Add simple Vec3 header file

include/vec3.h

@@ -0,0 +1,33 @@
+#ifndef VEC3_H
+#define VEC3_H
+
+template <typename T> struct Vec3 {
+  T x;
+  T y;
+  T z;
+
+  inline Vec3<T> operator+(Vec3<T> other) const {
+    return {x + other.x, y + other.y, z + other.z};
+  };
+
+  inline Vec3<T> operator-(Vec3<T> other) const {
+    return {x - other.x, y - other.y, z - other.z};
+  };
+
+  inline void scale(T scalar) {
+    x *= scalar;
+    y *= scalar;
+    z *= scalar;
+  };
+
+  inline T dot(Vec3<T> other) {
+    return x * other.x + y * other.y + z * other.z;
+  }
+
+  inline Vec3<T> cross(Vec3<T> other) {
+    return {y * other.z - z * other.y, z * other.x - x * other.z,
+            x * other.y - y * other.x};
+  }
+};
+
+#endif