eoc2: write up end of chapter 2 example.

rtchallenge/examples/eoc2.rs

@@ -0,0 +1,71 @@
+use anyhow::{bail, Result};
+
+use rtchallenge::{
+    canvas::{canvas, Canvas},
+    tuples::{color, point, vector, Tuple},
+};
+
+#[derive(Debug)]
+struct Environment {
+    gravity: Tuple,
+    wind: Tuple,
+}
+#[derive(Debug)]
+struct Projectile {
+    position: Tuple,
+    velocity: Tuple,
+}
+
+fn tick(env: &Environment, proj: &Projectile) -> Projectile {
+    let position = proj.position + proj.velocity;
+    let velocity = proj.velocity + env.gravity + env.wind;
+    Projectile { position, velocity }
+}
+
+fn draw_dot(c: &mut Canvas, x: usize, y: usize) {
+    let red = color(1., 0., 0.);
+    c.set(x.saturating_sub(1), y.saturating_sub(1), red);
+    c.set(x, y.saturating_sub(1), red);
+    c.set(x + 1, y.saturating_sub(1), red);
+    c.set(x.saturating_sub(1), y, red);
+    c.set(x, y, red);
+    c.set(x + 1, y, red);
+    c.set(x.saturating_sub(1), y + 1, red);
+    c.set(x, y + 1, red);
+    c.set(x + 1, y + 1, red);
+}
+fn main() -> Result<()> {
+    let mut p = Projectile {
+        position: point(0., 1., 0.),
+        velocity: 10. * vector(1., 2., 0.).normalize(),
+    };
+    let e = Environment {
+        gravity: vector(0., -0.1, 0.),
+        wind: vector(-0.01, 0., 0.),
+    };
+
+    let w = 800;
+    let h = 600;
+    let mut c = canvas(w, h);
+    let mut i = 0;
+    let w = w as f32;
+    let h = h as f32;
+    while p.position.y > 0. {
+        p = tick(&e, &p);
+        println!("tick {}: proj {:?}", i, p);
+        let x = p.position.x;
+        let y = p.position.y;
+        if x > 0. && x < w && y > 0. && y < h {
+            let x = x as usize;
+            let y = (h - y) as usize;
+            draw_dot(&mut c, x, y)
+        }
+        i += 1;
+        if i > 1000 {
+            bail!("too many iterations");
+        }
+    }
+
+    c.write_to_file("/tmp/output.png")?;
+    Ok(())
+}