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```
```use crate::math::{Isometry, Point, Vector};
use alga::linear::{Rotation, Translation};
use na::{self, RealField};

/// Geometric description of a polyline.
#[derive(Clone)]
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
pub struct Polyline<N: RealField> {
/// Coordinates of the polyline vertices.
coords: Vec<Point<N>>,
/// Coordinates of the polyline normals.
normals: Option<Vec<Vector<N>>>,
}

impl<N: RealField> Polyline<N> {
/// Creates a new polyline.
pub fn new(coords: Vec<Point<N>>, normals: Option<Vec<Vector<N>>>) -> Polyline<N> {
if let Some(ref ns) = normals {
assert!(
coords.len() == ns.len(),
"There must be exactly one normal per vertex."
);
}

Polyline { coords, normals }
}
}

impl<N: RealField> Polyline<N> {
/// Moves the polyline data out of it.
pub fn unwrap(self) -> (Vec<Point<N>>, Option<Vec<Vector<N>>>) {
(self.coords, self.normals)
}

/// The coordinates of this polyline vertices.
#[inline]
pub fn coords(&self) -> &[Point<N>] {
&self.coords[..]
}

/// The mutable coordinates of this polyline vertices.
#[inline]
pub fn coords_mut(&mut self) -> &mut [Point<N>] {
&mut self.coords[..]
}

/// The normals of this polyline vertices.
#[inline]
pub fn normals(&self) -> Option<&[Vector<N>]> {
self.normals.as_ref().map(Vec::as_slice)
}

/// The mutable normals of this polyline vertices.
#[inline]
pub fn normals_mut(&mut self) -> Option<&mut [Vector<N>]> {
self.normals.as_mut().map(Vec::as_mut_slice)
}

/// Translates each vertex of this polyline.
pub fn translate_by<T: Translation<Point<N>>>(&mut self, t: &T) {
for c in self.coords.iter_mut() {
*c = t.transform_point(c);
}
}

/// Rotates each vertex and normal of this polyline.
pub fn rotate_by<R: Rotation<Point<N>>>(&mut self, r: &R) {
for c in self.coords.iter_mut() {
*c = r.transform_point(c);
}

for n in self.normals.iter_mut() {
for n in n.iter_mut() {
*n = r.transform_vector(n);
}
}
}

/// Transforms each vertex and rotates each normal of this polyline.
pub fn transform_by(&mut self, t: &Isometry<N>) {
for c in self.coords.iter_mut() {
*c = t * *c;
}

for n in self.normals.iter_mut() {
for n in n.iter_mut() {
*n = t * &*n;
}
}
}

/// Apply a transformation to every vertex and normal of this polyline and returns it.
#[inline]
pub fn transformed(mut self, t: &Isometry<N>) -> Self {
self.transform_by(t);
self
}

/// Scales each vertex of this polyline.
pub fn scale_by_scalar(&mut self, s: &N) {
for c in self.coords.iter_mut() {
*c = *c * *s
}
// FIXME: do something for the normals?
}

/// Scales each vertex of this mesh.
#[inline]
pub fn scale_by(&mut self, s: &Vector<N>) {
for c in self.coords.iter_mut() {
for i in 0..na::dimension::<Vector<N>>() {
c[i] = (*c)[i] * s[i];
}
}
// FIXME: do something for the normals?
}

/// Apply a scaling to every vertex and normal of this polyline and returns it.
#[inline]
pub fn scaled(mut self, s: &Vector<N>) -> Self {
self.scale_by(s);
self
}
}
```