egui/crates/egui_plot/src/axis.rs

use std::{fmt::Debug, ops::RangeInclusive, sync::Arc};

use egui::emath::{remap_clamp, round_to_decimals, Pos2, Rect};
use egui::epaint::{Shape, TextShape};

use crate::{Response, Sense, TextStyle, Ui, WidgetText};

use super::{transform::PlotTransform, GridMark};

pub(super) type AxisFormatterFn = dyn Fn(f64, usize, &RangeInclusive<f64>) -> String;

/// X or Y axis.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Axis {
    /// Horizontal X-Axis
    X,

    /// Vertical Y-axis
    Y,
}

impl From<Axis> for usize {
    #[inline]
    fn from(value: Axis) -> Self {
        match value {
            Axis::X => 0,
            Axis::Y => 1,
        }
    }
}

/// Placement of the horizontal X-Axis.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum VPlacement {
    Top,
    Bottom,
}

/// Placement of the vertical Y-Axis.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum HPlacement {
    Left,
    Right,
}

/// Placement of an axis.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Placement {
    /// Bottom for X-axis, or left for Y-axis.
    LeftBottom,

    /// Top for x-axis and right for y-axis.
    RightTop,
}

impl From<HPlacement> for Placement {
    #[inline]
    fn from(placement: HPlacement) -> Self {
        match placement {
            HPlacement::Left => Placement::LeftBottom,
            HPlacement::Right => Placement::RightTop,
        }
    }
}

impl From<VPlacement> for Placement {
    #[inline]
    fn from(placement: VPlacement) -> Self {
        match placement {
            VPlacement::Top => Placement::RightTop,
            VPlacement::Bottom => Placement::LeftBottom,
        }
    }
}

/// Axis configuration.
///
/// Used to configure axis label and ticks.
#[derive(Clone)]
pub struct AxisHints {
    pub(super) label: WidgetText,
    pub(super) formatter: Arc<AxisFormatterFn>,
    pub(super) digits: usize,
    pub(super) placement: Placement,
}

// TODO: this just a guess. It might cease to work if a user changes font size.
const LINE_HEIGHT: f32 = 12.0;

impl Default for AxisHints {
    /// Initializes a default axis configuration for the specified axis.
    ///
    /// `label` is empty.
    /// `formatter` is default float to string formatter.
    /// maximum `digits` on tick label is 5.
    fn default() -> Self {
        Self {
            label: Default::default(),
            formatter: Arc::new(Self::default_formatter),
            digits: 5,
            placement: Placement::LeftBottom,
        }
    }
}

impl AxisHints {
    /// Specify custom formatter for ticks.
    ///
    /// The first parameter of `formatter` is the raw tick value as `f64`.
    /// The second parameter is the maximum number of characters that fit into y-labels.
    /// The second parameter of `formatter` is the currently shown range on this axis.
    pub fn formatter(
        mut self,
        fmt: impl Fn(f64, usize, &RangeInclusive<f64>) -> String + 'static,
    ) -> Self {
        self.formatter = Arc::new(fmt);
        self
    }

    fn default_formatter(tick: f64, max_digits: usize, _range: &RangeInclusive<f64>) -> String {
        if tick.abs() > 10.0_f64.powf(max_digits as f64) {
            let tick_rounded = tick as isize;
            return format!("{tick_rounded:+e}");
        }
        let tick_rounded = round_to_decimals(tick, max_digits);
        if tick.abs() < 10.0_f64.powf(-(max_digits as f64)) && tick != 0.0 {
            return format!("{tick_rounded:+e}");
        }
        tick_rounded.to_string()
    }

    /// Specify axis label.
    ///
    /// The default is 'x' for x-axes and 'y' for y-axes.
    #[inline]
    pub fn label(mut self, label: impl Into<WidgetText>) -> Self {
        self.label = label.into();
        self
    }

    /// Specify maximum number of digits for ticks.
    ///
    /// This is considered by the default tick formatter and affects the width of the y-axis
    #[inline]
    pub fn max_digits(mut self, digits: usize) -> Self {
        self.digits = digits;
        self
    }

    /// Specify the placement of the axis.
    ///
    /// For X-axis, use [`VPlacement`].
    /// For Y-axis, use [`HPlacement`].
    #[inline]
    pub fn placement(mut self, placement: impl Into<Placement>) -> Self {
        self.placement = placement.into();
        self
    }

    pub(super) fn thickness(&self, axis: Axis) -> f32 {
        match axis {
            Axis::X => {
                if self.label.is_empty() {
                    1.0 * LINE_HEIGHT
                } else {
                    3.0 * LINE_HEIGHT
                }
            }
            Axis::Y => {
                if self.label.is_empty() {
                    (self.digits as f32) * LINE_HEIGHT
                } else {
                    (self.digits as f32 + 1.0) * LINE_HEIGHT
                }
            }
        }
    }
}

#[derive(Clone)]
pub(super) struct AxisWidget {
    pub(super) range: RangeInclusive<f64>,
    pub(super) hints: AxisHints,
    pub(super) rect: Rect,
    pub(super) transform: Option<PlotTransform>,
    pub(super) steps: Arc<Vec<GridMark>>,
}

impl AxisWidget {
    /// if `rect` as width or height == 0, is will be automatically calculated from ticks and text.
    pub(super) fn new(hints: AxisHints, rect: Rect) -> Self {
        Self {
            range: (0.0..=0.0),
            hints,
            rect,
            transform: None,
            steps: Default::default(),
        }
    }

    pub fn ui(self, ui: &mut Ui, axis: Axis) -> Response {
        let response = ui.allocate_rect(self.rect, Sense::hover());

        if ui.is_rect_visible(response.rect) {
            let visuals = ui.style().visuals.clone();
            let text = self.hints.label;
            let galley = text.into_galley(ui, Some(false), f32::INFINITY, TextStyle::Body);
            let text_color = visuals
                .override_text_color
                .unwrap_or_else(|| ui.visuals().text_color());
            let angle: f32 = match axis {
                Axis::X => 0.0,
                Axis::Y => -std::f32::consts::TAU * 0.25,
            };
            // select text_pos and angle depending on placement and orientation of widget
            let text_pos = match self.hints.placement {
                Placement::LeftBottom => match axis {
                    Axis::X => {
                        let pos = response.rect.center_bottom();
                        Pos2 {
                            x: pos.x - galley.size().x / 2.0,
                            y: pos.y - galley.size().y * 1.25,
                        }
                    }
                    Axis::Y => {
                        let pos = response.rect.left_center();
                        Pos2 {
                            x: pos.x,
                            y: pos.y + galley.size().x / 2.0,
                        }
                    }
                },
                Placement::RightTop => match axis {
                    Axis::X => {
                        let pos = response.rect.center_top();
                        Pos2 {
                            x: pos.x - galley.size().x / 2.0,
                            y: pos.y + galley.size().y * 0.25,
                        }
                    }
                    Axis::Y => {
                        let pos = response.rect.right_center();
                        Pos2 {
                            x: pos.x - galley.size().y * 1.5,
                            y: pos.y + galley.size().x / 2.0,
                        }
                    }
                },
            };

            ui.painter()
                .add(TextShape::new(text_pos, galley, text_color).with_angle(angle));

            // --- add ticks ---
            let font_id = TextStyle::Body.resolve(ui.style());
            let Some(transform) = self.transform else {
                return response;
            };

            for step in self.steps.iter() {
                let text = (self.hints.formatter)(step.value, self.hints.digits, &self.range);
                if !text.is_empty() {
                    const MIN_TEXT_SPACING: f32 = 20.0;
                    const FULL_CONTRAST_SPACING: f32 = 40.0;
                    let spacing_in_points =
                        (transform.dpos_dvalue()[usize::from(axis)] * step.step_size).abs() as f32;

                    if spacing_in_points <= MIN_TEXT_SPACING {
                        continue;
                    }
                    let line_strength = remap_clamp(
                        spacing_in_points,
                        MIN_TEXT_SPACING..=FULL_CONTRAST_SPACING,
                        0.0..=1.0,
                    );

                    let line_color = super::color_from_strength(ui, line_strength);
                    let galley = ui
                        .painter()
                        .layout_no_wrap(text, font_id.clone(), line_color);

                    let text_pos = match axis {
                        Axis::X => {
                            let y = match self.hints.placement {
                                Placement::LeftBottom => self.rect.min.y,
                                Placement::RightTop => self.rect.max.y - galley.size().y,
                            };
                            let projected_point = super::PlotPoint::new(step.value, 0.0);
                            Pos2 {
                                x: transform.position_from_point(&projected_point).x
                                    - galley.size().x / 2.0,
                                y,
                            }
                        }
                        Axis::Y => {
                            let x = match self.hints.placement {
                                Placement::LeftBottom => self.rect.max.x - galley.size().x,
                                Placement::RightTop => self.rect.min.x,
                            };
                            let projected_point = super::PlotPoint::new(0.0, step.value);
                            Pos2 {
                                x,
                                y: transform.position_from_point(&projected_point).y
                                    - galley.size().y / 2.0,
                            }
                        }
                    };

                    ui.painter()
                        .add(Shape::galley(text_pos, galley, text_color));
                }
            }
        }

        response
    }
}