wip: big flat pt.4: extract layout crate

layout/src/direction.rs

@@ -0,0 +1,30 @@
+use crate::*;
+
+/// A cardinal direction.
+#[derive(Copy, Clone, PartialEq)]
+pub enum Direction { North, South, West, East, }
+pub use self::Direction::*;
+
+impl Direction {
+    #[inline]
+    pub fn split_fixed <N: Coordinate> (self, area: impl Area<N>, a: N) -> ([N;4],[N;4]) {
+        match self {
+            North => (
+                [area.x(), (area.y()+area.h()).minus(a), area.w(), a],
+                [area.x(), area.y(), area.w(), area.h().minus(a)],
+            ),
+            South => (
+                [area.x(), area.y(), area.w(), a],
+                [area.x(), area.y() + a, area.w(), area.h().minus(a)],
+            ),
+            East => (
+                [area.x(), area.y(), a, area.h()],
+                [area.x() + a, area.y(), area.w().minus(a), area.h()],
+            ),
+            West => (
+                [area.x() + area.w() - a, area.y(), a, area.h()],
+                [area.x(), area.y(), area.w() - a, area.h()],
+            ),
+        }
+    }
+}