Toplevel layout abstraction

src/widgets/toplevels/toplevel_layout/mod.rs

@@ -0,0 +1,35 @@
+// TODO: More generic widget in libcosmic? Improve iced layout system?
+// - preferred_size concept
+
+use cosmic::iced::{Length, Rectangle, Size};
+use std::marker::PhantomData;
+
+mod row_col_toplevel_layout;
+mod utils;
+pub(crate) use row_col_toplevel_layout::RowColToplevelLayout;
+
+pub(crate) struct LayoutToplevel<'a> {
+    //toplevel: &'a crate::Toplevel,
+    /// Preferred size of the child widget, if it fill the parent container
+    pub preferred_size: Size,
+    pub _phantom_data: PhantomData<&'a crate::Toplevel>,
+}
+
+/// An implementor of this trait defines a layout for the [`Toplevels`] widget
+/// as a pure function, without dealing with all the details of the iced layout
+/// system.
+pub(crate) trait ToplevelLayout {
+    /// [`Size`] the container widget should request
+    fn size(&self) -> Size<Length>;
+    /// Decide size and location of each widget
+    ///
+    /// - `max_limit` is the total size available for all children
+    /// - For each entry in `toplevels`, this should yield one `Rectangle`
+    ///
+    /// If a child doesn't use it's entire rectangle, it will be centered in that space.
+    fn layout(
+        &self,
+        max_limit: Size,
+        toplevels: &[LayoutToplevel<'_>],
+    ) -> impl Iterator<Item = Rectangle>;
+}

src/widgets/toplevels/toplevel_layout/row_col_toplevel_layout.rs

@@ -0,0 +1,51 @@
+use cosmic::iced::{advanced::layout::flex::Axis, Length, Point, Rectangle, Size};
+
+use super::{utils::AxisExt, LayoutToplevel, ToplevelLayout};
+
+pub(crate) struct RowColToplevelLayout {
+    pub axis: Axis,
+    pub spacing: u32,
+}
+
+impl ToplevelLayout for RowColToplevelLayout {
+    fn size(&self) -> Size<Length> {
+        Size {
+            width: Length::Fill,
+            // TODO Make depend on orientation or drop that option
+            height: Length::Shrink,
+        }
+    }
+
+    fn layout(
+        &self,
+        max_limit: Size,
+        toplevels: &[LayoutToplevel<'_>],
+    ) -> impl Iterator<Item = Rectangle> {
+        // Get total requested main axis length if widget could have all the space
+        let total_spacing = self.spacing as usize * (toplevels.len().saturating_sub(1)).max(0);
+        let requested_main_total: f32 = toplevels
+            .iter()
+            .map(|t| self.axis.main(t.preferred_size))
+            .sum::<f32>()
+            + total_spacing as f32;
+        let scale_factor = (self.axis.main(max_limit) / requested_main_total).min(1.0);
+        let max_cross = self.axis.cross(max_limit);
+
+        let mut total_main = 0.0;
+        let mut first = true;
+        toplevels.iter().map(move |child| {
+            let requested_main = self.axis.main(child.preferred_size);
+            if !first {
+                total_main += self.spacing as f32;
+            }
+            first = false;
+
+            let max_main = requested_main * scale_factor;
+
+            let (width, height) = self.axis.pack(max_main, max_cross);
+            let (x, y) = self.axis.pack(total_main, 0.0);
+            total_main += max_main;
+            Rectangle::new(Point::new(x, y), Size::new(width, height))
+        })
+    }
+}

src/widgets/toplevels/toplevel_layout/utils.rs

@@ -0,0 +1,31 @@
+use cosmic::iced::{advanced::layout::flex::Axis, Size};
+
+// Duplicate of private methods
+pub(super) trait AxisExt {
+    fn main(&self, size: Size) -> f32;
+    fn cross(&self, size: Size) -> f32;
+    fn pack(&self, main: f32, cross: f32) -> (f32, f32);
+}
+
+impl AxisExt for Axis {
+    fn main(&self, size: Size) -> f32 {
+        match self {
+            Axis::Horizontal => size.width,
+            Axis::Vertical => size.height,
+        }
+    }
+
+    fn cross(&self, size: Size) -> f32 {
+        match self {
+            Axis::Horizontal => size.height,
+            Axis::Vertical => size.width,
+        }
+    }
+
+    fn pack(&self, main: f32, cross: f32) -> (f32, f32) {
+        match self {
+            Axis::Horizontal => (main, cross),
+            Axis::Vertical => (cross, main),
+        }
+    }
+}