From 8c109a741b7c8b401d0d5cedf104936e6ececbf7 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Tue, 10 Oct 2023 17:25:56 -0400
Subject: [PATCH] Add Vector struct

---
 src/fart/vector.d | 190 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 190 insertions(+)
 create mode 100644 src/fart/vector.d

diff --git a/src/fart/vector.d b/src/fart/vector.d
new file mode 100644
index 0000000..9713c93
--- /dev/null
+++ b/src/fart/vector.d
@@ -0,0 +1,190 @@
+module fart.vector;
+
+import std.math;
+
+/**
+ * Structure to represent a 3-dimensional vector.
+ */
+struct Vector
+{
+    /** Vector X coordinate. */
+    double x;
+
+    /** Vector Y coordinate. */
+    double y;
+
+    /** Vector Z coordinate. */
+    double z;
+
+    /**
+     * Compute the cross product of two vectors.
+     */
+    public Vector cross()(auto ref const Vector other) const
+    {
+        return Vector(y * other.z - z * other.y,
+                z * other.x - x * other.z,
+                x * other.y - y * other.x);
+    }
+
+    /**
+     * Compute the dot product of two vectors.
+     */
+    public double dot()(auto ref const Vector other) const
+    {
+        return x * other.x + y * other.y + z * other.z;
+    }
+
+    /**
+     * Get the magnitude of the vector.
+     */
+    public double mag() const
+    {
+        return sqrt(mag2());
+    }
+
+    /**
+     * Get the squared magnitude of the vector.
+     */
+    public double mag2() const
+    {
+        return x * x + y * y + z * z;
+    }
+
+    /**
+     * Normalize the vector to have unit length.
+     */
+    public ref Vector normalize()
+    {
+        double mag = mag();
+        x /= mag;
+        y /= mag;
+        z /= mag;
+        return this;
+    }
+
+    /**
+     * Get a normalized vector in the same direction as this.
+     */
+    public Vector normalized() const
+    {
+        double mag = mag();
+        return Vector(x / mag, y / mag, z / mag);
+    }
+
+    /**
+     * Project the vector onto a target vector.
+     */
+    public Vector proj()(auto ref const Vector other) const
+    {
+        Vector on = other.normalized();
+        return on * dot(on);
+    }
+
+    /**
+     * Add two vectors.
+     */
+    public Vector opBinary(string op : "+")(auto ref const Vector other) const
+    {
+        return Vector(x + other.x, y + other.y, z + other.z);
+    }
+
+    /**
+     * Add two vectors and assign to self.
+     */
+    public Vector opOpAssign(string op : "+")(auto ref const Vector other)
+    {
+        x += other.x;
+        y += other.y;
+        z += other.z;
+        return this;
+    }
+
+    /**
+     * Negate a vector.
+     */
+    public Vector opUnary(string op : "-")() const
+    {
+        return Vector(-x, -y, -z);
+    }
+
+    /**
+     * Subtract two vectors.
+     */
+    public Vector opBinary(string op : "-")(auto ref const Vector other) const
+    {
+        return Vector(x - other.x, y - other.y, z - other.z);
+    }
+
+    /**
+     * Subtract two vectors and assign to self.
+     */
+    public Vector opOpAssign(string op : "-")(auto ref const Vector other)
+    {
+        x -= other.x;
+        y -= other.y;
+        z -= other.z;
+        return this;
+    }
+
+    /**
+     * Scale a vector.
+     */
+    public Vector opBinary(string op : "*")(double m) const
+    {
+        return Vector(x * m, y * m, z * m);
+    }
+
+    /**
+     * Scale a vector.
+     */
+    public Vector opBinaryRight(string op : "*")(double m) const
+    {
+        return Vector(x * m, y * m, z * m);
+    }
+
+    /**
+     * Compute the cross product of two vectors.
+     */
+    public Vector opBinary(string op : "*")(auto ref const Vector other) const
+    {
+        return cross(other);
+    }
+
+    public static immutable Vector X = Vector(1.0, 0.0, 0.0);
+    public static immutable Vector Y = Vector(0.0, 1.0, 0.0);
+    public static immutable Vector Z = Vector(0.0, 0.0, 1.0);
+}
+
+unittest
+{
+    Vector v = Vector(1, 2, 3);
+    const Vector w = Vector(0, 4, 5);
+
+    Vector v_times_2 = v * 2;
+    assert(v_times_2.x == 2);
+    assert(v_times_2.y == 4);
+    assert(v_times_2.z == 6);
+
+    Vector v_plus_w = v + w;
+    assert(v_plus_w == Vector(1, 6, 8));
+
+    Vector v_minus_w = v - w;
+    assert(v_minus_w == Vector(1, -2, -2));
+
+    assert(v_minus_w.mag2() == 9.0);
+    assert(v_minus_w.mag() == 3.0);
+
+    v += v_minus_w;
+    assert(v == 2 * Vector.X + 0 * Vector.Y + Vector.Z);
+
+    assert(Vector.X * Vector.Y == Vector.Z);
+    assert(Vector.Y * Vector.Z == Vector.X);
+    assert(Vector.Z * Vector.X == Vector.Y);
+    assert(Vector.Y * Vector.X == -Vector.Z);
+    assert(Vector.Z * Vector.Y == -Vector.X);
+    assert(Vector.X * Vector.Z == -Vector.Y);
+
+    assert(w.proj(Vector.X) == Vector(0, 0, 0));
+    assert(w.proj(Vector.Y) == Vector(0, 4, 0));
+    assert(w.proj(Vector.Z) == Vector(0, 0, 5));
+}