Add button to equalize the size of the children of a container (#6194)

### What

When drag-dropping tiles it's easy for the tiles to get very unevenly
sized. This helps.


https://github.com/rerun-io/rerun/assets/1148717/efc9f152-a724-4f9a-b505-40d5a22ecd4a

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6194?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/6194?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/6194)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

To run all checks from `main`, comment on the PR with `@rerun-bot
full-check`.

---------

Co-authored-by: Nikolaus West <[email protected]>

crates/re_viewer/src/ui/selection_panel.rs

@@ -720,6 +720,35 @@ fn container_top_level_properties(
                     },
                 );
             }
+            ui.end_row();
+
+            // ---
+
+            fn equal_shares(shares: &[f32]) -> bool {
+                shares.iter().all(|&share| share == shares[0])
+            }
+
+            let all_shares_are_equal =
+                equal_shares(&container.col_shares) && equal_shares(&container.row_shares);
+
+            if container.contents.len() > 1
+                && match container.container_kind {
+                    egui_tiles::ContainerKind::Tabs => false,
+                    egui_tiles::ContainerKind::Horizontal
+                    | egui_tiles::ContainerKind::Vertical
+                    | egui_tiles::ContainerKind::Grid => true,
+                }
+                && ui
+                    .add_enabled(
+                        !all_shares_are_equal,
+                        egui::Button::new("Distribute content equally"),
+                    )
+                    .on_hover_text("Make all children the same size")
+                    .clicked()
+            {
+                viewport.blueprint.make_all_children_same_size(container_id);
+            }
+            ui.end_row();
         });
 }
 

crates/re_viewport/src/viewport.rs

@@ -112,6 +112,9 @@ pub enum TreeAction {
     /// Simplify the container with the provided options
     SimplifyContainer(ContainerId, egui_tiles::SimplificationOptions),
 
+    /// Make all column and row shares the same for this container
+    MakeAllChildrenSameSize(ContainerId),
+
     /// Move some contents to a different container
     MoveContents {
         contents_to_move: Contents,
@@ -460,6 +463,24 @@ impl<'a, 'b> Viewport<'a, 'b> {
                     self.tree.simplify_children_of_tile(tile_id, &options);
                     self.tree_edited = true;
                 }
+                TreeAction::MakeAllChildrenSameSize(container_id) => {
+                    let tile_id = blueprint_id_to_tile_id(&container_id);
+                    if let Some(egui_tiles::Tile::Container(container)) =
+                        self.tree.tiles.get_mut(tile_id)
+                    {
+                        match container {
+                            egui_tiles::Container::Tabs(_) => {}
+                            egui_tiles::Container::Linear(linear) => {
+                                linear.shares = Default::default();
+                            }
+                            egui_tiles::Container::Grid(grid) => {
+                                grid.col_shares = Default::default();
+                                grid.row_shares = Default::default();
+                            }
+                        }
+                    }
+                    self.tree_edited = true;
+                }
                 TreeAction::MoveContents {
                     contents_to_move,
                     target_container,

crates/re_viewport/src/viewport_blueprint.rs

@@ -670,6 +670,11 @@ impl ViewportBlueprint {
         ));
     }
 
+    /// Make all children of the given container the same size.
+    pub fn make_all_children_same_size(&self, container_id: &ContainerId) {
+        self.send_tree_action(TreeAction::MakeAllChildrenSameSize(*container_id));
+    }
+
     /// Set the container that is currently identified as the drop target of an ongoing drag.
     ///
     /// This is used for highlighting the drop target in the UI. Note that the drop target container is reset at every