region: add tagged regions

algorithms/src/rect.rs

@@ -5,31 +5,72 @@ use {
     std::fmt::{Debug, Formatter},
 };
 
+pub trait Tag: Copy + Eq + Ord + Debug + Default + Sized {
+    const IS_SIGNIFICANT: bool;
+
+    fn constrain(self) -> Self;
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Default)]
+pub struct NoTag;
+
+impl Tag for NoTag {
+    const IS_SIGNIFICANT: bool = false;
+
+    #[inline(always)]
+    fn constrain(self) -> Self {
+        Self
+    }
+}
+
+impl Tag for u32 {
+    const IS_SIGNIFICANT: bool = true;
+
+    #[inline(always)]
+    fn constrain(self) -> Self {
+        self & 1
+    }
+}
+
 #[derive(Copy, Clone, Eq, PartialEq, Default)]
-pub struct RectRaw {
+pub struct RectRaw<T = NoTag>
+where
+    T: Tag,
+{
     pub x1: i32,
     pub y1: i32,
     pub x2: i32,
     pub y2: i32,
+    pub tag: T,
 }
 
-impl Debug for RectRaw {
+impl<T> Debug for RectRaw<T>
+where
+    T: Tag,
+{
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
-        f.debug_struct("Rect")
+        let mut debug = f.debug_struct("Rect");
+        debug
             .field("x1", &self.x1)
             .field("y1", &self.y1)
             .field("x2", &self.x2)
             .field("y2", &self.y2)
             .field("width", &(self.x2 - self.x1))
-            .field("height", &(self.y2 - self.y1))
-            .finish()
+            .field("height", &(self.y2 - self.y1));
+        if T::IS_SIGNIFICANT {
+            debug.field("tag", &self.tag);
+        }
+        debug.finish()
     }
 }
 
-impl RectRaw {
+impl<T> RectRaw<T>
+where
+    T: Tag,
+{
     fn is_empty(&self) -> bool {
         self.x1 == self.x2 || self.y1 == self.y2
     }
 }
 
-type Container = SmallVec<[RectRaw; 1]>;
+type Container<T = NoTag> = SmallVec<[RectRaw<T>; 1]>;