From b13cbe316d116e918b77d0e004b354fc479a3405 Mon Sep 17 00:00:00 2001
From: Matthew Gordon <matthew.scott.gordon@gmail.com>
Date: Thu, 12 Mar 2020 21:26:22 -0400
Subject: [PATCH] Add Transform trait and implement for Sphere

---
 src/raycasting/mod.rs    |  6 ++-
 src/raycasting/sphere.rs | 83 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 86 insertions(+), 3 deletions(-)

diff --git a/src/raycasting/mod.rs b/src/raycasting/mod.rs
index 7b09740..64e59e1 100644
--- a/src/raycasting/mod.rs
+++ b/src/raycasting/mod.rs
@@ -1,4 +1,4 @@
-use nalgebra::{Point3, Vector3};
+use nalgebra::{Point3, Transform3, Vector3};
 
 use super::materials::Material;
 use crate::Real;
@@ -68,6 +68,10 @@ pub trait HasBoundingBox<T: Real>: Send + Sync {
     fn bounding_box(&self) -> BoundingBox<T>;
 }
 
+pub trait Transform<T: Real>: Send + Sync {
+    fn transform(&mut self, transformation: &Transform3<T>) -> &Self;
+}
+
 pub trait Primitive<T: Real>: Intersect<T> + HasBoundingBox<T> {}
 
 #[cfg(test)]
diff --git a/src/raycasting/sphere.rs b/src/raycasting/sphere.rs
index 3bc3d22..762dbb4 100644
--- a/src/raycasting/sphere.rs
+++ b/src/raycasting/sphere.rs
@@ -1,9 +1,9 @@
-use nalgebra::{convert, Point3, Vector3};
+use nalgebra::{convert, Point3, Transform3, Vector3};
 
 use crate::materials::Material;
 use crate::Real;
 
-use super::{BoundingBox, HasBoundingBox, Intersect, IntersectionInfo, Primitive, Ray};
+use super::{BoundingBox, HasBoundingBox, Intersect, IntersectionInfo, Primitive, Ray, Transform};
 
 use std::sync::Arc;
 
@@ -24,6 +24,18 @@ impl<T: Real> Sphere<T> {
     }
 }
 
+impl<T: Real> Transform<T> for Sphere<T> {
+    fn transform(&mut self, transformation: &Transform3<T>) -> &Self {
+        self.centre = transformation.transform_point(&self.centre);
+        // This is not the most efficient way of calculating the radius,
+        //but will work as long as the resulting shape is still a sphere.
+        self.radius = transformation
+            .transform_vector(&Vector3::new(self.radius, T::zero(), T::zero()))
+            .norm();
+        self
+    }
+}
+
 impl<T: Real> Intersect<T> for Sphere<T> {
     fn intersect<'a>(&'a self, ray: &Ray<T>) -> Option<IntersectionInfo<T>> {
         let two: T = convert(2.0);
@@ -93,6 +105,8 @@ mod tests {
     use quickcheck::TestResult;
     use quickcheck_macros::quickcheck;
 
+    use nalgebra::{Rotation3, Translation3};
+
     use super::*;
     use crate::materials::LambertianMaterial;
 
@@ -183,4 +197,69 @@ mod tests {
         let bounding_box = target_sphere.bounding_box();
         bounding_box.contains_point(sphere_centre + radius_vector)
     }
+
+    #[quickcheck]
+    fn translation_moves_centre(
+        sphere_centre: Point3<f64>,
+        radius: f64,
+        translation_vector: Vector3<f64>,
+    ) -> TestResult {
+        if radius <= 0.0 {
+            return TestResult::discard();
+        };
+        let mut sphere = Sphere::new(
+            sphere_centre,
+            radius,
+            Arc::new(LambertianMaterial::new_dummy()),
+        );
+        let expected_centre = sphere.centre + translation_vector;
+        let mut transformation = Transform3::identity();
+        transformation *= Translation3::from(translation_vector);
+        sphere.transform(&transformation);
+        TestResult::from_bool(expected_centre == sphere.centre)
+    }
+
+    #[quickcheck]
+    fn translation_does_not_change_radius(
+        sphere_centre: Point3<f64>,
+        radius: f64,
+        translation_vector: Vector3<f64>,
+    ) -> TestResult {
+        if radius <= 0.0 {
+            return TestResult::discard();
+        };
+        let mut sphere = Sphere::new(
+            sphere_centre,
+            radius,
+            Arc::new(LambertianMaterial::new_dummy()),
+        );
+        let expected_radius = sphere.radius;
+        let mut transformation = Transform3::identity();
+        transformation *= Translation3::from(translation_vector);
+        sphere.transform(&transformation);
+        TestResult::from_bool(expected_radius == sphere.radius)
+    }
+
+    #[quickcheck]
+    fn rotation_about_centre_does_not_move_centre(
+        sphere_centre: Point3<f64>,
+        radius: f64,
+        rotation_vector: Vector3<f64>,
+    ) -> TestResult {
+        if radius <= 0.0 {
+            return TestResult::discard();
+        };
+        let mut sphere = Sphere::new(
+            sphere_centre,
+            radius,
+            Arc::new(LambertianMaterial::new_dummy()),
+        );
+        let expected_centre = sphere.centre;
+        let mut transformation = Transform3::identity();
+        transformation *= Translation3::from(sphere.centre.coords)
+            * Rotation3::new(rotation_vector)
+            * Translation3::from(-sphere.centre.coords);
+        sphere.transform(&transformation);
+        TestResult::from_bool(dbg!((expected_centre - sphere.centre).norm() < 0.000000001))
+    }
 }