Add `egui::Sides` for adding UI on left and right sides (#5036)

* Closes https://github.com/emilk/egui/issues/5015

crates/egui/src/containers/mod.rs

@@ -10,6 +10,7 @@ pub mod panel;
 pub mod popup;
 pub(crate) mod resize;
 pub mod scroll_area;
+mod sides;
 pub(crate) mod window;
 
 pub use {
@@ -21,5 +22,6 @@ pub use {
     popup::*,
     resize::Resize,
     scroll_area::ScrollArea,
+    sides::Sides,
     window::Window,
 };

crates/egui/src/containers/sides.rs

@@ -0,0 +1,120 @@
+use emath::Align;
+
+use crate::{Layout, Ui, UiBuilder};
+
+/// Put some widgets on the left and right sides of a ui.
+///
+/// The result will look like this:
+/// ```text
+///                        parent Ui
+///  ______________________________________________________
+/// |                    |           |                     |  ^
+/// | -> left widgets -> |    gap    | <- right widgets <- |  | height
+/// |____________________|           |_____________________|  v
+/// |                                                      |
+/// |                                                      |
+/// ```
+///
+/// The width of the gap is dynamic, based on the max width of the parent [`Ui`].
+/// When the parent is being auto-sized ([`Ui::is_sizing_pass`]) the gap will be as small as possible.
+///
+/// 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.
+///
+/// ```
+/// # egui::__run_test_ui(|ui| {
+/// egui::containers::Sides::new().show(ui,
+///     |ui| {
+///         ui.label("Left");
+///     },
+///     |ui| {
+///         ui.label("Right");
+///     }
+/// );
+/// # });
+/// ```
+#[must_use = "You should call sides.show()"]
+#[derive(Clone, Copy, Debug, Default)]
+pub struct Sides {
+    height: Option<f32>,
+    spacing: Option<f32>,
+}
+
+impl Sides {
+    #[inline]
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// The minimum height of the sides.
+    ///
+    /// The content will be centered vertically within this height.
+    /// The default height is [`crate::Spacing::interact_size`]`.y`.
+    #[inline]
+    pub fn height(mut self, height: f32) -> Self {
+        self.height = Some(height);
+        self
+    }
+
+    /// The horizontal spacing between the left and right UIs.
+    ///
+    /// This is the minimum gap.
+    /// The default is [`crate::Spacing::item_spacing`]`.x`.
+    #[inline]
+    pub fn spacing(mut self, spacing: f32) -> Self {
+        self.spacing = Some(spacing);
+        self
+    }
+
+    pub fn show(
+        self,
+        ui: &mut Ui,
+        add_left: impl FnOnce(&mut Ui),
+        add_right: impl FnOnce(&mut Ui),
+    ) {
+        let Self { height, spacing } = 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.max_rect();
+        top_rect.max.y = top_rect.min.y + height;
+
+        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)),
+            );
+            add_left(&mut left_ui);
+            left_ui.min_rect()
+        };
+
+        let right_rect = {
+            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)),
+            );
+            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);
+    }
+}

crates/egui/src/lib.rs

@@ -466,7 +466,7 @@ pub use self::{
     painter::Painter,
     response::{InnerResponse, Response},
     sense::Sense,
-    style::{FontSelection, Style, TextStyle, Visuals},
+    style::{FontSelection, Spacing, Style, TextStyle, Visuals},
     text::{Galley, TextFormat},
     ui::Ui,
     ui_builder::UiBuilder,

crates/egui_demo_lib/src/demo/table_demo.rs

@@ -20,6 +20,7 @@ pub struct TableDemo {
     scroll_to_row: Option<usize>,
     selection: std::collections::HashSet<usize>,
     checked: bool,
+    reversed: bool,
 }
 
 impl Default for TableDemo {
@@ -34,6 +35,7 @@ impl Default for TableDemo {
             scroll_to_row: None,
             selection: Default::default(),
             checked: false,
+            reversed: false,
         }
     }
 }
@@ -173,7 +175,16 @@ impl TableDemo {
         table
             .header(20.0, |mut header| {
                 header.col(|ui| {
-                    ui.strong("Row");
+                    egui::Sides::new().show(
+                        ui,
+                        |ui| {
+                            ui.strong("Row");
+                        },
+                        |ui| {
+                            self.reversed ^=
+                                ui.button(if self.reversed { "⬆" } else { "⬇" }).clicked();
+                        },
+                    );
                 });
                 header.col(|ui| {
                     ui.strong("Clipped text");
@@ -191,6 +202,12 @@ impl TableDemo {
             .body(|mut body| match self.demo {
                 DemoType::Manual => {
                     for row_index in 0..NUM_MANUAL_ROWS {
+                        let row_index = if self.reversed {
+                            NUM_MANUAL_ROWS - 1 - row_index
+                        } else {
+                            row_index
+                        };
+
                         let is_thick = thick_row(row_index);
                         let row_height = if is_thick { 30.0 } else { 18.0 };
                         body.row(row_height, |mut row| {
@@ -223,7 +240,12 @@ impl TableDemo {
                 }
                 DemoType::ManyHomogeneous => {
                     body.rows(text_height, self.num_rows, |mut row| {
-                        let row_index = row.index();
+                        let row_index = if self.reversed {
+                            self.num_rows - 1 - row.index()
+                        } else {
+                            row.index()
+                        };
+
                         row.set_selected(self.selection.contains(&row_index));
 
                         row.col(|ui| {
@@ -251,7 +273,12 @@ impl TableDemo {
                 DemoType::ManyHeterogenous => {
                     let row_height = |i: usize| if thick_row(i) { 30.0 } else { 18.0 };
                     body.heterogeneous_rows((0..self.num_rows).map(row_height), |mut row| {
-                        let row_index = row.index();
+                        let row_index = if self.reversed {
+                            self.num_rows - 1 - row.index()
+                        } else {
+                            row.index()
+                        };
+
                         row.set_selected(self.selection.contains(&row_index));
 
                         row.col(|ui| {

crates/egui_extras/src/table.rs

@@ -451,7 +451,7 @@ impl<'a> TableBuilder<'a> {
         let Self {
             ui,
             id_salt,
-            columns,
+            mut columns,
             striped,
             resizable,
             cell_layout,
@@ -459,6 +459,15 @@ impl<'a> TableBuilder<'a> {
             sense,
         } = self;
 
+        for (i, column) in columns.iter_mut().enumerate() {
+            let column_resize_id = ui.id().with("resize_column").with(i);
+            if let Some(response) = ui.ctx().read_response(column_resize_id) {
+                if response.double_clicked() {
+                    column.auto_size_this_frame = true;
+                }
+            }
+        }
+
         let striped = striped.unwrap_or(ui.visuals().striped);
 
         let state_id = ui.id().with(id_salt);
@@ -695,7 +704,7 @@ impl<'a> Table<'a> {
             ui,
             table_top,
             state_id,
-            mut columns,
+            columns,
             resizable,
             mut available_width,
             mut state,
@@ -719,15 +728,6 @@ impl<'a> Table<'a> {
             scroll_bar_visibility,
         } = scroll_options;
 
-        for (i, column) in columns.iter_mut().enumerate() {
-            let column_resize_id = ui.id().with("resize_column").with(i);
-            if let Some(response) = ui.ctx().read_response(column_resize_id) {
-                if response.double_clicked() {
-                    column.auto_size_this_frame = true;
-                }
-            }
-        }
-
         let cursor_position = ui.cursor().min;
 
         let mut scroll_area = ScrollArea::new([false, vscroll])

scripts/check.sh

@@ -21,7 +21,7 @@ cargo fmt --all -- --check
 cargo doc --quiet --lib --no-deps --all-features
 cargo doc --quiet --document-private-items --no-deps --all-features
 cargo clippy --quiet --all-targets --all-features -- -D warnings
-cargo clippy --all-targets --all-features --release -- -D warnings # we need to check release mode too
+cargo clippy --quiet --all-targets --all-features --release -- -D warnings # we need to check release mode too
 
 ./scripts/clippy_wasm.sh