1 files changed, 91 insertions, 0 deletions
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..8196108
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,91 @@
+use async_std::{fs::File, io, prelude::*, task, io::BufWriter};
+
+fn lerp(fraction: f64, from: f64, to: f64) -> f64 {
+    from + fraction * (to - from)
+}
+
+fn compute_pixel(re: f64, im: f64) -> u32 {
+    let mut a = re;
+    let mut b = im;
+    let mut a2 = a * a;
+    let mut b2 = b * b;
+    let mut niters = 0;
+    while a2 + b2 < 4.0 {
+        b = 2.0 * a * b + im;
+        a = a2 - b2 + re;
+        a2 = a * a;
+        b2 = b * b;
+        niters += 1;
+        if niters >= 10240 { break; }
+    }
+    niters
+}
+
+async fn compute_row(im: f64, re_min: f64, re_max: f64, width: usize) -> Vec<u32> {
+    let mut row = Vec::new();
+    row.resize(width, 0);
+    for i in 0..width {
+        row[i] = compute_pixel(lerp((i as f64) / (width as f64), re_min, re_max), im);
+    }
+    row
+}
+
+async fn write_image(fname: &str, rows: &Vec<Vec<u32>>) -> io::Result<()> {
+    let width = rows[0].len();
+    let height = rows.len();
+    let maxval = rows.iter().map(|row| row.iter().max().unwrap()).max().unwrap();
+
+    let mut out_vec: Vec<u8> = Vec::new();
+    let mut writer = BufWriter::new(&mut out_vec);
+    write!(writer, "P2\n{} {}\n{}\n", width, height, maxval).await?;
+    for row in rows {
+        for item in row {
+            write!(writer, "{} ", item).await?;
+        }
+        writeln!(writer).await?;
+    }
+
+    let mut file = File::create(fname).await?;
+    file.write(&out_vec).await?;
+    file.flush().await?;
+
+    Ok(())
+}
+
+async fn compute_brot(fname: &str, width: usize, height: usize, left_top: (f64, f64), right_bottom: (f64, f64)) -> io::Result<()> {
+    println!("Spawning...");
+    let mut join_handles = Vec::with_capacity(height);
+    for i in 0..height {
+        let im = lerp(i as f64 / height as f64, left_top.1, right_bottom.1);
+        // Note: spawn to not run within the same thread
+        join_handles.push(task::spawn(compute_row(im, left_top.0, right_bottom.0, width)));
+    }
+
+    println!("Awaiting...");
+    let mut rows = Vec::with_capacity(height);
+    for jh in join_handles {
+        rows.push(jh.await);
+    }
+
+    println!("Writing...");
+    write_image(fname, &rows).await
+}
+
+fn main() -> io::Result<()> {
+    // Note: the following does not work:
+    //    task::block_on(task::spawn(compute_brot("out.ppm", 1920, 1080, (-1.5, 1.0), (1.0, -1.0))))
+    // You get a scary large futures error about Send.
+
+    task::block_on(async {
+        let width = 1920;
+        let height = 1080;
+        let left = -1.8;
+        let right = 1.5;
+        let height_im = height as f64 / width as f64 * (right - left);
+        let top = height_im / 2.0;
+        let bottom = -height_im / 2.0;
+        compute_brot("out.ppm", width, height, (left, top), (right, bottom)).await
+    })
+}
+
+// vim: set sw=4 ts=4 et: