From 3e54b01003aa9d27de8f4ca13c9240fe785ec0e1 Mon Sep 17 00:00:00 2001
From: Justin Worthe <justin@worthe-it.co.za>
Date: Mon, 22 Apr 2019 14:38:40 +0200
Subject: Structures representing game state

---
 src/geometry/vec.rs | 154 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 src/geometry/vec.rs

(limited to 'src/geometry/vec.rs')

diff --git a/src/geometry/vec.rs b/src/geometry/vec.rs
new file mode 100644
index 0000000..f6bd29f
--- /dev/null
+++ b/src/geometry/vec.rs
@@ -0,0 +1,154 @@
+use std::ops::*;
+use num_traits::{NumOps, NumAssignOps};
+use num_traits::pow::Pow;
+use num_traits::real::Real;
+
+macro_rules! fold_array {
+    ($method:ident, { $x:expr }) => { $x };
+    ($method:ident, { $x:expr, $y:expr }) => { $x.$method($y) };
+    ($method:ident, { $x:expr, $y:expr, $z:expr }) => { $x.$method($y).$method($z) };
+}
+
+macro_rules! impl_vector {
+    ($VecN:ident { $($field:ident),+ }) => {
+        #[derive(Debug, Default, Clone, Copy, Hash, PartialEq, Eq)]
+        pub struct $VecN<T> {
+            $(pub $field: T),+
+        }
+        
+        impl<T> $VecN<T> {
+            pub fn new($($field: T),+) -> $VecN<T> {
+                $VecN { $($field),+ }
+            }
+        }
+        
+        impl<T: NumOps + Pow<u8, Output=T> + Copy> $VecN<T> {
+            pub fn magnitude_squared(&self) -> T {
+                fold_array!(add, { $(self.$field.pow(2)),+ })
+            }
+        }
+
+        impl<T: Real + Pow<u8, Output=T>> $VecN<T> {
+            pub fn magnitude(&self) -> T {
+                self.magnitude_squared().sqrt()
+            }
+
+            pub fn unit(&self) -> $VecN<T> {
+                let mag = self.magnitude();
+                $VecN {
+                    $($field: self.$field / mag),+
+                }
+            }
+        }
+
+        impl<T: NumOps + Copy> $VecN<T> {
+            pub fn dot(&self, other: $VecN<T>) -> T {
+                fold_array!(add, { $(self.$field * other.$field),+ })
+            }
+        }
+
+        impl<T: NumOps> Add for $VecN<T> {
+            type Output = Self;
+
+            fn add(self, other: Self) -> Self {
+                $VecN {
+                    $($field: self.$field + other.$field),+
+                }
+            }
+        }
+
+        impl<T: NumAssignOps> AddAssign for $VecN<T> {
+            fn add_assign(&mut self, other: Self) {
+                $(self.$field += other.$field);+
+            }
+        }
+
+        impl<T: NumOps> Sub for $VecN<T> {
+            type Output = Self;
+
+            fn sub(self, other: Self) -> Self {
+                $VecN {
+                    $($field: self.$field - other.$field),+
+                }
+            }
+        }
+
+        impl<T: NumOps + Copy> Mul<T> for $VecN<T> {
+            type Output = Self;
+
+            fn mul(self, rhs: T) -> Self {
+                $VecN {
+                    $($field: self.$field * rhs),+
+                }
+            }
+        }
+
+        impl<T: Neg<Output=T>> Neg for $VecN<T> {
+            type Output = Self;
+
+            fn neg(self) -> Self {
+                $VecN {
+                    $($field: -self.$field),+
+                }
+            }
+        }
+
+    }
+}
+
+impl_vector!(Vec2d { x, y });
+impl_vector!(Vec3d { x, y, z });
+
+impl<T: Real + Pow<u8, Output=T>> Vec2d<T> {
+    pub fn angle(&self) -> T {
+        self.y.atan2(self.x)
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn right_angles_in_2d_vectors() {
+        use std::f32::consts::{FRAC_PI_2, PI};
+
+        assert_eq!(0., Vec2d::new(1., 0.).angle());
+        assert_eq!(FRAC_PI_2, Vec2d::new(0., 1.).angle());
+        assert_eq!(PI, Vec2d::new(-1., 0.).angle());
+        assert_eq!(-FRAC_PI_2, Vec2d::new(0., -1.).angle());
+    }
+
+    #[test]
+    fn unit_normalizes_2d_vector() {
+        let before = Vec2d::new(2., 10.);
+        let after = before.unit();
+
+        assert_eq!(1., after.magnitude());
+        assert_eq!(before.angle(), after.angle());
+    }
+
+    #[test]
+    fn unit_normalizes_3d_vector() {
+        let before = Vec3d::new(2., 10., -5.);
+        let after = before.unit();
+
+        assert_eq!(1., after.magnitude());
+        // How to define 3d angle? 2 angles I suppose?
+        // assert_eq!(before.angle(), after.angle());
+    }
+    
+    #[test]
+    fn dot_product_example_2d() {
+        let a = Vec2d::new(-6., 8.);
+        let b = Vec2d::new(5., 12.);
+        assert_eq!(66., a.dot(b));
+    }
+
+    #[test]
+    fn magnitude_squared_of_an_integer() {
+        let a = Vec2d::new(3, 4);
+        assert_eq!(25, a.magnitude_squared());
+    }
+}
-- 
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