Toplevel layout abstraction

src/widgets/toplevels/mod.rs

@@ -6,61 +6,34 @@ use cosmic::iced::{
         Clipboard, Layout, Shell, Widget,
     },
     event::{self, Event},
-    Length, Point, Rectangle, Size,
+    Length, Rectangle, Size, Vector,
 };
 use std::marker::PhantomData;
 
-// Duplicate of private methods
-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),
-        }
-    }
-}
+mod toplevel_layout;
+use toplevel_layout::{LayoutToplevel, RowColToplevelLayout, ToplevelLayout};
 
 pub fn toplevels<Msg>(children: Vec<cosmic::Element<Msg>>) -> Toplevels<Msg> {
     Toplevels {
-        axis: Axis::Horizontal,
+        layout: RowColToplevelLayout {
+            // TODO configurable
+            spacing: 16,
+            axis: Axis::Horizontal,
+        },
         children,
         _msg: PhantomData,
     }
 }
 
 pub struct Toplevels<'a, Msg> {
-    axis: Axis,
+    layout: RowColToplevelLayout,
     children: Vec<cosmic::Element<'a, Msg>>,
     _msg: PhantomData<Msg>,
 }
 
 impl<'a, Msg> Widget<Msg, cosmic::Theme, cosmic::Renderer> for Toplevels<'a, Msg> {
     fn size(&self) -> Size<Length> {
-        Size {
-            width: Length::Fill,
-            // TODO Make depend on orientation or drop that option
-            height: Length::Shrink,
-        }
+        self.layout.size()
     }
 
     fn layout(
@@ -69,60 +42,42 @@ impl<'a, Msg> Widget<Msg, cosmic::Theme, cosmic::Renderer> for Toplevels<'a, Msg
         renderer: &cosmic::Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
-        // TODO configurable
-        let spacing = 16;
-
-        // Get total requested main axis length if widget could have all the space
-        let total_spacing = spacing * (self.children.len().saturating_sub(1)).max(0);
-        let requested_mains = self
+        // Call `.layout()` on each child with full limits to determine "preferred" sizes
+        let layout_toplevels = self
             .children
             .iter()
             .zip(tree.children.iter_mut())
             .map(|(child, tree)| {
-                let child_limits = layout::Limits::new(Size::ZERO, limits.max());
-                let layout = child.as_widget().layout(tree, renderer, &child_limits);
-                self.axis.main(layout.size())
+                let preferred_size = child.as_widget().layout(tree, renderer, limits).size();
+                LayoutToplevel {
+                    preferred_size,
+                    _phantom_data: PhantomData,
+                }
             })
             .collect::<Vec<_>>();
-        let requested_main_total: f32 = requested_mains.iter().sum::<f32>() + total_spacing as f32;
 
-        let scale_factor = (self.axis.main(limits.max()) / requested_main_total).min(1.0);
+        // Assign rectangles for each child using `ToplevelLayout` backend
+        let assigned_rects = self.layout.layout(limits.max(), &layout_toplevels);
 
-        let max_cross = self.axis.cross(limits.max());
-
-        // XXX sill allocating maximum main axis?
-        // - what was it doing before?
-        let mut total_main = 0.0;
-        let mut first = true;
         let nodes = self
             .children
             .iter()
             .zip(tree.children.iter_mut())
-            .zip(requested_mains.iter())
-            .map(|((child, tree), requested_main)| {
-                if !first {
-                    total_main += spacing as f32;
-                }
-                first = false;
+            .zip(assigned_rects)
+            .map(|((child, tree), assigned_rect)| {
+                let child_limits = layout::Limits::new(Size::ZERO, assigned_rect.size());
+                let layout = child.as_widget().layout(tree, renderer, &child_limits);
 
-                let max_main = requested_main * scale_factor;
+                // Center on both axes, if child didn't consume full size allocation
+                let centering_offset = Vector::new(
+                    ((assigned_rect.size().width - layout.size().width) / 2.).max(0.),
+                    ((assigned_rect.size().height - layout.size().height) / 2.).max(0.),
+                );
 
-                let (max_width, max_height) = self.axis.pack(max_main, max_cross);
-                let child_limits =
-                    layout::Limits::new(Size::ZERO, Size::new(max_width, max_height));
-                let mut layout = child.as_widget().layout(tree, renderer, &child_limits);
-                // Center on cross axis
-                let cross = ((max_cross - self.axis.cross(layout.size())) / 2.).max(0.);
-                let (x, y) = self.axis.pack(total_main, cross);
-                layout = layout.move_to(Point::new(x, y));
-                total_main += self.axis.main(layout.size());
-                layout
+                layout.move_to(assigned_rect.position() + centering_offset)
             })
             .collect();
-
-        let (total_width, total_height) = self.axis.pack(total_main, max_cross);
-        let size = Size::new(total_width, total_height);
-        layout::Node::with_children(size, nodes)
+        layout::Node::with_children(limits.max(), nodes)
     }
 
     fn operate(

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),
+        }
+    }
+}