * 180.0f / MathHelper.Pi;
Vector2 hitPoint;
CircleShape circShape = fix.Shape as CircleShape;
if (circShape != null)
{
hitPoint = fix.Body.GetWorldPoint(circShape.Position);
}
else
{
PolygonShape shape = fix.Shape as PolygonShape;
hitPoint = fix.Body.GetWorldPoint(shape.MassData.Centroid);
}
Vector2 vectImp = impulse * (hitPoint - pos);
List<Vector2> vectorList = new List<Vector2>();
vectorList.Add(vectImp);
fix.Body.ApplyLinearImpulse(ref vectImp, ref hitPoint);
if (!_exploded.ContainsKey(fix))
_exploded.Add(fix, vectorList);
}
return _exploded;
}
}
}
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