output: more big refactors

output/src/space/space_direction.rs

@@ -0,0 +1,21 @@
+use crate::*;
+
+/// A cardinal direction.
+#[derive(Copy, Clone, PartialEq, Debug)]
+#[cfg_attr(test, derive(Arbitrary))]
+pub enum Direction {
+    North, South, East, West, Above, Below
+}
+
+impl Direction {
+    pub fn split_fixed <N: Coordinate> (self, area: impl Area<N>, a: N) -> ([N;4],[N;4]) {
+        let [x, y, w, h] = area.xywh();
+        match self {
+            North => ([x, y.plus(h).minus(a), w, a], [x, y, w, h.minus(a)]),
+            South => ([x, y, w, a], [x, y.plus(a), w, h.minus(a)]),
+            East  => ([x, y, a, h], [x.plus(a), y, w.minus(a), h]),
+            West  => ([x.plus(w).minus(a), y, a, h], [x, y, w.minus(a), h]),
+            Above | Below => (area.xywh(), area.xywh())
+        }
+    }
+}