ggplot_rs/render/

plotters_backend.rs

use std::collections::HashSet;
use std::sync::{Mutex, OnceLock};

use plotters::prelude::*;
use plotters::style::FontStyle;

use super::backend::{
    DrawBackend, LineStyle, PointShape, PointStyle, RectStyle, TextAnchor, TextStyle,
};
use super::{Rect, RenderError};

/// A font bundled into the binary so text renders in a headless container with
/// no system fonts / fontconfig. DejaVu Sans (Bitstream Vera–derived license,
/// freely redistributable) — broad glyph coverage keeps labels tofu-free.
const BUNDLED_FONT: &[u8] = include_bytes!("../../assets/fonts/DejaVuSans.ttf");

fn registered_families() -> &'static Mutex<HashSet<String>> {
    static REGISTERED: OnceLock<Mutex<HashSet<String>>> = OnceLock::new();
    REGISTERED.get_or_init(|| Mutex::new(HashSet::new()))
}

/// Ensure the bundled font is registered under `family` (idempotent).
///
/// With plotters' `ab_glyph` backend there is no system-font lookup: every
/// family used for layout must be registered first. We map *all* requested
/// families to the one bundled font, so any family name lays out correctly
/// headlessly; SVG output still carries the requested family name for browsers.
fn ensure_font(family: &str) {
    let mut set = registered_families().lock().unwrap();
    if set.insert(family.to_string()) {
        for style in [
            FontStyle::Normal,
            FontStyle::Bold,
            FontStyle::Italic,
            FontStyle::Oblique,
        ] {
            // Ignore the result: a malformed font would surface as a draw error.
            let _ = plotters::style::register_font(family, style, BUNDLED_FONT);
        }
    }
}

/// Adapter from plotters' DrawingArea to our DrawBackend trait.
pub struct PlottersAdapter<'a, DB: DrawingBackend> {
    area: &'a DrawingArea<DB, plotters::coord::Shift>,
    plot_area: Rect,
    total_area: Rect,
}

impl<'a, DB: DrawingBackend> PlottersAdapter<'a, DB> {
    pub fn new(area: &'a DrawingArea<DB, plotters::coord::Shift>, plot_area: Rect) -> Self {
        let (w, h) = area.dim_in_pixel();
        PlottersAdapter {
            area,
            plot_area,
            total_area: Rect {
                x: 0.0,
                y: 0.0,
                width: w as f64,
                height: h as f64,
            },
        }
    }
}

fn to_rgba(color: (u8, u8, u8), alpha: f64) -> RGBAColor {
    RGBAColor(color.0, color.1, color.2, alpha)
}

/// Clip a point to the given rectangle bounds. Returns None if fully outside.
fn clip_point(x: f64, y: f64, rect: &Rect) -> (f64, f64) {
    (
        x.clamp(rect.x, rect.x + rect.width),
        y.clamp(rect.y, rect.y + rect.height),
    )
}

/// Check if a point is inside the rectangle (with small margin).
fn point_in_rect(x: f64, y: f64, rect: &Rect) -> bool {
    let margin = 2.0;
    x >= rect.x - margin
        && x <= rect.x + rect.width + margin
        && y >= rect.y - margin
        && y <= rect.y + rect.height + margin
}

/// Cohen-Sutherland line clipping. Returns clipped line segment or None if fully outside.
fn clip_line_segment(
    mut x0: f64,
    mut y0: f64,
    mut x1: f64,
    mut y1: f64,
    rect: &Rect,
) -> Option<((f64, f64), (f64, f64))> {
    let xmin = rect.x;
    let xmax = rect.x + rect.width;
    let ymin = rect.y;
    let ymax = rect.y + rect.height;

    const INSIDE: u8 = 0;
    const LEFT: u8 = 1;
    const RIGHT: u8 = 2;
    const BOTTOM: u8 = 4;
    const TOP: u8 = 8;

    let outcode = |x: f64, y: f64| -> u8 {
        let mut code = INSIDE;
        if x < xmin {
            code |= LEFT;
        } else if x > xmax {
            code |= RIGHT;
        }
        if y < ymin {
            code |= TOP;
        } else if y > ymax {
            code |= BOTTOM;
        }
        code
    };

    let mut code0 = outcode(x0, y0);
    let mut code1 = outcode(x1, y1);

    for _ in 0..20 {
        if (code0 | code1) == 0 {
            return Some(((x0, y0), (x1, y1)));
        }
        if (code0 & code1) != 0 {
            return None;
        }

        let code_out = if code0 != 0 { code0 } else { code1 };
        let (x, y);

        if code_out & TOP != 0 {
            x = x0 + (x1 - x0) * (ymin - y0) / (y1 - y0);
            y = ymin;
        } else if code_out & BOTTOM != 0 {
            x = x0 + (x1 - x0) * (ymax - y0) / (y1 - y0);
            y = ymax;
        } else if code_out & RIGHT != 0 {
            y = y0 + (y1 - y0) * (xmax - x0) / (x1 - x0);
            x = xmax;
        } else {
            y = y0 + (y1 - y0) * (xmin - x0) / (x1 - x0);
            x = xmin;
        }

        if code_out == code0 {
            x0 = x;
            y0 = y;
            code0 = outcode(x0, y0);
        } else {
            x1 = x;
            y1 = y;
            code1 = outcode(x1, y1);
        }
    }

    None
}

fn map_err<E: std::fmt::Debug>(e: E) -> RenderError {
    RenderError::BackendError(format!("{:?}", e))
}

/// Segment a polyline according to a dash pattern, returning visible sub-paths.
fn segment_dashed(points: &[(f64, f64)], pattern: &[(f64, f64)]) -> Vec<Vec<(f64, f64)>> {
    if pattern.is_empty() || points.len() < 2 {
        return vec![points.to_vec()];
    }

    let mut segments: Vec<Vec<(f64, f64)>> = Vec::new();
    let mut current_seg: Vec<(f64, f64)> = Vec::new();
    let mut drawing = true;
    let mut pat_idx = 0;
    let mut remaining_in_pat = pattern[0].0; // start with draw phase

    for window in points.windows(2) {
        let (x0, y0) = window[0];
        let (x1, y1) = window[1];
        let dx = x1 - x0;
        let dy = y1 - y0;
        let seg_len = (dx * dx + dy * dy).sqrt();
        if seg_len < 0.001 {
            continue;
        }
        let ux = dx / seg_len;
        let uy = dy / seg_len;
        let mut consumed = 0.0;

        while consumed < seg_len - 0.001 {
            let available = seg_len - consumed;
            let step = remaining_in_pat.min(available);
            let px = x0 + ux * (consumed + step);
            let py = y0 + uy * (consumed + step);

            if drawing {
                if current_seg.is_empty() {
                    current_seg.push((x0 + ux * consumed, y0 + uy * consumed));
                }
                current_seg.push((px, py));
            }

            consumed += step;
            remaining_in_pat -= step;

            if remaining_in_pat < 0.001 {
                if drawing {
                    if current_seg.len() >= 2 {
                        segments.push(std::mem::take(&mut current_seg));
                    } else {
                        current_seg.clear();
                    }
                    drawing = false;
                    remaining_in_pat = pattern[pat_idx].1; // gap
                } else {
                    drawing = true;
                    pat_idx = (pat_idx + 1) % pattern.len();
                    remaining_in_pat = pattern[pat_idx].0; // draw
                }
            }
        }
    }

    if drawing && current_seg.len() >= 2 {
        segments.push(current_seg);
    }

    segments
}

impl<'a, DB: DrawingBackend> DrawBackend for PlottersAdapter<'a, DB> {
    fn draw_circle(
        &mut self,
        center: (f64, f64),
        radius: f64,
        style: &PointStyle,
    ) -> Result<(), RenderError> {
        // Clip: skip points entirely outside the plot area
        if !point_in_rect(center.0, center.1, &self.plot_area) {
            return Ok(());
        }
        let color = to_rgba(style.color, style.alpha);
        if style.filled {
            self.area
                .draw(&Circle::new(
                    (center.0 as i32, center.1 as i32),
                    radius as i32,
                    color.filled(),
                ))
                .map_err(map_err)?;
        } else {
            self.area
                .draw(&Circle::new(
                    (center.0 as i32, center.1 as i32),
                    radius as i32,
                    color.stroke_width(1),
                ))
                .map_err(map_err)?;
        }
        Ok(())
    }

    fn draw_line(&mut self, points: &[(f64, f64)], style: &LineStyle) -> Result<(), RenderError> {
        if points.len() < 2 {
            return Ok(());
        }
        // Simulate sub-pixel line widths: render as 1px with reduced opacity
        let (pixel_width, alpha) = if style.width >= 1.0 {
            (style.width as u32, style.alpha)
        } else if style.width > 0.0 {
            (1, style.alpha * style.width)
        } else {
            (0, style.alpha)
        };
        let color = to_rgba(style.color, alpha);
        let stroke = color.stroke_width(pixel_width);

        let pattern = style.linetype.pattern();
        let sub_paths = segment_dashed(points, pattern);

        for path in &sub_paths {
            for window in path.windows(2) {
                // Clip each line segment to plot area
                if let Some((p1, p2)) = clip_line_segment(
                    window[0].0,
                    window[0].1,
                    window[1].0,
                    window[1].1,
                    &self.plot_area,
                ) {
                    self.area
                        .draw(&PathElement::new(
                            vec![(p1.0 as i32, p1.1 as i32), (p2.0 as i32, p2.1 as i32)],
                            stroke,
                        ))
                        .map_err(map_err)?;
                }
            }
        }
        Ok(())
    }

    fn draw_rect(
        &mut self,
        top_left: (f64, f64),
        bottom_right: (f64, f64),
        style: &RectStyle,
    ) -> Result<(), RenderError> {
        let (tl, br) = if style.clip {
            // Clamp rect to plot area (data elements only)
            let clamped_tl = clip_point(top_left.0, top_left.1, &self.plot_area);
            let clamped_br = clip_point(bottom_right.0, bottom_right.1, &self.plot_area);

            // Skip if fully collapsed after clamping
            if (clamped_tl.0 - clamped_br.0).abs() < 0.5
                && (clamped_tl.1 - clamped_br.1).abs() < 0.5
            {
                // But don't skip if original rect was already small (it's a real data rect)
                if (top_left.0 - bottom_right.0).abs() > 1.0
                    || (top_left.1 - bottom_right.1).abs() > 1.0
                {
                    return Ok(());
                }
            }

            (
                (clamped_tl.0 as i32, clamped_tl.1 as i32),
                (clamped_br.0 as i32, clamped_br.1 as i32),
            )
        } else {
            // No clipping — backgrounds, strips, legends
            (
                (top_left.0 as i32, top_left.1 as i32),
                (bottom_right.0 as i32, bottom_right.1 as i32),
            )
        };

        if let Some(fill) = style.fill {
            let fill_color = to_rgba(fill, style.alpha);
            self.area
                .draw(&plotters::prelude::Rectangle::new(
                    [tl, br],
                    fill_color.filled(),
                ))
                .map_err(map_err)?;
        }

        if let Some(stroke) = style.stroke {
            let stroke_color = to_rgba(stroke, style.alpha);
            self.area
                .draw(&plotters::prelude::Rectangle::new(
                    [tl, br],
                    stroke_color.stroke_width(if style.stroke_width > 0.0 {
                        (style.stroke_width as u32).max(1)
                    } else {
                        0
                    }),
                ))
                .map_err(map_err)?;
        }

        Ok(())
    }

    fn draw_text(
        &mut self,
        text: &str,
        pos: (f64, f64),
        style: &TextStyle,
    ) -> Result<(), RenderError> {
        let color = to_rgba(style.color, 1.0);
        let family = style.family.as_deref().unwrap_or("sans-serif");
        ensure_font(family);
        let font = (family, style.size).into_font();

        let pos_adj = match style.anchor {
            TextAnchor::Start => plotters::style::text_anchor::Pos::new(
                plotters::style::text_anchor::HPos::Left,
                plotters::style::text_anchor::VPos::Center,
            ),
            TextAnchor::Middle => plotters::style::text_anchor::Pos::new(
                plotters::style::text_anchor::HPos::Center,
                plotters::style::text_anchor::VPos::Center,
            ),
            TextAnchor::End => plotters::style::text_anchor::Pos::new(
                plotters::style::text_anchor::HPos::Right,
                plotters::style::text_anchor::VPos::Center,
            ),
        };

        let angle_i = style.angle.round() as i32;
        if angle_i != 0 {
            let (font_transform, rotated_pos) = match angle_i.rem_euclid(360) {
                80..=100 => (
                    FontTransform::Rotate90,
                    plotters::style::text_anchor::Pos::new(
                        plotters::style::text_anchor::HPos::Center,
                        plotters::style::text_anchor::VPos::Center,
                    ),
                ),
                170..=190 => (
                    FontTransform::Rotate180,
                    plotters::style::text_anchor::Pos::new(
                        plotters::style::text_anchor::HPos::Center,
                        plotters::style::text_anchor::VPos::Center,
                    ),
                ),
                // 270° or -90° or 45° approximation (common ggplot2 x-axis rotation)
                _ => (
                    FontTransform::Rotate270,
                    plotters::style::text_anchor::Pos::new(
                        plotters::style::text_anchor::HPos::Right,
                        plotters::style::text_anchor::VPos::Center,
                    ),
                ),
            };

            let text_style = plotters::prelude::TextStyle::from((family, style.size).into_font())
                .color(&color)
                .transform(font_transform)
                .pos(rotated_pos);

            self.area
                .draw_text(text, &text_style, (pos.0 as i32, pos.1 as i32))
                .map_err(map_err)?;
        } else {
            let text_style = plotters::prelude::TextStyle::from(font)
                .color(&color)
                .pos(pos_adj);
            self.area
                .draw_text(text, &text_style, (pos.0 as i32, pos.1 as i32))
                .map_err(map_err)?;
        }

        Ok(())
    }

    fn draw_polygon(
        &mut self,
        points: &[(f64, f64)],
        style: &RectStyle,
    ) -> Result<(), RenderError> {
        if points.len() < 3 {
            return Ok(());
        }
        let int_points: Vec<(i32, i32)> =
            points.iter().map(|(x, y)| (*x as i32, *y as i32)).collect();

        if let Some(fill) = style.fill {
            let fill_color = to_rgba(fill, style.alpha);
            self.area
                .draw(&Polygon::new(int_points.clone(), fill_color.filled()))
                .map_err(map_err)?;
        }

        Ok(())
    }

    fn draw_shape(
        &mut self,
        center: (f64, f64),
        radius: f64,
        style: &PointStyle,
    ) -> Result<(), RenderError> {
        // Clip: skip shapes entirely outside the plot area
        if !point_in_rect(center.0, center.1, &self.plot_area) {
            return Ok(());
        }
        let color = to_rgba(style.color, style.alpha);
        let (cx, cy) = (center.0 as i32, center.1 as i32);
        let r = radius as i32;

        match style.shape {
            PointShape::Circle => self.draw_circle(center, radius, style),
            PointShape::Square => {
                let tl = (cx - r, cy - r);
                let br = (cx + r, cy + r);
                if style.filled {
                    self.area
                        .draw(&plotters::prelude::Rectangle::new([tl, br], color.filled()))
                        .map_err(map_err)?;
                } else {
                    self.area
                        .draw(&plotters::prelude::Rectangle::new(
                            [tl, br],
                            color.stroke_width(1),
                        ))
                        .map_err(map_err)?;
                }
                Ok(())
            }
            PointShape::Triangle => {
                let pts = vec![(cx, cy - r), (cx - r, cy + r), (cx + r, cy + r)];
                if style.filled {
                    self.area
                        .draw(&Polygon::new(pts, color.filled()))
                        .map_err(map_err)?;
                } else {
                    let outline = vec![
                        (cx, cy - r),
                        (cx - r, cy + r),
                        (cx + r, cy + r),
                        (cx, cy - r),
                    ];
                    self.area
                        .draw(&PathElement::new(outline, color.stroke_width(1)))
                        .map_err(map_err)?;
                }
                Ok(())
            }
            PointShape::Diamond => {
                let pts = vec![(cx, cy - r), (cx + r, cy), (cx, cy + r), (cx - r, cy)];
                if style.filled {
                    self.area
                        .draw(&Polygon::new(pts, color.filled()))
                        .map_err(map_err)?;
                } else {
                    let outline = vec![
                        (cx, cy - r),
                        (cx + r, cy),
                        (cx, cy + r),
                        (cx - r, cy),
                        (cx, cy - r),
                    ];
                    self.area
                        .draw(&PathElement::new(outline, color.stroke_width(1)))
                        .map_err(map_err)?;
                }
                Ok(())
            }
            PointShape::Cross => {
                // X shape
                self.area
                    .draw(&PathElement::new(
                        vec![(cx - r, cy - r), (cx + r, cy + r)],
                        color.stroke_width(1),
                    ))
                    .map_err(map_err)?;
                self.area
                    .draw(&PathElement::new(
                        vec![(cx - r, cy + r), (cx + r, cy - r)],
                        color.stroke_width(1),
                    ))
                    .map_err(map_err)?;
                Ok(())
            }
            PointShape::Plus => {
                // + shape
                self.area
                    .draw(&PathElement::new(
                        vec![(cx - r, cy), (cx + r, cy)],
                        color.stroke_width(1),
                    ))
                    .map_err(map_err)?;
                self.area
                    .draw(&PathElement::new(
                        vec![(cx, cy - r), (cx, cy + r)],
                        color.stroke_width(1),
                    ))
                    .map_err(map_err)?;
                Ok(())
            }
        }
    }

    fn plot_area(&self) -> Rect {
        self.plot_area.clone()
    }

    fn total_area(&self) -> Rect {
        self.total_area.clone()
    }
}