2 files changed, 118 insertions, 0 deletions

diff --git a/src/grid.rs b/src/grid.rs
new file mode 100644
index 0000000..38efaba
--- /dev/null
+++ b/src/grid.rs
@@ -0,0 +1,107 @@
+// most of this module was written out of frustration
+// TODO: make all this less messy
+
+use sdl2::{pixels::Color, rect::Point, render::Canvas, video::Window};
+
+use crate::{
+    consts::{colors::*, ANGLE},
+    rect,
+};
+
+#[derive(Debug, Copy, Clone)]
+pub enum GridKind {
+    Rectangle,
+    Isometric,
+}
+
+pub struct Grid {
+    pub enabled: bool,
+    pub color: Color,
+    pub kind: GridKind,
+}
+
+impl Grid {
+    pub fn new() -> Self {
+        Self {
+            enabled: true,
+            color: GRID_COLOR,
+            kind: GridKind::Rectangle,
+        }
+    }
+
+    pub fn draw(
+        &self,
+        canvas: &mut Canvas<Window>,
+        zoom: u8,
+        start: &Point,
+        width: u32,
+        height: u32,
+    ) {
+        let cs = zoom as u32;
+        let (x, y) = (start.x(), start.y());
+        canvas.set_draw_color(self.color);
+
+        match self.kind {
+            GridKind::Rectangle => {
+                let mut vertical_tuples = (1..width)
+                    .map(|i| {
+                        let x = (i * cs) as i32;
+                        let y = (height * cs) as i32;
+                        if i % 2 == 0 {
+                            (*start + Point::new(x, 0), *start + Point::new(x, y))
+                        } else {
+                            (*start + Point::new(x, y), *start + Point::new(x, 0))
+                        }
+                    })
+                    .collect::<Vec<_>>();
+
+                // SAFETY
+                // The mem space occupied by a [(T, T); N] is the same as twice the mem space of a
+                // [T; 2 * N], where T is not a dynamically sized type.
+                let verticals: Vec<Point> = unsafe {
+                    vertical_tuples.set_len(vertical_tuples.len() * 2);
+                    std::mem::transmute(vertical_tuples)
+                };
+
+                let mut horizontal_tuples = (1..height)
+                    .map(|j| {
+                        let x = (width * cs) as i32;
+                        let y = (j * cs) as i32;
+                        if j % 2 == 0 {
+                            (*start + Point::new(0, y), *start + Point::new(x, y))
+                        } else {
+                            (*start + Point::new(x, y), *start + Point::new(0, y))
+                        }
+                    })
+                    .collect::<Vec<_>>();
+                let horizontals: Vec<Point> = unsafe {
+                    horizontal_tuples.set_len(horizontal_tuples.len() * 2);
+                    std::mem::transmute(horizontal_tuples)
+                };
+
+                canvas.draw_lines(&verticals[..]).unwrap();
+                canvas.draw_lines(&horizontals[..]).unwrap();
+            }
+            GridKind::Isometric => {
+                // tan 26.525 ~= 0.5
+                canvas.set_clip_rect(Some(rect!(x, y, width * cs, height * cs)));
+                for i in (0..2 * height + width).step_by(4) {
+                    let begin = Point::from(((i * cs) as i32, 0i32));
+                    let end = Point::from((0i32, ((i * cs) as f64 * 0.5).floor() as i32));
+                    canvas.draw_line(*start + begin, *start + end).unwrap();
+                }
+                for j in (0..height + width / 2).step_by(2) {
+                    let idx = (j as i32 - (width as i32 / 2)) * cs as i32;
+                    let begin = Point::from((-100i32, idx));
+                    let end = Point::from((
+                        (width * cs) as i32,
+                        (idx as f64 + (width * cs) as f64 * ANGLE.to_radians().tan()).floor()
+                            as i32,
+                    ));
+                    canvas.draw_line(*start + begin, *start + end).unwrap();
+                }
+                canvas.set_clip_rect(None);
+            }
+        }
+    }
+}
diff --git a/src/lisp/prelude.rs b/src/lisp/prelude.rs
index fee787e..d0667d8 100644
--- a/src/lisp/prelude.rs
+++ b/src/lisp/prelude.rs
@@ -1,6 +1,7 @@
 use crate::{
     bitmap::MapPoint,
     brush::Brush,
+    grid::{Grid, GridKind},
     guide::Guide,
     lisp::{
         error::{EvalError, LispError},
@@ -257,6 +258,16 @@ pub fn new_env() -> Result<Environment, LispError> {
         Ok(LispExpr::Unit)
     });
 
+    primitive!(env, Arity::Exact(0), "grid-rectangle", |_, app| {
+        app.grid.kind = GridKind::Rectangle;
+        Ok(LispExpr::Unit)
+    });
+
+    primitive!(env, Arity::Exact(0), "grid-isometric", |_, app| {
+        app.grid.kind = GridKind::Isometric;
+        Ok(LispExpr::Unit)
+    });
+
     primitive!(env, Arity::Exact(0), "brush-fill", |_, app| {
         app.brush = Brush::Fill;
         Ok(LispExpr::Unit)