A simple 2D plot library

egui/src/input_state.rs

@@ -31,7 +31,9 @@ pub struct InputState {
     pub time: f64,
 
     /// Time since last frame, in seconds.
-    /// This can be very unstable in reactive mode (when we don't paint each frame).
+    ///
+    /// This can be very unstable in reactive mode (when we don't paint each frame)
+    /// so it can be smart ot use e.g. `unstable_dt.min(1.0 / 30.0)`.
     pub unstable_dt: f32,
 
     /// Used for animations to get instant feedback (avoid frame delay).

egui/src/lib.rs

@@ -51,8 +51,32 @@
 //!         /* take some action here */
 //!     }
 //! });
+//! ```
 //!
 //!
+//! # Code snippets
+//!
+//! ```
+//! # let ui = &mut egui::Ui::__test();
+//! # let mut some_bool = true;
+//! // Some examples, tips and tricks, etc.
+//!
+//! ui.checkbox(&mut some_bool, "Click to toggle");
+//!
+//! ui.horizontal(|ui|{
+//!     // `radio_value` also works for enums, integers, and more.
+//!     ui.radio_value(&mut some_bool, false, "Off");
+//!     ui.radio_value(&mut some_bool, true, "On");
+//! });
+//!
+//! if ui.button("Click me!").clicked() { }
+//!
+//! // Change test color on subsequent widgets:
+//! ui.visuals_mut().override_text_color = Some(egui::Color32::RED);
+//!
+//! // Turn off text wrapping on subsequent widgets:
+//! ui.style_mut().wrap = Some(false);
+//! ```
 
 #![cfg_attr(not(debug_assertions), deny(warnings))] // Forbid warnings in release builds
 #![forbid(unsafe_code)]

egui/src/style.rs

@@ -16,6 +16,10 @@ pub struct Style {
     /// If set, labels buttons wtc will use this to determine whether or not
     /// to wrap the text at the right edge of the `Ui` they are in.
     /// By default this is `None`.
+    ///
+    /// * `None`: follow layout
+    /// * `Some(true)`: default on
+    /// * `Some(false)`: default off
     pub wrap: Option<bool>,
 
     pub spacing: Spacing,

egui/src/widgets/mod.rs

@@ -14,6 +14,7 @@ mod drag_value;
 mod hyperlink;
 mod image;
 mod label;
+pub mod plot;
 mod selected_label;
 mod separator;
 mod slider;

egui/src/widgets/plot.rs

@@ -0,0 +1,759 @@
+//! Simple plotting library.
+
+#![allow(clippy::comparison_chain)]
+
+use crate::*;
+
+// ----------------------------------------------------------------------------
+
+/// A value in the value-space of the plot.
+///
+/// Uses f64 for improved accuracy to enable plotting
+/// large values (e.g. unix time on x axis).
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct Value {
+    /// This is often something monotonically increasing, such as time, but doesn't have to be.
+    /// Goes from left to right.
+    pub x: f64,
+    /// Goes from bottom to top (inverse of everything else in egui!).
+    pub y: f64,
+}
+
+impl Value {
+    pub fn new(x: impl Into<f64>, y: impl Into<f64>) -> Self {
+        Self {
+            x: x.into(),
+            y: y.into(),
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// 2D bounding box of f64 precision.
+/// The range of data values we show.
+#[derive(Clone, Copy, PartialEq)]
+struct Bounds {
+    min: [f64; 2],
+    max: [f64; 2],
+}
+
+impl Bounds {
+    pub const NOTHING: Self = Self {
+        min: [f64::INFINITY; 2],
+        max: [-f64::INFINITY; 2],
+    };
+
+    pub fn width(&self) -> f64 {
+        self.max[0] - self.min[0]
+    }
+
+    pub fn height(&self) -> f64 {
+        self.max[1] - self.min[1]
+    }
+
+    pub fn is_finite(&self) -> bool {
+        self.min[0].is_finite()
+            && self.min[1].is_finite()
+            && self.max[0].is_finite()
+            && self.max[1].is_finite()
+    }
+
+    pub fn extend_with(&mut self, value: &Value) {
+        self.extend_with_x(value.x);
+        self.extend_with_y(value.y);
+    }
+
+    /// Expand to include the given x coordinate
+    pub fn extend_with_x(&mut self, x: f64) {
+        self.min[0] = self.min[0].min(x);
+        self.max[0] = self.max[0].max(x);
+    }
+
+    /// Expand to include the given y coordinate
+    pub fn extend_with_y(&mut self, y: f64) {
+        self.min[1] = self.min[1].min(y);
+        self.max[1] = self.max[1].max(y);
+    }
+
+    pub fn expand_x(&mut self, pad: f64) {
+        self.min[0] -= pad;
+        self.max[0] += pad;
+    }
+
+    pub fn expand_y(&mut self, pad: f64) {
+        self.min[1] -= pad;
+        self.max[1] += pad;
+    }
+
+    pub fn union_mut(&mut self, other: &Bounds) {
+        self.min[0] = self.min[0].min(other.min[0]);
+        self.min[1] = self.min[1].min(other.min[1]);
+        self.max[0] = self.max[0].max(other.max[0]);
+        self.max[1] = self.max[1].max(other.max[1]);
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// A horizontal line in a plot, filling the full width
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct HLine {
+    y: f64,
+    stroke: Stroke,
+}
+
+impl HLine {
+    pub fn new(y: impl Into<f64>, stroke: impl Into<Stroke>) -> Self {
+        Self {
+            y: y.into(),
+            stroke: stroke.into(),
+        }
+    }
+}
+
+/// A vertical line in a plot, filling the full width
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct VLine {
+    x: f64,
+    stroke: Stroke,
+}
+
+impl VLine {
+    pub fn new(x: impl Into<f64>, stroke: impl Into<Stroke>) -> Self {
+        Self {
+            x: x.into(),
+            stroke: stroke.into(),
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// A series of values forming a path.
+#[derive(Clone, PartialEq)]
+pub struct Curve {
+    values: Vec<Value>,
+    bounds: Bounds,
+    stroke: Stroke,
+    name: String,
+}
+
+impl Curve {
+    pub fn from_values(values: Vec<Value>) -> Self {
+        let mut bounds = Bounds::NOTHING;
+        for value in &values {
+            bounds.extend_with(value);
+        }
+        Self {
+            values,
+            bounds,
+            stroke: Stroke::new(2.0, Color32::from_gray(120)),
+            name: Default::default(),
+        }
+    }
+
+    pub fn from_values_iter(iter: impl Iterator<Item = Value>) -> Self {
+        Self::from_values(iter.collect())
+    }
+
+    /// From a series of y-values.
+    /// The x-values will be the indices of these values
+    pub fn from_ys_f32(ys: &[f32]) -> Self {
+        let values: Vec<Value> = ys
+            .iter()
+            .enumerate()
+            .map(|(i, &y)| Value {
+                x: i as f64,
+                y: y as f64,
+            })
+            .collect();
+        Self::from_values(values)
+    }
+
+    pub fn stroke(mut self, stroke: impl Into<Stroke>) -> Self {
+        self.stroke = stroke.into();
+        self
+    }
+
+    /// Stroke width (in points).
+    pub fn width(mut self, width: f32) -> Self {
+        self.stroke.width = width;
+        self
+    }
+
+    /// Stroke color.
+    pub fn color(mut self, color: impl Into<Color32>) -> Self {
+        self.stroke.color = color.into();
+        self
+    }
+
+    /// Name of this curve.
+    pub fn name(mut self, name: impl Into<String>) -> Self {
+        self.name = name.into();
+        self
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+/// A 2D plot, e.g. a graph of a function.
+///
+/// `Plot` supports multiple curves.
+///
+/// ```
+/// # let ui = &mut egui::Ui::__test();
+/// use egui::Color32;
+/// use egui::plot::{Curve, Plot, Value};
+/// let sin = (0..1000).map(|i| {
+///     let x = i as f64 * 0.01;
+///     Value::new(x, x.sin())
+/// });
+/// let curve = Curve::from_values_iter(sin).color(Color32::from_rgb(50, 200, 50));
+/// ui.add(
+///     Plot::default().curve(curve).view_aspect(2.0)
+/// );
+/// ```
+#[derive(Clone, PartialEq)]
+pub struct Plot {
+    curves: Vec<Curve>,
+    hlines: Vec<HLine>,
+    vlines: Vec<VLine>,
+
+    bounds: Bounds,
+    symmetrical_x_bounds: bool,
+    symmetrical_y_bounds: bool,
+    margin_fraction: Vec2,
+
+    min_size: Vec2,
+    width: Option<f32>,
+    height: Option<f32>,
+    data_aspect: Option<f32>,
+    view_aspect: Option<f32>,
+
+    show_x: bool,
+    show_y: bool,
+}
+
+impl Default for Plot {
+    fn default() -> Self {
+        Self {
+            curves: Default::default(),
+            hlines: Default::default(),
+            vlines: Default::default(),
+
+            bounds: Bounds::NOTHING,
+            symmetrical_x_bounds: false,
+            symmetrical_y_bounds: false,
+            margin_fraction: Vec2::splat(0.05),
+
+            min_size: Vec2::splat(64.0),
+            width: None,
+            height: None,
+            data_aspect: None,
+            view_aspect: None,
+
+            show_x: true,
+            show_y: true,
+        }
+    }
+}
+
+impl Plot {
+    /// Add a data curve.
+    /// You can add multiple curves.
+    pub fn curve(mut self, curve: Curve) -> Self {
+        self.bounds.union_mut(&curve.bounds);
+        self.curves.push(curve);
+        self
+    }
+
+    /// Add a horizontal line.
+    /// Can be useful e.g. to show min/max bounds or similar.
+    /// Always fills the full width of the plot.
+    pub fn hline(mut self, hline: HLine) -> Self {
+        self = self.include_y(hline.y);
+        self.hlines.push(hline);
+        self
+    }
+
+    /// Add a vertical line.
+    /// Can be useful e.g. to show min/max bounds or similar.
+    /// Always fills the full height of the plot.
+    pub fn vline(mut self, vline: VLine) -> Self {
+        self = self.include_x(vline.x);
+        self.vlines.push(vline);
+        self
+    }
+
+    /// Expand bounds to include the given x value.
+    pub fn include_x(mut self, x: impl Into<f64>) -> Self {
+        self.bounds.extend_with_x(x.into());
+        self
+    }
+
+    /// Expand bounds to include the given y value.
+    /// For instance, to always show the x axis, call `plot.include_y(0.0)`.
+    pub fn include_y(mut self, y: impl Into<f64>) -> Self {
+        self.bounds.extend_with_y(y.into());
+        self
+    }
+
+    /// If true, the x-bounds will be symmetrical, so that the x=0 zero line
+    /// is always in the center.
+    pub fn symmetrical_x_bounds(mut self, symmetrical_x_bounds: bool) -> Self {
+        self.symmetrical_x_bounds = symmetrical_x_bounds;
+        self
+    }
+
+    /// If true, the y-bounds will be symmetrical, so that the y=0 zero line
+    /// is always in the center.
+    pub fn symmetrical_y_bounds(mut self, symmetrical_y_bounds: bool) -> Self {
+        self.symmetrical_y_bounds = symmetrical_y_bounds;
+        self
+    }
+
+    /// width / height ratio of the data.
+    /// For instance, it can be useful to set this to `1.0` for when the two axes show the same unit.
+    pub fn data_aspect(mut self, data_aspect: f32) -> Self {
+        self.data_aspect = Some(data_aspect);
+        self
+    }
+
+    /// width / height ratio of the plot region.
+    /// By default no fixed aspect ratio is set (and width/height will fill the ui it is in).
+    pub fn view_aspect(mut self, view_aspect: f32) -> Self {
+        self.view_aspect = Some(view_aspect);
+        self
+    }
+
+    /// Width of plot. By default a plot will fill the ui it is in.
+    /// If you set [`Self::view_aspect`], the width can be calculated from the height.
+    pub fn width(mut self, width: f32) -> Self {
+        self.width = Some(width);
+        self
+    }
+
+    /// Height of plot. By default a plot will fill the ui it is in.
+    /// If you set [`Self::view_aspect`], the height can be calculated from the width.
+    pub fn height(mut self, height: f32) -> Self {
+        self.height = Some(height);
+        self
+    }
+
+    /// Minimum size of the plot view.
+    pub fn min_size(mut self, min_size: Vec2) -> Self {
+        self.min_size = min_size;
+        self
+    }
+
+    /// Show the x-value (e.g. when hovering). Default: `true`.
+    pub fn show_x(mut self, show_x: bool) -> Self {
+        self.show_x = show_x;
+        self
+    }
+
+    /// Show the y-value (e.g. when hovering). Default: `true`.
+    pub fn show_y(mut self, show_y: bool) -> Self {
+        self.show_y = show_y;
+        self
+    }
+}
+
+impl Widget for Plot {
+    fn ui(self, ui: &mut Ui) -> Response {
+        let Self {
+            curves,
+            hlines,
+            vlines,
+            bounds,
+            symmetrical_x_bounds,
+            symmetrical_y_bounds,
+            margin_fraction,
+            width,
+            height,
+            min_size,
+            data_aspect,
+            view_aspect,
+            show_x,
+            show_y,
+        } = self;
+
+        let size = {
+            let width = width.map(|w| w.at_least(min_size.x));
+            let height = height.map(|w| w.at_least(min_size.y));
+
+            let width = width.unwrap_or_else(|| {
+                if let (Some(height), Some(aspect)) = (height, view_aspect) {
+                    height * aspect
+                } else {
+                    ui.available_size_before_wrap_finite().x
+                }
+            });
+            let width = width.at_least(min_size.x);
+
+            let height = height.unwrap_or_else(|| {
+                if let Some(aspect) = view_aspect {
+                    width / aspect
+                } else {
+                    ui.available_size_before_wrap_finite().y
+                }
+            });
+            let height = height.at_least(min_size.y);
+            vec2(width, height)
+        };
+
+        let (rect, response) = ui.allocate_exact_size(size, Sense::hover());
+
+        let mut bounds = bounds;
+
+        if symmetrical_x_bounds {
+            let x_abs = bounds.min[0].abs().max(bounds.max[0].abs());
+            bounds.min[0] = -x_abs;
+            bounds.max[0] = x_abs;
+        };
+        if symmetrical_y_bounds {
+            let y_abs = bounds.min[1].abs().max(bounds.max[1].abs());
+            bounds.min[1] = -y_abs;
+            bounds.max[1] = y_abs;
+        };
+
+        bounds.expand_x(margin_fraction.x as f64 * bounds.width());
+        bounds.expand_y(margin_fraction.y as f64 * bounds.height());
+
+        if let Some(data_aspect) = data_aspect {
+            let data_aspect = data_aspect as f64;
+            let rw = rect.width() as f64;
+            let rh = rect.height() as f64;
+            let current_data_aspect = (bounds.width() / rw) / (bounds.height() / rh);
+            if current_data_aspect < data_aspect {
+                bounds.expand_x((data_aspect / current_data_aspect - 1.0) * bounds.width() * 0.5);
+            } else {
+                bounds.expand_y((current_data_aspect / data_aspect - 1.0) * bounds.height() * 0.5);
+            }
+        }
+
+        // Background:
+        ui.painter().add(Shape::Rect {
+            rect,
+            corner_radius: 2.0,
+            fill: ui.visuals().extreme_bg_color,
+            stroke: ui.visuals().window_stroke(),
+        });
+
+        if bounds.is_finite() && bounds.width() > 0.0 && bounds.height() > 0.0 {
+            let prepared = Prepared {
+                curves,
+                hlines,
+                vlines,
+                rect,
+                bounds,
+                show_x,
+                show_y,
+            };
+            prepared.ui(ui, &response);
+        }
+
+        response
+    }
+}
+
+struct Prepared {
+    curves: Vec<Curve>,
+    hlines: Vec<HLine>,
+    vlines: Vec<VLine>,
+    /// Screen space position of the plot
+    rect: Rect,
+    bounds: Bounds,
+    show_x: bool,
+    show_y: bool,
+}
+
+impl Prepared {
+    fn position_from_value(&self, value: &Value) -> Pos2 {
+        let x = remap(
+            value.x,
+            self.bounds.min[0]..=self.bounds.max[0],
+            (self.rect.left() as f64)..=(self.rect.right() as f64),
+        );
+        let y = remap(
+            value.y,
+            self.bounds.min[1]..=self.bounds.max[1],
+            (self.rect.bottom() as f64)..=(self.rect.top() as f64), // negated y axis!
+        );
+        pos2(x as f32, y as f32)
+    }
+
+    /// delta position / delta value
+    fn dpos_dvalue_x(&self) -> f64 {
+        self.rect.width() as f64 / self.bounds.width()
+    }
+
+    /// delta position / delta value
+    fn dpos_dvalue_y(&self) -> f64 {
+        -self.rect.height() as f64 / self.bounds.height() // negated y axis!
+    }
+
+    /// delta position / delta value
+    fn dpos_dvalue(&self) -> [f64; 2] {
+        [self.dpos_dvalue_x(), self.dpos_dvalue_y()]
+    }
+
+    /// delta value / delta position
+    fn dvalue_dpos(&self) -> [f64; 2] {
+        [1.0 / self.dpos_dvalue_x(), 1.0 / self.dpos_dvalue_y()]
+    }
+
+    fn value_from_position(&self, pos: Pos2) -> Value {
+        let x = remap(
+            pos.x as f64,
+            (self.rect.left() as f64)..=(self.rect.right() as f64),
+            self.bounds.min[0]..=self.bounds.max[0],
+        );
+        let y = remap(
+            pos.y as f64,
+            (self.rect.bottom() as f64)..=(self.rect.top() as f64), // negated y axis!
+            self.bounds.min[1]..=self.bounds.max[1],
+        );
+        Value::new(x, y)
+    }
+
+    fn ui(&self, ui: &mut Ui, response: &Response) {
+        let mut shapes = Vec::with_capacity(self.hlines.len() + self.curves.len() + 2);
+
+        for d in 0..2 {
+            self.paint_axis(ui, d, &mut shapes);
+        }
+
+        for &hline in &self.hlines {
+            let HLine { y, stroke } = hline;
+            let points = [
+                self.position_from_value(&Value::new(self.bounds.min[0], y)),
+                self.position_from_value(&Value::new(self.bounds.max[0], y)),
+            ];
+            shapes.push(Shape::line_segment(points, stroke));
+        }
+
+        for &vline in &self.vlines {
+            let VLine { x, stroke } = vline;
+            let points = [
+                self.position_from_value(&Value::new(x, self.bounds.min[1])),
+                self.position_from_value(&Value::new(x, self.bounds.max[1])),
+            ];
+            shapes.push(Shape::line_segment(points, stroke));
+        }
+
+        for curve in &self.curves {
+            let stroke = curve.stroke;
+            let values = &curve.values;
+            if values.len() == 1 {
+                let point = self.position_from_value(&values[0]);
+                shapes.push(Shape::circle_filled(
+                    point,
+                    stroke.width / 2.0,
+                    stroke.color,
+                ));
+            } else if values.len() > 1 {
+                shapes.push(Shape::line(
+                    values.iter().map(|v| self.position_from_value(v)).collect(),
+                    stroke,
+                ));
+            }
+        }
+
+        if response.hovered() {
+            if let Some(pointer) = ui.input().pointer.tooltip_pos() {
+                self.hover(ui, pointer, &mut shapes);
+            }
+        }
+
+        ui.painter().sub_region(self.rect).extend(shapes);
+    }
+
+    fn paint_axis(&self, ui: &Ui, axis: usize, shapes: &mut Vec<Shape>) {
+        let bounds = self.bounds;
+        let text_style = TextStyle::Body;
+
+        let base: f64 = 10.0;
+
+        let min_label_spacing_in_points = 60.0; // TODO: large enough for a wide label
+        let step_size = self.dvalue_dpos()[axis] * min_label_spacing_in_points;
+        let step_size = base.powi(step_size.abs().log(base).ceil() as i32);
+
+        let step_size_in_points = (self.dpos_dvalue()[axis] * step_size) as f32;
+
+        // Where on the cross-dimension to show the label values
+        let value_cross = clamp(0.0, bounds.min[1 - axis]..=bounds.max[1 - axis]);
+
+        for i in 0.. {
+            let value_main = step_size * (bounds.min[axis] / step_size + i as f64).floor();
+            if value_main > bounds.max[axis] {
+                break;
+            }
+
+            let value = if axis == 0 {
+                Value::new(value_main, value_cross)
+            } else {
+                Value::new(value_cross, value_main)
+            };
+            let pos_in_gui = self.position_from_value(&value);
+
+            {
+                // Grid: subdivide each label tick in `n` grid lines:
+                let n = if step_size_in_points.abs() < 40.0 {
+                    2
+                } else if step_size_in_points.abs() < 100.0 {
+                    5
+                } else {
+                    10
+                };
+
+                for i in 0..n {
+                    let strength = if i == 0 && value_main == 0.0 {
+                        Strength::Strong
+                    } else if i == 0 {
+                        Strength::Middle
+                    } else {
+                        Strength::Weak
+                    };
+                    let color = line_color(ui, strength);
+
+                    let mut pos_in_gui = pos_in_gui;
+                    pos_in_gui[axis] += step_size_in_points * (i as f32) / (n as f32);
+                    let mut p0 = pos_in_gui;
+                    let mut p1 = pos_in_gui;
+                    p0[1 - axis] = self.rect.min[1 - axis];
+                    p1[1 - axis] = self.rect.max[1 - axis];
+                    shapes.push(Shape::line_segment([p0, p1], Stroke::new(1.0, color)));
+                }
+            }
+
+            let text = emath::round_to_decimals(value_main, 5).to_string(); // hack
+
+            let font = &ui.fonts()[text_style];
+            let galley = font.layout_multiline(text, f32::INFINITY);
+
+            let mut text_pos = pos_in_gui + vec2(1.0, -galley.size.y);
+
+            // Make sure we see the labels, even if the axis is off-screen:
+            text_pos[1 - axis] = text_pos[1 - axis]
+                .at_most(self.rect.max[1 - axis] - galley.size[1 - axis] - 2.0)
+                .at_least(self.rect.min[1 - axis] + 1.0);
+
+            shapes.push(Shape::Text {
+                pos: text_pos,
+                galley,
+                text_style,
+                color: ui.visuals().text_color(),
+                fake_italics: false,
+            });
+        }
+    }
+
+    fn hover(&self, ui: &Ui, pointer: Pos2, shapes: &mut Vec<Shape>) {
+        if !self.show_x && !self.show_y {
+            return;
+        }
+
+        let interact_radius: f32 = 16.0;
+        let mut closest_value = None;
+        let mut closest_curve = None;
+        let mut closest_dist_sq = interact_radius.powi(2);
+        for curve in &self.curves {
+            for value in &curve.values {
+                let pos = self.position_from_value(value);
+                let dist_sq = pointer.distance_sq(pos);
+                if dist_sq < closest_dist_sq {
+                    closest_dist_sq = dist_sq;
+                    closest_value = Some(value);
+                    closest_curve = Some(curve);
+                }
+            }
+        }
+
+        let mut prefix = String::new();
+        if let Some(curve) = closest_curve {
+            if !curve.name.is_empty() {
+                prefix = format!("{}\n", curve.name);
+            }
+        }
+
+        let line_color = line_color(ui, Strength::Strong);
+
+        let value = if let Some(value) = closest_value {
+            let position = self.position_from_value(value);
+            shapes.push(Shape::circle_filled(position, 3.0, line_color));
+            *value
+        } else {
+            self.value_from_position(pointer)
+        };
+        let pointer = self.position_from_value(&value);
+
+        let rect = self.rect;
+
+        if self.show_x {
+            // vertical line
+            shapes.push(Shape::line_segment(
+                [pos2(pointer.x, rect.top()), pos2(pointer.x, rect.bottom())],
+                (1.0, line_color),
+            ));
+        }
+        if self.show_y {
+            // horizontal line
+            shapes.push(Shape::line_segment(
+                [pos2(rect.left(), pointer.y), pos2(rect.right(), pointer.y)],
+                (1.0, line_color),
+            ));
+        }
+
+        let text = {
+            let scale = self.dvalue_dpos();
+            let x_decimals = ((-scale[0].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+            let y_decimals = ((-scale[1].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+            if self.show_x && self.show_y {
+                format!(
+                    "{}x = {:.*}\ny = {:.*}",
+                    prefix, x_decimals, value.x, y_decimals, value.y
+                )
+            } else if self.show_x {
+                format!("{}x = {:.*}", prefix, x_decimals, value.x)
+            } else if self.show_y {
+                format!("{}y = {:.*}", prefix, y_decimals, value.y)
+            } else {
+                unreachable!()
+            }
+        };
+
+        shapes.push(Shape::text(
+            ui.fonts(),
+            pointer + vec2(3.0, -2.0),
+            Align2::LEFT_BOTTOM,
+            text,
+            TextStyle::Body,
+            ui.visuals().text_color(),
+        ));
+    }
+}
+
+#[derive(Clone, Copy)]
+enum Strength {
+    Strong,
+    Middle,
+    Weak,
+}
+
+fn line_color(ui: &Ui, strength: Strength) -> Color32 {
+    if ui.visuals().dark_mode {
+        match strength {
+            Strength::Strong => Color32::from_gray(130).additive(),
+            Strength::Middle => Color32::from_gray(55).additive(),
+            Strength::Weak => Color32::from_gray(25).additive(),
+        }
+    } else {
+        match strength {
+            Strength::Strong => Color32::from_black_alpha(220),
+            Strength::Middle => Color32::from_black_alpha(120),
+            Strength::Weak => Color32::from_black_alpha(35),
+        }
+    }
+}

egui_demo_lib/src/apps/demo/demo_windows.rs

@@ -18,6 +18,7 @@ impl Default for Demos {
             Box::new(super::font_book::FontBook::default()),
             Box::new(super::DemoWindow::default()),
             Box::new(super::painting::Painting::default()),
+            Box::new(super::plot_demo::PlotDemo::default()),
             Box::new(super::scrolling::Scrolling::default()),
             Box::new(super::sliders::Sliders::default()),
             Box::new(super::widget_gallery::WidgetGallery::default()),

egui_demo_lib/src/apps/demo/mod.rs

@@ -14,6 +14,7 @@ pub mod font_contents_emoji;
 pub mod font_contents_ubuntu;
 pub mod layout_test;
 pub mod painting;
+pub mod plot_demo;
 pub mod scrolling;
 pub mod sliders;
 pub mod tests;

egui_demo_lib/src/apps/demo/plot_demo.rs

@@ -0,0 +1,155 @@
+use egui::plot::{Curve, Plot, Value};
+use egui::*;
+use std::f64::consts::TAU;
+
+#[derive(PartialEq)]
+pub struct PlotDemo {
+    animate: bool,
+    time: f64,
+    circle_radius: f32,
+    circle_center: Pos2,
+    square: bool,
+    proportional: bool,
+}
+
+impl Default for PlotDemo {
+    fn default() -> Self {
+        Self {
+            animate: true,
+            time: 0.0,
+            circle_radius: 0.5,
+            circle_center: Pos2::new(0.0, 0.0),
+            square: false,
+            proportional: true,
+        }
+    }
+}
+
+impl super::Demo for PlotDemo {
+    fn name(&self) -> &str {
+        "🗠 Plot"
+    }
+
+    fn show(&mut self, ctx: &CtxRef, open: &mut bool) {
+        use super::View;
+        Window::new(self.name())
+            .open(open)
+            .default_size(vec2(512.0, 512.0))
+            .scroll(false)
+            .show(ctx, |ui| self.ui(ui));
+    }
+}
+
+impl PlotDemo {
+    fn options_ui(&mut self, ui: &mut Ui) {
+        ui.vertical_centered(|ui| {
+            egui::reset_button(ui, self);
+            ui.add(crate::__egui_github_link_file!());
+        });
+        ui.separator();
+
+        let Self {
+            animate,
+            time: _,
+            circle_radius,
+            circle_center,
+            square,
+            proportional,
+        } = self;
+
+        ui.horizontal(|ui| {
+            ui.group(|ui| {
+                ui.vertical(|ui| {
+                    ui.label("Circle:");
+                    ui.add(
+                        egui::Slider::f32(circle_radius, 1e-4..=1e4)
+                            .logarithmic(true)
+                            .smallest_positive(1e-2)
+                            .text("radius"),
+                    );
+                    ui.add(
+                        egui::Slider::f32(&mut circle_center.x, -1e4..=1e4)
+                            .logarithmic(true)
+                            .smallest_positive(1e-2)
+                            .text("center x"),
+                    );
+                    ui.add(
+                        egui::Slider::f32(&mut circle_center.y, -1e4..=1e4)
+                            .logarithmic(true)
+                            .smallest_positive(1e-2)
+                            .text("center y"),
+                    );
+                });
+            });
+
+            ui.vertical(|ui| {
+                ui.style_mut().wrap = Some(false);
+                ui.checkbox(animate, "animate");
+                ui.advance_cursor(8.0);
+                ui.checkbox(square, "square view");
+                ui.checkbox(proportional, "proportional data axes");
+            });
+        });
+    }
+
+    fn circle(&self) -> Curve {
+        let n = 512;
+        let circle = (0..=n).map(|i| {
+            let t = remap(i as f64, 0.0..=(n as f64), 0.0..=TAU);
+            let r = self.circle_radius as f64;
+            Value::new(
+                r * t.cos() + self.circle_center.x as f64,
+                r * t.sin() + self.circle_center.y as f64,
+            )
+        });
+        Curve::from_values_iter(circle)
+            .color(Color32::from_rgb(100, 200, 100))
+            .name("circle")
+    }
+
+    fn sin(&self) -> Curve {
+        let n = 512;
+        let circle = (0..=n).map(|i| {
+            let t = remap(i as f64, 0.0..=(n as f64), -TAU..=TAU);
+            Value::new(t / 5.0, 0.5 * (self.time + t).sin())
+        });
+        Curve::from_values_iter(circle)
+            .color(Color32::from_rgb(200, 100, 100))
+            .name("0.5 * sin(x / 5)")
+    }
+
+    fn thingy(&self) -> Curve {
+        let n = 512;
+        let complex_curve = (0..=n).map(|i| {
+            let t = remap(i as f64, 0.0..=(n as f64), 0.0..=TAU);
+            Value::new((2.0 * t + self.time).sin(), (3.0 * t).sin())
+        });
+        Curve::from_values_iter(complex_curve)
+            .color(Color32::from_rgb(100, 150, 250))
+            .name("x = sin(2t), y = sin(3t)")
+    }
+}
+
+impl super::View for PlotDemo {
+    fn ui(&mut self, ui: &mut Ui) {
+        self.options_ui(ui);
+
+        if self.animate {
+            ui.ctx().request_repaint();
+            self.time += ui.input().unstable_dt.at_most(1.0 / 30.0) as f64;
+        };
+
+        let mut plot = Plot::default()
+            .curve(self.circle())
+            .curve(self.sin())
+            .curve(self.thingy())
+            .min_size(Vec2::new(400.0, 300.0));
+        if self.square {
+            plot = plot.view_aspect(1.0);
+        }
+        if self.proportional {
+            plot = plot.data_aspect(1.0);
+        }
+        ui.add(plot);
+    }
+}

emath/src/pos2.rs

@@ -8,7 +8,7 @@ use crate::*;
 ///
 /// Mathematically this is known as a "point", but the term position was chosen so not to
 /// conflict with the unit (one point = X physical pixels).
-#[derive(Clone, Copy, Default)]
+#[derive(Clone, Copy, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct Pos2 {
     pub x: f32,
@@ -145,11 +145,27 @@ impl Pos2 {
     }
 }
 
-impl PartialEq for Pos2 {
+impl std::ops::Index<usize> for Pos2 {
-    fn eq(&self, other: &Self) -> bool {
+    type Output = f32;
-        self.x == other.x && self.y == other.y
+    fn index(&self, index: usize) -> &f32 {
+        match index {
+            0 => &self.x,
+            1 => &self.y,
+            _ => panic!("Pos2 index out of bounds: {}", index),
+        }
     }
 }
+
+impl std::ops::IndexMut<usize> for Pos2 {
+    fn index_mut(&mut self, index: usize) -> &mut f32 {
+        match index {
+            0 => &mut self.x,
+            1 => &mut self.y,
+            _ => panic!("Pos2 index out of bounds: {}", index),
+        }
+    }
+}
+
 impl Eq for Pos2 {}
 
 impl AddAssign<Vec2> for Pos2 {

emath/src/rect.rs

@@ -180,6 +180,18 @@ impl Rect {
         self.max = self.max.max(p);
     }
 
+    /// Expand to include the given x coordinate
+    pub fn extend_with_x(&mut self, x: f32) {
+        self.min.x = self.min.x.min(x);
+        self.max.x = self.max.x.max(x);
+    }
+
+    /// Expand to include the given y coordinate
+    pub fn extend_with_y(&mut self, y: f32) {
+        self.min.y = self.min.y.min(y);
+        self.max.y = self.max.y.max(y);
+    }
+
     pub fn union(self, other: Rect) -> Rect {
         Rect {
             min: self.min.min(other.min),

emath/src/rect_transform.rs

@@ -26,6 +26,11 @@ impl RectTransform {
         &self.to
     }
 
+    /// The scale factors.
+    pub fn scale(&self) -> Vec2 {
+        self.to.size() / self.from.size()
+    }
+
     pub fn inverse(&self) -> RectTransform {
         Self::from_to(self.to, self.from)
     }

emath/src/vec2.rs

@@ -8,7 +8,7 @@ use crate::*;
 /// emath represents positions using [`Pos2`].
 ///
 /// Normally the units are points (logical pixels).
-#[derive(Clone, Copy, Default)]
+#[derive(Clone, Copy, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct Vec2 {
     pub x: f32,
@@ -186,11 +186,27 @@ impl Vec2 {
     }
 }
 
-impl PartialEq for Vec2 {
+impl std::ops::Index<usize> for Vec2 {
-    fn eq(&self, other: &Self) -> bool {
+    type Output = f32;
-        self.x == other.x && self.y == other.y
+    fn index(&self, index: usize) -> &f32 {
+        match index {
+            0 => &self.x,
+            1 => &self.y,
+            _ => panic!("Vec2 index out of bounds: {}", index),
+        }
     }
 }
+
+impl std::ops::IndexMut<usize> for Vec2 {
+    fn index_mut(&mut self, index: usize) -> &mut f32 {
+        match index {
+            0 => &mut self.x,
+            1 => &mut self.y,
+            _ => panic!("Vec2 index out of bounds: {}", index),
+        }
+    }
+}
+
 impl Eq for Vec2 {}
 
 impl Neg for Vec2 {
@@ -239,6 +255,28 @@ impl Sub for Vec2 {
     }
 }
 
+/// Element-wise multiplication
+impl Mul<Vec2> for Vec2 {
+    type Output = Vec2;
+    fn mul(self, vec: Vec2) -> Vec2 {
+        Vec2 {
+            x: self.x * vec.x,
+            y: self.y * vec.y,
+        }
+    }
+}
+
+/// Element-wise division
+impl Div<Vec2> for Vec2 {
+    type Output = Vec2;
+    fn div(self, rhs: Vec2) -> Vec2 {
+        Vec2 {
+            x: self.x / rhs.x,
+            y: self.y / rhs.y,
+        }
+    }
+}
+
 impl MulAssign<f32> for Vec2 {
     fn mul_assign(&mut self, rhs: f32) {
         self.x *= rhs;

epaint/src/color.rs

@@ -124,6 +124,12 @@ impl Color32 {
         Rgba::from(self).to_opaque().into()
     }
 
+    /// Returns an additive version of self
+    pub fn additive(self) -> Self {
+        let [r, g, b, _] = self.to_array();
+        Self([r, g, b, 0])
+    }
+
     /// Premultiplied RGBA
     pub fn to_array(&self) -> [u8; 4] {
         [self.r(), self.g(), self.b(), self.a()]