1 files changed, 47 insertions, 19 deletions

diff --git a/src/dither.rs b/src/dither.rs
index c19bd6d..99e2839 100644
--- a/src/dither.rs
+++ b/src/dither.rs
@@ -1,24 +1,5 @@
 use crate::bitmap::MapPoint;
 
-// dither intensities (rylander)
-//  0: none
-//  1: (1, 3)
-//  2: (3, 1)
-//  3: (3, 3)
-//  4: (1, 1)
-//  5: (1, 2)
-//  6: (3, 0)
-//  7: (3, 2)
-//  8: (1, 0)
-//  9: (0, 3)
-// 10: (2, 1)
-// 11: (2, 3)
-// 12: (0, 1)
-// 13: (0, 2)
-// 14: (2, 0)
-// 15: (2, 2)
-// 16: (0, 0)
-
 // dither intensities (bayers)
 //  0: none
 //  1: (0, 0)
@@ -65,3 +46,50 @@ pub fn bayer(level: u8, pt: MapPoint) -> bool {
         }
     }
 }
+
+// dither intensities (rylander)
+//  0: none
+//  1: (1, 3)
+//  2: (3, 1)
+//  3: (3, 3)
+//  4: (1, 1)
+//  5: (1, 2)
+//  6: (3, 0)
+//  7: (3, 2)
+//  8: (1, 0)
+//  9: (0, 3)
+// 10: (2, 1)
+// 11: (2, 3)
+// 12: (0, 1)
+// 13: (0, 2)
+// 14: (2, 0)
+// 15: (2, 2)
+// 16: (0, 0)
+
+pub fn rylander(level: u8, pt: MapPoint) -> bool {
+    if level == 0 {
+        false
+    } else {
+        let MapPoint { x, y } = pt;
+        let r = (x % 4, y % 4);
+        match level {
+            01 => r == (1, 3) || rylander(00, pt),
+            02 => r == (3, 1) || rylander(01, pt),
+            03 => r == (3, 3) || rylander(02, pt),
+            04 => r == (1, 1) || rylander(03, pt),
+            05 => r == (1, 2) || rylander(04, pt),
+            06 => r == (3, 0) || rylander(05, pt),
+            07 => r == (3, 2) || rylander(06, pt),
+            08 => r == (1, 0) || rylander(07, pt),
+            09 => r == (0, 3) || rylander(08, pt),
+            10 => r == (2, 1) || rylander(09, pt),
+            11 => r == (2, 3) || rylander(10, pt),
+            12 => r == (0, 1) || rylander(11, pt),
+            13 => r == (0, 2) || rylander(12, pt),
+            14 => r == (2, 0) || rylander(13, pt),
+            15 => r == (2, 2) || rylander(14, pt),
+            16 => r == (0, 0) || rylander(15, pt),
+            _ => panic!("Invalid dither level!"),
+        }
+    }
+}