/// <summary>
/// This is a high-level function to cuts fixtures inside the given world, using the start and end points.
/// Note: We don't support cutting when the start or end is inside a shape.
/// </summary>
/// <param name="world">The world.</param>
/// <param name="start">The startpoint.</param>
/// <param name="end">The endpoint.</param>
/// <param name="thickness">The thickness of the cut</param>
public static Vector2 Cut(World world, Vector2 start, Vector2 end, float thickness, Category collisionCategories = Category.None)
{
// The left side of the cut will remain part of the existing body;
// the right side will be made into a new body
List<Fixture> fixtures = new List<Fixture>();
List<Vector2> entryPoints = new List<Vector2>();
List<Vector2> exitPoints = new List<Vector2>();
List<RayCastResult> results = new List<RayCastResult>();
//float blockingFraction = float.MaxValue;
Vector2 stoppingPoint = end;
//We don't support cutting when the start or end is inside a shape.
//if (world.TestPoint(start) != null || world.TestPoint(end) != null)
// return;
//Get the entry points
world.RayCast((f, p, n, fr) =>
{
RayCastResult r = new RayCastResult();
r.f = f;
r.p = p;
r.fr = fr;
results.Add(r);
return 1;
}, start, end);
results = results.OrderBy(p => p.fr).ToList();
foreach (RayCastResult r in results)
{
if ((r.f.CollisionCategories & collisionCategories) != Category.None)
{
stoppingPoint = r.p;
break;
}
if (!r.f.TestPoint(ref end))
{
if (world.FixtureCut != null)
world.FixtureCut(r.f);
fixtures.Add(r.f);
entryPoints.Add(r.p);
}
}
//Reverse the ray to get the exitpoints
world.RayCast((f, p, n, fr) =>
{
if (fixtures.Contains(f))
{
exitPoints.Add(p);
}
return 1;
}, end, start);
Debug.Assert(entryPoints.Count == exitPoints.Count && entryPoints.Count == fixtures.Count);
//Fixture containsEnd = world.TestPoint(end);
//if (containsEnd != null)
//{
// entryPoints.RemoveAt(0);
// fixtures.Remove(containsEnd);
//}
//Fixture containsStart = world.TestPoint(start);
//if (containsStart != null)
//{
// exitPoints.RemoveAt(exitPoints.Count - 1);
// fixtures.Remove(containsStart);
//}
//We only have a single point. We need at least 2
if (entryPoints.Count + exitPoints.Count < 2)
return stoppingPoint;
var query =
(from fix in fixtures
select fix.Body).Distinct();
foreach (Body b in query)
{
if (b == null || b.BodyType == BodyType.Static)
continue;
ContactEdge edge = b.ContactList;
while (edge != null)
{
Contact c = edge.Contact;
edge = edge.Next;
world.ContactManager.Destroy(c);
}
List<Body> leftBodies = new List<Body>();
List<Body> rightBodies = new List<Body>();
//Body rightBody = new Body(world);
List<Joint> leftJoints = new List<Joint>();
List<Joint> rightJoints = new List<Joint>();
foreach (Joint j in b.JointList)
{
if (isLeft(start, end, j.WorldAnchorA))
leftJoints.Add(j);
else
rightJoints.Add(j);
}
//List<Fixture> leftList = new List<Fixture>();
//List<Fixture> rightList = new List<Fixture>();
Fixture[] bodyFixtures = new Fixture[b.FixtureList.Count];
b.FixtureList.CopyTo(bodyFixtures);
b.FixtureList.Clear();
//leftBodies.Add(b);
// For each fixture that was sliced through...
foreach (Fixture fix in (from f in bodyFixtures where fixtures.Contains(f) select f))
{
int i = fixtures.IndexOf(fix);
// split this in half and put the halves in the over/under lists
Vertices first;
Vertices second;
SplitShape(fix, entryPoints[i], exitPoints[i], thickness, out first, out second);
if (!SanityCheck(first) || !SanityCheck(second))
{
continue;
}
PolygonShape leftShape = new PolygonShape(first, fix.Shape.Density);
PolygonShape rightShape = new PolygonShape(second, fix.Shape.Density);
if (!b.FixtureList.Any())
{
if (leftShape.MassData.Area > rightShape.MassData.Area)
{
b.CreateFixture(leftShape, fix.UserData);
leftBodies.Add(b);
GlomFixture(world, b, rightBodies, rightShape, fix.UserData, rightJoints);
}
else
{
b.CreateFixture(rightShape, fix.UserData);
rightBodies.Add(b);
GlomFixture(world, b, leftBodies, leftShape, fix.UserData, leftJoints);
}
}
else
{
GlomFixture(world, b, leftBodies, leftShape, fix.UserData, leftJoints);
GlomFixture(world, b, rightBodies, rightShape, fix.UserData, rightJoints);
}
}
// for each fixture that was NOT sliced through...
foreach (Fixture fix in (from f in bodyFixtures where !fixtures.Contains(f) select f)) {
if (isLeft(start, end, fix))
{
GlomFixture(world, b, leftBodies, fix.Shape, fix.UserData, leftJoints);
}
else
{
GlomFixture(world, b, rightBodies, fix.Shape, fix.UserData, rightJoints);
//rightBody.CreateFixture(fix.Shape.Clone(), fix.UserData);
}
}
foreach (Body bod in leftBodies.Concat(rightBodies))
{
bod.ResetMassData();
bod.BodyType = BodyType.Dynamic;
bod.Rotation = b.Rotation;
bod.LinearVelocity = b.LinearVelocity;
bod.AngularVelocity = b.AngularVelocity;
bod.Position = b.Position;
}
//b.JointList = null;
//world.RemoveBody(b);
foreach (Fixture f in bodyFixtures)
{
b.DestroyFixture(f);
}
world.ProcessChanges();
}
return stoppingPoint;
}
