Return more info from ScrollArea::show (#1166)

CHANGELOG.md

@@ -33,7 +33,8 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 * Replaced `Style::body_text_style` with more generic `Style::text_styles` ([#1154](https://github.com/emilk/egui/pull/1154)).
 * `TextStyle` is no longer `Copy` ([#1154](https://github.com/emilk/egui/pull/1154)).
 * Replaced `TextEdit::text_style` with `TextEdit::font` ([#1154](https://github.com/emilk/egui/pull/1154)).
-* `Plot::highlight` now takes a `bool` argument ([#1159](https://github.com/emilk/egui/pull/1159)),
+* `Plot::highlight` now takes a `bool` argument ([#1159](https://github.com/emilk/egui/pull/1159)).
+* `ScrollArea::show` now returns a `ScrollAreaOutput`, so you might need to add `.inner` after the call to it ([#1166](https://github.com/emilk/egui/pull/1166)).
 
 ### Fixed 🐛
 * Context menu now respects the theme ([#1043](https://github.com/emilk/egui/pull/1043))

egui/src/containers/combo_box.rs

@@ -196,6 +196,7 @@ fn combo_box_dyn<'c, R>(
         ScrollArea::vertical()
             .max_height(ui.spacing().combo_height)
             .show(ui, menu_contents)
+            .inner
     });
 
     InnerResponse {

egui/src/containers/scroll_area.rs

@@ -10,9 +10,9 @@ use crate::*;
 #[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
-pub(crate) struct State {
+pub struct State {
     /// Positive offset means scrolling down/right
-    offset: Vec2,
+    pub offset: Vec2,
 
     show_scroll: [bool; 2],
 
@@ -51,6 +51,20 @@ impl State {
     }
 }
 
+pub struct ScrollAreaOutput<R> {
+    /// What the user closure returned.
+    pub inner: R,
+
+    /// `Id` of the `ScrollArea`.
+    pub id: Id,
+
+    /// The current state of the scroll area.
+    pub state: State,
+
+    /// Where on the screen the content is (excludes scroll bars).
+    pub inner_rect: Rect,
+}
+
 /// Add vertical and/or horizontal scrolling to a contained [`Ui`].
 ///
 /// ```
@@ -258,6 +272,7 @@ struct Prepared {
     /// width of the vertical bar, and the height of the horizontal bar?
     current_bar_use: Vec2,
     always_show_scroll: bool,
+    /// Where on the screen the content is (excludes scroll bars).
     inner_rect: Rect,
     content_ui: Ui,
     /// Relative coordinates: the offset and size of the view of the inner UI.
@@ -365,7 +380,11 @@ impl ScrollArea {
     /// Show the `ScrollArea`, and add the contents to the viewport.
     ///
     /// If the inner area can be very long, consider using [`Self::show_rows`] instead.
-    pub fn show<R>(self, ui: &mut Ui, add_contents: impl FnOnce(&mut Ui) -> R) -> R {
+    pub fn show<R>(
+        self,
+        ui: &mut Ui,
+        add_contents: impl FnOnce(&mut Ui) -> R,
+    ) -> ScrollAreaOutput<R> {
         self.show_viewport_dyn(ui, Box::new(|ui, _viewport| add_contents(ui)))
     }
 
@@ -391,7 +410,7 @@ impl ScrollArea {
         row_height_sans_spacing: f32,
         total_rows: usize,
         add_contents: impl FnOnce(&mut Ui, std::ops::Range<usize>) -> R,
-    ) -> R {
+    ) -> ScrollAreaOutput<R> {
         let spacing = ui.spacing().item_spacing;
         let row_height_with_spacing = row_height_sans_spacing + spacing.y;
         self.show_viewport(ui, |ui, viewport| {
@@ -420,7 +439,11 @@ impl ScrollArea {
     ///
     /// `add_contents` is past the viewport, which is the relative view of the content.
     /// So if the passed rect has min = zero, then show the top left content (the user has not scrolled).
-    pub fn show_viewport<R>(self, ui: &mut Ui, add_contents: impl FnOnce(&mut Ui, Rect) -> R) -> R {
+    pub fn show_viewport<R>(
+        self,
+        ui: &mut Ui,
+        add_contents: impl FnOnce(&mut Ui, Rect) -> R,
+    ) -> ScrollAreaOutput<R> {
         self.show_viewport_dyn(ui, Box::new(add_contents))
     }
 
@@ -428,16 +451,23 @@ impl ScrollArea {
         self,
         ui: &mut Ui,
         add_contents: Box<dyn FnOnce(&mut Ui, Rect) -> R + 'c>,
-    ) -> R {
+    ) -> ScrollAreaOutput<R> {
         let mut prepared = self.begin(ui);
-        let ret = add_contents(&mut prepared.content_ui, prepared.viewport);
+        let id = prepared.id;
-        prepared.end(ui);
+        let inner_rect = prepared.inner_rect;
-        ret
+        let inner = add_contents(&mut prepared.content_ui, prepared.viewport);
+        let state = prepared.end(ui);
+        ScrollAreaOutput {
+            inner,
+            id,
+            state,
+            inner_rect,
+        }
     }
 }
 
 impl Prepared {
-    fn end(self, ui: &mut Ui) {
+    fn end(self, ui: &mut Ui) -> State {
         let Prepared {
             id,
             mut state,
@@ -747,6 +777,8 @@ impl Prepared {
         state.show_scroll = show_scroll_this_frame;
 
         state.store(ui.ctx(), id);
+
+        state
     }
 }
 

egui/src/containers/window.rs

@@ -354,7 +354,7 @@ impl<'open> Window<'open> {
                         }
 
                         if scroll.has_any_bar() {
-                            scroll.show(ui, add_contents)
+                            scroll.show(ui, add_contents).inner
                         } else {
                             add_contents(ui)
                         }

egui/src/response.rs

@@ -586,7 +586,9 @@ impl std::ops::BitOrAssign for Response {
 /// ```
 #[derive(Debug)]
 pub struct InnerResponse<R> {
+    /// What the user closure returned.
     pub inner: R,
+    /// The response of the area.
     pub response: Response,
 }
 

egui_demo_lib/src/apps/demo/scrolling.rs

@@ -210,32 +210,34 @@ impl super::View for ScrollTo {
         }
 
         ui.separator();
-        let (current_scroll, max_scroll) = scroll_area.show(ui, |ui| {
+        let (current_scroll, max_scroll) = scroll_area
-            if scroll_top {
+            .show(ui, |ui| {
-                ui.scroll_to_cursor(Align::TOP);
+                if scroll_top {
-            }
+                    ui.scroll_to_cursor(Align::TOP);
-            ui.vertical(|ui| {
-                for item in 1..=50 {
-                    if track_item && item == self.track_item {
-                        let response =
-                            ui.colored_label(Color32::YELLOW, format!("This is item {}", item));
-                        response.scroll_to_me(self.tack_item_align);
-                    } else {
-                        ui.label(format!("This is item {}", item));
-                    }
                 }
-            });
+                ui.vertical(|ui| {
+                    for item in 1..=50 {
+                        if track_item && item == self.track_item {
+                            let response =
+                                ui.colored_label(Color32::YELLOW, format!("This is item {}", item));
+                            response.scroll_to_me(self.tack_item_align);
+                        } else {
+                            ui.label(format!("This is item {}", item));
+                        }
+                    }
+                });
 
-            if scroll_bottom {
+                if scroll_bottom {
-                ui.scroll_to_cursor(Align::BOTTOM);
+                    ui.scroll_to_cursor(Align::BOTTOM);
-            }
+                }
 
-            let margin = ui.visuals().clip_rect_margin;
+                let margin = ui.visuals().clip_rect_margin;
 
-            let current_scroll = ui.clip_rect().top() - ui.min_rect().top() + margin;
+                let current_scroll = ui.clip_rect().top() - ui.min_rect().top() + margin;
-            let max_scroll = ui.min_rect().height() - ui.clip_rect().height() + 2.0 * margin;
+                let max_scroll = ui.min_rect().height() - ui.clip_rect().height() + 2.0 * margin;
-            (current_scroll, max_scroll)
+                (current_scroll, max_scroll)
-        });
+            })
+            .inner;
         ui.separator();
 
         ui.label(format!(