tri-mesh 0.6.1

//! See [Mesh](crate::mesh::Mesh).

use crate::mesh::*;
use crate::Error;

/// # Edit
impl Mesh {
    /// Moves the vertex to the specified position.
    pub fn set_vertex_position(&mut self, vertex_id: VertexID, value: Vec3) {
        self.connectivity_info.set_position(vertex_id, value);
    }

    /// Flip the given edge such that the edge after the flip is connected to the
    /// other pair of the four vertices connected to the two adjacent faces.
    ///
    /// ```text
    ///   /\          /|\
    ///  /  \        / | \
    /// /____\  --> /  |  \
    /// \    /      \  |  /
    ///  \  /        \ | /
    ///   \/          \|/
    /// ```
    ///
    /// # Error
    ///
    /// Returns an error if trying to flip an edge on the boundary or the flip will connect two vertices that are already connected by another edge.
    ///
    pub fn flip_edge(&mut self, halfedge_id: HalfEdgeID) -> Result<(), Error> {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        let face_id = walker
            .face_id()
            .ok_or(Error::ActionWillResultInInvalidMesh(format!(
                "Trying to flip edge on boundary"
            )))?;
        let next_id = walker.next_id().unwrap();
        let previous_id = walker.previous_id().unwrap();
        let v0 = walker.vertex_id().unwrap();
        walker.as_next();
        let v3 = walker.vertex_id().unwrap();
        walker.as_previous();

        walker.as_twin();
        let twin_id = walker.halfedge_id().unwrap();
        let twin_face_id = walker
            .face_id()
            .ok_or(Error::ActionWillResultInInvalidMesh(format!(
                "Trying to flip edge on boundary"
            )))?;
        let twin_next_id = walker.next_id().unwrap();
        let twin_previous_id = walker.previous_id().unwrap();
        let v1 = walker.vertex_id().unwrap();
        let v2 = walker.as_next().vertex_id().unwrap();

        if self.connecting_edge(v2, v3).is_some() {
            Err(Error::ActionWillResultInInvalidMesh ( format!("Trying to flip edge which will connect two vertices that are already connected by another edge")))?;
        }

        self.connectivity_info
            .set_face_halfedge(face_id, previous_id);
        self.connectivity_info
            .set_face_halfedge(twin_face_id, twin_previous_id);

        self.connectivity_info
            .set_vertex_halfedge(v0, Some(next_id));
        self.connectivity_info
            .set_vertex_halfedge(v1, Some(twin_next_id));

        self.connectivity_info
            .set_halfedge_next(halfedge_id, Some(previous_id));
        self.connectivity_info
            .set_halfedge_next(next_id, Some(twin_id));
        self.connectivity_info
            .set_halfedge_next(previous_id, Some(twin_next_id));
        self.connectivity_info
            .set_halfedge_next(twin_id, Some(twin_previous_id));
        self.connectivity_info
            .set_halfedge_next(twin_next_id, Some(halfedge_id));
        self.connectivity_info
            .set_halfedge_next(twin_previous_id, Some(next_id));

        self.connectivity_info.set_halfedge_vertex(halfedge_id, v3);
        self.connectivity_info.set_halfedge_vertex(twin_id, v2);

        self.connectivity_info
            .set_halfedge_face(next_id, Some(twin_face_id));
        self.connectivity_info
            .set_halfedge_face(twin_next_id, Some(face_id));

        Ok(())
    }

    /// Split the given edge into two.
    /// Returns the id of the new vertex positioned at the given position.
    pub fn split_edge(&mut self, halfedge_id: HalfEdgeID, position: Vec3) -> VertexID {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        if walker.face_id().is_none() {
            walker.as_twin();
        }
        let split_halfedge_id = walker.halfedge_id().unwrap();

        walker.as_twin();
        let twin_halfedge_id = walker.halfedge_id().unwrap();
        let twin_vertex_id = walker.vertex_id();
        let is_boundary = walker.face_id().is_none();

        let new_vertex_id = self.connectivity_info.new_vertex(position);
        self.split_one_face(split_halfedge_id, twin_halfedge_id, new_vertex_id);

        if !is_boundary {
            self.split_one_face(twin_halfedge_id, split_halfedge_id, new_vertex_id);
        } else {
            let new_halfedge_id = self
                .connectivity_info
                .new_halfedge(twin_vertex_id, None, None);
            self.connectivity_info
                .set_halfedge_twin(split_halfedge_id, new_halfedge_id);
            self.connectivity_info
                .set_halfedge_vertex(twin_halfedge_id, new_vertex_id);
        };

        new_vertex_id
    }

    /// Split the given face into three new faces.
    /// Returns the id of the new vertex positioned at the given position.
    pub fn split_face(&mut self, face_id: FaceID, position: Vec3) -> VertexID {
        let new_vertex_id = self.connectivity_info.new_vertex(position);

        let mut walker = self.walker_from_face(face_id);
        let halfedge_id1 = walker.halfedge_id().unwrap();
        let vertex_id1 = walker.vertex_id().unwrap();

        walker.as_next();
        let halfedge_id2 = walker.halfedge_id().unwrap();
        let vertex_id2 = walker.vertex_id().unwrap();

        walker.as_next();
        let halfedge_id3 = walker.halfedge_id().unwrap();
        let vertex_id3 = walker.vertex_id().unwrap();

        let face_id1 = self.connectivity_info.create_face_with_existing_halfedge(
            vertex_id1,
            vertex_id2,
            new_vertex_id,
            halfedge_id2,
        );
        let face_id2 = self.connectivity_info.create_face_with_existing_halfedge(
            vertex_id2,
            vertex_id3,
            new_vertex_id,
            halfedge_id3,
        );

        let new_halfedge_id2 = self.connectivity_info.new_halfedge(
            Some(vertex_id3),
            Some(halfedge_id1),
            Some(face_id),
        );
        let new_halfedge_id1 = self.connectivity_info.new_halfedge(
            Some(new_vertex_id),
            Some(new_halfedge_id2),
            Some(face_id),
        );
        self.connectivity_info
            .set_halfedge_next(halfedge_id1, Some(new_halfedge_id1));
        self.connectivity_info
            .set_face_halfedge(face_id, halfedge_id1);

        // Update twin information
        let mut new_halfedge_id = unsafe { HalfEdgeID::new(0) };
        for halfedge_id in self.face_halfedge_iter(face_id1) {
            let vid = self.walker_from_halfedge(halfedge_id).vertex_id().unwrap();
            if vid == vertex_id1 {
                self.connectivity_info
                    .set_halfedge_twin(new_halfedge_id1, halfedge_id);
            } else if vid == new_vertex_id {
                new_halfedge_id = halfedge_id;
            }
        }
        for halfedge_id in self.face_halfedge_iter(face_id2) {
            let vid = self.walker_from_halfedge(halfedge_id).vertex_id().unwrap();
            if vid == vertex_id2 {
                self.connectivity_info
                    .set_halfedge_twin(new_halfedge_id, halfedge_id);
            } else if vid == new_vertex_id {
                self.connectivity_info
                    .set_halfedge_twin(new_halfedge_id2, halfedge_id);
            }
        }
        new_vertex_id
    }

    fn split_one_face(
        &mut self,
        halfedge_id: HalfEdgeID,
        twin_halfedge_id: HalfEdgeID,
        new_vertex_id: VertexID,
    ) {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        let vertex_id1 = walker.vertex_id().unwrap();
        let old_face_id = walker.face_id().unwrap();

        walker.as_next();
        let halfedge_to_reuse_vertex = walker.vertex_id().unwrap();
        let halfedge_to_reuse = walker.halfedge_id().unwrap();
        let halfedge_to_reuse_next = walker.next_id().unwrap();

        // Create new face
        let new_face_id = self.connectivity_info.create_face_with_existing_halfedge(
            vertex_id1,
            halfedge_to_reuse_vertex,
            new_vertex_id,
            halfedge_to_reuse,
        );

        // Update old face
        let new_halfedge_id = self.connectivity_info.new_halfedge(
            Some(halfedge_to_reuse_vertex),
            Some(halfedge_to_reuse_next),
            Some(old_face_id),
        );
        self.connectivity_info
            .set_halfedge_vertex(halfedge_id, new_vertex_id);
        self.connectivity_info
            .set_halfedge_next(halfedge_id, Some(new_halfedge_id));
        self.connectivity_info
            .set_face_halfedge(old_face_id, halfedge_id);

        // Update twin information
        for halfedge_id in self.face_halfedge_iter(new_face_id) {
            let vid = self.walker_from_halfedge(halfedge_id).vertex_id().unwrap();
            if vid == vertex_id1 {
                self.connectivity_info
                    .set_halfedge_twin(twin_halfedge_id, halfedge_id);
            } else if vid == new_vertex_id {
                self.connectivity_info
                    .set_halfedge_twin(new_halfedge_id, halfedge_id);
            }
        }
    }

    ///
    /// Collapses the given edge. Consequently, the to adjacent faces are removed and
    /// the two adjacent vertices are merged into one vertex
    /// which position is the average of the original vertex positions.
    /// Returns the merged vertex.
    ///
    /// **Note:** This might make some faces degenerate or produce edges and vertices that are not connected.
    ///
    pub fn collapse_edge(&mut self, halfedge_id: HalfEdgeID) -> VertexID {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        let surviving_vertex_id = walker.vertex_id().unwrap();
        walker.as_twin();
        let dying_vertex_id = walker.vertex_id().unwrap();
        let new_position = 0.5
            * (self.vertex_position(surviving_vertex_id) + self.vertex_position(dying_vertex_id));

        // Update halfedges pointing to dying vertex
        for halfedge_id in self.vertex_halfedge_iter(dying_vertex_id) {
            self.connectivity_info.set_halfedge_vertex(
                self.walker_from_halfedge(halfedge_id).twin_id().unwrap(),
                surviving_vertex_id,
            );
        }

        // Remove first face + halfedges
        let mut he_id1 = walker.halfedge_id();
        if walker.face_id().is_some() {
            walker.as_previous();
            self.connectivity_info
                .set_vertex_halfedge(surviving_vertex_id, walker.twin_id());
            walker.as_next();
        } else {
            self.connectivity_info.remove_halfedge(he_id1.unwrap());
            he_id1 = None;
        }

        // Remove second face + halfedges
        walker.as_twin();
        let he_id2 = walker.halfedge_id().unwrap();
        if walker.face_id().is_some() {
            walker.as_previous();
            self.connectivity_info
                .set_vertex_halfedge(surviving_vertex_id, walker.twin_id());
            self.remove_one_face(he_id2);
        } else {
            self.connectivity_info.remove_halfedge(he_id2);
        }

        if let Some(he_id_to_remove) = he_id1 {
            self.remove_one_face(he_id_to_remove);
        }

        // Remove dying vertex
        self.connectivity_info.remove_vertex(dying_vertex_id);

        self.move_vertex_to(surviving_vertex_id, new_position);
        surviving_vertex_id
    }

    fn remove_one_face(&mut self, halfedge_id: HalfEdgeID) {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        let face_id = walker.face_id().unwrap();

        walker.as_next();
        let halfedge_id1 = walker.halfedge_id().unwrap();
        let twin_id1 = walker.twin_id().unwrap();
        let vertex_id = walker.vertex_id().unwrap();
        walker.as_next();
        let halfedge_id2 = walker.halfedge_id().unwrap();
        let twin_id2 = walker.twin_id().unwrap();

        self.connectivity_info.remove_face(face_id);
        self.connectivity_info.remove_halfedge(halfedge_id);
        self.connectivity_info.remove_halfedge(halfedge_id1);
        self.connectivity_info.remove_halfedge(halfedge_id2);
        self.connectivity_info.set_halfedge_twin(twin_id1, twin_id2);
        self.connectivity_info
            .set_vertex_halfedge(vertex_id, Some(twin_id1));

        walker.as_twin();
    }

    ///
    /// Adds a vertex to the mesh which is not connected to anything.
    /// Usually used in combination with [Mesh::add_face].
    ///
    pub fn add_vertex(&mut self, position: Vec3) -> VertexID {
        self.connectivity_info.new_vertex(position)
    }

    ///
    /// Adds a face to the mesh and connects it to the given vertices which can be created using the [Mesh::add_vertex] method.
    /// Also creates edges between the vertices if they do not already exist.
    ///
    pub fn add_face(
        &mut self,
        vertex_id1: VertexID,
        vertex_id2: VertexID,
        vertex_id3: VertexID,
    ) -> FaceID {
        let edges = [
            self.connecting_edge(vertex_id1, vertex_id2),
            self.connecting_edge(vertex_id2, vertex_id3),
            self.connecting_edge(vertex_id3, vertex_id1),
        ];

        let face_id = self
            .connectivity_info
            .create_face(vertex_id1, vertex_id2, vertex_id3);

        for halfedge in self.face_halfedge_iter(face_id) {
            let target_vertex = self.walker_from_halfedge(halfedge).vertex_id().unwrap();
            let i = if target_vertex == vertex_id2 {
                0
            } else if target_vertex == vertex_id3 {
                1
            } else {
                2
            };
            let twin = if let Some(old_halfedge) = edges[i] {
                let twin = self.walker_from_halfedge(old_halfedge).twin_id().unwrap();
                self.connectivity_info.remove_halfedge(old_halfedge);
                twin
            } else {
                let walker = self.walker_from_halfedge(halfedge);
                let new_halfedge = self.connectivity_info.new_halfedge(
                    walker.into_next().into_next().vertex_id(),
                    None,
                    None,
                );
                new_halfedge
            };
            self.connectivity_info.set_halfedge_twin(twin, halfedge);
        }
        face_id
    }

    ///
    /// Removes the given face and also the adjacent edges and vertices if they are not connected to any other face.
    ///
    pub fn remove_face(&mut self, face_id: FaceID) {
        let edges: Vec<HalfEdgeID> = self.face_halfedge_iter(face_id).collect();
        self.remove_face_unsafe(face_id);
        for halfedge_id in edges {
            self.remove_edge_if_lonely(halfedge_id);
        }
    }

    pub(super) fn remove_face_unsafe(&mut self, face_id: FaceID) {
        let mut walker = self.walker_from_face(face_id);
        let he_id1 = walker.halfedge_id().unwrap();
        walker.as_next();
        let he_id2 = walker.halfedge_id().unwrap();
        walker.as_next();
        let he_id3 = walker.halfedge_id().unwrap();

        self.connectivity_info.set_halfedge_face(he_id1, None);
        self.connectivity_info.set_halfedge_face(he_id2, None);
        self.connectivity_info.set_halfedge_face(he_id3, None);

        self.connectivity_info.set_halfedge_next(he_id1, None);
        self.connectivity_info.set_halfedge_next(he_id2, None);
        self.connectivity_info.set_halfedge_next(he_id3, None);

        self.connectivity_info.remove_face(face_id);
    }

    /// Removes edges and vertices that are not connected to any face.
    pub fn remove_lonely_primitives(&mut self) {
        let edges: Vec<HalfEdgeID> = self.edge_iter().collect();
        for halfedge_id in edges {
            self.remove_edge_if_lonely(halfedge_id);
        }

        for vertex_id in self.vertex_iter() {
            self.remove_vertex_if_lonely(vertex_id);
        }
    }

    pub(super) fn remove_edge_if_lonely(&mut self, halfedge_id: HalfEdgeID) {
        let mut walker = self.walker_from_halfedge(halfedge_id);
        if walker.face_id().is_none() && walker.as_twin().face_id().is_none() {
            let vertex_id1 = walker.vertex_id().unwrap();
            let halfedge_id1 = walker.halfedge_id().unwrap();
            walker.as_twin();
            let vertex_id2 = walker.vertex_id().unwrap();
            let halfedge_id2 = walker.halfedge_id().unwrap();

            self.connectivity_info.remove_halfedge(halfedge_id1);
            self.connectivity_info.remove_halfedge(halfedge_id2);

            let find_new_edge_connectivity =
                |mesh: &Mesh, vertex_id: VertexID| -> Option<HalfEdgeID> {
                    for halfedge_id in mesh.halfedge_iter() {
                        let walker = mesh.walker_from_halfedge(halfedge_id);
                        if walker.vertex_id().unwrap() == vertex_id {
                            return walker.twin_id();
                        }
                    }
                    None
                };

            if self.walker_from_vertex(vertex_id1).halfedge_id().unwrap() == halfedge_id2 {
                let new_edge = find_new_edge_connectivity(&self, vertex_id1);
                self.connectivity_info
                    .set_vertex_halfedge(vertex_id1, new_edge);
                self.remove_vertex_if_lonely(vertex_id1);
            }
            if self.walker_from_vertex(vertex_id2).halfedge_id().unwrap() == halfedge_id1 {
                let new_edge = find_new_edge_connectivity(&self, vertex_id2);
                self.connectivity_info
                    .set_vertex_halfedge(vertex_id2, new_edge);
                self.remove_vertex_if_lonely(vertex_id2);
            }
        }
    }

    fn remove_vertex_if_lonely(&mut self, vertex_id: VertexID) {
        if self.connectivity_info.vertex_halfedge(vertex_id).is_none() {
            self.connectivity_info.remove_vertex(vertex_id);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use three_d_asset::{Indices, Positions, TriMesh};

    #[test]
    fn test_flip_edge() {
        let mut no_flips = 0;
        let mut mesh = crate::test_utility::square();
        let no_edges = mesh.no_halfedges();
        for halfedge_id in mesh.halfedge_iter() {
            let (v0, v1) = mesh.edge_vertices(halfedge_id);

            if mesh.flip_edge(halfedge_id).is_ok() {
                mesh.is_valid().unwrap();

                let (v2, v3) = mesh.edge_vertices(halfedge_id);
                assert_ne!(v0, v2);
                assert_ne!(v1, v2);
                assert_ne!(v0, v3);
                assert_ne!(v1, v3);

                assert!(mesh.connecting_edge(v0, v1).is_none());
                assert!(mesh.connecting_edge(v2, v3).is_some());

                let edge = mesh.connecting_edge(v2, v3).unwrap();
                let twin = mesh.walker_from_halfedge(edge).twin_id().unwrap();
                assert!(edge == halfedge_id || twin == halfedge_id,
                        "Flipped edge {} or flipped edge twin {} should be equal to before flipped edge id {}", edge, twin, halfedge_id);
                no_flips = no_flips + 1;
            }
        }
        assert_eq!(no_edges, mesh.no_halfedges());
        assert_eq!(no_flips, 2);
    }

    #[test]
    fn test_flip_multiple_edges() {
        let mut no_flips = 0;
        let mut mesh: Mesh = TriMesh::sphere(3).into();
        let no_edges = mesh.no_halfedges();
        for halfedge_id in mesh.halfedge_iter() {
            let (v0, v1) = mesh.edge_vertices(halfedge_id);

            if mesh.flip_edge(halfedge_id).is_ok() {
                mesh.is_valid().unwrap();

                let (v2, v3) = mesh.edge_vertices(halfedge_id);
                assert_ne!(v0, v2);
                assert_ne!(v1, v2);
                assert_ne!(v0, v3);
                assert_ne!(v1, v3);

                assert!(mesh.connecting_edge(v0, v1).is_none());
                assert!(mesh.connecting_edge(v2, v3).is_some());

                let edge = mesh.connecting_edge(v2, v3).unwrap();
                let twin = mesh.walker_from_halfedge(edge).twin_id().unwrap();
                assert!(edge == halfedge_id || twin == halfedge_id,
                        "Flipped edge {} or flipped edge twin {} should be equal to before flipped edge id {}", edge, twin, halfedge_id);
                no_flips = no_flips + 1;
            }
        }
        assert_eq!(no_edges, mesh.no_halfedges());
        assert!(no_flips > 0);
    }

    #[test]
    fn test_split_edge_on_boundary() {
        let mut mesh = crate::test_utility::triangle();
        for halfedge_id in mesh.halfedge_iter() {
            if mesh.walker_from_halfedge(halfedge_id).face_id().is_some() {
                mesh.split_edge(halfedge_id, vec3(-1.0, -1.0, -1.0));

                assert_eq!(mesh.no_vertices(), 4);
                assert_eq!(mesh.no_halfedges(), 2 * 3 + 4);
                assert_eq!(mesh.no_faces(), 2);

                let mut walker = mesh.walker_from_halfedge(halfedge_id);
                assert!(walker.halfedge_id().is_some());
                assert!(walker.face_id().is_some());
                assert!(walker.vertex_id().is_some());

                walker.as_twin();
                assert!(walker.halfedge_id().is_some());
                assert!(walker.face_id().is_none());
                assert!(walker.vertex_id().is_some());

                walker.as_twin().as_next().as_twin();
                assert!(walker.halfedge_id().is_some());
                assert!(walker.face_id().is_some());
                assert!(walker.vertex_id().is_some());

                walker.as_next().as_next().as_twin();
                assert!(walker.halfedge_id().is_some());
                assert!(walker.face_id().is_none());
                assert!(walker.vertex_id().is_some());

                mesh.is_valid().unwrap();

                break;
            }
        }
    }

    #[test]
    fn test_split_edge() {
        let mut mesh = crate::test_utility::square();
        for halfedge_id in mesh.halfedge_iter() {
            let mut walker = mesh.walker_from_halfedge(halfedge_id);
            if walker.face_id().is_some() && walker.as_twin().face_id().is_some() {
                let vertex_id = mesh.split_edge(halfedge_id, vec3(-1.0, -1.0, -1.0));
                assert_eq!(mesh.no_vertices(), 5);
                assert_eq!(mesh.no_halfedges(), 4 * 3 + 4);
                assert_eq!(mesh.no_faces(), 4);

                let mut w = mesh.walker_from_vertex(vertex_id);
                let start_halfedge_id = w.halfedge_id();
                let mut end_halfedge_id = w.twin_id();
                for _ in 0..4 {
                    assert!(w.halfedge_id().is_some());
                    assert!(w.twin_id().is_some());
                    assert!(w.vertex_id().is_some());
                    assert!(w.face_id().is_some());
                    w.as_previous().as_twin();
                    end_halfedge_id = w.halfedge_id();
                }
                assert_eq!(
                    start_halfedge_id, end_halfedge_id,
                    "Did not go the full round"
                );

                mesh.is_valid().unwrap();
                break;
            }
        }
    }

    #[test]
    fn test_split_face() {
        let mut mesh = crate::test_utility::triangle();
        let face_id = mesh.face_iter().next().unwrap();

        let vertex_id = mesh.split_face(face_id, vec3(-1.0, -1.0, -1.0));

        assert_eq!(mesh.no_vertices(), 4);
        assert_eq!(mesh.no_halfedges(), 3 * 3 + 3);
        assert_eq!(mesh.no_faces(), 3);

        let mut walker = mesh.walker_from_vertex(vertex_id);
        let start_edge = walker.halfedge_id().unwrap();
        let one_round_edge = walker
            .as_previous()
            .as_twin()
            .as_previous()
            .as_twin()
            .as_previous()
            .as_twin()
            .halfedge_id()
            .unwrap();
        assert_eq!(start_edge, one_round_edge);

        assert!(walker.face_id().is_some());
        walker.as_next().as_twin();
        assert!(walker.face_id().is_none());

        walker.as_twin().as_next().as_twin().as_next().as_twin();
        assert!(walker.face_id().is_none());

        walker.as_twin().as_next().as_twin().as_next().as_twin();
        assert!(walker.face_id().is_none());

        mesh.is_valid().unwrap();
    }

    #[test]
    fn test_collapse_edge_on_boundary1() {
        let mut mesh: Mesh = TriMesh {
            indices: Indices::U8(vec![0, 1, 2, 1, 3, 2, 2, 3, 4]),
            positions: Positions::F64(vec![
                vec3(0.0, 0.0, 0.0),
                vec3(0.0, 0.0, 1.0),
                vec3(1.0, 0.0, 0.0),
                vec3(1.0, 0.0, 1.0),
                vec3(2.0, 0.0, 0.5),
            ]),
            ..Default::default()
        }
        .into();

        for halfedge_id in mesh.halfedge_iter() {
            let mut walker = mesh.walker_from_halfedge(halfedge_id);
            if walker.face_id().is_none()
                && walker.as_twin().as_next().as_twin().face_id().is_some()
                && walker.as_twin().as_next().as_twin().face_id().is_some()
            {
                mesh.collapse_edge(halfedge_id);

                assert_eq!(mesh.no_vertices(), 4);
                assert_eq!(mesh.no_halfedges(), 10);
                assert_eq!(mesh.no_faces(), 2);

                mesh.is_valid().unwrap();

                break;
            }
        }
    }

    #[test]
    fn test_collapse_edge_on_boundary2() {
        let mut mesh: Mesh = TriMesh {
            indices: Indices::U8(vec![0, 2, 3, 0, 3, 1]),
            positions: Positions::F64(vec![
                vec3(0.0, 0.0, 0.0),
                vec3(0.0, 0.0, 1.0),
                vec3(1.0, 0.0, 0.0),
                vec3(1.0, 0.0, 1.0),
            ]),
            ..Default::default()
        }
        .into();
        for halfedge_id in mesh.halfedge_iter() {
            if mesh.is_edge_on_boundary(halfedge_id) {
                mesh.collapse_edge(halfedge_id);

                assert_eq!(mesh.no_vertices(), 3);
                assert_eq!(mesh.no_halfedges(), 6);
                assert_eq!(mesh.no_faces(), 1);

                mesh.is_valid().unwrap();

                break;
            }
        }
    }

    #[test]
    fn test_collapse_edge() {
        let mut mesh = crate::test_utility::subdivided_triangle();
        for halfedge_id in mesh.halfedge_iter() {
            if !mesh.is_edge_on_boundary(halfedge_id) {
                mesh.collapse_edge(halfedge_id);
                assert_eq!(mesh.no_vertices(), 3);
                assert_eq!(mesh.no_halfedges(), 6);
                assert_eq!(mesh.no_faces(), 1);

                mesh.is_valid().unwrap();
                break;
            }
        }
    }

    #[test]
    fn test_recursive_collapse_edge() {
        let mut mesh: Mesh = TriMesh {
            indices: Indices::U8(vec![0, 1, 2, 1, 3, 2, 2, 3, 4]),
            positions: Positions::F64(vec![
                vec3(0.0, 0.0, 0.0),
                vec3(0.0, 0.0, 1.0),
                vec3(1.0, 0.0, 0.0),
                vec3(1.0, 0.0, 1.0),
                vec3(2.0, 0.0, 0.5),
            ]),
            ..Default::default()
        }
        .into();

        while mesh.no_faces() > 1 {
            for halfedge_id in mesh.halfedge_iter() {
                if mesh.is_edge_on_boundary(halfedge_id) {
                    mesh.collapse_edge(halfedge_id);
                    break;
                }
            }
        }
        assert_eq!(mesh.no_vertices(), 3);
        assert_eq!(mesh.no_halfedges(), 6);
        assert_eq!(mesh.no_faces(), 1);
        mesh.is_valid().unwrap();
    }

    #[test]
    fn test_remove_face_when_unconnected() {
        let mut mesh: Mesh = TriMesh {
            positions: Positions::F64(vec![
                vec3(1.0, 0.0, 0.0),
                vec3(0.0, 0.0, 0.0),
                vec3(0.0, 0.0, -1.0),
                vec3(1.0, 0.0, 0.0),
                vec3(0.0, 0.0, 0.0),
                vec3(0.0, 0.0, -1.0),
            ]),
            ..Default::default()
        }
        .into();

        let faces: Vec<FaceID> = mesh.face_iter().into_iter().collect();

        mesh.remove_face(faces[0]);

        assert_eq!(3, mesh.no_vertices());
        assert_eq!(6, mesh.no_halfedges());
        assert_eq!(1, mesh.no_faces());
        mesh.is_valid().unwrap();
    }

    #[test]
    fn test_remove_face_when_connected() {
        let mut mesh = crate::test_utility::square();

        let face_id = mesh.face_iter().next().unwrap();

        mesh.remove_face(face_id);

        assert_eq!(3, mesh.no_vertices());
        assert_eq!(6, mesh.no_halfedges());
        assert_eq!(1, mesh.no_faces());
        mesh.is_valid().unwrap();
    }

    #[test]
    fn test_remove_face_when_three_connected_faces() {
        let mut mesh = crate::test_utility::subdivided_triangle();

        let face_id = mesh.face_iter().next().unwrap();

        mesh.remove_face(face_id);

        assert_eq!(4, mesh.no_vertices());
        assert_eq!(10, mesh.no_halfedges());
        assert_eq!(2, mesh.no_faces());
        mesh.is_valid().unwrap();
    }

    #[test]
    fn test_add_face() {
        let mut mesh = Mesh::new(&three_d_asset::TriMesh::default());
        for i in 0..3 {
            let vertex_id1 = mesh.add_vertex(vec3(1.0, i as f64, 0.0));
            let vertex_id2 = mesh.add_vertex(vec3(0.0, i as f64, 0.0));
            let vertex_id3 = mesh.add_vertex(vec3(0.0, i as f64, 1.0));
            mesh.add_face(vertex_id1, vertex_id2, vertex_id3);
            let vertex_id4 = mesh.add_vertex(vec3(1.0, i as f64, 1.0));
            mesh.add_face(vertex_id1, vertex_id3, vertex_id4);
            let vertex_id5 = mesh.add_vertex(vec3(2.0, i as f64, 2.0));
            mesh.add_face(vertex_id1, vertex_id4, vertex_id5);
        }

        assert_eq!(mesh.no_vertices(), 15);
        assert_eq!(mesh.no_edges(), 21);
        assert_eq!(mesh.no_halfedges(), 42);
        assert_eq!(mesh.no_faces(), 9);
        mesh.is_valid().unwrap()
    }
}