camera: cache inverse tranform for huge speed up on ray_for_pixel.

WIP parallel render function.

rtchallenge/Cargo.lock

@@ -441,6 +441,7 @@ dependencies = [
  "anyhow",
  "criterion",
  "png",
+ "rayon",
  "thiserror",
 ]
 

rtchallenge/Cargo.toml

@@ -10,9 +10,13 @@ edition = "2018"
 anyhow = "1.0.41"
 criterion = "0.3.4"
 png = "0.16.8"
+rayon = "1.5.1"
 thiserror = "1.0.25"
 
 
 [[bench]]
 name = "matrices"
 harness = false
+
+[profile.release]
+debug = true

rtchallenge/examples/eoc7.rs

@@ -25,7 +25,7 @@ fn main() -> Result<()> {
     let from = Tuple::point(0., 1.5, -5.);
     let to = Tuple::point(0., 1., 0.);
     let up = Tuple::point(0., 1., 0.);
-    camera.transform = view_transform(from, to, up);
+    camera.set_transform(view_transform(from, to, up));
 
     let mut floor = Sphere::default();
     floor.set_transform(Matrix4x4::scaling(10., 0.01, 10.));

rtchallenge/src/camera.rs

@@ -1,10 +1,15 @@
+use std::sync::Mutex;
+
+use rayon::iter::{IntoParallelIterator, ParallelIterator};
+
 use crate::{canvas::Canvas, matrices::Matrix4x4, rays::Ray, tuples::Tuple, world::World, BLACK};
 
 pub struct Camera {
     hsize: usize,
     vsize: usize,
     field_of_view: f32,
-    pub transform: Matrix4x4,
+    transform: Matrix4x4,
+    inverse_transform: Matrix4x4,
     pixel_size: f32,
     half_width: f32,
     half_height: f32,
@@ -50,6 +55,7 @@ impl Camera {
             vsize,
             field_of_view,
             transform: Matrix4x4::identity(),
+            inverse_transform: Matrix4x4::identity(),
             pixel_size,
             half_height,
             half_width,
@@ -67,6 +73,10 @@ impl Camera {
     pub fn transform(&self) -> Matrix4x4 {
         self.transform
     }
+    pub fn set_transform(&mut self, t: Matrix4x4) {
+        self.transform = t;
+        self.inverse_transform = t.inverse();
+    }
     pub fn pixel_size(&self) -> f32 {
         self.pixel_size
     }
@@ -94,7 +104,7 @@ impl Camera {
     ///
     /// // Constructing a ray when the camera is transformed.
     /// let mut c = Camera::new(201, 101, PI / 2.);
-    /// c.transform = Matrix4x4::rotation_y(PI / 4.) * Matrix4x4::translation(0., -2., 5.);
+    /// c.set_transform(Matrix4x4::rotation_y(PI / 4.) * Matrix4x4::translation(0., -2., 5.));
     /// let r = c.ray_for_pixel(100, 50);
     /// assert_eq!(r.origin, Tuple::point(0., 2., -5.));
     /// assert_eq!(
@@ -115,8 +125,8 @@ impl Camera {
         // Using the camera matrix, transofmrm the canvas point and the origin,
         // and then compute the ray's direction vector.
         // (Remember that the canves is at z>=-1).
-        let pixel = self.transform.inverse() * Tuple::point(world_x, world_y, -1.);
-        let origin = self.transform.inverse() * Tuple::point(0., 0., 0.);
+        let pixel = self.inverse_transform * Tuple::point(world_x, world_y, -1.);
+        let origin = self.inverse_transform * Tuple::point(0., 0., 0.);
         let direction = (pixel - origin).normalize();
 
         Ray::new(origin, direction)
@@ -141,11 +151,37 @@ impl Camera {
     /// let from = Tuple::point(0., 0., -5.);
     /// let to = Tuple::point(0., 0., 0.);
     /// let up = Tuple::vector(0., 1., 0.);
-    /// c.transform = view_transform(from, to, up);
+    /// c.set_transform(view_transform(from, to, up));
     /// let image = c.render(&w);
     /// assert_eq!(image.get(5, 5), Color::new(0.38066, 0.47583, 0.2855));
     /// ```
     pub fn render(&self, w: &World) -> Canvas {
+        self.render_serial(w)
+    }
+
+    #[allow(dead_code)]
+    fn render_parallel(&self, w: &World) -> Canvas {
+        let image_mu = Mutex::new(Canvas::new(self.hsize, self.vsize, BLACK));
+
+        (0..self.vsize).into_par_iter().for_each(|y| {
+            let mut row_image = Canvas::new(self.hsize, 1, BLACK);
+            for x in 0..self.hsize {
+                let ray = self.ray_for_pixel(x, y);
+                let color = w.color_at(&ray);
+                row_image.set(x, 0, color);
+            }
+            // TODO(wathiede): create a row based setter for memcpying the row as a whole.
+            let mut image = image_mu.lock().expect("failed to lock image mutex");
+            for x in 0..self.hsize {
+                image.set(x, y, row_image.get(x, 0));
+            }
+        });
+        image_mu
+            .into_inner()
+            .expect("failed to get image out of mutex")
+    }
+
+    fn render_serial(&self, w: &World) -> Canvas {
         let mut image = Canvas::new(self.hsize, self.vsize, BLACK);
         for y in 0..self.vsize {
             for x in 0..self.hsize {