How to cut a mesh by plane in Unity3d

Question

I want to cut meshes by plane. try this code, but get only one of parts of cutting mesh.

Screenshot 1

Screenshot 2

public void SliceIt()
{
    Vector3[] vertices = mesh.vertices;

    Transform clone = clone = ((Transform)Instantiate(transform, transform.position + new Vector3(0, 0.25f, 0), transform.rotation));

    Mesh meshSlice  = clone.GetComponent<MeshFilter>().sharedMesh;
    Vector3[] verticesSlice = meshSlice.vertices;

    List<Vector3> verticesSlice2 = new List<Vector3>();

    Mesh cutplanemesh  = cutplane.GetComponent<MeshFilter>().sharedMesh;
    Vector3[] cutplanevertices = cutplanemesh.vertices;

    p1 = cutplane.TransformPoint(cutplanevertices[40]);
    p2 = cutplane.TransformPoint(cutplanevertices[20]);
    p3 = cutplane.TransformPoint(cutplanevertices[0]);
    var myplane = new Plane(p1, p2, p3);

    for (var i = 0; i < vertices.Length; i++)
    {
        var tmpverts = transform.TransformPoint(vertices[i]); // original object vertices

        if (myplane.GetSide(tmpverts))
        {
            vertices[i] = transform.InverseTransformPoint(new Vector3(tmpverts.x, tmpverts.y - (myplane.GetDistanceToPoint(tmpverts)), tmpverts.z));

            verticesSlice[i] = transform.InverseTransformPoint(new Vector3(tmpverts.x, tmpverts.y, tmpverts.z));
            var v = transform.InverseTransformPoint(new Vector3(tmpverts.x, tmpverts.y, tmpverts.z));
            verticesSlice2.Add(v);
        }
        else
        {
            var v = transform.InverseTransformPoint(new Vector3(tmpverts.x, tmpverts.y - (myplane.GetDistanceToPoint(tmpverts)), tmpverts.z));
            verticesSlice2.Add(v);
        }
    }

    mesh.vertices = verticesSlice;
    mesh.RecalculateBounds();

    meshSlice.vertices = verticesSlice2.ToArray();
    meshSlice.RecalculateBounds();

}

I got this code from here.

I also read this question, but I couldn't figure how to split triangles which belong to positive and negative sides of plane.

Answer 1

You can use already existing assets on asset store: https://www.assetstore.unity3d.com/#!/content/59618

It is not only cut a mesh, it also cut colliders, do some optimizations and it is extandable.