Move Bresenham line drawing into library from Hough example

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;
+        }
+    }
+}

src/lib.rs

@@ -1,4 +1,5 @@
 pub mod contour;
+pub mod draw;
 pub mod filter;
 pub mod hough;
 pub mod image;