Add Ui::is_sizing_pass for better size estimation of Areas, and menus in particular

Cargo.lock

@@ -3628,6 +3628,14 @@ dependencies = [
  "env_logger",
 ]
 
+[[package]]
+name = "test_size_pass"
+version = "0.1.0"
+dependencies = [
+ "eframe",
+ "env_logger",
+]
+
 [[package]]
 name = "test_viewports"
 version = "0.1.0"

crates/egui/src/containers/area.rs

@@ -69,6 +69,7 @@ pub struct Area {
     constrain_rect: Option<Rect>,
     order: Order,
     default_pos: Option<Pos2>,
+    default_size: Vec2,
     pivot: Align2,
     anchor: Option<(Align2, Vec2)>,
     new_pos: Option<Pos2>,
@@ -87,6 +88,7 @@ impl Area {
             enabled: true,
             order: Order::Middle,
             default_pos: None,
+            default_size: Vec2::NAN,
             new_pos: None,
             pivot: Align2::LEFT_TOP,
             anchor: None,
@@ -163,6 +165,35 @@ impl Area {
         self
     }
 
+    /// The size used for the [`Ui::max_rect`] the first frame.
+    ///
+    /// Text will wrap at this width, and images that expand to fill the available space
+    /// will expand to this size.
+    ///
+    /// If the contents are smaller than this size, the area will shrink to fit the contents.
+    /// If the contents overflow, the area will grow.
+    ///
+    /// If not set, [`style::Spacing::default_area_size`] will be used.
+    #[inline]
+    pub fn default_size(mut self, default_size: impl Into<Vec2>) -> Self {
+        self.default_size = default_size.into();
+        self
+    }
+
+    /// See [`Self::default_size`].
+    #[inline]
+    pub fn default_width(mut self, default_width: f32) -> Self {
+        self.default_size.x = default_width;
+        self
+    }
+
+    /// See [`Self::default_size`].
+    #[inline]
+    pub fn default_height(mut self, default_height: f32) -> Self {
+        self.default_size.y = default_height;
+        self
+    }
+
     /// Positions the window and prevents it from being moved
     #[inline]
     pub fn fixed_pos(mut self, fixed_pos: impl Into<Pos2>) -> Self {
@@ -247,7 +278,7 @@ pub(crate) struct Prepared {
     /// This is so that we use the first frame to calculate the window size,
     /// and then can correctly position the window and its contents the next frame,
     /// without having one frame where the window is wrongly positioned or sized.
-    temporarily_invisible: bool,
+    sizing_pass: bool,
 }
 
 impl Area {
@@ -272,6 +303,7 @@ impl Area {
             interactable,
             enabled,
             default_pos,
+            default_size,
             new_pos,
             pivot,
             anchor,
@@ -292,11 +324,29 @@ impl Area {
         if is_new {
             ctx.request_repaint(); // if we don't know the previous size we are likely drawing the area in the wrong place
         }
-        let mut state = state.unwrap_or_else(|| State {
-            pivot_pos: default_pos.unwrap_or_else(|| automatic_area_position(ctx)),
-            pivot,
-            size: Vec2::ZERO,
-            interactable,
+        let mut state = state.unwrap_or_else(|| {
+            // during the sizing pass we will use this as the max size
+            let mut size = default_size;
+
+            let default_area_size = ctx.style().spacing.default_area_size;
+            if size.x.is_nan() {
+                size.x = default_area_size.x;
+            }
+            if size.y.is_nan() {
+                size.y = default_area_size.y;
+            }
+
+            if constrain {
+                let constrain_rect = constrain_rect.unwrap_or_else(|| ctx.screen_rect());
+                size = size.at_most(constrain_rect.size());
+            }
+
+            State {
+                pivot_pos: default_pos.unwrap_or_else(|| automatic_area_position(ctx)),
+                pivot,
+                size,
+                interactable,
+            }
         });
         state.pivot_pos = new_pos.unwrap_or(state.pivot_pos);
         state.interactable = interactable;
@@ -365,7 +415,7 @@ impl Area {
             enabled,
             constrain,
             constrain_rect,
-            temporarily_invisible: is_new,
+            sizing_pass: is_new,
         }
     }
 
@@ -431,12 +481,7 @@ impl Prepared {
             }
         };
 
-        let max_rect = Rect::from_min_max(
-            self.state.left_top_pos(),
-            constrain_rect
-                .max
-                .at_least(self.state.left_top_pos() + Vec2::splat(32.0)),
-        );
+        let max_rect = Rect::from_min_size(self.state.left_top_pos(), self.state.size);
 
         let clip_rect = constrain_rect; // Don't paint outside our bounds
 
@@ -448,7 +493,9 @@ impl Prepared {
             clip_rect,
         );
         ui.set_enabled(self.enabled);
-        ui.set_visible(!self.temporarily_invisible);
+        if self.sizing_pass {
+            ui.set_sizing_pass();
+        }
         ui
     }
 
@@ -461,11 +508,20 @@ impl Prepared {
             enabled: _,
             constrain: _,
             constrain_rect: _,
-            temporarily_invisible: _,
+            sizing_pass,
         } = self;
 
         state.size = content_ui.min_size();
 
+        if sizing_pass {
+            // If during the sizing pass we measure our width to `123.45` and
+            // then try to wrap to exactly that next frame,
+            // we may accidentally wrap the last letter of some text.
+            // We only do this after the initial sizing pass though;
+            // otherwise we could end up with for-ever expanding areas.
+            state.size = state.size.ceil();
+        }
+
         ctx.memory_mut(|m| m.areas_mut().set_state(layer_id, state));
 
         move_response

crates/egui/src/containers/frame.rs

@@ -266,7 +266,8 @@ impl Frame {
         self.show_dyn(ui, Box::new(add_contents))
     }
 
-    fn show_dyn<'c, R>(
+    /// Show using dynamic dispatch.
+    pub fn show_dyn<'c, R>(
         self,
         ui: &mut Ui,
         add_contents: Box<dyn FnOnce(&mut Ui) -> R + 'c>,

crates/egui/src/containers/popup.rs

@@ -260,15 +260,11 @@ fn show_tooltip_area_dyn<'c, R>(
     Area::new(area_id)
         .order(Order::Tooltip)
         .fixed_pos(window_pos)
+        .default_width(ctx.style().spacing.tooltip_width)
         .constrain_to(ctx.screen_rect())
         .interactable(false)
         .show(ctx, |ui| {
-            Frame::popup(&ctx.style())
-                .show(ui, |ui| {
-                    ui.set_max_width(ui.spacing().tooltip_width);
-                    add_contents(ui)
-                })
-                .inner
+            Frame::popup(&ctx.style()).show_dyn(ui, add_contents).inner
         })
 }
 

crates/egui/src/menu.rs

@@ -133,10 +133,10 @@ pub(crate) fn submenu_button<R>(
 }
 
 /// wrapper for the contents of every menu.
-pub(crate) fn menu_ui<'c, R>(
+fn menu_popup<'c, R>(
     ctx: &Context,
-    menu_id: Id,
     menu_state_arc: &Arc<RwLock<MenuState>>,
+    menu_id: Id,
     add_contents: impl FnOnce(&mut Ui) -> R + 'c,
 ) -> InnerResponse<R> {
     let pos = {
@@ -150,14 +150,14 @@ pub(crate) fn menu_ui<'c, R>(
         .fixed_pos(pos)
         .constrain_to(ctx.screen_rect())
         .interactable(true)
+        .default_width(ctx.style().spacing.menu_width)
         .sense(Sense::hover());
 
     let area_response = area.show(ctx, |ui| {
         set_menu_style(ui.style_mut());
 
         Frame::menu(ui.style())
             .show(ui, |ui| {
-                ui.set_max_width(ui.spacing().menu_width);
                 ui.set_menu_state(Some(menu_state_arc.clone()));
                 ui.with_layout(Layout::top_down_justified(Align::LEFT), add_contents)
                     .inner
@@ -306,8 +306,7 @@ impl MenuRoot {
         add_contents: impl FnOnce(&mut Ui) -> R,
     ) -> (MenuResponse, Option<InnerResponse<R>>) {
         if self.id == button.id {
-            let inner_response =
-                MenuState::show(&button.ctx, &self.menu_state, self.id, add_contents);
+            let inner_response = menu_popup(&button.ctx, &self.menu_state, self.id, add_contents);
             let menu_state = self.menu_state.read();
 
             if menu_state.response.is_close() {
@@ -593,23 +592,14 @@ impl MenuState {
         self.response = MenuResponse::Close;
     }
 
-    pub fn show<R>(
-        ctx: &Context,
-        menu_state: &Arc<RwLock<Self>>,
-        id: Id,
-        add_contents: impl FnOnce(&mut Ui) -> R,
-    ) -> InnerResponse<R> {
-        crate::menu::menu_ui(ctx, id, menu_state, add_contents)
-    }
-
     fn show_submenu<R>(
         &mut self,
         ctx: &Context,
         id: Id,
         add_contents: impl FnOnce(&mut Ui) -> R,
     ) -> Option<R> {
         let (sub_response, response) = self.submenu(id).map(|sub| {
-            let inner_response = Self::show(ctx, sub, id, add_contents);
+            let inner_response = menu_popup(ctx, sub, id, add_contents);
             (sub.read().response, inner_response.inner)
         })?;
         self.cascade_close_response(sub_response);

crates/egui/src/style.rs

@@ -316,10 +316,21 @@ pub struct Spacing {
     /// This is the spacing between the icon and the text
     pub icon_spacing: f32,
 
+    /// The size used for the [`Ui::max_rect`] the first frame.
+    ///
+    /// Text will wrap at this width, and images that expand to fill the available space
+    /// will expand to this size.
+    ///
+    /// If the contents are smaller than this size, the area will shrink to fit the contents.
+    /// If the contents overflow, the area will grow.
+    pub default_area_size: Vec2,
+
     /// Width of a tooltip (`on_hover_ui`, `on_hover_text` etc).
     pub tooltip_width: f32,
 
-    /// The default width of a menu.
+    /// The default wrapping width of a menu.
+    ///
+    /// Items longer than this will wrap to a new line.
     pub menu_width: f32,
 
     /// Horizontal distance between a menu and a submenu.
@@ -1073,8 +1084,9 @@ impl Default for Spacing {
             icon_width: 14.0,
             icon_width_inner: 8.0,
             icon_spacing: 4.0,
+            default_area_size: vec2(600.0, 400.0),
             tooltip_width: 600.0,
-            menu_width: 150.0,
+            menu_width: 400.0,
             menu_spacing: 2.0,
             combo_height: 200.0,
             scroll: Default::default(),
@@ -1459,6 +1471,7 @@ impl Spacing {
             icon_width,
             icon_width_inner,
             icon_spacing,
+            default_area_size,
             tooltip_width,
             menu_width,
             menu_spacing,
@@ -1509,6 +1522,10 @@ impl Spacing {
                 ui.add(DragValue::new(combo_width).clamp_range(0.0..=1000.0));
                 ui.end_row();
 
+                ui.label("Default area size");
+                ui.add(two_drag_values(default_area_size, 0.0..=1000.0));
+                ui.end_row();
+
                 ui.label("TextEdit width");
                 ui.add(DragValue::new(text_edit_width).clamp_range(0.0..=1000.0));
                 ui.end_row();

crates/egui/src/ui.rs

@@ -61,6 +61,10 @@ pub struct Ui {
     /// and all widgets will assume a gray style.
     enabled: bool,
 
+    /// Set to true in special cases where we do one frame
+    /// where we size up the contents of the Ui, without actually showing it.
+    sizing_pass: bool,
+
     /// Indicates whether this Ui belongs to a Menu.
     menu_state: Option<Arc<RwLock<MenuState>>>,
 }
@@ -82,6 +86,7 @@ impl Ui {
             style,
             placer: Placer::new(max_rect, Layout::default()),
             enabled: true,
+            sizing_pass: false,
             menu_state: None,
         };
 
@@ -108,9 +113,18 @@ impl Ui {
     pub fn child_ui_with_id_source(
         &mut self,
         max_rect: Rect,
-        layout: Layout,
+        mut layout: Layout,
         id_source: impl Hash,
     ) -> Self {
+        if self.sizing_pass {
+            // During the sizing pass we want widgets to use up as little space as possible,
+            // so that we measure the only the space we _need_.
+            layout.cross_justify = false;
+            if layout.cross_align == Align::Center {
+                layout.cross_align = Align::Min;
+            }
+        }
+
         debug_assert!(!max_rect.any_nan());
         let next_auto_id_source = Id::new(self.next_auto_id_source).with("child").value();
         self.next_auto_id_source = self.next_auto_id_source.wrapping_add(1);
@@ -121,6 +135,7 @@ impl Ui {
             style: self.style.clone(),
             placer: Placer::new(max_rect, layout),
             enabled: self.enabled,
+            sizing_pass: self.sizing_pass,
             menu_state: self.menu_state.clone(),
         };
 
@@ -140,6 +155,26 @@ impl Ui {
 
     // -------------------------------------------------
 
+    /// Set to true in special cases where we do one frame
+    /// where we size up the contents of the Ui, without actually showing it.
+    ///
+    /// This will also turn the Ui invisible.
+    /// Should be called right after [`Self::new`], if at all.
+    #[inline]
+    pub fn set_sizing_pass(&mut self) {
+        self.sizing_pass = true;
+        self.set_visible(false);
+    }
+
+    /// Set to true in special cases where we do one frame
+    /// where we size up the contents of the Ui, without actually showing it.
+    #[inline]
+    pub fn is_sizing_pass(&self) -> bool {
+        self.sizing_pass
+    }
+
+    // -------------------------------------------------
+
     /// A unique identity of this [`Ui`].
     #[inline]
     pub fn id(&self) -> Id {