canvas: add parameter to constructor to set background color.

rtchallenge/examples/eoc2.rs

@@ -44,7 +44,8 @@ fn main() -> Result<()> {
 
     let w = 800;
     let h = 600;
-    let mut c = Canvas::new(w, h);
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
     let mut i = 0;
     let w = w as f32;
     let h = h as f32;

rtchallenge/examples/eoc4.rs

@@ -23,7 +23,8 @@ fn draw_dot(c: &mut Canvas, x: usize, y: usize) {
 fn main() -> Result<()> {
     let w = 200;
     let h = w;
-    let mut c = Canvas::new(w, h);
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
     let t = Matrix4x4::translation(0., 0.4, 0.);
     let p = Tuple::point(0., 0., 0.);
     let rot_hour = Matrix4x4::rotation_z(-PI / 6.);

rtchallenge/examples/eoc5.rs

@@ -4,6 +4,7 @@ use anyhow::Result;
 
 use rtchallenge::{
     canvas::Canvas,
+    matrices::Matrix4x4,
     rays::Ray,
     spheres::{intersect, Sphere},
     tuples::{Color, Tuple},
@@ -12,14 +13,17 @@ use rtchallenge::{
 fn main() -> Result<()> {
     let w = 200;
     let h = w;
-    let mut c = Canvas::new(w, h);
+    let bg = Color::new(0.2, 0.2, 0.2);
+    let mut c = Canvas::new(w, h, bg);
     let ray_origin = Tuple::point(0., 0., -5.);
     let wall_z = 10.;
     let wall_size = 7.;
     let pixel_size = wall_size / w as f32;
     let half = wall_size / 2.;
     let color = Color::new(1., 0., 0.);
-    let shape = Sphere::default();
+    let mut shape = Sphere::default();
+    shape.transform =
+        Matrix4x4::shearing(1., 0., 0., 0., 0., 0.) * Matrix4x4::scaling(0.5, 1., 1.0);
 
     for y in 0..h {
         let world_y = half - pixel_size * y as f32;