Add trail deposition, diffusion and decay.

src/blur.rs

@@ -32,8 +32,7 @@ impl Blur {
     fn boxes_for_gaussian<const N: usize>(sigma: f32) -> ([usize; N]) {
         let w_ideal = (12.0 * sigma * sigma / N as f32 + 1.0).sqrt();
         let mut w = w_ideal as usize;
-        w -= 1 - w & 1;
-
+        w -= 1 - (w & 1);
         let mut m = 0.25 * (N * (w + 3)) as f32;
         m -= 3.0 * sigma * sigma / (w + 1) as f32;
         let m = m.round() as usize;
@@ -145,4 +144,16 @@ mod tests {
             ]
         )
     }
+
+    #[test]
+    fn test_boxes_for_gaussian() {
+        let boxes = Blur::boxes_for_gaussian::<3>(1.5);
+        assert_eq!(boxes, [1, 1, 1]);
+
+        let boxes = Blur::boxes_for_gaussian::<3>(1.8);
+        assert_eq!(boxes, [1, 1, 2]);
+
+        let boxes = Blur::boxes_for_gaussian::<3>(2.5);
+        assert_eq!(boxes, [2, 2, 2]);
+    }
 }

src/grid.rs

@@ -17,8 +17,7 @@ pub struct Grid {
 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 {
-        use crate::util::is_power_of_two;
-        if !is_power_of_two(width) || !is_power_of_two(height) {
+        if !width.is_power_of_two() || !height.is_power_of_two() {
             panic!("Grid dimensitions must be a power of two.");
         }
         let rng = rand::thread_rng();

src/model.rs

@@ -1,6 +1,6 @@
 use crate::grid::Grid;
 
-use rand::{seq::SliceRandom, thread_rng, Rng};
+use rand::{seq::SliceRandom, Rng};
 use rayon::prelude::*;
 
 /// A single Physarum agent. The x and y positions are continuous, hence we use floating point
@@ -49,6 +49,7 @@ struct PopulationConfig {
     decay_factor: f32,
     sensor_angle: f32,
     rotation_angle: f32,
+    deposition_amount: f32,
 }
 
 impl PopulationConfig {
@@ -77,6 +78,8 @@ impl PopulationConfig {
             rotation_angle: rng
                 .gen_range(Self::ROTATION_ANGLE_MIN..=Self::ROTATION_ANGLE_MAX)
                 .to_radians(),
+            deposition_amount: rng
+                .gen_range(Self::DEPOSITION_AMOUNT_MIN..=Self::DEPOSITION_AMOUNT_MAX),
         }
     }
 }
@@ -163,8 +166,14 @@ impl Model {
             agent.rotate_and_move(direction, rotation_angle, step_distance, width, height);
         });
 
-        // Deposit + Diffuse + Decay
-
+        // Deposit
+        for agent in self.agents.iter() {
+            self.grid
+                .add(agent.x, agent.y, self.config.deposition_amount);
+        }
+        // Diffuse + Decay
+        self.grid
+            .diffuse(self.diffusivity, self.config.decay_factor);
         self.iteration += 1;
     }
 }

src/util.rs

@@ -1,8 +1,3 @@
-#[inline(always)]
-pub fn is_power_of_two(x: usize) -> bool {
-    (x & (x - 1)) == 0
-}
-
 #[inline(always)]
 pub fn wrap(x: f32, max: f32) -> f32 {
     x - max * ((x > max) as i32 as f32 - (x < 0.0_f32) as i32 as f32)