Fix inner/outer detection in contour tracing

examples/contours.rs

@@ -1,30 +1,38 @@
 mod common;
 
+use ccvl::kernel::Kernel;
 use ccvl::*;
 
-fn draw(contour: &contour::Contour, img: &mut image::Image<image::SRGBA>) {
+fn draw(
-    let n = contour.vertices.len();
+    img: &mut image::Image<image::SRGBA>,
+    path: &Vec<(usize, usize)>,
+    colour: image::SRGBA,
+) {
+    let n = path.len();
     for i in 0..n {
-        let (x0, y0) = contour.vertices[i];
+        let (x0, y0) = path[i];
-        let (x1, y1) = contour.vertices[(i + 1) % n];
+        let (x1, y1) = path[(i + 1) % n];
-        let colour = match contour.kind {
-            contour::Kind::Outer => colours::GREEN,
-            contour::Kind::Inner => colours::BLUE,
-        };
         draw::line(x0, y0, x1, y1, img, colour);
     }
 }
 
+fn approx(a: f32, b: f32, epsilon: f32) -> bool {
+    (a - b).abs() <= epsilon
+}
+
 fn main() -> std::process::ExitCode {
     common::process_image(|mut img| {
         let greyscale = img.map(|p| image::Luminance::from(p));
-        let thresholded = filter::threshold_auto(greyscale);
+        let blurred = kernel::gaussian::<5>(1.2).convolve_sat(&greyscale);
-
+        let thresholded = filter::threshold_auto(blurred);
-        let contours = contour::find(thresholded);
+        let contours =
+            contour::find(&thresholded, image::Luminance { y: 0.0 });
         for contour in contours {
-            draw(&contour, &mut img);
+            draw(&mut img, &contour.vertices, match contour.kind {
+				contour::Kind::Outer => colours::GREEN,
+				contour::Kind::Inner => colours::BLUE,
+			});
         }
-
         img
     })
 }

src/contour.rs

@@ -45,12 +45,15 @@ trait Coordinate {
     fn set<P>(&self, img: &mut image::Image<P>, value: P);
 }
 
-pub fn find(img: image::Image<image::Luminance>) -> Vec<Contour> {
+pub fn find<P>(img: &image::Image<P>, fg: P) -> Vec<Contour>
+where
+    P: PartialEq + Copy + Send + Sync,
+{
     let mut map = img.map(|p| {
-        if p.y == 1.0 {
+        if p == fg {
-            Pixel::Background
-        } else {
             Pixel::Foreground
+        } else {
+            Pixel::Background
         }
     });
 
@@ -83,7 +86,8 @@ fn add(
     map: &mut image::Image<Pixel>,
 ) {
     let label = contours.len();
-    let vertices = trace(map, start, kind.start_dir(), label);
+    let dir = kind.find_start_dir(start, map);
+    let vertices = trace(map, start, dir, label);
     contours.push(Contour::new(parent, kind, vertices));
     if let Some(index) = parent {
         contours[index].add_child(label);
@@ -98,9 +102,6 @@ fn trace(
 ) -> Vec<(usize, usize)> {
     let mut q = start_q;
     let mut dir = start_dir;
-    while background(img, dir.from(q)) {
-        dir.next();
-    }
 
     let mut vertices = Vec::new();
     loop {
@@ -124,20 +125,17 @@ fn trace(
             dir = dir.next();
         };
 
-        if q == start_q || !q.in_bounds(img.extent) {
+        if q == start_q && dir == start_dir || !q.in_bounds(img.extent) {
-            if dir != start_dir {
-                vertices.push(q);
-            }
             break;
         }
     }
 
-    // println!();
     // for y in 0..img.extent.y {
+    //     print!("  ");
     //     for x in 0..img.extent.x {
     //         if let Some(label) = traced_up(img, (x, y)) {
     //             print!("{:1}", label);
-    //         } else if let Some(label) = traced_down(img, (x, y)) {
+    //         } else if let Some(_) = traced_down(img, (x, y)) {
     //             print!("-")
     //         } else if foreground(img, (x, y)) {
     //             print!(".");
@@ -183,11 +181,19 @@ fn traced_down(
 }
 
 impl Kind {
-    fn start_dir(self) -> Dir {
+    fn find_start_dir(
-        match self {
+        self,
-            Kind::Outer => Dir::E,
+        q: (usize, usize),
-            Kind::Inner => Dir::W,
+        img: &image::Image<Pixel>,
+    ) -> Dir {
+        let mut dir = match self {
+            Kind::Outer => Dir::W,
+            Kind::Inner => Dir::E,
+        };
+        while background(img, dir.from(q)) {
+            dir = dir.prev()
         }
+        dir.flip()
     }
 }
 
@@ -205,6 +211,19 @@ impl Dir {
         }
     }
 
+    fn prev(self) -> Self {
+        match self {
+            Self::N => Self::NW,
+            Self::NE => Self::N,
+            Self::E => Self::NE,
+            Self::SE => Self::E,
+            Self::S => Self::SE,
+            Self::SW => Self::S,
+            Self::W => Self::SW,
+            Self::NW => Self::W,
+        }
+    }
+
     fn flip(self) -> Self {
         match self {
             Self::N => Self::S,
@@ -292,3 +311,127 @@ impl Default for Pixel {
         Self::Background
     }
 }
+
+#[cfg(test)]
+#[rustfmt::skip]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn simple_block() {
+		let img = image::Image::<usize> {
+			extent: image::Extent { x: 4, y: 4 },
+			pixels: vec![
+				0, 0, 0, 0,
+				0, 1, 1, 0,
+				0, 1, 1, 0,
+				0, 0, 0, 0,
+			]
+		};
+
+		let contours = find(&img, 1);
+		assert_eq!(contours.len(), 1);
+
+		let contour = &contours[0];
+		assert_eq!(contour.kind, Kind::Outer);
+		assert_eq!(contour.vertices, vec![
+			(1, 1), (2, 1), (2, 2), (1, 2)
+		]);
+	}
+
+	#[test]
+	fn simple_block_with_hole() {
+		let img = image::Image::<usize> {
+			extent: image::Extent { x: 8, y: 8 },
+			pixels: vec![
+				0, 0, 0, 0, 0, 0, 0, 0,
+				0, 1, 1, 1, 1, 1, 1, 0,
+				0, 1, 1, 1, 1, 1, 1, 0,
+				0, 1, 1, 0, 0, 1, 1, 0,
+				0, 1, 1, 0, 0, 1, 1, 0,
+				0, 1, 1, 1, 1, 1, 1, 0,
+				0, 1, 1, 1, 1, 1, 1, 0,
+				0, 0, 0, 0, 0, 0, 0, 0,
+			]
+		};
+
+		let contours = find(&img, 1);
+		assert_eq!(contours.len(), 2);
+
+		let contour = &contours[0];
+		assert_eq!(contour.parent, None);
+		assert_eq!(contour.kind, Kind::Outer);
+		assert_eq!(contour.vertices, vec![
+			(1, 1), (6, 1), (6, 6), (1, 6)
+		]);
+		assert_eq!(contour.children, vec![ 1 ]);
+
+		let contour = &contours[1];
+		assert_eq!(contour.parent, Some(0));
+		assert_eq!(contour.kind, Kind::Inner);
+		assert_eq!(contour.vertices, vec![
+			(2, 3), (2, 4), (3, 5), (4, 5),
+			(5, 4), (5, 3), (4, 2), (3, 2),
+		]);
+	}
+
+	#[test]
+	fn diagonally_connected_block_with_hole() {
+		let img = image::Image::<usize> {
+			extent: image::Extent { x: 8, y: 8 },
+			pixels: vec![
+				0, 0, 0, 0, 0, 0, 0, 0,
+				0, 0, 0, 1, 1, 1, 1, 0,
+				0, 0, 0, 1, 1, 1, 1, 0,
+				0, 1, 1, 0, 0, 1, 1, 0,
+				0, 1, 1, 0, 0, 1, 1, 0,
+				0, 0, 0, 1, 1, 1, 1, 0,
+				0, 0, 0, 1, 1, 1, 1, 0,
+				0, 0, 0, 0, 0, 0, 0, 0,
+			]
+		};
+
+		let contours = find(&img, 1);
+		assert_eq!(contours.len(), 2);
+
+		let contour = &contours[0];
+		assert_eq!(contour.parent, None);
+		assert_eq!(contour.kind, Kind::Outer);
+		assert_eq!(contour.vertices, vec![
+			(3, 1), (6, 1), (6, 6), (3, 6), (3, 5),
+			(2, 4), (1, 4), (1, 3), (2, 3), (3, 2),
+		]);
+		assert_eq!(contour.children, vec![ 1 ]);
+
+		let contour = &contours[1];
+		assert_eq!(contour.parent, Some(0));
+		assert_eq!(contour.kind, Kind::Inner);
+		assert_eq!(contour.vertices, vec![
+			(2, 3), (2, 4), (3, 5), (4, 5),
+			(5, 4), (5, 3), (4, 2), (3, 2),
+		]);
+	}
+
+	#[test]
+	fn contour_passes_through_start() {
+		let img = image::Image::<usize> {
+			extent: image::Extent { x: 5, y: 5 },
+			pixels: vec![
+				0, 0, 0, 0, 0,
+				0, 0, 1, 1, 0,
+				0, 1, 0, 0, 0,
+				0, 1, 0, 0, 0,
+				0, 0, 0, 0, 0,
+			]
+		};
+
+		let contours = find(&img, 1);
+		assert_eq!(contours.len(), 1);
+
+		let contour = &contours[0];
+		assert_eq!(contour.kind, Kind::Outer);
+		assert_eq!(contour.vertices, vec![
+			(2, 1), (3, 1), (2, 1), (1, 2), (1, 3), (1, 2)
+		]);
+	}
+}