Fix typo in test

Fixed an issue that prevented the image from converging.

(Technically, the convergence was happening and the issue was the final
calculation of the displayed colours, but the visual effect was the same as
failure to converge.)

src/accumulation_buffer.rs

@@ -56,7 +56,7 @@ impl AccumulationBuffer {
         let colour_sum_t = buffer_colour_sum.values + colour_sum_y;
         buffer_colour_bias.values = (colour_sum_t - buffer_colour_sum.values) - colour_sum_y;
         buffer_colour_sum.values = colour_sum_t;
-        buffer_colour.values = buffer_colour_sum.values * (1.0 / *buffer_weight);
+        buffer_colour.values = buffer_colour_sum.values / *buffer_weight;
     }
 
     pub fn merge_tile(&mut self, tile: &Tile, src: &AccumulationBuffer) {

src/camera.rs

@@ -175,10 +175,10 @@ mod tests {
             };
             let expected_x: f64 =
                 ImageSampler::scale(200, 800, target.film_width) - target.film_width * 0.5;
-            assert!((point_on_film_plane.x() - expected_x).abs() < 0.5 / 200.0);
+            assert!((point_on_film_plane.x() - expected_x).abs() < 0.5 / 800.0);
             let expected_y =
                 -ImageSampler::scale(100, 600, target.film_height) + target.film_height * 0.5;
-            assert!((point_on_film_plane.y() - expected_y).abs() < 0.5 / 800.0);
+            assert!((point_on_film_plane.y() - expected_y).abs() < 0.5 / 600.0);
         }
     }
 }

src/math/vec3.rs

@@ -2,7 +2,7 @@ use super::Mat3;
 
 use itertools::izip;
 
-use std::ops::{Add, AddAssign, Index, IndexMut, Mul, MulAssign, Neg, Sub, SubAssign};
+use std::ops::{Add, AddAssign, Div, Index, IndexMut, Mul, MulAssign, Neg, Sub, SubAssign};
 
 #[derive(Copy, Clone, PartialEq, Debug, Default)]
 pub struct Vec3 {
@@ -316,6 +316,30 @@ impl Mul<&Vec3> for f64 {
     }
 }
 
+impl Div<f64> for &Vec3 {
+    type Output = Vec3;
+
+    fn div(self, rhs: f64) -> Vec3 {
+        let mut coords = [0.0; 3];
+        for (r, a) in coords.iter_mut().zip(self.coords.iter()) {
+            *r = a / rhs;
+        }
+        Vec3 { coords }
+    }
+}
+
+impl Div<f64> for Vec3 {
+    type Output = Vec3;
+
+    fn div(self, rhs: f64) -> Vec3 {
+        let mut coords = [0.0; 3];
+        for (r, a) in coords.iter_mut().zip(self.coords.iter()) {
+            *r = a / rhs;
+        }
+        Vec3 { coords }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -459,6 +483,14 @@ mod tests {
         assert!(a * b == c);
     }
 
+    #[test]
+    fn div_by_scalar_returns_correct_result() {
+        let a = Vec3::new(1.0, 2.0, 3.0);
+        let b = 2.0;
+        let c = Vec3::new(0.5, 1.0, 1.5);
+        assert!(dbg!(a / b) == dbg!(c));
+    }
+
     #[test]
     fn mul_assign_by_scalar_returns_correct_result() {
         let mut a = Vec3::new(1.0, 2.0, 3.0);