From 245b02b443a88f4d55d5ed93cc12d70063f9316f Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Mon, 5 Jul 2021 18:36:43 -0700
Subject: [PATCH] matrices: implement Matrix4x4:rotation_[xyz]

---
 rtchallenge/src/matrices.rs | 111 ++++++++++++++++++++++++++++++++++++
 rtchallenge/src/tuples.rs   |  36 ++++++++++++
 2 files changed, 147 insertions(+)

diff --git a/rtchallenge/src/matrices.rs b/rtchallenge/src/matrices.rs
index 294667a..834f261 100644
--- a/rtchallenge/src/matrices.rs
+++ b/rtchallenge/src/matrices.rs
@@ -283,6 +283,117 @@ impl Matrix4x4 {
         )
     }
 
+    /// Creates a 4x4 matrix representing a rotation around the x-axis.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::f32::consts::PI;
+    ///
+    /// use float_cmp::approx_eq;
+    ///
+    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
+    ///
+    /// // A scaling matrix applied to a point.
+    /// let p = Tuple::point(0., 1., 0.);
+    /// let half_quarter = Matrix4x4::rotation_x(PI / 4.);
+    /// let full_quarter = Matrix4x4::rotation_x(PI / 2.);
+    ///
+    /// assert_eq!(
+    ///     half_quarter * p,
+    ///     Tuple::point(0., 2_f32.sqrt() / 2., 2_f32.sqrt() / 2.)
+    /// );
+    /// assert!(approx_eq!(
+    ///     Tuple,
+    ///     full_quarter * p,
+    ///     Tuple::point(0., 0., 1.),
+    ///     epsilon = 0.0001
+    /// ));
+    /// ```
+    pub fn rotation_x(radians: f32) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [1., 0., 0., 0.],
+            [0., r.cos(), -r.sin(), 0.],
+            [0., r.sin(), r.cos(), 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a rotation around the y-axis.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::f32::consts::PI;
+    ///
+    /// use float_cmp::approx_eq;
+    ///
+    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
+    ///
+    /// // A scaling matrix applied to a point.
+    /// let p = Tuple::point(0., 0., 1.);
+    /// let half_quarter = Matrix4x4::rotation_y(PI / 4.);
+    /// let full_quarter = Matrix4x4::rotation_y(PI / 2.);
+    ///
+    /// assert_eq!(
+    ///     half_quarter * p,
+    ///     Tuple::point(2_f32.sqrt() / 2., 0., 2_f32.sqrt() / 2.)
+    /// );
+    /// assert!(approx_eq!(
+    ///     Tuple,
+    ///     full_quarter * p,
+    ///     Tuple::point(1., 0., 0.,),
+    ///     epsilon = 0.0001
+    /// ));
+    /// ```
+    pub fn rotation_y(radians: f32) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [r.cos(), 0., r.sin(), 0.],
+            [0., 1., 0., 0.],
+            [-r.sin(), 0., r.cos(), 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
+    /// Creates a 4x4 matrix representing a rotation around the z-axis.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::f32::consts::PI;
+    ///
+    /// use float_cmp::approx_eq;
+    ///
+    /// use rtchallenge::{matrices::Matrix4x4, tuples::Tuple};
+    ///
+    /// // A scaling matrix applied to a point.
+    /// let p = Tuple::point(0., 1., 0.);
+    /// let half_quarter = Matrix4x4::rotation_z(PI / 4.);
+    /// let full_quarter = Matrix4x4::rotation_z(PI / 2.);
+    ///
+    /// assert_eq!(
+    ///     half_quarter * p,
+    ///     Tuple::point(-2_f32.sqrt() / 2., 2_f32.sqrt() / 2., 0.)
+    /// );
+    /// assert!(approx_eq!(
+    ///     Tuple,
+    ///     full_quarter * p,
+    ///     Tuple::point(-1., 0., 0.,),
+    ///     epsilon = 0.0001
+    /// ));
+    /// ```
+    pub fn rotation_z(radians: f32) -> Matrix4x4 {
+        let r = radians;
+        Matrix4x4::new(
+            [r.cos(), -r.sin(), 0., 0.],
+            [r.sin(), r.cos(), 0., 0.],
+            [0., 0., 1., 0.],
+            [0., 0., 0., 1.],
+        )
+    }
+
     /// Transpose self, returning a new matrix that has been reflected across the diagonal.
     /// # Examples
     ///
diff --git a/rtchallenge/src/tuples.rs b/rtchallenge/src/tuples.rs
index 6308789..efe9c7b 100644
--- a/rtchallenge/src/tuples.rs
+++ b/rtchallenge/src/tuples.rs
@@ -1,5 +1,7 @@
 use std::ops::{Add, Div, Mul, Neg, Sub};
 
+use float_cmp::{ApproxEq, F32Margin};
+
 #[derive(Debug, PartialEq, Copy, Clone)]
 pub struct Tuple {
     pub x: f32,
@@ -43,6 +45,40 @@ impl Tuple {
     }
 }
 
+impl ApproxEq for Tuple {
+    type Margin = F32Margin;
+
+    /// Implement float_cmp::ApproxEq for Tuple
+    ///
+    /// # Examples
+    /// ```
+    /// use float_cmp::approx_eq;
+    /// use rtchallenge::tuples::Tuple;
+    ///
+    /// assert!(approx_eq!(
+    ///     Tuple,
+    ///     Tuple::point(1., 1., 0.),
+    ///     Tuple::point(1., 1., 0.),
+    ///     ulps = 1
+    /// ));
+    ///
+    /// assert!(approx_eq!(
+    ///     Tuple,
+    ///     Tuple::vector(1., 1., 0.),
+    ///     Tuple::vector(1., 1., 0.),
+    ///     ulps = 1
+    /// ));
+    /// ```
+    fn approx_eq<T: Into<Self::Margin>>(self, t2: Self, margin: T) -> bool {
+        let t = self;
+        let margin = margin.into();
+        t.x.approx_eq(t2.x, margin)
+            && t.y.approx_eq(t2.y, margin)
+            && t.z.approx_eq(t2.z, margin)
+            && t.w.approx_eq(t2.w, margin)
+    }
+}
+
 impl Add for Tuple {
     type Output = Self;
     fn add(self, other: Self) -> Self {