Fade out the edges of ScrollAreas (#8018)

## Before:
<img width="381" height="307" alt="image"
src="https://github.com/user-attachments/assets/0528ae2a-44bf-4d9e-89a4-c3f4ab438eb2"
/>

It is very hard here to realize this is a scrollable area

## After
<img width="383" height="310" alt="image"
src="https://github.com/user-attachments/assets/9e0ee6de-8b96-4e5c-a505-f57977010990"
/>

The fade at the bottom tells the user they should try scrolling.

You can turn if off with `style.spacing.scroll.fade.enabled`

crates/egui/src/containers/scroll_area.rs

@@ -5,7 +5,7 @@
 use std::ops::{Add, AddAssign, BitOr, BitOrAssign};
 
 use emath::GuiRounding as _;
-use epaint::Margin;
+use epaint::{Color32, Direction, Margin, Shape};
 
 use crate::{
     Context, CursorIcon, Id, NumExt as _, Pos2, Rangef, Rect, Response, Sense, Ui, UiBuilder,
@@ -1019,13 +1019,17 @@ impl ScrollArea {
             .inner;
 
         let (content_size, state) = prepared.end(ui);
-        ScrollAreaOutput {
+        let output = ScrollAreaOutput {
             inner,
             id,
             state,
             content_size,
             inner_rect,
-        }
+        };
+
+        paint_fade_areas(ui, &output);
+
+        output
     }
 }
 
@@ -1504,3 +1508,89 @@ impl Prepared {
         (content_size, state)
     }
 }
+
+/// Paint fade-out gradients at the top and/or bottom of a scroll area to
+/// indicate that more content is available beyond the visible region.
+fn paint_fade_areas<R>(ui: &Ui, scroll_output: &ScrollAreaOutput<R>) {
+    let crate::style::ScrollFadeStyle {
+        enabled,
+        size: fade_size,
+    } = ui.spacing().scroll.fade;
+
+    if !enabled {
+        return;
+    }
+
+    let bg = ui.stack().bg_color();
+
+    let offset = scroll_output.state.offset;
+    let overflow = scroll_output.content_size - scroll_output.inner_rect.size();
+
+    let paint_rect = scroll_output
+        .inner_rect
+        .intersect(ui.min_rect())
+        .expand(ui.visuals().clip_rect_margin);
+
+    // Top fade: animate opacity based on how far we've scrolled down.
+    if 0.0 < offset.y {
+        let t = (offset.y / fade_size).clamp(0.0, 1.0);
+        let bg_faded = bg.gamma_multiply(t);
+        let rect = Rect::from_min_max(
+            paint_rect.left_top(),
+            pos2(paint_rect.right(), paint_rect.top() + fade_size),
+        );
+        ui.painter().add(Shape::gradient_rect(
+            rect,
+            Direction::TopDown,
+            [bg_faded, Color32::TRANSPARENT],
+        ));
+    }
+
+    // Bottom fade: animate opacity based on distance from the bottom.
+    let distance_from_bottom = overflow.y - offset.y;
+    if 0.0 < distance_from_bottom {
+        let t = (distance_from_bottom / fade_size).clamp(0.0, 1.0);
+        let bg_faded = bg.gamma_multiply(t);
+        let rect = Rect::from_min_max(
+            pos2(paint_rect.left(), paint_rect.bottom() - fade_size),
+            paint_rect.right_bottom(),
+        );
+        ui.painter().add(Shape::gradient_rect(
+            rect,
+            Direction::BottomUp,
+            [bg_faded, Color32::TRANSPARENT],
+        ));
+    }
+
+    // Left fade: animate opacity based on how far we've scrolled right.
+
+    if 0.0 < offset.x {
+        let t = (offset.x / fade_size).clamp(0.0, 1.0);
+        let bg_faded = bg.gamma_multiply(t);
+        let rect = Rect::from_min_max(
+            paint_rect.left_top(),
+            pos2(paint_rect.left() + fade_size, paint_rect.bottom()),
+        );
+        ui.painter().add(Shape::gradient_rect(
+            rect,
+            Direction::LeftToRight,
+            [bg_faded, Color32::TRANSPARENT],
+        ));
+    }
+
+    // Right fade: animate opacity based on distance from the right edge.
+    let distance_from_right = overflow.x - offset.x;
+    if 0.0 < distance_from_right {
+        let t = (distance_from_right / fade_size).clamp(0.0, 1.0);
+        let bg_faded = bg.gamma_multiply(t);
+        let rect = Rect::from_min_max(
+            pos2(paint_rect.right() - fade_size, paint_rect.top()),
+            paint_rect.right_bottom(),
+        );
+        ui.painter().add(Shape::gradient_rect(
+            rect,
+            Direction::RightToLeft,
+            [bg_faded, Color32::TRANSPARENT],
+        ));
+    }
+}

crates/egui/src/layout.rs

@@ -1,7 +1,7 @@
 use emath::GuiRounding as _;
 
 use crate::{
-    Align,
+    Align, Direction,
     emath::{Align2, NumExt as _, Pos2, Rect, Vec2, pos2, vec2},
 };
 const INFINITY: f32 = f32::INFINITY;
@@ -87,36 +87,6 @@ impl Region {
 
 // ----------------------------------------------------------------------------
 
-/// Layout direction, one of [`LeftToRight`](Direction::LeftToRight), [`RightToLeft`](Direction::RightToLeft), [`TopDown`](Direction::TopDown), [`BottomUp`](Direction::BottomUp).
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
-pub enum Direction {
-    LeftToRight,
-    RightToLeft,
-    TopDown,
-    BottomUp,
-}
-
-impl Direction {
-    #[inline(always)]
-    pub fn is_horizontal(self) -> bool {
-        match self {
-            Self::LeftToRight | Self::RightToLeft => true,
-            Self::TopDown | Self::BottomUp => false,
-        }
-    }
-
-    #[inline(always)]
-    pub fn is_vertical(self) -> bool {
-        match self {
-            Self::LeftToRight | Self::RightToLeft => false,
-            Self::TopDown | Self::BottomUp => true,
-        }
-    }
-}
-
-// ----------------------------------------------------------------------------
-
 /// The layout of a [`Ui`][`crate::Ui`], e.g. "vertical & centered".
 ///
 /// ```

crates/egui/src/lib.rs

@@ -449,7 +449,7 @@ pub use emath::{
     remap_clamp, vec2,
 };
 pub use epaint::{
-    ClippedPrimitive, ColorImage, CornerRadius, ImageData, Margin, Mesh, PaintCallback,
+    ClippedPrimitive, ColorImage, CornerRadius, Direction, ImageData, Margin, Mesh, PaintCallback,
     PaintCallbackInfo, Shadow, Shape, Stroke, StrokeKind, TextureHandle, TextureId, mutex,
     text::{FontData, FontDefinitions, FontFamily, FontId, FontTweak},
     textures::{TextureFilter, TextureOptions, TextureWrapMode, TexturesDelta},

crates/egui/src/style.rs

@@ -586,6 +586,8 @@ pub struct ScrollStyle {
     /// This is only for floating scroll bars.
     /// Solid scroll bars are always opaque.
     pub interact_handle_opacity: f32,
+
+    pub fade: ScrollFadeStyle,
 }
 
 impl Default for ScrollStyle {
@@ -616,6 +618,8 @@ impl ScrollStyle {
             dormant_handle_opacity: 0.0,
             active_handle_opacity: 0.6,
             interact_handle_opacity: 1.0,
+
+            fade: Default::default(),
         }
     }
 
@@ -699,6 +703,8 @@ impl ScrollStyle {
             dormant_handle_opacity,
             active_handle_opacity,
             interact_handle_opacity,
+
+            fade,
         } = self;
 
         ui.horizontal(|ui| {
@@ -772,6 +778,49 @@ impl ScrollStyle {
                 ui.label("Inner margin");
             });
         }
+
+        ui.separator();
+        fade.ui(ui);
+    }
+}
+
+/// Controls if and how to fade out the sides of a [`crate::ScrollArea`]
+/// to indicate there is more there if you scroll.
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", serde(default))]
+pub struct ScrollFadeStyle {
+    /// Show fade areas?
+    pub enabled: bool,
+
+    /// Size of the fade-area (height for vertical scrolling,
+    /// width for horizontal scrolling).
+    pub size: f32,
+}
+
+impl Default for ScrollFadeStyle {
+    fn default() -> Self {
+        Self {
+            enabled: true,
+            size: 20.0,
+        }
+    }
+}
+
+impl ScrollFadeStyle {
+    pub fn ui(&mut self, ui: &mut Ui) {
+        let Self { enabled, size } = self;
+
+        ui.horizontal(|ui| {
+            ui.checkbox(enabled, "Fade edges");
+        });
+
+        if *enabled {
+            ui.horizontal(|ui| {
+                ui.add(DragValue::new(size).range(0.0..=64.0));
+                ui.label("Fade size");
+            });
+        }
     }
 }
 

crates/egui/src/ui_stack.rs

@@ -256,7 +256,7 @@ impl UiStack {
         !self.info.frame.stroke.is_empty()
     }
 
-    /// The background color of this [`Ui`].
+    /// The background color of this [`crate::Ui`].
     ///
     /// This blend together all [`Frame::fill`] colors
     /// up to the root.

crates/egui_demo_app/tests/snapshots/easymarkeditor.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:b9ad01a55950f96a3ae9e48a2c026143d11ffee62bff4f83b4529cd884ce11f0
-size 169683
+oid sha256:65776e4d9e31e7163117166915a0cfaaece98b1dd69695533655dee889ac5597
+size 169277

crates/egui_demo_lib/src/demo/strip_demo.rs

@@ -27,7 +27,7 @@ impl crate::Demo for StripDemo {
 impl crate::View for StripDemo {
     fn ui(&mut self, ui: &mut egui::Ui) {
         let dark_mode = ui.visuals().dark_mode;
-        let faded_color = ui.visuals().window_fill();
+        let faded_color = ui.stack().bg_color();
         let faded_color = |color: Color32| -> Color32 {
             use egui::Rgba;
             let t = if dark_mode { 0.95 } else { 0.8 };

crates/egui_demo_lib/tests/snapshots/demos/Font Book.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:8c630df841e98043132b920338793745549116890c1bc52d8d10b0def896a1e6
-size 114409
+oid sha256:583003c59f40515a5de435ee1eea2ee6fceae409c7881456401b004c6409896a
+size 114575

crates/egui_demo_lib/tests/snapshots/demos/Panels.png

@@ -1,3 +1,3 @@
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-oid sha256:627114dcbda4f3d2255d34926ed0b77c679d248ed1d822d723479b1e6652c67a
-size 249258
+oid sha256:8815473873602211a95e0a077dc77560de154a0a1a2f9c1418d90746670075f7
+size 248630

crates/egui_demo_lib/tests/snapshots/demos/Scrolling.png

@@ -1,3 +1,3 @@
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-oid sha256:b5b965a7c690fd8e8646812513e2417170b687fd37e29d220c29127ba0cc200c
-size 172609
+oid sha256:2881255fa694b713a3c3049f30143ee60a20b68105fb724fbba188f81d34e572
+size 171778

crates/egui_demo_lib/tests/snapshots/demos/Table.png

@@ -1,3 +1,3 @@
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-oid sha256:931f38ade8373ff79801c05c5d4397f2c5fcfa27022f2e1abe9eb29d561a3aef
-size 76022
+oid sha256:63fb9d15956efa69818cfd5398b4dfaa796dfbe1df3fb171b8ae413a6f641c9f
+size 76049

crates/egui_demo_lib/tests/snapshots/demos/Tooltips.png

@@ -1,3 +1,3 @@
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-oid sha256:89986132c5d2a3ccccf0a16cb2b0be07b7c5512838cc10ec9067022e7a238515
-size 63918
+oid sha256:4ac837d03e3e8959196942d030a8511d00cdd0d5ac9bfe761d80b59d32e73581
+size 63967

crates/egui_demo_lib/tests/snapshots/demos/Window Resize Test.png

@@ -1,3 +1,3 @@
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-oid sha256:9c81d5a5915dac60297293b90cd3fc0d188a9335e99b318996e3e2934de7bee1
-size 483497
+oid sha256:4107ba4569b3e37ce6720595cfc4de60aec11dcfdb835720442b244e121209fc
+size 482862

crates/egui_kittest/tests/snapshots/test_scroll_initial.png

@@ -1,3 +1,3 @@
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-oid sha256:eb8737af84c3d3b0c054b7e2a8bcb04685243d84cb13b72a1372dc40dbfd14fb
-size 7267
+oid sha256:6f6d516cc3d1439256a19f72153468125bac1647e2e211e841579545570faef7
+size 7366

crates/egui_kittest/tests/snapshots/test_scroll_scrolled.png

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:f1651bb1b9bbaa3c65ecd07c39c57527f4beb4c607581a5b2596a49dcf4c5db3
-size 7996
+oid sha256:2e05d28e5541eb5926b4758e611f5c340311269fcd8b63055ff3a6793abbb140
+size 8279

crates/epaint/src/direction.rs

@@ -0,0 +1,27 @@
+/// A cardinal direction, one of [`LeftToRight`](Direction::LeftToRight), [`RightToLeft`](Direction::RightToLeft), [`TopDown`](Direction::TopDown), [`BottomUp`](Direction::BottomUp).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum Direction {
+    LeftToRight,
+    RightToLeft,
+    TopDown,
+    BottomUp,
+}
+
+impl Direction {
+    #[inline(always)]
+    pub fn is_horizontal(self) -> bool {
+        match self {
+            Self::LeftToRight | Self::RightToLeft => true,
+            Self::TopDown | Self::BottomUp => false,
+        }
+    }
+
+    #[inline(always)]
+    pub fn is_vertical(self) -> bool {
+        match self {
+            Self::LeftToRight | Self::RightToLeft => false,
+            Self::TopDown | Self::BottomUp => true,
+        }
+    }
+}

crates/epaint/src/lib.rs

@@ -27,6 +27,7 @@ mod brush;
 pub mod color;
 mod corner_radius;
 mod corner_radius_f32;
+mod direction;
 pub mod image;
 mod margin;
 mod margin_f32;
@@ -50,6 +51,7 @@ pub use self::{
     color::ColorMode,
     corner_radius::CornerRadius,
     corner_radius_f32::CornerRadiusF32,
+    direction::Direction,
     image::{AlphaFromCoverage, ColorImage, ImageData, ImageDelta},
     margin::Margin,
     margin_f32::*,

crates/epaint/src/mesh.rs

@@ -23,6 +23,18 @@ pub struct Vertex {
     pub color: Color32, // 32 bit
 }
 
+impl Vertex {
+    /// An untextured vertex
+    #[inline]
+    pub fn untextured(pos: Pos2, color: Color32) -> Self {
+        Self {
+            pos,
+            uv: WHITE_UV,
+            color,
+        }
+    }
+}
+
 #[repr(C)]
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 #[cfg(all(feature = "unity", not(feature = "_override_unity")))]
@@ -159,11 +171,7 @@ impl Mesh {
             self.texture_id == TextureId::default(),
             "Mesh has an assigned texture"
         );
-        self.vertices.push(Vertex {
-            pos,
-            uv: WHITE_UV,
-            color,
-        });
+        self.vertices.push(Vertex::untextured(pos, color));
     }
 
     /// Add a triangle.

crates/epaint/src/shapes/shape.rs

@@ -5,7 +5,7 @@ use std::sync::Arc;
 use emath::{Align2, Pos2, Rangef, Rect, TSTransform, Vec2, pos2};
 
 use crate::{
-    Color32, CornerRadius, Mesh, Stroke, StrokeKind, TextureId,
+    Color32, CornerRadius, Direction, Mesh, Stroke, StrokeKind, TextureId, Vertex,
     stroke::PathStroke,
     text::{FontId, FontsView, Galley},
 };
@@ -297,6 +297,32 @@ impl Shape {
         Self::Rect(RectShape::stroke(rect, corner_radius, stroke, stroke_kind))
     }
 
+    /// Paints a gradient rectangle that transitions from `color_from` to `color_to`
+    /// along the given `direction`.
+    ///
+    /// For example, [`Direction::TopDown`] paints `color_from` at the top edge fading
+    /// to `color_to` at the bottom edge.
+    #[inline]
+    pub fn gradient_rect(rect: Rect, direction: Direction, [from, to]: [Color32; 2]) -> Self {
+        let (left_top, right_top, left_bottom, right_bottom) = match direction {
+            Direction::TopDown => (from, from, to, to),
+            Direction::BottomUp => (to, to, from, from),
+            Direction::LeftToRight => (from, to, from, to),
+            Direction::RightToLeft => (to, from, to, from),
+        };
+
+        Self::from(Mesh {
+            indices: vec![0, 1, 2, 2, 1, 3],
+            vertices: vec![
+                Vertex::untextured(rect.left_top(), left_top),
+                Vertex::untextured(rect.right_top(), right_top),
+                Vertex::untextured(rect.left_bottom(), left_bottom),
+                Vertex::untextured(rect.right_bottom(), right_bottom),
+            ],
+            texture_id: Default::default(),
+        })
+    }
+
     #[expect(clippy::needless_pass_by_value)]
     pub fn text(
         fonts: &mut FontsView<'_>,

crates/epaint/src/tessellator.rs

@@ -10,8 +10,8 @@ use emath::{GuiRounding as _, NumExt as _, Pos2, Rect, Rot2, Vec2, pos2, remap,
 use crate::{
     CircleShape, ClippedPrimitive, ClippedShape, Color32, CornerRadiusF32, CubicBezierShape,
     EllipseShape, Mesh, PathShape, Primitive, QuadraticBezierShape, RectShape, Shape, Stroke,
-    StrokeKind, TextShape, TextureId, Vertex, WHITE_UV, color::ColorMode, emath,
-    stroke::PathStroke, texture_atlas::PreparedDisc,
+    StrokeKind, TextShape, TextureId, Vertex, color::ColorMode, emath, stroke::PathStroke,
+    texture_atlas::PreparedDisc,
 };
 
 // ----------------------------------------------------------------------------
@@ -809,11 +809,8 @@ fn fill_closed_path(feathering: f32, path: &mut [PathPoint], fill_color: Color32
     } else {
         out.reserve_triangles(n as usize);
         let idx = out.vertices.len() as u32;
-        out.vertices.extend(path.iter().map(|p| Vertex {
-            pos: p.pos,
-            uv: WHITE_UV,
-            color: fill_color,
-        }));
+        out.vertices
+            .extend(path.iter().map(|p| Vertex::untextured(p.pos, fill_color)));
         for i in 2..n {
             out.add_triangle(idx, idx + i - 1, idx + i);
         }

tests/egui_tests/tests/snapshots/text_edit_scroll_0_focus.png

@@ -1,3 +1,3 @@
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+size 1861

tests/egui_tests/tests/snapshots/text_edit_scroll_1_5.png

@@ -1,3 +1,3 @@
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+size 1953