Add a grid layouter

2 files changed, 79 insertions, 0 deletions

diff --git a/src/library/grid.rs b/src/library/grid.rs
new file mode 100644
index 00000000..0aa1fc9d
--- /dev/null
+++ b/src/library/grid.rs
@@ -0,0 +1,76 @@
+use crate::layout::GridNode;
+
+use super::*;
+
+/// `stack`: Stack children along an axis.
+///
+/// # Positional parameters
+/// - Children: variadic, of type `template`.
+///
+/// # Named parameters
+/// - Column widths: `columns`, of type `Array<GridUnit>`.
+/// - Row widths: `rows`, of type `Array<GridUnit>`.
+/// - Gutter: `gutter-vertical` and `gutter-horizontal` for individual track axis or `gutter` for both, of type `Array<GridUnit>` respectively.
+/// - Stacking direction: `dir`, of type `direction`.
+///
+/// # Return value
+/// A template that arranges its children along the specified grid cells.
+///
+/// # Relevant types and constants
+/// - Type `direction`
+///   - `ltr`
+///   - `rtl`
+///   - `ttb`
+///   - `btt`
+pub fn grid(ctx: &mut EvalContext, args: &mut FuncArgs) -> Value {
+    let cols = args.eat_named::<GridUnits>(ctx, "columns").unwrap_or_default();
+    let rows = args.eat_named::<GridUnits>(ctx, "rows").unwrap_or_default();
+
+    let gutter = args.eat_named(ctx, "gutter");
+    let gutter_vertical = args
+        .eat_named::<GridUnits>(ctx, "gutter-col")
+        .or_else(|| gutter.clone())
+        .unwrap_or_default();
+    let gutter_horizontal = args
+        .eat_named::<GridUnits>(ctx, "gutter-row")
+        .or(gutter)
+        .unwrap_or_default();
+
+    let dir = args.eat_named(ctx, "dir");
+    let children = args.eat_all::<TemplateValue>(ctx);
+
+    Value::template("grid", move |ctx| {
+        let children =
+            children.iter().map(|child| ctx.exec_template_stack(child).into()).collect();
+        ctx.push(GridNode {
+            dir: dir.unwrap_or_else(|| ctx.state.lang.dir),
+            children,
+            gutter: Gen::new(gutter_vertical.clone(), gutter_horizontal.clone()),
+            tracks: Gen::new(cols.clone(), rows.clone()),
+        })
+    })
+}
+
+/// A list of [`GridUnit`]s.
+#[derive(Default, Debug, Clone, PartialEq, Hash)]
+pub struct GridUnits(pub Vec<TrackSizing>);
+
+impl GridUnits {
+    pub fn get(&self, index: usize) -> TrackSizing {
+        if self.0.is_empty() {
+            TrackSizing::Auto
+        } else {
+            *self.0.get(index).unwrap_or(self.0.last().unwrap())
+        }
+    }
+}
+
+value! {
+    GridUnits: "array of fractional values, lengths, and the `auto` keyword",
+    Value::TrackSizing(value) => Self(vec![value]),
+    Value::Array(values) => Self(values
+        .into_iter()
+        .filter_map(|v| v.cast().ok())
+        .collect()
+    ),
+}
diff --git a/src/library/mod.rs b/src/library/mod.rs
index f9e4f68a..8caddc4c 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -6,6 +6,7 @@
 mod align;
 mod basic;
 mod font;
+mod grid;
 mod image;
 mod lang;
 mod math;
@@ -20,6 +21,7 @@ pub use self::image::*;
 pub use align::*;
 pub use basic::*;
 pub use font::*;
+pub use grid::*;
 pub use lang::*;
 pub use math::*;
 pub use pad::*;
@@ -47,6 +49,7 @@ pub fn new() -> Scope {
     std.def_func("circle", circle);
     std.def_func("ellipse", ellipse);
     std.def_func("font", font);
+    std.def_func("grid", grid);
     std.def_func("h", h);
     std.def_func("image", image);
     std.def_func("lang", lang);