Start working on morton (z-order sorting)

src/util/mod.rs

@@ -3,4 +3,5 @@ pub use interval::Interval;
 
 pub mod algebra_utils;
 pub mod axis_aligned_bounding_box;
+pub mod morton;
 pub mod normalizer;

src/util/morton.rs

@@ -0,0 +1,49 @@
+use nalgebra::Point3;
+
+use crate::Real;
+
+//use std::cmp::Ordering;
+
+fn spread_bits(v: u32) -> u32 {
+    let mut result = 0;
+    for power in 0..9 {
+        result |= ((1 << power) & v) << power * 2;
+    }
+    dbg!(format!("{:b}", result));
+    result
+}
+
+pub fn morton_order_value<T: Real>(p: Point3<T>) -> u32 {
+    let x = p.x.normalized_to_u32(10);
+    let y = p.y.normalized_to_u32(10);
+    let z = p.z.normalized_to_u32(10);
+    (spread_bits(x) << 2) | (spread_bits(y) << 1) | spread_bits(z)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    mod spread_bits {
+        use super::*;
+
+        #[test]
+        fn zero_yields_zero() {
+            assert!(spread_bits(0) == 0);
+        }
+
+        #[test]
+        fn one_yields_one() {
+            assert!(spread_bits(1) == 1);
+        }
+
+        #[test]
+        fn b1111_yields_b1001001001() {
+            assert!(spread_bits(0b1111) == 0b1001001001);
+        }
+
+        #[test]
+        fn b1010_yields_b1000001000() {
+            assert!(spread_bits(0b1010) == 0b1000001000);
+        }
+    }
+}