Let the theme style submenus, and let a button's fill bleed out of its box

Three things a menu needs and nothing else does:

* A submenu asked `Frame::menu` for its frame directly, so it ignored the
  theme. It now resolves the same `PopupStyle` a `Popup` does — it needs the
  margin itself, to place the submenu and to decide how much of the parent
  menu counts as hovered.
* `ScrollStyle::overflow_margin` lets a scroll area's contents paint a little
  outside the viewport, at the ends of the scroll range where nothing could
  scroll into view through the gap. A menu item whose fill bleeds past its
  own box needs it; without it the fill is sliced.
* A frameless button dropped its inner margin but kept the outer one, so its
  contents shifted as soon as it was hovered.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/egui/src/containers/menu.rs

@@ -9,9 +9,13 @@
 //! See [`MenuBar`] for an example.
 
 use crate::style::StyleModifier;
+use crate::widget_style::{
+    Classes, HasClasses as _, MENU_CLASS, PopupStyle, StyleArgs, WidgetState,
+};
 use crate::{
-    Button, Color32, Context, Frame, Id, InnerResponse, IntoAtoms, Layout, PointerButton, Popup,
-    PopupCloseBehavior, Response, Style, Ui, UiBuilder, UiKind, UiStack, UiStackInfo, Widget as _,
+    Button, Color32, Context, Id, InnerResponse, IntoAtoms, Layout, PointerButton, Popup,
+    PopupCloseBehavior, PopupKind, Response, Style, Ui, UiBuilder, UiKind, UiStack, UiStackInfo,
+    Widget as _,
 };
 use emath::{Align, RectAlign, Vec2, vec2};
 use epaint::Stroke;
@@ -429,10 +433,22 @@ impl SubMenu {
         button_response: &Response,
         content: impl FnOnce(&mut Ui) -> R,
     ) -> Option<InnerResponse<R>> {
-        let frame = Frame::menu(ui.style());
-
         let id = Self::id_from_widget_id(button_response.id);
 
+        // A submenu is a menu, so the theme frames it like one. `Popup` computes the same style
+        // itself; we need it here too, because its margin decides where the submenu sits and how
+        // much of the parent menu counts as hovered. A popup frame does not depend on any widget
+        // state, so we ask for it directly rather than through `Ui::widget_style`, which would
+        // want a response that does not exist while the submenu is closed.
+        let classes = Classes::default().with_class(MENU_CLASS);
+        let PopupStyle { frame, .. } = ui.ctx().get_widget_style(&StyleArgs {
+            classes: &classes,
+            state: WidgetState::default(),
+            stack: ui.stack(),
+            style: ui.style(),
+            ctx: ui.ctx(),
+        });
+
         // Get the state from the parent menu
         let (open_item, menu_id, parent_config) = MenuState::from_ui(ui, |state, stack| {
             (state.open_item, stack.id, MenuConfig::from_stack(stack))
@@ -501,12 +517,12 @@ impl SubMenu {
 
         let popup_response = Popup::from_response(&response)
             .id(id)
+            .kind(PopupKind::Menu)
             .open(is_open)
             .align(RectAlign::RIGHT_START)
             .layout(Layout::top_down_justified(Align::Min))
             .gap(gap)
             .style(menu_config.style.clone())
-            .frame(frame)
             // The close behavior is handled by the menu (see below)
             .close_behavior(PopupCloseBehavior::IgnoreClicks)
             .info(

crates/egui/src/containers/popup.rs

@@ -637,6 +637,7 @@ impl<'a> Popup<'a> {
             // The theme decides how the popup is framed and how tightly its items sit together.
             let popup_style: PopupStyle = ui.widget_style(id, &classes);
             ui.spacing_mut().item_spacing = popup_style.item_spacing;
+            ui.spacing_mut().scroll.overflow_margin = popup_style.scroll_overflow_margin;
 
             let frame = frame.unwrap_or(popup_style.frame);
             frame.show(ui, content).inner

crates/egui/src/containers/scroll_area.rs

@@ -36,6 +36,11 @@ pub struct State {
     /// The content were to large to fit large frame.
     content_is_too_large: Vec2b,
 
+    /// The largest offset the content allowed last frame.
+    ///
+    /// Zero or less when the content fits, so there is nothing to scroll.
+    max_offset: Vec2,
+
     /// Did the user interact (hover or drag) the scroll bars last frame?
     scroll_bar_interaction: Vec2b,
 
@@ -62,6 +67,7 @@ impl Default for State {
             offset_target: Default::default(),
             show_scroll: Vec2b::FALSE,
             content_is_too_large: Vec2b::FALSE,
+            max_offset: Vec2::ZERO,
             scroll_bar_interaction: Vec2b::FALSE,
             vel: Vec2::ZERO,
             scroll_start_offset_from_top_left: [None; 2],
@@ -353,6 +359,7 @@ pub struct ScrollArea {
     wheel_scroll_multiplier: Vec2,
 
     content_margin: Option<Margin>,
+    overflow_margin: Option<Margin>,
 
     /// If true for vertical or horizontal the scroll wheel will stick to the
     /// end position until user manually changes position. It will become true
@@ -407,6 +414,7 @@ impl ScrollArea {
             scroll_source: ScrollSource::default(),
             wheel_scroll_multiplier: Vec2::splat(1.0),
             content_margin: None,
+            overflow_margin: None,
             stick_to_end: Vec2b::FALSE,
             animated: true,
         }
@@ -633,6 +641,19 @@ impl ScrollArea {
         self
     }
 
+    /// How far the contents may paint outside the viewport.
+    ///
+    /// Some widgets paint outside their own box — a menu item whose fill bleeds past it, say — and
+    /// the scroll area would otherwise cut that off. Only the ends of the scroll range are
+    /// widened, where there is nothing that could scroll into view through the gap.
+    ///
+    /// Default: [`crate::style::ScrollStyle::overflow_margin`].
+    #[inline]
+    pub fn overflow_margin(mut self, margin: impl Into<Margin>) -> Self {
+        self.overflow_margin = Some(margin.into());
+        self
+    }
+
     /// The scroll handle will stick to the rightmost position even while the content size
     /// changes dynamically. This can be useful to simulate text scrollers coming in from right
     /// hand side. The scroll handle remains stuck until user manually changes position. Once "unstuck"
@@ -724,6 +745,7 @@ impl ScrollArea {
             scroll_source,
             wheel_scroll_multiplier,
             content_margin: _, // Used elsewhere
+            overflow_margin,
             stick_to_end,
             animated,
         } = self;
@@ -811,6 +833,11 @@ impl ScrollArea {
         {
             // Clip the content, but only when we really need to:
             let mut content_clip_rect = ui.clip_rect();
+            let overflow_margin =
+                overflow_margin.unwrap_or_else(|| ui.spacing().scroll.overflow_margin);
+            let overflow_min = Vec2::new(overflow_margin.leftf(), overflow_margin.topf());
+            let overflow_max = Vec2::new(overflow_margin.rightf(), overflow_margin.bottomf());
+
             for d in 0..2 {
                 if direction_enabled[d] {
                     content_clip_rect.min[d] = inner_rect.min[d];
@@ -819,8 +846,18 @@ impl ScrollArea {
                     // Nice handling of forced resizing beyond the possible:
                     content_clip_rect.max[d] = ui.clip_rect().max[d] - current_bar_use[d];
                 }
+
+                // Let the contents paint a little outside the viewport, but only where nothing
+                // could scroll into view through the gap: at the start of the scroll range there
+                // is nothing above the first item, and at its end nothing below the last one.
+                if !direction_enabled[d] || state.offset[d] <= 0.0 {
+                    content_clip_rect.min[d] -= overflow_min[d];
+                }
+                if !direction_enabled[d] || state.max_offset[d] <= state.offset[d] {
+                    content_clip_rect.max[d] += overflow_max[d];
+                }
             }
-            // Make sure we didn't accidentally expand the clip rect
+            // Make sure we didn't grow past what our parent allows
             content_clip_rect = content_clip_rect.intersect(ui.clip_rect());
             content_ui.set_clip_rect(content_clip_rect);
         }
@@ -1551,6 +1588,7 @@ impl Prepared {
 
         state.show_scroll = show_scroll_this_frame;
         state.content_is_too_large = content_is_too_large;
+        state.max_offset = max_offset;
         state.interact_rect = Some(inner_rect);
 
         state.store(ui.ctx(), id);

crates/egui/src/style.rs

@@ -508,6 +508,13 @@ pub struct ScrollStyle {
     /// depending on the value of [`Self::floating`].
     pub content_margin: Margin,
 
+    /// How far the contents of a [`crate::ScrollArea`] may paint outside its viewport.
+    ///
+    /// Some widgets paint outside their own box — a menu item whose fill bleeds past it, say — and
+    /// a [`crate::ScrollArea`] would otherwise cut that off. Only the ends of the scroll range are
+    /// widened, where there is nothing that could scroll into view through the gap.
+    pub overflow_margin: Margin,
+
     /// The width of the scroll bars at it largest.
     pub bar_width: f32,
 
@@ -594,6 +601,7 @@ impl ScrollStyle {
         Self {
             floating: false,
             content_margin: Margin::ZERO,
+            overflow_margin: Margin::ZERO,
             bar_width: 6.0,
             handle_min_length: 12.0,
             bar_inner_margin: 4.0,
@@ -679,6 +687,7 @@ impl ScrollStyle {
             floating,
 
             content_margin,
+            overflow_margin,
 
             bar_width,
             handle_min_length,
@@ -710,6 +719,11 @@ impl ScrollStyle {
             content_margin.ui(ui);
         });
 
+        ui.horizontal(|ui| {
+            ui.label("Overflow margin:");
+            overflow_margin.ui(ui);
+        });
+
         ui.horizontal(|ui| {
             ui.add(DragValue::new(bar_width).range(0.0..=32.0));
             ui.label("Full bar width");

crates/egui/src/theme/default_style.rs

@@ -106,6 +106,7 @@ impl StyleProvider<PopupStyle> for DefaultStyle {
         PopupStyle {
             frame: Frame::popup(style),
             item_spacing: style.spacing.item_spacing,
+            scroll_overflow_margin: style.spacing.scroll.overflow_margin,
         }
     }
 }

crates/egui/src/widget_style/mod.rs

@@ -14,7 +14,7 @@ use emath::Vec2;
 use epaint::{Color32, FontId, Stroke, text::TextWrapMode};
 
 use crate::{
-    Context, Frame, Response, Style, TextStyle, UiStack,
+    Context, Frame, Margin, Response, Style, TextStyle, UiStack,
     style::{WidgetVisuals, Widgets},
 };
 
@@ -109,6 +109,13 @@ pub struct PopupStyle {
     /// A menu wants its items flush against each other, while a tooltip wants them spaced out
     /// like any other content.
     pub item_spacing: Vec2,
+
+    /// How far the contents of a [`crate::ScrollArea`] inside the popup may paint outside it.
+    ///
+    /// A [`crate::ScrollArea`] clips to its viewport, which would cut off anything a widget paints
+    /// outside its own box — an item whose fill bleeds past it, say. This is how much room such a
+    /// widget gets, applied via [`crate::style::ScrollStyle::overflow_margin`].
+    pub scroll_overflow_margin: Margin,
 }
 
 impl WidgetStyle for PopupStyle {}

crates/egui/src/widgets/button.rs

@@ -366,6 +366,12 @@ impl<'a> Button<'a> {
 
         frame = frame.inner_margin(button_padding);
 
+        if !has_frame_margin {
+            // A frameless button asks for no padding, so any outer margin the theme used to
+            // compensate for that padding has to go as well.
+            frame = frame.outer_margin(Margin::ZERO);
+        }
+
         // Apply the style font and color as fallback
         layout = layout
             .fallback_font(text_style.font_id.clone())
@@ -375,7 +381,13 @@ impl<'a> Button<'a> {
         layout = if has_frame_margin && (state != WidgetState::Inactive || frame_when_inactive) {
             layout.frame(frame)
         } else {
-            layout.frame(Frame::new().inner_margin(frame.inner_margin))
+            // The frame is not painted, but it still takes up the same space: keep both margins,
+            // or the contents would move as soon as the button is hovered or selected.
+            layout.frame(
+                Frame::new()
+                    .inner_margin(frame.inner_margin)
+                    .outer_margin(frame.outer_margin),
+            )
         };
 
         let mut prepared = layout.min_size(min_size).allocate(ui);