Bug in grid indexing.

src/grid.rs

@@ -18,7 +18,7 @@ impl Grid {
     /// Create a new grid filled with random floats in the [0.0..1.0) range.
     pub fn new(width: usize, height: usize) -> Self {
         if !width.is_power_of_two() || !height.is_power_of_two() {
-            panic!("Grid dimensitions must be a power of two.");
+            panic!("Grid dimensions must be a power of two.");
         }
         let rng = rand::thread_rng();
         let range = Uniform::from(0.0..1.0);
@@ -35,8 +35,9 @@ impl Grid {
 
     /// Truncate x and y and return a corresponding index into the data slice.
     fn index(&self, x: f32, y: f32) -> usize {
-        let i = (x as usize + self.width) & (self.width - 1);
-        let j = (y as usize + self.height) & (self.height - 1);
+        // x/y can come in negative, hence we shift them by width/height.
+        let i = (x + self.width as f32) as usize & (self.width - 1);
+        let j = (y + self.height as f32) as usize & (self.height - 1);
         j * self.width + i
     }
 

src/main.rs

@@ -1,9 +1,27 @@
+use indicatif::{ProgressBar, ProgressStyle};
 use physarum::model;
 
 fn main() {
-    let mut model = model::Model::new(128, 128, 4096, 1);
-    println!("{:#?}", model);
-    model.step();
-    model.step();
-    model.save_to_image();
+    let n_iterations = 400;
+    let pb = ProgressBar::new(n_iterations);
+    pb.set_style(
+        ProgressStyle::default_bar()
+            .template(
+                "{spinner:.green} [{elapsed_precise}] [{bar:40.cyan/blue}] {pos}/{len} ({eta})",
+            )
+            .progress_chars("#>-"),
+    );
+
+    let (width, height) = (1024, 1024);
+    let n_particles = 1 << 22;
+    let diffusivity = 1;
+    let mut model = model::Model::new(width, height, n_particles, diffusivity);
+    println!("Model configuration: {:#?}", model.config);
+
+    for i in 0..n_iterations {
+        model.step();
+        pb.set_position(i);
+    }
+    pb.finish_with_message("Finished!");
+    model.save_to_image("out.png");
 }

src/model.rs

@@ -2,6 +2,7 @@ use crate::grid::Grid;
 
 use rand::{seq::SliceRandom, Rng};
 use rayon::prelude::*;
+use std::f32::consts::TAU;
 
 /// A single Physarum agent. The x and y positions are continuous, hence we use floating point
 /// numbers instead of integers.
@@ -19,7 +20,7 @@ impl Agent {
         Agent {
             x: x * width as f32,
             y: y * height as f32,
-            angle: angle * std::f32::consts::TAU,
+            angle: angle * TAU,
         }
     }
 
@@ -34,7 +35,7 @@ impl Agent {
     ) {
         use crate::util::wrap;
         let delta_angle = rotation_angle * direction;
-        self.angle = wrap(self.angle + delta_angle, std::f32::consts::TAU);
+        self.angle = wrap(self.angle + delta_angle, TAU);
         self.x = wrap(self.x + step_distance * self.angle.cos(), width as f32);
         self.y = wrap(self.y + step_distance * self.angle.sin(), height as f32);
     }
@@ -43,7 +44,7 @@ impl Agent {
 /// A model configuration. We make it into a separate type, because we will eventually have multiple
 /// configurations in one model.
 #[derive(Debug)]
-struct PopulationConfig {
+pub struct PopulationConfig {
     sensor_distance: f32,
     step_distance: f32,
     decay_factor: f32,
@@ -95,7 +96,7 @@ pub struct Model {
 
     // Simulation parameters.
     diffusivity: usize,
-    config: PopulationConfig,
+    pub config: PopulationConfig,
 
     iteration: i32,
     width: usize,
@@ -178,7 +179,7 @@ impl Model {
     }
 
     /// Output the current trail layer as a grayscale image.
-    pub fn save_to_image(&self) {
+    pub fn save_to_image(&self, name: &str) {
         let mut img = image::GrayImage::new(self.width as u32, self.height as u32);
         let max_value = self.grid.quantile(0.999);
 
@@ -188,6 +189,6 @@ impl Model {
             let c = (value / max_value).clamp(0.0, 1.0) * 255.0;
             img.put_pixel(x, y, image::Luma([c as u8]));
         }
-        img.save("out.png").unwrap();
+        img.save(name).unwrap();
     }
 }