Add `egui::Sides` `shrink_left` / `shrink_right` (#7295)

This allows contents (on one of the sides) in egui::Sides to shrink. 

* related https://github.com/rerun-io/rerun/issues/10494

crates/egui/src/containers/sides.rs

@@ -1,4 +1,4 @@
-use emath::Align;
+use emath::{Align, NumExt as _};
 
 use crate::{Layout, Ui, UiBuilder};
 
@@ -20,8 +20,13 @@ use crate::{Layout, Ui, UiBuilder};
 ///
 /// If the parent is not wide enough to fit all widgets, the parent will be expanded to the right.
 ///
-/// The left widgets are first added to the ui, left-to-right.
-/// Then the right widgets are added, right-to-left.
+/// The left widgets are added left-to-right.
+/// The right widgets are added right-to-left.
+///
+/// Which side is first depends on the configuration:
+///  - [`Sides::extend`] - left widgets are added first
+///  - [`Sides::shrink_left`] - right widgets are added first
+///  - [`Sides::shrink_right`] - left widgets are added first
 ///
 /// ```
 /// # egui::__run_test_ui(|ui| {
@@ -40,6 +45,16 @@ use crate::{Layout, Ui, UiBuilder};
 pub struct Sides {
     height: Option<f32>,
     spacing: Option<f32>,
+    kind: SidesKind,
+    wrap_mode: Option<crate::TextWrapMode>,
+}
+
+#[derive(Clone, Copy, Debug, Default)]
+enum SidesKind {
+    #[default]
+    Extend,
+    ShrinkLeft,
+    ShrinkRight,
 }
 
 impl Sides {
@@ -68,58 +83,175 @@ impl Sides {
         self
     }
 
+    /// Try to shrink widgets on the left side.
+    ///
+    /// Right widgets will be added first. The left [`Ui`]s max rect will be limited to the
+    /// remaining space.
+    #[inline]
+    pub fn shrink_left(mut self) -> Self {
+        self.kind = SidesKind::ShrinkLeft;
+        self
+    }
+
+    /// Try to shrink widgets on the right side.
+    ///
+    /// Left widgets will be added first. The right [`Ui`]s max rect will be limited to the
+    /// remaining space.
+    #[inline]
+    pub fn shrink_right(mut self) -> Self {
+        self.kind = SidesKind::ShrinkRight;
+        self
+    }
+
+    /// Extend the left and right sides to fill the available space.
+    ///
+    /// This is the default behavior.
+    /// The left widgets will be added first, followed by the right widgets.
+    #[inline]
+    pub fn extend(mut self) -> Self {
+        self.kind = SidesKind::Extend;
+        self
+    }
+
+    /// The text wrap mode for the shrinking side.
+    ///
+    /// Does nothing if [`Self::extend`] is used (the default).
+    #[inline]
+    pub fn wrap_mode(mut self, wrap_mode: crate::TextWrapMode) -> Self {
+        self.wrap_mode = Some(wrap_mode);
+        self
+    }
+
+    /// Truncate the text on the shrinking side.
+    ///
+    /// This is a shortcut for [`Self::wrap_mode`].
+    /// Does nothing if [`Self::extend`] is used (the default).
+    #[inline]
+    pub fn truncate(mut self) -> Self {
+        self.wrap_mode = Some(crate::TextWrapMode::Truncate);
+        self
+    }
+
+    /// Wrap the text on the shrinking side.
+    ///
+    /// This is a shortcut for [`Self::wrap_mode`].
+    /// Does nothing if [`Self::extend`] is used (the default).
+    #[inline]
+    pub fn wrap(mut self) -> Self {
+        self.wrap_mode = Some(crate::TextWrapMode::Wrap);
+        self
+    }
+
     pub fn show<RetL, RetR>(
         self,
         ui: &mut Ui,
         add_left: impl FnOnce(&mut Ui) -> RetL,
         add_right: impl FnOnce(&mut Ui) -> RetR,
     ) -> (RetL, RetR) {
-        let Self { height, spacing } = self;
+        let Self {
+            height,
+            spacing,
+            mut kind,
+            mut wrap_mode,
+        } = self;
         let height = height.unwrap_or_else(|| ui.spacing().interact_size.y);
         let spacing = spacing.unwrap_or_else(|| ui.spacing().item_spacing.x);
 
         let mut top_rect = ui.available_rect_before_wrap();
         top_rect.max.y = top_rect.min.y + height;
 
-        let result_left;
-        let result_right;
+        if ui.is_sizing_pass() {
+            kind = SidesKind::Extend;
+            wrap_mode = None;
+        }
 
-        let left_rect = {
-            let left_max_rect = top_rect;
-            let mut left_ui = ui.new_child(
-                UiBuilder::new()
-                    .max_rect(left_max_rect)
-                    .layout(Layout::left_to_right(Align::Center)),
+        match kind {
+            SidesKind::ShrinkLeft => {
+                let (right_rect, result_right) = Self::create_ui(
+                    ui,
+                    top_rect,
+                    Layout::right_to_left(Align::Center),
+                    add_right,
+                    None,
+                );
+                let available_width = top_rect.width() - right_rect.width() - spacing;
+                let left_rect_constraint =
+                    top_rect.with_max_x(top_rect.min.x + available_width.at_least(0.0));
+                let (left_rect, result_left) = Self::create_ui(
+                    ui,
+                    left_rect_constraint,
+                    Layout::left_to_right(Align::Center),
+                    add_left,
+                    wrap_mode,
                 );
-            result_left = add_left(&mut left_ui);
-            left_ui.min_rect()
-        };
 
-        let right_rect = {
+                ui.advance_cursor_after_rect(left_rect.union(right_rect));
+                (result_left, result_right)
+            }
+            SidesKind::ShrinkRight => {
+                let (left_rect, result_left) = Self::create_ui(
+                    ui,
+                    top_rect,
+                    Layout::left_to_right(Align::Center),
+                    add_left,
+                    None,
+                );
+                let right_rect_constraint = top_rect.with_min_x(left_rect.max.x + spacing);
+                let (right_rect, result_right) = Self::create_ui(
+                    ui,
+                    right_rect_constraint,
+                    Layout::right_to_left(Align::Center),
+                    add_right,
+                    wrap_mode,
+                );
+
+                ui.advance_cursor_after_rect(left_rect.union(right_rect));
+                (result_left, result_right)
+            }
+            SidesKind::Extend => {
+                let (left_rect, result_left) = Self::create_ui(
+                    ui,
+                    top_rect,
+                    Layout::left_to_right(Align::Center),
+                    add_left,
+                    None,
+                );
                 let right_max_rect = top_rect.with_min_x(left_rect.max.x);
-            let mut right_ui = ui.new_child(
-                UiBuilder::new()
-                    .max_rect(right_max_rect)
-                    .layout(Layout::right_to_left(Align::Center)),
+                let (right_rect, result_right) = Self::create_ui(
+                    ui,
+                    right_max_rect,
+                    Layout::right_to_left(Align::Center),
+                    add_right,
+                    None,
                 );
-            result_right = add_right(&mut right_ui);
-            right_ui.min_rect()
-        };
 
                 let mut final_rect = left_rect.union(right_rect);
                 let min_width = left_rect.width() + spacing + right_rect.width();
 
                 if ui.is_sizing_pass() {
-            // Make as small as possible:
                     final_rect.max.x = left_rect.min.x + min_width;
                 } else {
-            // If the rects overlap, make sure we expand the allocated rect so that the parent
-            // ui knows we overflowed, and resizes:
                     final_rect.max.x = final_rect.max.x.max(left_rect.min.x + min_width);
                 }
 
                 ui.advance_cursor_after_rect(final_rect);
-
                 (result_left, result_right)
             }
         }
+    }
+
+    fn create_ui<Ret>(
+        ui: &mut Ui,
+        max_rect: emath::Rect,
+        layout: Layout,
+        add_content: impl FnOnce(&mut Ui) -> Ret,
+        wrap_mode: Option<crate::TextWrapMode>,
+    ) -> (emath::Rect, Ret) {
+        let mut child_ui = ui.new_child(UiBuilder::new().max_rect(max_rect).layout(layout));
+        if let Some(wrap_mode) = wrap_mode {
+            child_ui.style_mut().wrap_mode = Some(wrap_mode);
+        }
+        let result = add_content(&mut child_ui);
+        (child_ui.min_rect(), result)
+    }
+}

tests/egui_tests/tests/snapshots/sides/default_long.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b7ceaa95512c67dcbf1c8ba5a8f33bf4833c2e863d09903fb71b5aa2822cc086
+size 7889

tests/egui_tests/tests/snapshots/sides/default_long_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:931af33f4548924b3bb75a2e513b9e689bce94436b10a9f811140eb11e9d6442
+size 8552

tests/egui_tests/tests/snapshots/sides/default_short.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6448d44c1c9bed08cd6a4af39b141f3a4ca203ca5f7b967cbc0e0d0c2b4fb73f
+size 1647

tests/egui_tests/tests/snapshots/sides/default_short_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44622002ebe287208d26359a06804b1f8737f86eb482322bdf3881a1fe53941f
+size 1276

tests/egui_tests/tests/snapshots/sides/shrink_left_long.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:88e1557dffa7295e7e7e37ed175fcec40aab939f9b67137a1ce33811e8ae4722
+size 7148

tests/egui_tests/tests/snapshots/sides/shrink_left_long_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:931af33f4548924b3bb75a2e513b9e689bce94436b10a9f811140eb11e9d6442
+size 8552

tests/egui_tests/tests/snapshots/sides/shrink_left_short.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6448d44c1c9bed08cd6a4af39b141f3a4ca203ca5f7b967cbc0e0d0c2b4fb73f
+size 1647

tests/egui_tests/tests/snapshots/sides/shrink_left_short_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44622002ebe287208d26359a06804b1f8737f86eb482322bdf3881a1fe53941f
+size 1276

tests/egui_tests/tests/snapshots/sides/shrink_right_long.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:508209ca303751ef323301b25bb3878410742ea79339b75363d2681b98d2712b
+size 7068

tests/egui_tests/tests/snapshots/sides/shrink_right_long_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:931af33f4548924b3bb75a2e513b9e689bce94436b10a9f811140eb11e9d6442
+size 8552

tests/egui_tests/tests/snapshots/sides/shrink_right_short.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6448d44c1c9bed08cd6a4af39b141f3a4ca203ca5f7b967cbc0e0d0c2b4fb73f
+size 1647

tests/egui_tests/tests/snapshots/sides/shrink_right_short_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44622002ebe287208d26359a06804b1f8737f86eb482322bdf3881a1fe53941f
+size 1276

tests/egui_tests/tests/snapshots/sides/wrap_left_long.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:a0c9e39c18fc5bb1fc02a86dbf02e3ffca5537dbe8986d5c5b50cb4984c97466
+size 9085

tests/egui_tests/tests/snapshots/sides/wrap_left_long_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:931af33f4548924b3bb75a2e513b9e689bce94436b10a9f811140eb11e9d6442
+size 8552

tests/egui_tests/tests/snapshots/sides/wrap_left_short.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6448d44c1c9bed08cd6a4af39b141f3a4ca203ca5f7b967cbc0e0d0c2b4fb73f
+size 1647

tests/egui_tests/tests/snapshots/sides/wrap_left_short_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44622002ebe287208d26359a06804b1f8737f86eb482322bdf3881a1fe53941f
+size 1276

tests/egui_tests/tests/snapshots/sides/wrap_right_long.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:a6e9ba0acb573853ef5b3dedb1156d99cdf80338ccb160093960e8aaa41bd5df
+size 9048

tests/egui_tests/tests/snapshots/sides/wrap_right_long_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:931af33f4548924b3bb75a2e513b9e689bce94436b10a9f811140eb11e9d6442
+size 8552

tests/egui_tests/tests/snapshots/sides/wrap_right_short.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6448d44c1c9bed08cd6a4af39b141f3a4ca203ca5f7b967cbc0e0d0c2b4fb73f
+size 1647

tests/egui_tests/tests/snapshots/sides/wrap_right_short_fit_contents.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44622002ebe287208d26359a06804b1f8737f86eb482322bdf3881a1fe53941f
+size 1276

tests/egui_tests/tests/test_sides.rs

@@ -0,0 +1,76 @@
+use egui::{TextWrapMode, Vec2, containers::Sides};
+use egui_kittest::{Harness, SnapshotResults};
+
+#[test]
+fn sides_container_tests() {
+    let mut results = SnapshotResults::new();
+
+    test_variants("default", |sides| sides, &mut results);
+
+    test_variants(
+        "shrink_left",
+        |sides| sides.shrink_left().truncate(),
+        &mut results,
+    );
+
+    test_variants(
+        "shrink_right",
+        |sides| sides.shrink_right().truncate(),
+        &mut results,
+    );
+
+    test_variants(
+        "wrap_left",
+        |sides| sides.shrink_left().wrap_mode(TextWrapMode::Wrap),
+        &mut results,
+    );
+
+    test_variants(
+        "wrap_right",
+        |sides| sides.shrink_right().wrap_mode(TextWrapMode::Wrap),
+        &mut results,
+    );
+}
+
+fn test_variants(
+    name: &str,
+    mut create_sides: impl FnMut(Sides) -> Sides,
+    results: &mut SnapshotResults,
+) {
+    for (variant_name, left_text, right_text, fit_contents) in [
+        ("short", "Left", "Right", false),
+        (
+            "long",
+            "Very long left content that should not fit.",
+            "Very long right text that should also not fit.",
+            false,
+        ),
+        ("short_fit_contents", "Left", "Right", true),
+        (
+            "long_fit_contents",
+            "Very long left content that should not fit.",
+            "Very long right text that should also not fit.",
+            true,
+        ),
+    ] {
+        let mut harness = Harness::builder()
+            .with_size(Vec2::new(400.0, 50.0))
+            .build_ui(|ui| {
+                create_sides(Sides::new()).show(
+                    ui,
+                    |left| {
+                        left.label(left_text);
+                    },
+                    |right| {
+                        right.label(right_text);
+                    },
+                );
+            });
+
+        if fit_contents {
+            harness.fit_contents();
+        }
+
+        results.add(harness.try_snapshot(&format!("sides/{name}_{variant_name}")));
+    }
+}