Progress bar (#519)

* add progress bar

* update changelog

* apply suggestions

* disable animation by default and tweak colors

* allow toggling the animation by clicking

* Update egui/src/widgets/progress_bar.rs

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

* Update egui/src/widgets/progress_bar.rs

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

* Update egui/src/widgets/progress_bar.rs

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

* address review comments

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

CHANGELOG.md

@@ -6,6 +6,7 @@ NOTE: [`eframe`](eframe/CHANGELOG.md), [`egui_web`](egui_web/CHANGELOG.md) and [
 
 
 ## Unreleased
+* [Progress bar](https://github.com/emilk/egui/pull/519)
 
 
 ## 0.13.1 - 2021-06-28 - Plot fixes

egui/src/widgets/mod.rs

@@ -13,6 +13,7 @@ mod hyperlink;
 mod image;
 mod label;
 pub mod plot;
+mod progress_bar;
 mod selected_label;
 mod separator;
 mod slider;
@@ -20,6 +21,7 @@ pub(crate) mod text_edit;
 
 pub use hyperlink::*;
 pub use label::*;
+pub use progress_bar::ProgressBar;
 pub use selected_label::*;
 pub use separator::*;
 pub use {button::*, drag_value::DragValue, image::Image, slider::*, text_edit::*};

egui/src/widgets/progress_bar.rs

@@ -0,0 +1,141 @@
+use crate::*;
+
+enum ProgressBarText {
+    Custom(String),
+    Percentage,
+}
+
+/// A simple progress bar.
+pub struct ProgressBar {
+    progress: f32,
+    desired_width: Option<f32>,
+    text: Option<ProgressBarText>,
+    animate: bool,
+}
+
+impl ProgressBar {
+    /// Progress in the `[0, 1]` range, where `1` means "completed".
+    pub fn new(progress: f32) -> Self {
+        Self {
+            progress: progress.clamp(0.0, 1.0),
+            desired_width: None,
+            text: None,
+            animate: false,
+        }
+    }
+
+    /// The desired width of the bar. Will use all horizonal space if not set.
+    pub fn desired_width(mut self, desired_width: f32) -> Self {
+        self.desired_width = Some(desired_width);
+        self
+    }
+
+    /// A custom text to display on the progress bar.
+    #[allow(clippy::needless_pass_by_value)]
+    pub fn text(mut self, text: impl ToString) -> Self {
+        self.text = Some(ProgressBarText::Custom(text.to_string()));
+        self
+    }
+
+    /// Show the progress in percent on the progress bar.
+    pub fn show_percentage(mut self) -> Self {
+        self.text = Some(ProgressBarText::Percentage);
+        self
+    }
+
+    /// Whether to display a loading animation when progress `< 1`.
+    /// Note that this require the UI to be redrawn.
+    /// Defaults to `false`.
+    pub fn animate(mut self, animate: bool) -> Self {
+        self.animate = animate;
+        self
+    }
+}
+
+impl Widget for ProgressBar {
+    fn ui(self, ui: &mut Ui) -> Response {
+        let ProgressBar {
+            progress,
+            desired_width,
+            text,
+            mut animate,
+        } = self;
+
+        animate &= progress < 1.0;
+
+        let desired_width = desired_width.unwrap_or(ui.available_size_before_wrap().x);
+        let height = ui.spacing().interact_size.y;
+        let (outer_rect, response) =
+            ui.allocate_exact_size(vec2(desired_width, height), Sense::hover());
+        let visuals = ui.style().visuals.clone();
+        let corner_radius = outer_rect.height() / 2.0;
+        ui.painter().rect(
+            outer_rect,
+            corner_radius,
+            visuals.extreme_bg_color,
+            Stroke::none(),
+        );
+        let inner_rect = Rect::from_min_size(
+            outer_rect.min,
+            vec2(
+                (outer_rect.width() * progress).at_least(outer_rect.height()),
+                outer_rect.height(),
+            ),
+        );
+
+        let (dark, bright) = (0.7, 1.0);
+        let color_factor = if animate {
+            ui.ctx().request_repaint();
+            lerp(dark..=bright, ui.input().time.cos().abs())
+        } else {
+            bright
+        };
+
+        ui.painter().rect(
+            inner_rect,
+            corner_radius,
+            Color32::from(Rgba::from(visuals.selection.bg_fill) * color_factor as f32),
+            Stroke::none(),
+        );
+
+        if animate {
+            let n_points = 20;
+            let start_angle = ui.input().time as f64 * 360f64.to_radians();
+            let end_angle = start_angle + 240f64.to_radians() * ui.input().time.sin();
+            let circle_radius = corner_radius - 2.0;
+            let points: Vec<Pos2> = (0..n_points)
+                .map(|i| {
+                    let angle = lerp(start_angle..=end_angle, i as f64 / n_points as f64);
+                    let (sin, cos) = angle.sin_cos();
+                    inner_rect.right_center()
+                        + circle_radius * vec2(cos as f32, sin as f32)
+                        + vec2(-corner_radius, 0.0)
+                })
+                .collect();
+            ui.painter().add(Shape::Path {
+                points,
+                closed: false,
+                fill: Color32::TRANSPARENT,
+                stroke: Stroke::new(2.0, visuals.faint_bg_color),
+            });
+        }
+
+        if let Some(text_kind) = text {
+            let text = match text_kind {
+                ProgressBarText::Custom(string) => string,
+                ProgressBarText::Percentage => format!("{}%", (progress * 100.0) as usize),
+            };
+            ui.painter().sub_region(outer_rect).text(
+                outer_rect.left_center() + vec2(ui.spacing().item_spacing.x, 0.0),
+                Align2::LEFT_CENTER,
+                text,
+                TextStyle::Button,
+                visuals
+                    .override_text_color
+                    .unwrap_or(visuals.selection.stroke.color),
+            );
+        }
+
+        response
+    }
+}

egui_demo_lib/src/apps/demo/widget_gallery.rs

@@ -16,6 +16,7 @@ pub struct WidgetGallery {
     scalar: f32,
     string: String,
     color: egui::Color32,
+    animate_progress_bar: bool,
 }
 
 impl Default for WidgetGallery {
@@ -28,6 +29,7 @@ impl Default for WidgetGallery {
             scalar: 42.0,
             string: Default::default(),
             color: egui::Color32::LIGHT_BLUE.linear_multiply(0.5),
+            animate_progress_bar: false,
         }
     }
 }
@@ -95,6 +97,7 @@ impl WidgetGallery {
             scalar,
             string,
             color,
+            animate_progress_bar,
         } = self;
 
         ui.add(doc_link_label("Label", "label,heading"));
@@ -157,6 +160,17 @@ impl WidgetGallery {
         ui.add(egui::Slider::new(scalar, 0.0..=360.0).suffix("°"));
         ui.end_row();
 
+        ui.add(doc_link_label("ProgressBar", "ProgressBar"));
+        let progress = *scalar / 360.0;
+        let progress_bar = egui::ProgressBar::new(progress)
+            .show_percentage()
+            .animate(*animate_progress_bar);
+        *animate_progress_bar = ui
+            .add(progress_bar)
+            .on_hover_text("The progress bar can be animated!")
+            .hovered();
+        ui.end_row();
+
         ui.add(doc_link_label("DragValue", "DragValue"));
         ui.add(egui::DragValue::new(scalar).speed(1.0));
         ui.end_row();