From d550a7e71ec9aee3f44b47b1867b322ac8edbd12 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Thu, 29 Oct 2026 10:39:25 +0000
Subject: [PATCH] Move Bresenham line drawing into library from Hough example

---
 examples/hough.rs | 130 +++++++++++++---------------------------------
 src/draw.rs       |  43 +++++++++++++++
 src/lib.rs        |   1 +
 3 files changed, 81 insertions(+), 93 deletions(-)
 create mode 100644 src/draw.rs

diff --git a/examples/hough.rs b/examples/hough.rs
index 7be8ad0..8a4e7ec 100644
--- a/examples/hough.rs
+++ b/examples/hough.rs
@@ -1,10 +1,8 @@
 mod common;
 
-use ccvl::filter::*;
-use ccvl::hough;
-use ccvl::image::*;
+use ccvl::*;
 
-const LINE: SRGBA = SRGBA {
+const LINE: image::SRGBA = image::SRGBA {
     r: 1.0,
     g: 0.0,
     b: 0.0,
@@ -13,102 +11,48 @@ const LINE: SRGBA = SRGBA {
 
 fn main() -> std::process::ExitCode {
     common::process_image(|mut img| {
-        let greyscale = img.map(|p| Luminance::from(p));
-        let edges = canny(greyscale);
+        let greyscale = img.map(|p| image::Luminance::from(p));
+        let edges = filter::canny(greyscale);
         for line in hough::lines(10.0, edges) {
-            draw(line, &mut img);
+			let ((x0, y0), (x1, y1)) = endpoints(line, img.extent);
+			draw::line(x0, y0, x1, y1, &mut img, LINE);
         }
         img
     })
 }
 
-fn in_bounds(q: &(f32, f32), lim: Extent) -> bool {
+fn endpoints(
+    l: hough::Line,
+    lim: image::Extent,
+) -> ((usize, usize), (usize, usize)) {
+    if l.theta.abs() < 1e-3 {
+        ((l.rho as usize, 0), (l.rho as usize, lim.y - 1))
+    } else if l.theta - std::f32::consts::PI / 2.0 < 1e-3 {
+        ((0, l.rho as usize), (lim.x - 1, l.rho as usize))
+    } else {
+        let w = lim.x as f32 - 1e-3;
+        let h = lim.y as f32 - 1e-3;
+
+        let ros = l.rho / l.theta.sin();
+        let roc = l.rho / l.theta.cos();
+        let t = l.theta.tan();
+
+        let candidates: [(f32, f32); 4] =
+            [(roc - h * t, h), (0.0, ros), (roc, 0.0), (w, ros - w / t)];
+        let res = candidates
+            .into_iter()
+            .filter(|p| in_bounds(p, lim))
+            .map(|(x, y)| (x as usize, y as usize))
+            .collect::<Vec<_>>();
+        if res.len() != 2 {
+            panic!("Unexpected number of endpoints for {:?}", l);
+        }
+        (res[0], res[1])
+    }
+}
+
+fn in_bounds(q: &(f32, f32), lim: image::Extent) -> bool {
     let x_in = 0.0 <= q.0 && q.0 < lim.x as f32;
     let y_in = 0.0 <= q.1 && q.1 < lim.y as f32;
     x_in && y_in
 }
-
-fn endpoints(
-    l: hough::Line,
-    lim: Extent,
-) -> ((usize, usize), (usize, usize)) {
-    let w = lim.x as f32 - 1e-3;
-    let h = lim.y as f32 - 1e-3;
-
-    let ros = l.rho / l.theta.sin();
-    let roc = l.rho / l.theta.cos();
-    let t = l.theta.tan();
-
-    let candidates: [(f32, f32); 4] =
-        [(roc - h * t, h), (0.0, ros), (roc, 0.0), (w, ros - w / t)];
-    let res = candidates
-        .into_iter()
-        .filter(|p| in_bounds(p, lim))
-        .map(|(x, y)| (x as usize, y as usize))
-        .collect::<Vec<_>>();
-    if res.len() != 2 {
-        panic!("Unexpected number of endpoints for {:?}", l);
-    }
-    (res[0], res[1])
-}
-
-fn draw(l: hough::Line, img: &mut Image<SRGBA>) {
-    if l.theta.abs() < 1e-3 {
-        // vertical line
-        let x = l.rho as usize;
-        for y in 0..img.extent.y {
-            if x >= img.extent.x || y >= img.extent.y {
-                return;
-            }
-            *img.at_mut(x, y) = LINE;
-        }
-    } else if (l.theta - std::f32::consts::PI / 2.0) < 1e-3 {
-        // horizontal line
-        let y = l.rho as usize;
-        for x in 0..img.extent.x {
-            if x >= img.extent.x || y >= img.extent.y {
-                return;
-            }
-            *img.at_mut(x, y) = LINE;
-        }
-    } else {
-        bresenham(endpoints(l, img.extent), img);
-    }
-}
-
-fn bresenham(qs: ((usize, usize), (usize, usize)), img: &mut Image<SRGBA>) {
-    let ((x0, y0), (x1, y1)) = qs;
-
-    let dx = x0.abs_diff(x1) as isize;
-    let dy = -(y0.abs_diff(y1) as isize);
-
-    let sx = if x0 < x1 { 1 } else { -1 };
-    let sy = if y0 < y1 { 1 } else { -1 };
-
-    let mut x = x0;
-    let mut y = y0;
-    let mut error = dx + dy;
-
-    loop {
-        if x >= img.extent.x || y >= img.extent.y {
-            return;
-        }
-
-        *img.at_mut(x, y) = LINE;
-        let e2 = 2 * error;
-        if e2 >= dy {
-            if x == x1 {
-                break;
-            }
-            error += dy;
-            x = (x as isize + sx) as usize;
-        }
-        if e2 <= dx {
-            if y == y1 {
-                break;
-            }
-            error += dx;
-            y = (y as isize + sy) as usize;
-        }
-    }
-}
diff --git a/src/draw.rs b/src/draw.rs
new file mode 100644
index 0000000..d82b4df
--- /dev/null
+++ b/src/draw.rs
@@ -0,0 +1,43 @@
+use crate::*;
+
+pub fn line<P: Copy>(
+    x0: usize,
+    y0: usize,
+    x1: usize,
+    y1: usize,
+    img: &mut image::Image<P>,
+    colour: P,
+) {
+    let dx = x0.abs_diff(x1) as isize;
+    let dy = -(y0.abs_diff(y1) as isize);
+
+    let sx = if x0 < x1 { 1 } else { -1 };
+    let sy = if y0 < y1 { 1 } else { -1 };
+
+    let mut x = x0;
+    let mut y = y0;
+    let mut error = dx + dy;
+
+    loop {
+        if x >= img.extent.x || y >= img.extent.y {
+            return;
+        }
+
+        *img.at_mut(x, y) = colour;
+        let e2 = 2 * error;
+        if e2 >= dy {
+            if x == x1 {
+                break;
+            }
+            error += dy;
+            x = (x as isize + sx) as usize;
+        }
+        if e2 <= dx {
+            if y == y1 {
+                break;
+            }
+            error += dx;
+            y = (y as isize + sy) as usize;
+        }
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index d538bd8..6e07453 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 pub mod contour;
+pub mod draw;
 pub mod filter;
 pub mod hough;
 pub mod image;