3 files changed, 72 insertions, 24 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!"),
+        }
+    }
+}
diff --git a/src/guide.rs b/src/guide.rs
new file mode 100644
index 0000000..006566e
--- /dev/null
+++ b/src/guide.rs
@@ -0,0 +1,7 @@
+use crate::bitmap::Axis;
+
+#[derive(Debug)]
+pub struct Guide {
+    axis: Axis,
+    offset: u32,
+}
diff --git a/src/lisp/prelude.rs b/src/lisp/prelude.rs
index 4a6a4ed..372bb00 100644
--- a/src/lisp/prelude.rs
+++ b/src/lisp/prelude.rs
@@ -27,6 +27,13 @@ macro_rules! primitive {
 }
 
 #[macro_export]
+macro_rules! define {
+    ($env:expr, $name:expr, $value:expr) => {
+        let _ = $env.insert($name.to_string(), $value);
+    };
+}
+
+#[macro_export]
 macro_rules! type_match {
     ($args:expr, $($range:literal => $kind:pat),+) => {
         {
@@ -54,6 +61,8 @@ macro_rules! type_match {
 pub fn new_env() -> Result<Environment, LispError> {
     let mut env = Environment::new();
 
+    define!(env, "else", LispExpr::BoolLit(true));
+
     primitive!(env, Arity::Atleast(2), "+", |args, _| {
         let nums = args
             .into_iter()
@@ -98,11 +107,6 @@ pub fn new_env() -> Result<Environment, LispError> {
         Ok(LispExpr::Number(acc))
     });
 
-    primitive!(env, Arity::Exact(0), "toggle-grid", |_, app| {
-        app.toggle_grid();
-        Ok(LispExpr::Unit)
-    });
-
     primitive!(env, Arity::Atleast(2), "and", |args, _| {
         if args
             .iter()
@@ -252,6 +256,15 @@ pub fn new_env() -> Result<Environment, LispError> {
         }
     });
 
+    primitive!(env, Arity::Exact(0), "grid-enabled?", |_, app| {
+        Ok(LispExpr::BoolLit(app.grid.enabled))
+    });
+
+    primitive!(env, Arity::Exact(1), "set-grid!", |args, app| {
+        app.grid.enabled = args[0].cast_bool();
+        Ok(LispExpr::Unit)
+    });
+
     primitive!(env, Arity::Exact(0), "brush-fill", |_, app| {
         app.brush = Brush::Fill;
         return Ok(LispExpr::Unit);