blur: boxes_for_gaussian changes

Cargo.lock

@@ -739,9 +739,9 @@ checksum = "830b246a0e5f20af87141b25c173cd1b609bd7779a4617d6ec582abaf90870f3"
 
 [[package]]
 name = "once_cell"
-version = "1.21.2"
+version = "1.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c2806eaa3524762875e21c3dcd057bc4b7bfa01ce4da8d46be1cd43649e1cc6b"
+checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
 
 [[package]]
 name = "oorandom"

src/blur.rs

@@ -30,18 +30,17 @@ impl Blur {
 
     /// Approximate 1D Gaussian filter of standard deviation sigma with N box filter passes. Each element in the output array contains the radius of the box filter for the corresponding pass.
     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 sigma_sq = sigma.powi(2);
+        let w_ideal = (12.0 * sigma_sq / N as f32 + 1.0).sqrt();
         let mut w = w_ideal as usize;
         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;
+        let m = (0.25 * (N * (w + 3)) as f32 - 3.0 * sigma_sq / (w + 1) as f32).round() as usize;
 
-        let mut result = [0; N];
-        for (i, value) in result.iter_mut().enumerate() {
-            *value = (if i < m { w - 1 } else { w + 1 }) / 2;
-        }
-        result
+        (0..N)
+            .map(|i| (w + 1 - 2 * (i < m) as usize) / 2)
+            .collect::<Vec<_>>()
+            .try_into()
+            .unwrap()
     }
 
     /// Perform one pass of the 2D box filter of the given radius. The result will be written to the src slice, while the buf slice is used as a scratch space.
@@ -67,7 +66,7 @@ impl Blur {
             .for_each(|(src_row, dst_row)| {
                 // First we build a value for the beginning of each row. We assume periodic boundary conditions, so we need to push the left index to the opposite side of the row.
                 let width_sub_radius = width - radius;
-                let mut value = src_row[width - radius - 1];
+                let mut value = src_row[width_sub_radius - 1];
                 for j in 0..radius {
                     value += src_row[width_sub_radius + j] + src_row[j];
                 }