public static CompoundCollidable CreatePartialCompoundCollidable(CompoundShape shape, IList<int> childIndices)
{
if (childIndices.Count == 0)
throw new Exception("Cannot create a compound from zero shapes.");
CompoundCollidable compound = new CompoundCollidable();
Vector3 center = new Vector3();
float totalWeight = 0;
for (int i = 0; i < childIndices.Count; i++)
{
//Create and add the child object itself.
var entry = shape.shapes[childIndices[i]];
compound.children.Add(new CompoundChild(shape, entry.Shape.GetCollidableInstance(), childIndices[i]));
//Grab its entry to compute the center of mass of this subset.
Vector3 toAdd;
Vector3.Multiply(ref entry.LocalTransform.Position, entry.Weight, out toAdd);
Vector3.Add(ref center, ref toAdd, out center);
totalWeight += entry.Weight;
}
if (totalWeight <= 0)
{
throw new Exception("Compound has zero total weight; invalid configuration.");
}
Vector3.Divide(ref center, totalWeight, out center);
//Our subset of the compound is not necessarily aligned with the shape's origin.
//By default, an object will rotate around the center of the collision shape.
//We can't modify the shape data itself since it could be shared, which leaves
//modifying the local position of the collidable.
//We have the subset position in shape space, so pull the collidable back into alignment
//with the origin.
//This approach matches the rest of the CompoundHelper's treatment of subsets.
compound.LocalPosition = -center;
//Recompute the hierarchy for the compound.
compound.hierarchy.Tree.Reconstruct(compound.children);
compound.Shape = shape;
return compound;
}
