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use crate::{CoordFloat, CoordsIter, Polygon, Triangle, coord};
use earcut::Earcut;
/// Triangulate polygons using an [ear-cutting algorithm](https://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf).
///
/// Requires the `"earcut"` feature, which is enabled by default.
pub trait TriangulateEarcut<T: CoordFloat> {
/// # Examples
///
/// ```
/// use geo::{coord, polygon, Triangle, TriangulateEarcut};
///
/// let square_polygon = polygon![
/// (x: 0., y: 0.), // SW
/// (x: 10., y: 0.), // SE
/// (x: 10., y: 10.), // NE
/// (x: 0., y: 10.), // NW
/// (x: 0., y: 0.), // SW
/// ];
///
/// let triangles = square_polygon.earcut_triangles();
///
/// assert_eq!(
/// vec![
/// Triangle(
/// coord! { x: 0., y: 0. }, // SW
/// coord! { x: 10., y: 0. }, // SE
/// coord! { x: 10., y: 10. }, // NE
/// ),
/// Triangle(
/// coord! { x: 10., y: 10. }, // NE
/// coord! { x: 0., y: 10. }, // NW
/// coord! { x: 0., y: 0. }, // SW
/// ),
/// ],
/// triangles,
/// );
/// ```
fn earcut_triangles(&self) -> Vec<Triangle<T>> {
self.earcut_triangles_iter().collect()
}
/// # Examples
///
/// ```
/// use geo::{coord, polygon, Triangle, TriangulateEarcut};
///
/// let square_polygon = polygon![
/// (x: 0., y: 0.), // SW
/// (x: 10., y: 0.), // SE
/// (x: 10., y: 10.), // NE
/// (x: 0., y: 10.), // NW
/// (x: 0., y: 0.), // SW
/// ];
///
/// let mut triangles_iter = square_polygon.earcut_triangles_iter();
///
/// assert_eq!(
/// Some(Triangle(
/// coord! { x: 0., y: 0. }, // SW
/// coord! { x: 10., y: 0. }, // SE
/// coord! { x: 10., y: 10. }, // NE
/// )),
/// triangles_iter.next(),
/// );
///
/// assert_eq!(
/// Some(Triangle(
/// coord! { x: 10., y: 10. }, // NE
/// coord! { x: 0., y: 10. }, // NW
/// coord! { x: 0., y: 0. }, // SW
/// )),
/// triangles_iter.next(),
/// );
///
/// assert!(triangles_iter.next().is_none());
/// ```
fn earcut_triangles_iter(&self) -> Iter<T> {
Iter(self.earcut_triangles_raw())
}
/// Return the raw result from the `earcut` library: a one-dimensional vector of polygon
/// vertices (in XY order), and the indices of the triangles within the vertices vector. This
/// method is less ergonomic than the `earcut_triangles` and `earcut_triangles_iter`
/// methods, but can be helpful when working in graphics contexts that expect flat vectors of
/// data.
///
/// # Examples
///
/// ```
/// use geo::{coord, polygon, Triangle, TriangulateEarcut};
/// use geo::triangulate_earcut::RawTriangulation;
///
/// let square_polygon = polygon![
/// (x: 0., y: 0.), // SW
/// (x: 10., y: 0.), // SE
/// (x: 10., y: 10.), // NE
/// (x: 0., y: 10.), // NW
/// (x: 0., y: 0.), // SW
/// ];
///
/// let mut triangles_raw = square_polygon.earcut_triangles_raw();
///
/// assert_eq!(
/// RawTriangulation {
/// vertices: vec![
/// [0., 0.], // SW
/// [10., 0.], // SE
/// [10., 10.], // NE
/// [0., 10.], // NW
/// ],
/// triangle_indices: vec![
/// 2, 3, 0, // NE-NW-SW
/// 0, 1, 2, // SW-SE-NE
/// ],
/// },
/// triangles_raw,
/// );
/// ```
fn earcut_triangles_raw(&self) -> RawTriangulation<T>;
}
impl<T: CoordFloat> TriangulateEarcut<T> for Polygon<T> {
fn earcut_triangles_raw(&self) -> RawTriangulation<T> {
let mut earcut = Earcut::new();
let input = EarcutInput::from(self);
// PERF: expose a way to pass in a re-usable output vector for those who are triangulating
// in a hot loop
let mut triangle_indices = vec![];
earcut.earcut(
input.vertices.clone(), // PERF: iterate `vertices` lazily rather than create a Vec
&input.interior_indexes,
&mut triangle_indices,
);
RawTriangulation {
// PERF: As mentioned above, if we don't manifest a concrete vertices Vec,
// we'll need to return some kind of "getter" that translates triangle_indices back to polygon coords, accounting
// for the lack of an explicit "closing" coordinate in the triangle_indices
//
// We'll need to measure if all that indirection is cheaper than just manifesting the Vec.
vertices: input.vertices,
triangle_indices,
}
}
}
/// The raw result of triangulating a polygon from `earcut`.
#[derive(Debug, PartialEq, Clone)]
pub struct RawTriangulation<T: CoordFloat> {
/// Flattened vector of polygon vertices (in XY order).
pub vertices: Vec<[T; 2]>,
/// Indices of the triangles within the vertices vector.
pub triangle_indices: Vec<usize>,
}
#[derive(Debug)]
pub struct Iter<T: CoordFloat>(RawTriangulation<T>);
impl<T: CoordFloat> Iterator for Iter<T> {
type Item = Triangle<T>;
fn next(&mut self) -> Option<Self::Item> {
let triangle_index_1 = self.0.triangle_indices.pop()?;
let triangle_index_2 = self.0.triangle_indices.pop()?;
let triangle_index_3 = self.0.triangle_indices.pop()?;
Some(Triangle::new(
self.triangle_index_to_coord(triangle_index_1),
self.triangle_index_to_coord(triangle_index_2),
self.triangle_index_to_coord(triangle_index_3),
))
}
}
impl<T: CoordFloat> Iter<T> {
fn triangle_index_to_coord(&self, triangle_index: usize) -> crate::Coord<T> {
coord! {
x: self.0.vertices[triangle_index][0],
y: self.0.vertices[triangle_index][1],
}
}
}
struct EarcutInput<T: CoordFloat> {
pub vertices: Vec<[T; 2]>,
pub interior_indexes: Vec<usize>,
}
impl<'a, T: CoordFloat> From<&'a Polygon<T>> for EarcutInput<T> {
fn from(polygon: &'a Polygon<T>) -> EarcutInput<T> {
let mut vertices = Vec::with_capacity(polygon.coords_count() - 1);
let mut interior_indexes = Vec::with_capacity(polygon.interiors().len());
debug_assert!(polygon.exterior().0.len() >= 4);
flatten_ring(polygon.exterior(), &mut vertices);
for interior in polygon.interiors() {
debug_assert!(interior.0.len() >= 4);
interior_indexes.push(vertices.len());
flatten_ring(interior, &mut vertices);
}
Self {
vertices,
interior_indexes,
}
}
}
fn flatten_ring<T: CoordFloat>(line_string: &crate::LineString<T>, vertices: &mut Vec<[T; 2]>) {
if line_string.0.is_empty() {
return;
}
debug_assert!(line_string.is_closed(), "Only suitable for polygon rings");
// skip final (redundant) coord for closed line_string to match
// earcutr's expected input
for coord in &line_string.0[0..line_string.0.len() - 1] {
vertices.push([coord.x, coord.y]);
}
}
#[cfg(test)]
mod test {
use super::TriangulateEarcut;
use crate::{polygon, wkt};
#[test]
fn test_triangle() {
let triangle_polygon = polygon![
(x: 0., y: 0.),
(x: 10., y: 0.),
(x: 10., y: 10.),
(x: 0., y: 0.),
];
let triangles = triangle_polygon.earcut_triangles();
assert_eq!(&[wkt!(TRIANGLE(10.0 0.0,10.0 10.0,0.0 0.0))][..], triangles,);
}
#[test]
fn test_square() {
let square_polygon = polygon![
(x: 0., y: 0.),
(x: 10., y: 0.),
(x: 10., y: 10.),
(x: 0., y: 10.),
(x: 0., y: 0.),
];
let triangles = square_polygon.earcut_triangles();
assert_eq!(
&[
wkt!(TRIANGLE(0.0 0.0,10.0 0.0,10.0 10.0)),
wkt!(TRIANGLE(10.0 10.0,0.0 10.0,0.0 0.0))
][..],
&triangles,
);
}
#[test]
fn test_square_raw() {
let square_polygon = wkt!(POLYGON(
(0. 0.,10. 0., 10. 10., 0. 10.)
));
let triangles = square_polygon.earcut_triangles_raw();
assert_eq!(
triangles.vertices,
vec![[0., 0.], [10., 0.], [10., 10.], [0., 10.]] // exterior
);
assert_eq!(triangles.triangle_indices, vec![2, 3, 0, 0, 1, 2]);
}
#[test]
fn test_square_with_hole_raw() {
let poly_with_hole = wkt!(POLYGON(
(0. 0.,10. 0., 10. 10., 0. 10.,0. 0.),
(2. 2., 8. 2., 8. 8., 2. 8.,2. 2.)
));
let triangles = poly_with_hole.earcut_triangles_raw();
assert_eq!(
triangles.vertices,
vec![
// exterior
[0., 0.],
[10., 0.],
[10., 10.],
[0., 10.],
// interior hole
[2., 2.],
[8., 2.],
[8., 8.],
[2., 8.],
]
);
// manually inspected that the output was a reasonable triangulation.
// let output = poly_with_hole.earcut_triangles();
// let mp = crate::MultiPolygon::new(output.iter().map(|tri| tri.to_polygon()).collect());
// dbg!(mp);
assert_eq!(
triangles.triangle_indices,
vec![
0, 4, 7, 5, 4, 0, 3, 0, 7, 5, 0, 1, 2, 3, 7, 6, 5, 1, 2, 7, 6, 6, 1, 2
]
);
}
}