fix(size_cross_nth): get max_cross after constraining main

Prevents visual cross sizes for the main widget and other children from becoming different.
This happened when the title height became a significant-enough chunk of max main that it interfered with the preview aspect ratio after its relayout with the previously unaccounted for title height, which caused its width to shrink (to keep the aspect ratio), while the title remained at `max_cross`.

src/widgets/size_cross_nth.rs

@@ -1,10 +1,10 @@
 // This widget defines it's cross axis size as the `index`th child's size
 
 use cosmic::iced::advanced::layout::flex::Axis;
-use cosmic::iced::advanced::layout::{self};
+use cosmic::iced::advanced::layout::{self, Limits};
 use cosmic::iced::advanced::widget::{Operation, Tree};
 use cosmic::iced::advanced::{Clipboard, Layout, Shell, Widget, mouse, renderer};
-use cosmic::iced::event::{self, Event};
+use cosmic::iced::event::Event;
 use cosmic::iced::{Length, Point, Rectangle, Size};
 use std::marker::PhantomData;
 
@@ -74,25 +74,38 @@ impl<Msg> Widget<Msg, cosmic::Theme, cosmic::Renderer> for SizeCrossNth<'_, Msg>
         &mut self,
         tree: &mut Tree,
         renderer: &cosmic::Renderer,
-        limits: &layout::Limits,
+        limits: &Limits,
     ) -> layout::Node {
         let max_main = self.axis.main(limits.max());
         let max_cross = self.axis.cross(limits.max());
 
-        // XXX cleaner solution
+        // Lay out all non-reference children to get their total main size
-        // Get layout of main widget, to set overall cross axis size
+        let mut total_main = 0.0;
-        let (max_width, max_height) = self.axis.pack(max_main, max_cross);
+        for (i, (child, tree)) in self
-        let child_limits = layout::Limits::new(Size::ZERO, Size::new(max_width, max_height));
+            .children
+            .iter_mut()
+            .zip(tree.children.iter_mut())
+            .enumerate()
+        {
+            if i != self.index {
+                let (max_width, max_height) = self.axis.pack(max_main - total_main, max_cross);
+                let child_limits = Limits::new(Size::ZERO, Size::new(max_width, max_height));
+                let layout = child.as_widget_mut().layout(tree, renderer, &child_limits);
+                total_main += self.axis.main(layout.size());
+            }
+        }
+
+        // Lay out reference child with remaining main to get max cross size
+        let (max_width, max_height) = self.axis.pack(max_main - total_main, max_cross);
+        let child_limits = Limits::new(Size::ZERO, Size::new(max_width, max_height));
         let layout = self.children[self.index].as_widget_mut().layout(
             &mut tree.children[self.index],
             renderer,
             &child_limits,
         );
-
         let max_cross = self.axis.cross(layout.size());
 
-        // XXX sill allocating maximum main axis?
+        // Lay out all children constrained to reference cross
-        // - what was it doing before?
         let mut total_main = 0.0;
         let nodes = self
             .children
@@ -100,8 +113,7 @@ impl<Msg> Widget<Msg, cosmic::Theme, cosmic::Renderer> for SizeCrossNth<'_, Msg>
             .zip(tree.children.iter_mut())
             .map(|(child, tree)| {
                 let (max_width, max_height) = self.axis.pack(max_main - total_main, max_cross);
-                let child_limits =
+                let child_limits = Limits::new(Size::ZERO, Size::new(max_width, max_height));
-                    layout::Limits::new(Size::ZERO, Size::new(max_width, max_height));
                 let mut layout = child.as_widget_mut().layout(tree, renderer, &child_limits);
                 // Center on cross axis
                 let cross = ((max_cross - self.axis.cross(layout.size())) / 2.).max(0.);