diff --git a/rtchallenge/Cargo.lock b/rtchallenge/Cargo.lock
index c47050a..d19b78a 100644
--- a/rtchallenge/Cargo.lock
+++ b/rtchallenge/Cargo.lock
@@ -1,11 +1,60 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "adler32"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aae1277d39aeec15cb388266ecc24b11c80469deae6067e17a1a7aa9e5c1f234"
+
+[[package]]
+name = "anyhow"
+version = "1.0.41"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "15af2628f6890fe2609a3b91bef4c83450512802e59489f9c1cb1fa5df064a61"
+
 [[package]]
 name = "autocfg"
 version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
+[[package]]
+name = "bitflags"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
+
+[[package]]
+name = "byteorder"
+version = "1.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14c189c53d098945499cdfa7ecc63567cf3886b3332b312a5b4585d8d3a6a610"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "crc32fast"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "81156fece84ab6a9f2afdb109ce3ae577e42b1228441eded99bd77f627953b1a"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "deflate"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73770f8e1fe7d64df17ca66ad28994a0a623ea497fa69486e14984e715c5d174"
+dependencies = [
+ "adler32",
+ "byteorder",
+]
+
 [[package]]
 name = "float-cmp"
 version = "0.8.0"
@@ -15,6 +64,15 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "miniz_oxide"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "791daaae1ed6889560f8c4359194f56648355540573244a5448a83ba1ecc7435"
+dependencies = [
+ "adler32",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.14"
@@ -24,9 +82,79 @@ dependencies = [
  "autocfg",
 ]
 
+[[package]]
+name = "png"
+version = "0.16.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c3287920cb847dee3de33d301c463fba14dda99db24214ddf93f83d3021f4c6"
+dependencies = [
+ "bitflags",
+ "crc32fast",
+ "deflate",
+ "miniz_oxide",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0d8caf72986c1a598726adc988bb5984792ef84f5ee5aa50209145ee8077038"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d0b9745dc2debf507c8422de05d7226cc1f0644216dfdfead988f9b1ab32a7"
+dependencies = [
+ "proc-macro2",
+]
+
 [[package]]
 name = "rtchallenge"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "float-cmp",
+ "png",
+ "thiserror",
 ]
+
+[[package]]
+name = "syn"
+version = "1.0.73"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f71489ff30030d2ae598524f61326b902466f72a0fb1a8564c001cc63425bcc7"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa6f76457f59514c7eeb4e59d891395fab0b2fd1d40723ae737d64153392e9c6"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a36768c0fbf1bb15eca10defa29526bda730a2376c2ab4393ccfa16fb1a318d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
diff --git a/rtchallenge/Cargo.toml b/rtchallenge/Cargo.toml
index 5fb80a0..162f92a 100644
--- a/rtchallenge/Cargo.toml
+++ b/rtchallenge/Cargo.toml
@@ -7,4 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.41"
 float-cmp = "0.8.0"
+png = "0.16.8"
+thiserror = "1.0.25"
diff --git a/rtchallenge/examples/eoc2.rs b/rtchallenge/examples/eoc2.rs
new file mode 100644
index 0000000..885af1f
--- /dev/null
+++ b/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(())
+}