Make sure scroll bars are always visible (#2371)

* Nicer debug rectangles

* Move scrollbars into the clip-rect so they are always visible

* Improve table demo

* Add options for controlling inner and outer margin of the scroll bars

* Add line to changelog

* Update egui_extras changelog with recent Table improvements

* Refactor Table:s scroll options

* Add Table::auto_size

* Rename it auto_shrink

CHANGELOG.md

@@ -34,7 +34,8 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Improved text rendering ([#2071](https://github.com/emilk/egui/pull/2071)).
 * Less jitter when calling `Context::set_pixels_per_point` ([#2239](https://github.com/emilk/egui/pull/2239)).
 * Fixed popups and color edit going outside the screen.
-* Fixed keyboard support in `DragValue`. ([#2342](https://github.com/emilk/egui/pull/2342)).
+* Fixed keyboard support in `DragValue` ([#2342](https://github.com/emilk/egui/pull/2342)).
+* If you nest `ScrollAreas` inside each other, the inner area will now move its scroll bar so it is always visible ([#2371](https://github.com/emilk/egui/pull/2371)).
 
 
 ## 0.19.0 - 2022-08-20

crates/egui/src/containers/scroll_area.rs

@@ -635,23 +635,7 @@ impl Prepared {
                 };
             }
 
-            let mut inner_rect = Rect::from_min_size(inner_rect.min, inner_size);
-
-            // The window that egui sits in can't be expanded by egui, so we need to respect it:
-            for d in 0..2 {
-                if !has_bar[d] {
-                    // HACK for when we have a vertical-only scroll area in a top level panel,
-                    // and that panel is not wide enough for the contents.
-                    // This code ensures we still see the scroll bar!
-                    let max = ui.input().screen_rect().max[d]
-                        - current_bar_use[d]
-                        - ui.spacing().item_spacing[d];
-                    inner_rect.max[d] = inner_rect.max[d].at_most(max);
-                    // TODO(emilk): maybe auto-enable horizontal/vertical scrolling if this limit is reached
-                }
-            }
-
-            inner_rect
+            Rect::from_min_size(inner_rect.min, inner_size)
         };
 
         let outer_rect = Rect::from_min_size(inner_rect.min, inner_rect.size() + current_bar_use);
@@ -703,13 +687,29 @@ impl Prepared {
                 continue;
             }
 
-            // margin between contents and scroll bar
-            let margin = animation_t * ui.spacing().item_spacing.x;
-            let min_cross = inner_rect.max[1 - d] + margin; // left of vertical scroll (d == 1)
-            let max_cross = outer_rect.max[1 - d]; // right of vertical scroll (d == 1)
+            // margin on either side of the scroll bar
+            let inner_margin = animation_t * ui.spacing().scroll_bar_inner_margin;
+            let outer_margin = animation_t * ui.spacing().scroll_bar_outer_margin;
+            let mut min_cross = inner_rect.max[1 - d] + inner_margin; // left of vertical scroll (d == 1)
+            let mut max_cross = outer_rect.max[1 - d] - outer_margin; // right of vertical scroll (d == 1)
             let min_main = inner_rect.min[d]; // top of vertical scroll (d == 1)
             let max_main = inner_rect.max[d]; // bottom of vertical scroll (d == 1)
 
+            if ui.clip_rect().max[1 - d] < max_cross + outer_margin {
+                // Move the scrollbar so it is visible. This is needed in some cases.
+                // For instance:
+                // * When we have a vertical-only scroll area in a top level panel,
+                //   and that panel is not wide enough for the contents.
+                // * When one ScrollArea is nested inside another, and the outer
+                //   is scrolled so that the scroll-bars of the inner ScrollArea (us)
+                //   is outside the clip rectangle.
+                // Really this should use the tighter clip_rect that ignores clip_rect_margin, but we don't store that.
+                // clip_rect_margin is quite a hack. It would be nice to get rid of it.
+                let width = max_cross - min_cross;
+                max_cross = ui.clip_rect().max[1 - d] - outer_margin;
+                min_cross = max_cross - width;
+            }
+
             let outer_scroll_rect = if d == 0 {
                 Rect::from_min_max(
                     pos2(inner_rect.left(), min_cross),
@@ -865,5 +865,7 @@ impl Prepared {
 
 /// Width of a vertical scrollbar, or height of a horizontal scroll bar
 fn max_scroll_bar_width_with_margin(ui: &Ui) -> f32 {
-    ui.spacing().item_spacing.x + ui.spacing().scroll_bar_width
+    ui.spacing().scroll_bar_inner_margin
+        + ui.spacing().scroll_bar_width
+        + ui.spacing().scroll_bar_outer_margin
 }

crates/egui/src/painter.rs

@@ -208,7 +208,12 @@ impl Painter {
 impl Painter {
     #[allow(clippy::needless_pass_by_value)]
     pub fn debug_rect(&self, rect: Rect, color: Color32, text: impl ToString) {
-        self.rect_stroke(rect, 0.0, (1.0, color));
+        self.rect(
+            rect,
+            0.0,
+            color.additive().linear_multiply(0.015),
+            (1.0, color),
+        );
         self.text(
             rect.min,
             Align2::LEFT_TOP,

crates/egui/src/style.rs

@@ -292,6 +292,11 @@ pub struct Spacing {
     pub combo_height: f32,
 
     pub scroll_bar_width: f32,
+
+    /// Margin between contents and scroll bar.
+    pub scroll_bar_inner_margin: f32,
+    /// Margin between scroll bar and the outer container (e.g. right of a vertical scroll bar).
+    pub scroll_bar_outer_margin: f32,
 }
 
 impl Spacing {
@@ -658,6 +663,8 @@ impl Default for Spacing {
             tooltip_width: 600.0,
             combo_height: 200.0,
             scroll_bar_width: 8.0,
+            scroll_bar_inner_margin: 4.0,
+            scroll_bar_outer_margin: 0.0,
             indent_ends_with_horizontal_line: false,
         }
     }
@@ -941,6 +948,8 @@ impl Spacing {
             indent_ends_with_horizontal_line,
             combo_height,
             scroll_bar_width,
+            scroll_bar_inner_margin,
+            scroll_bar_outer_margin,
         } = self;
 
         ui.add(slider_vec2(item_spacing, 0.0..=20.0, "Item spacing"));
@@ -1021,7 +1030,15 @@ impl Spacing {
         });
         ui.horizontal(|ui| {
             ui.add(DragValue::new(scroll_bar_width).clamp_range(0.0..=32.0));
-            ui.label("Scroll-bar width width");
+            ui.label("Scroll-bar width");
+        });
+        ui.horizontal(|ui| {
+            ui.add(DragValue::new(scroll_bar_inner_margin).clamp_range(0.0..=32.0));
+            ui.label("Scroll-bar inner margin");
+        });
+        ui.horizontal(|ui| {
+            ui.add(DragValue::new(scroll_bar_outer_margin).clamp_range(0.0..=32.0));
+            ui.label("Scroll-bar outer margin");
         });
 
         ui.horizontal(|ui| {

crates/egui_demo_lib/src/demo/scrolling.rs

@@ -7,6 +7,7 @@ enum ScrollDemo {
     ManyLines,
     LargeCanvas,
     StickToEnd,
+    Bidirectional,
 }
 
 impl Default for ScrollDemo {
@@ -55,6 +56,7 @@ impl super::View for Scrolling {
                 "Scroll a large canvas",
             );
             ui.selectable_value(&mut self.demo, ScrollDemo::StickToEnd, "Stick to end");
+            ui.selectable_value(&mut self.demo, ScrollDemo::Bidirectional, "Bidirectional");
         });
         ui.separator();
         match self.demo {
@@ -70,6 +72,14 @@ impl super::View for Scrolling {
             ScrollDemo::StickToEnd => {
                 self.scroll_stick_to.ui(ui);
             }
+            ScrollDemo::Bidirectional => {
+                egui::ScrollArea::both().show(ui, |ui| {
+                    ui.style_mut().wrap = Some(false);
+                    for _ in 0..100 {
+                        ui.label(crate::LOREM_IPSUM);
+                    }
+                });
+            }
         }
     }
 }

crates/egui_demo_lib/src/demo/table_demo.rs

@@ -47,7 +47,7 @@ impl super::Demo for TableDemo {
     }
 }
 
-const NUM_MANUAL_ROWS: usize = 32;
+const NUM_MANUAL_ROWS: usize = 20;
 
 impl super::View for TableDemo {
     fn ui(&mut self, ui: &mut egui::Ui) {
@@ -101,11 +101,13 @@ impl super::View for TableDemo {
         // Leave room for the source code link after the table demo:
         use egui_extras::{Size, StripBuilder};
         StripBuilder::new(ui)
-            .size(Size::remainder()) // for the table
+            .size(Size::remainder().at_least(100.0)) // for the table
             .size(Size::exact(10.0)) // for the source code link
             .vertical(|mut strip| {
                 strip.cell(|ui| {
-                    self.table_ui(ui);
+                    egui::ScrollArea::horizontal().show(ui, |ui| {
+                        self.table_ui(ui);
+                    });
                 });
                 strip.cell(|ui| {
                     ui.vertical_centered(|ui| {
@@ -133,7 +135,8 @@ impl TableDemo {
                     .resizable(true)
                     .clip(true),
             )
-            .column(Column::remainder());
+            .column(Column::remainder())
+            .min_scrolled_height(0.0);
 
         if let Some(row_nr) = self.scroll_to_row.take() {
             table = table.scroll_to_row(row_nr, None);

crates/egui_extras/CHANGELOG.md

@@ -5,6 +5,21 @@ All notable changes to the `egui_extras` integration will be noted in this file.
 ## Unreleased
 * Added `TableBuilder::vertical_scroll_offset`: method to set vertical scroll offset position for a table ([#1946](https://github.com/emilk/egui/pull/1946)).
 * Added `RetainedImage::from_svg_bytes_with_size` to be able to specify a size for SVGs to be rasterized at.
+* Big `Table` improvements ([#2369](https://github.com/emilk/egui/pull/2369)):
+    * Double-click column separators to auto-size the column.
+    * All `Table` now store state. You may see warnings about reused table ids. Use `ui.push_id` to fix this.
+    * `TableBuilder::column` takes a `Column` instead of a `Size`.
+    * `Column` controls default size, size range, resizing, and clipping of columns.
+    * `Column::auto` will pick a size automatically
+    * Added `Table::scroll_to_row`.
+    * Added `Table::min_scrolled_height` and `Table::max_scroll_height`.
+    * Added `TableBody::max_size`.
+    * `Table::scroll` renamed to `Table::vscroll`.
+    * `egui_extras::Strip` now has `clip: false` by default.
+    * Fix bugs when putting `Table` inside of a horizontal `ScrollArea`.
+    * Many other bug fixes.
+* Add `Table::auto_shrink` - set to `false` to expand table to fit its containing `Ui` ([#2371](https://github.com/emilk/egui/pull/2371)).
+
 
 ## 0.19.0 - 2022-08-20
 * MSRV (Minimum Supported Rust Version) is now `1.61.0` ([#1846](https://github.com/emilk/egui/pull/1846)).