Allow changing handle shape of a slider (#3429)

* Closes #1974

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---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui/src/style.rs

@@ -815,6 +815,11 @@ pub struct Visuals {
     /// Enabling this will affect ALL sliders, and can be enabled/disabled per slider with [`Slider::trailing_fill`].
     pub slider_trailing_fill: bool,
 
+    /// Shape of the handle for sliders and similar widgets.
+    ///
+    /// Changing this will affect ALL sliders, and can be enabled/disabled per slider with [`Slider::handle_shape`].
+    pub handle_shape: HandleShape,
+
     /// Should the cursor change when the user hovers over an interactive/clickable item?
     ///
     /// This is consistent with a lot of browser-based applications (vscode, github
@@ -880,6 +885,20 @@ pub struct Selection {
     pub stroke: Stroke,
 }
 
+/// Shape of the handle for sliders and similar widgets.
+#[derive(Clone, Copy, Debug, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum HandleShape {
+    /// Circular handle
+    Circle,
+
+    /// Rectangular handle
+    Rect {
+        /// Aspect ratio of the rectangle. Set to < 1.0 to make it narrower.
+        aspect_ratio: f32,
+    },
+}
+
 /// The visuals of widgets for different states of interaction.
 #[derive(Clone, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
@@ -1125,6 +1144,7 @@ impl Visuals {
             striped: false,
 
             slider_trailing_fill: false,
+            handle_shape: HandleShape::Circle,
 
             interact_cursor: None,
 
@@ -1687,6 +1707,7 @@ impl Visuals {
             striped,
 
             slider_trailing_fill,
+            handle_shape,
             interact_cursor,
 
             image_loading_spinners,
@@ -1755,6 +1776,8 @@ impl Visuals {
 
         ui.checkbox(slider_trailing_fill, "Add trailing color to sliders");
 
+        handle_shape.ui(ui);
+
         ComboBox::from_label("Interact Cursor")
             .selected_text(format!("{interact_cursor:?}"))
             .show_ui(ui, |ui| {
@@ -1877,3 +1900,21 @@ fn rounding_ui(ui: &mut Ui, rounding: &mut Rounding) {
         }
     });
 }
+
+impl HandleShape {
+    pub fn ui(&mut self, ui: &mut Ui) {
+        ui.label("Widget handle shape");
+        ui.horizontal(|ui| {
+            ui.radio_value(self, HandleShape::Circle, "Circle");
+            if ui
+                .radio(matches!(self, HandleShape::Rect { .. }), "Rectangle")
+                .clicked()
+            {
+                *self = HandleShape::Rect { aspect_ratio: 0.5 };
+            }
+            if let HandleShape::Rect { aspect_ratio } = self {
+                ui.add(Slider::new(aspect_ratio, 0.1..=3.0).text("Aspect ratio"));
+            }
+        });
+    }
+}

crates/egui/src/widgets/slider.rs

@@ -2,7 +2,7 @@
 
 use std::ops::RangeInclusive;
 
-use crate::*;
+use crate::{style::HandleShape, *};
 
 // ----------------------------------------------------------------------------
 
@@ -87,6 +87,7 @@ pub struct Slider<'a> {
     custom_formatter: Option<NumFormatter<'a>>,
     custom_parser: Option<NumParser<'a>>,
     trailing_fill: Option<bool>,
+    handle_shape: Option<HandleShape>,
 }
 
 impl<'a> Slider<'a> {
@@ -133,6 +134,7 @@ impl<'a> Slider<'a> {
             custom_formatter: None,
             custom_parser: None,
             trailing_fill: None,
+            handle_shape: None,
         }
     }
 
@@ -302,6 +304,16 @@ impl<'a> Slider<'a> {
         self
     }
 
+    /// Change the shape of the slider handle
+    ///
+    /// This setting can be enabled globally for all sliders with [`Visuals::handle_shape`].
+    /// Changing it here will override the above setting ONLY for this individual slider.
+    #[inline]
+    pub fn handle_shape(mut self, handle_shape: HandleShape) -> Self {
+        self.handle_shape = Some(handle_shape);
+        self
+    }
+
     /// Set custom formatter defining how numbers are converted into text.
     ///
     /// A custom formatter takes a `f64` for the numeric value and a `RangeInclusive<usize>` representing
@@ -570,7 +582,10 @@ impl<'a> Slider<'a> {
     /// Just the slider, no text
     fn slider_ui(&mut self, ui: &Ui, response: &Response) {
         let rect = &response.rect;
-        let position_range = self.position_range(rect);
+        let handle_shape = self
+            .handle_shape
+            .unwrap_or_else(|| ui.style().visuals.handle_shape);
+        let position_range = self.position_range(rect, &handle_shape);
 
         if let Some(pointer_position_2d) = response.interact_pointer_pos() {
             let position = self.pointer_position(pointer_position_2d);
@@ -696,12 +711,37 @@ impl<'a> Slider<'a> {
                 );
             }
 
-            ui.painter().add(epaint::CircleShape {
+            let radius = self.handle_radius(rect);
-                center,
+
-                radius: self.handle_radius(rect) + visuals.expansion,
+            let handle_shape = self
-                fill: visuals.bg_fill,
+                .handle_shape
-                stroke: visuals.fg_stroke,
+                .unwrap_or_else(|| ui.style().visuals.handle_shape);
-            });
+            match handle_shape {
+                style::HandleShape::Circle => {
+                    ui.painter().add(epaint::CircleShape {
+                        center,
+                        radius: radius + visuals.expansion,
+                        fill: visuals.bg_fill,
+                        stroke: visuals.fg_stroke,
+                    });
+                }
+                style::HandleShape::Rect { aspect_ratio } => {
+                    let v = match self.orientation {
+                        SliderOrientation::Horizontal => Vec2::new(radius * aspect_ratio, radius),
+                        SliderOrientation::Vertical => Vec2::new(radius, radius * aspect_ratio),
+                    };
+                    let v = v + Vec2::splat(visuals.expansion);
+                    let rect = Rect::from_center_size(center, 2.0 * v);
+                    ui.painter().add(epaint::RectShape {
+                        fill: visuals.bg_fill,
+                        stroke: visuals.fg_stroke,
+                        rect,
+                        rounding: visuals.rounding,
+                        fill_texture_id: Default::default(),
+                        uv: Rect::ZERO,
+                    });
+                }
+            }
         }
     }
 
@@ -719,8 +759,12 @@ impl<'a> Slider<'a> {
         }
     }
 
-    fn position_range(&self, rect: &Rect) -> Rangef {
+    fn position_range(&self, rect: &Rect, handle_shape: &style::HandleShape) -> Rangef {
         let handle_radius = self.handle_radius(rect);
+        let handle_radius = match handle_shape {
+            style::HandleShape::Circle => handle_radius,
+            style::HandleShape::Rect { aspect_ratio } => handle_radius * aspect_ratio,
+        };
         match self.orientation {
             SliderOrientation::Horizontal => rect.x_range().shrink(handle_radius),
             // The vertical case has to be flipped because the largest slider value maps to the
@@ -842,7 +886,10 @@ impl<'a> Slider<'a> {
         let slider_response = response.clone();
 
         let value_response = if self.show_value {
-            let position_range = self.position_range(&response.rect);
+            let handle_shape = self
+                .handle_shape
+                .unwrap_or_else(|| ui.style().visuals.handle_shape);
+            let position_range = self.position_range(&response.rect, &handle_shape);
             let value_response = self.value_ui(ui, position_range);
             if value_response.gained_focus()
                 || value_response.has_focus()

crates/egui_demo_lib/src/demo/sliders.rs

@@ -1,4 +1,4 @@
-use egui::*;
+use egui::{style::HandleShape, *};
 use std::f64::INFINITY;
 
 /// Showcase sliders
@@ -17,6 +17,7 @@ pub struct Sliders {
     pub vertical: bool,
     pub value: f64,
     pub trailing_fill: bool,
+    pub handle_shape: HandleShape,
 }
 
 impl Default for Sliders {
@@ -33,6 +34,7 @@ impl Default for Sliders {
             vertical: false,
             value: 10.0,
             trailing_fill: false,
+            handle_shape: HandleShape::Circle,
         }
     }
 }
@@ -67,6 +69,7 @@ impl super::View for Sliders {
             vertical,
             value,
             trailing_fill,
+            handle_shape,
         } = self;
 
         ui.label("You can click a slider value to edit it with the keyboard.");
@@ -99,7 +102,8 @@ impl super::View for Sliders {
                     .orientation(orientation)
                     .text("i32 demo slider")
                     .step_by(istep)
-                    .trailing_fill(*trailing_fill),
+                    .trailing_fill(*trailing_fill)
+                    .handle_shape(*handle_shape),
             );
             *value = value_i32 as f64;
         } else {
@@ -111,7 +115,8 @@ impl super::View for Sliders {
                     .orientation(orientation)
                     .text("f64 demo slider")
                     .step_by(istep)
-                    .trailing_fill(*trailing_fill),
+                    .trailing_fill(*trailing_fill)
+                    .handle_shape(*handle_shape),
             );
 
             ui.label(
@@ -132,20 +137,26 @@ impl super::View for Sliders {
                 .logarithmic(true)
                 .smart_aim(*smart_aim)
                 .text("left")
-                .trailing_fill(*trailing_fill),
+                .trailing_fill(*trailing_fill)
+                .handle_shape(*handle_shape),
         );
         ui.add(
             Slider::new(max, type_min..=type_max)
                 .logarithmic(true)
                 .smart_aim(*smart_aim)
                 .text("right")
-                .trailing_fill(*trailing_fill),
+                .trailing_fill(*trailing_fill)
+                .handle_shape(*handle_shape),
         );
 
         ui.separator();
 
         ui.checkbox(trailing_fill, "Toggle trailing color");
-        ui.label("When enabled, trailing color will be painted up until the circle.");
+        ui.label("When enabled, trailing color will be painted up until the handle.");
+
+        ui.separator();
+
+        handle_shape.ui(ui);
 
         ui.separator();