1 files changed, 149 insertions, 0 deletions
diff --git a/src/frontier.rs b/src/frontier.rs
new file mode 100644
index 0000000..7143cb7
--- /dev/null
+++ b/src/frontier.rs
@@ -0,0 +1,149 @@
+//! Frontiers on which to place pixels.
+
+pub mod image;
+pub mod mean;
+pub mod min;
+
+use crate::color::{ColorSpace, Rgb8};
+use crate::metric::kd::Cartesian;
+use crate::metric::soft::SoftDelete;
+use crate::metric::Metric;
+
+use std::cell::Cell;
+use std::rc::Rc;
+
+/// A frontier of pixels.
+pub trait Frontier {
+    /// The width of the image.
+    fn width(&self) -> u32;
+
+    /// The height of the image.
+    fn height(&self) -> u32;
+
+    /// The number of pixels currently on the frontier.
+    fn len(&self) -> usize;
+
+    /// Place the given color on the frontier, and return its position.
+    fn place(&mut self, rgb8: Rgb8) -> Option<(u32, u32)>;
+}
+
+/// A pixel on a frontier.
+#[derive(Debug)]
+struct Pixel<C> {
+    pos: (u32, u32),
+    color: C,
+    deleted: Cell<bool>,
+}
+
+impl<C: ColorSpace> Pixel<C> {
+    fn new(x: u32, y: u32, color: C) -> Self {
+        Self {
+            pos: (x, y),
+            color,
+            deleted: Cell::new(false),
+        }
+    }
+
+    fn delete(&self) {
+        self.deleted.set(true);
+    }
+}
+
+impl<C: Metric> Metric<Pixel<C>> for C {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &Pixel<C>) -> Self::Distance {
+        self.distance(&other.color)
+    }
+}
+
+impl<C: Metric<[f64]>> Metric<[f64]> for Pixel<C> {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &[f64]) -> Self::Distance {
+        self.color.distance(other)
+    }
+}
+
+impl<C: Metric> Metric for Pixel<C> {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &Pixel<C>) -> Self::Distance {
+        self.color.distance(&other.color)
+    }
+}
+
+impl<C: Cartesian> Cartesian for Pixel<C> {
+    fn dimensions(&self) -> usize {
+        self.color.dimensions()
+    }
+
+    fn coordinate(&self, i: usize) -> f64 {
+        self.color.coordinate(i)
+    }
+}
+
+impl<C> SoftDelete for Pixel<C> {
+    fn is_deleted(&self) -> bool {
+        self.deleted.get()
+    }
+}
+
+impl<C: Metric<[f64]>> Metric<[f64]> for Rc<Pixel<C>> {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &[f64]) -> Self::Distance {
+        (**self).distance(other)
+    }
+}
+
+impl<C: Metric> Metric<Rc<Pixel<C>>> for C {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &Rc<Pixel<C>>) -> Self::Distance {
+        self.distance(&other.color)
+    }
+}
+
+impl<C: Metric> Metric for Rc<Pixel<C>> {
+    type Distance = C::Distance;
+
+    fn distance(&self, other: &Self) -> Self::Distance {
+        (**self).distance(&**other)
+    }
+}
+
+impl<C: Cartesian> Cartesian for Rc<Pixel<C>> {
+    fn dimensions(&self) -> usize {
+        (**self).dimensions()
+    }
+
+    fn coordinate(&self, i: usize) -> f64 {
+        (**self).coordinate(i)
+    }
+}
+
+impl<C> SoftDelete for Rc<Pixel<C>> {
+    fn is_deleted(&self) -> bool {
+        (**self).is_deleted()
+    }
+}
+
+/// Return all the neighbors of a pixel location.
+fn neighbors(x: u32, y: u32) -> [(u32, u32); 8] {
+    let xm1 = x.wrapping_sub(1);
+    let ym1 = y.wrapping_sub(1);
+    let xp1 = x + 1;
+    let yp1 = y + 1;
+
+    [
+        (xm1, ym1),
+        (xm1, y),
+        (xm1, yp1),
+        (x, ym1),
+        (x, yp1),
+        (xp1, ym1),
+        (xp1, y),
+        (xp1, yp1),
+    ]
+}