From e9900af986f1bd52079dd7f64487c47a795b6d08 Mon Sep 17 00:00:00 2001
From: Matthew Gordon <matthew.scott.gordon@gmail.com>
Date: Tue, 12 Nov 2019 07:31:02 -0500
Subject: [PATCH] Some cleanup and added unit test for pixel ray generation

---
 src/camera.rs | 102 ++++++++++++++++++++++++--------------------------
 1 file changed, 49 insertions(+), 53 deletions(-)

diff --git a/src/camera.rs b/src/camera.rs
index 53b0883..c241cb2 100644
--- a/src/camera.rs
+++ b/src/camera.rs
@@ -1,70 +1,60 @@
-use nalgebra::{RealField, Vector3};
+use nalgebra::{convert, RealField, Vector3};
 
 use super::image::OutputImage;
-use super::raycasting::{Intersect, IntersectionInfo, Ray};
+use super::raycasting::{Intersect, IntersectionInfo, Plane, Ray};
 
-struct ImageSampler<T: RealField + From<u32> + From<f64>> {
+struct ImageSampler<T: RealField> {
     image_height_pixels: u32,
     image_width_pixels: u32,
 
-    fov_width: T,
-    fov_height: T,
-
-    current_row: u32,
-    current_column: u32,
+    film_width: T,
+    film_height: T,
 
     camera_location: Vector3<T>,
-    film_plane_distance: T,
+    film_distance: T,
 }
 
-impl<T: RealField + From<u32> + From<f64>> ImageSampler<T> {
+impl<T: RealField> ImageSampler<T> {
     pub fn new(width: u32, height: u32, camera_location: Vector3<T>) -> ImageSampler<T> {
-        let (fov_width, fov_height) = if (width > height) {
-            (T::from(width) / (T::from(height)), T::from(1.0))
-        } else {
-            (T::from(1.0), T::from(width) / T::from(height))
+        let (film_width, film_height) = {
+            let width: T = convert(width as f64);
+            let height: T = convert(height as f64);
+            let film_size: T = convert(1.0);
+            if width > height {
+                (width / height, film_size)
+            } else {
+                (film_size, width / height)
+            }
         };
         ImageSampler {
             image_height_pixels: height,
             image_width_pixels: width,
-            current_row: 0,
-            current_column: 0,
-            film_plane_distance: T::from(1.0),
-            fov_width,
-            fov_height,
+            film_distance: convert(1.0),
+            film_width,
+            film_height,
             camera_location,
         }
     }
 
     fn scale(i: u32, n: u32, l: T) -> T {
-        let pixel_size = l * (T::from(1.0) / T::from(n));
-        (T::from(i) + T::from(0.5)) * pixel_size
+        let one: T = convert(1.0);
+        let n: T = convert(n as f64);
+        let i: T = convert(i as f64);
+        let pixel_size: T = l * (one / n);
+        (i + convert(0.5)) * pixel_size
     }
-}
 
-impl<T: RealField + From<u32> + From<f64>> Iterator for ImageSampler<T> {
-    type Item = Ray<T>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.current_row >= self.image_height_pixels {
-            return None;
-        }
-
-        let result = Ray::new(
+    fn ray_for_pixel(&self, row: u32, column: u32) -> Ray<T> {
+        Ray::new(
             self.camera_location,
             Vector3::new(
-                Self::scale(self.current_column, self.image_width_pixels, self.fov_width),
-                Self::scale(self.current_row, self.image_height_pixels, self.fov_height),
-                self.film_plane_distance,
+                Self::scale(column, self.image_width_pixels, self.film_width)
+                    - self.film_width * convert(0.5),
+                Self::scale(row, self.image_height_pixels, self.film_height)
+                    - self.film_height * convert(0.5),
+                self.film_distance,
             ),
-        );
-
-        self.current_column += 1;
-        if (self.current_column >= self.image_width_pixels) {
-            self.current_column = 0;
-            self.current_row += 1;
-        }
-        Some(result)
+        )
     }
 }
 
@@ -78,25 +68,31 @@ mod tests {
         #[test]
         fn scale_returns_correct_value_for_zero() {
             let correct_value = (3.0 / 10.0) / 2.0;
-            assert!((ImageSampler::scale(0, 10, 3.0) - correct_value).abs() < 0.0000000001)
+            assert!((ImageSampler::scale(0, 10, 3.0f64) - correct_value).abs() < 0.0000000001)
         }
 
         #[test]
         fn scale_returns_correct_value_for_last_pixel() {
             let correct_value = 3.0 - (3.0 / 10.0) / 2.0;
-            assert!((ImageSampler::scale(9, 10, 3.0) - correct_value).abs() < 0.0000000001)
+            assert!((ImageSampler::scale(9, 10, 3.0f64) - correct_value).abs() < 0.0000000001)
         }
 
         #[test]
-        fn iterates_over_correct_number_of_samples() {
-            let width = 100;
-            let height = 200;
-            let target = ImageSampler::new(width, height, Vector3::new(0.0, 0.0, 0.0));
-            let mut count = 0;
-            for sample in target {
-                count += 1;
-            }
-            assert!(count == width * height);
+        fn ray_for_pixel_returns_value_that_intersects_film_plane_at_expected_location() {
+            let target = ImageSampler::new(800, 600, Vector3::new(0.0, 0.0, 0.0));
+            let ray = target.ray_for_pixel(100, 200);
+            let film_plane = Plane::new(Vector3::new(0.0, 0.0, 1.0), target.film_distance);
+            let point_on_film_plane = match film_plane.intersect(&ray) {
+                Some(IntersectionInfo { location, distance }) => location,
+                None => panic!(),
+            };
+            let expected_x: f64 =
+                ImageSampler::scale(200, 800, target.film_width) - target.film_width * 0.5;
+            print!("{}, {}", expected_x, point_on_film_plane);
+            assert!((point_on_film_plane.x - expected_x).abs() < 0.0000000001);
+            let expected_y =
+                ImageSampler::scale(100, 600, target.film_height) - target.film_height * 0.5;
+            assert!((point_on_film_plane.y - expected_y).abs() < 0.0000000001);
         }
     }
 }