Modify contour finding to return path vertices instead of trace

examples/contours.rs

@@ -21,12 +21,15 @@ fn main() -> std::process::ExitCode {
 		let thresholded = filter::threshold_auto(greyscale);
         let contours = contour::find(thresholded);
         for contour in contours {
-            for (x, y) in contour.trace {
-                *img.at_mut(x, y) = match contour.kind {
-                    contour::Kind::Inner => INNER,
-                    contour::Kind::Outer => OUTER,
-                };
-            }
+			let n = contour.vertices.len();
+			for i in 0..n {
+				let (x0, y0) = contour.vertices[i];
+				let (x1, y1) = contour.vertices[(i + 1) % n];
+				draw::line(x0, y0, x1, y1, &mut img, match contour.kind {
+					contour::Kind::Outer => OUTER,
+					contour::Kind::Inner => INNER,
+				});
+			}
         }
         img
     })

src/contour.rs

@@ -8,7 +8,7 @@ pub enum Kind {
 
 #[derive(Debug, PartialEq)]
 pub struct Contour {
-    pub trace: Vec<(usize, usize)>,
+    pub vertices: Vec<(usize, usize)>,
     pub children: Vec<usize>,
     pub parent: Option<usize>,
     pub kind: Kind,
@@ -58,66 +58,73 @@ pub fn find(img: image::Image<image::Luminance>) -> Vec<Contour> {
         let mut parent = None;
         for x in 0..map.extent.x {
             let q = (x, y);
-            if foreground(&map, q) {
-				let prev_bg = background(&map, q.prev_x());
-				let next_bg = background(&map, q.next_x());
-				if prev_bg || next_bg {
-					let (dir, kind) = if prev_bg {
-						(Dir::W, Kind::Outer)
-					} else {
-						(Dir::E, Kind::Inner)
-					};
-					let label = contours.len();
-					let trace = trace(&mut map, q, dir, label);
-					contours.push(Contour::new(parent, kind, trace));
-					if let Some(index) = parent {
-						contours[index].add_child(label);
-					}
-				}
+            if foreground(&map, q) && background(&map, q.prev_x()) {
+                add(q, Kind::Outer, parent, &mut contours, &mut map);
+            } else if foreground(&map, q) && background(&map, q.next_x()) {
+                add(q, Kind::Inner, parent, &mut contours, &mut map);
             } else if let Some(label) = traced(&map, q) {
-				if background(&map, q.prev_x()) {
-					parent = Some(label);
-				} else if background(&map, q.next_x()) {
-					parent = contours[label].parent;
-				}
-			}
+                if background(&map, q.prev_x()) {
+                    parent = Some(label);
+                } else if background(&map, q.next_x()) {
+                    parent = contours[label].parent;
+                }
+            }
         }
     }
     contours
 }
 
+fn add(
+    start: (usize, usize),
+    kind: Kind,
+    parent: Option<usize>,
+    contours: &mut Vec<Contour>,
+    map: &mut image::Image<Pixel>,
+) {
+    let label = contours.len();
+    let vertices = trace(map, start, kind.start_dir(), label);
+    contours.push(Contour::new(parent, kind, vertices));
+    if let Some(index) = parent {
+        contours[index].add_child(label);
+    }
+}
+
 fn trace(
     img: &mut image::Image<Pixel>,
     start_q: (usize, usize),
-    mut dir: Dir,
+    start_dir: Dir,
     label: usize,
 ) -> Vec<(usize, usize)> {
     let mut q = start_q;
-    dir = dir.next();
+    let mut dir = start_dir;
+    while background(img, dir.from(q)) {
+        dir.next();
+    }
 
-    let mut path = Vec::new();
-    'outer: loop {
-        if !q.in_bounds(img.extent) {
-            break;
-        }
+    let mut vertices = Vec::new();
+    loop {
         q.set(img, Pixel::Traced(label));
-        path.push(q);
 
-        let start = dir;
-        while background(img, dir.from(q)) {
-            dir = dir.next();
-            if dir == start {
-                break 'outer;
-            }
-        }
-        q = dir.from(q);
+        let prev_dir = dir;
         dir = dir.flip().next();
+        q = loop {
+            let qp = dir.from(q);
+            if !background(img, qp) {
+                if dir != prev_dir {
+                    vertices.push(q)
+                }
+                break qp;
+            }
+            dir = dir.next();
+        };
 
-        if q == start_q {
-            break;
+        if q == start_q || !q.in_bounds(img.extent) {
+            if dir != start_dir {
+                vertices.push(q);
+            }
+            break vertices;
         }
     }
-    path
 }
 
 fn foreground(img: &image::Image<Pixel>, q: (usize, usize)) -> bool {
@@ -141,6 +148,15 @@ fn traced(img: &image::Image<Pixel>, q: (usize, usize)) -> Option<usize> {
     }
 }
 
+impl Kind {
+    fn start_dir(self) -> Dir {
+        match self {
+            Kind::Outer => Dir::E,
+            Kind::Inner => Dir::W,
+        }
+    }
+}
+
 impl Dir {
     fn next(self) -> Self {
         match self {
@@ -222,19 +238,19 @@ impl Contour {
     fn new(
         parent: Option<usize>,
         kind: Kind,
-        trace: Vec<(usize, usize)>,
+        vertices: Vec<(usize, usize)>,
     ) -> Self {
         Self {
-            trace,
+            vertices,
             children: Vec::new(),
             parent,
             kind,
         }
     }
 
-	fn add_child(&mut self, child: usize) {
-		self.children.push(child);
-	}
+    fn add_child(&mut self, child: usize) {
+        self.children.push(child);
+    }
 }
 
 impl Default for Pixel {