cadcraft/crates/io/src/plotter.rs

//! The plot hook the apps install ([`plot`]): PDF, PNG or SVG output of a plotter configuration (`output`), on the
//! device's paper (`width`/`height`, `margins` in mm) at its `resolution`.
//!
//! PDF goes to [`crate::pdf`]. PNG draws the sheet on white paper at the device resolution
//! (capped at [`MAX_PNG_PIXELS`]), with the plot style table and lineweights as PDF uses them.
//! SVG shows the sheet of a layout or the model-space extents.

use std::sync::Arc;

use cadcraft_color::Rgb;
use cadcraft_doc::{Drawing, Space};
use cadcraft_geom::{Bounds2, Vec2};
use cadcraft_render::{Sheet, paper, raster};
use serde_json::Value;

use crate::{IoError, PdfOptions, Result, pdf};

/// Largest PNG plot (pixels); larger sheets are drawn at a lower resolution.
pub const MAX_PNG_PIXELS: f64 = 40.0e6;

/// Plot `space` with JSON options (the engine's `plot` hook): PDF unless `output` is `png` or
/// `svg`. `margins: [l, b, r, t]` (mm) bound the printable area of this plot (model space or a
/// layout).
pub fn plot(d: &Drawing, space: &Space, opts: &Value) -> Result<Vec<u8>> {
    let margins = pdf::margins(opts.get("margins"));
    let with_margins;
    let d = match (space, margins) {
        (Space::Paper(n), Some(m)) => {
            let mut c = d.clone();
            if let Some(l) = c.layouts.iter_mut().find(|l| l.name.eq_ignore_ascii_case(n)) {
                l.page.margins_mm = m;
            }
            with_margins = c;
            &with_margins
        }
        _ => d,
    };
    match opts.get("output").and_then(Value::as_str).map(str::to_ascii_lowercase).as_deref() {
        None | Some("pdf") => pdf::plot(d, space, opts),
        Some("png") => png(d, space, opts),
        Some("svg") => svg(d, space, opts),
        Some(other) => Err(IoError::Unsupported(other.to_string())),
    }
}

/// The sheet a plot draws on (a model-space plot's printable area inside the device margins).
fn sheet(d: &Drawing, space: &Space, o: &PdfOptions) -> Result<(Sheet, cadcraft_doc::PageSetup)> {
    let page = pdf::page_for(d, space, o)?;
    Ok((Sheet::from_page(&page, paper::paper_unit_mm(d)), page))
}

/// Paper units per drawing unit fitting `b` into the printable area (or the `scale` option).
fn fit_scale(b: &Bounds2, sheet: &Sheet, o: &PdfOptions) -> f64 {
    if let Some(s) = o.scale.filter(|s| s.is_finite() && *s > 0.0)
        && o.fit == Some(false)
    {
        return s;
    }
    if b.is_empty() {
        return 1.0;
    }
    let s = (sheet.printable.width() / b.width().max(1e-12)).min(sheet.printable.height() / b.height().max(1e-12));
    if s.is_finite() && s > 0.0 { s } else { 1.0 }
}

fn png(d: &Drawing, space: &Space, opts: &Value) -> Result<Vec<u8>> {
    let o = PdfOptions::from_json(opts);
    let (sheet, page) = sheet(d, space, &o)?;
    let dpi = opts.get("resolution").and_then(Value::as_f64).filter(|r| r.is_finite()).unwrap_or(300.0).clamp(50.0, 2400.0);
    // Pixels per paper unit, lowered so the image stays within the caps.
    let mut k = sheet.unit_mm / 25.4 * dpi;
    let (w, h) = (sheet.size.x * k, sheet.size.y * k);
    let shrink = (MAX_PNG_PIXELS / (w * h).max(1.0)).sqrt().min(16384.0 / w.max(h).max(1.0)).min(1.0);
    if !(shrink.is_finite() && shrink > 0.0) {
        return Err(IoError::Format("the sheet is too large to plot as an image".into()));
    }
    k *= shrink;
    let px = |v: f64| (v * k).round().clamp(1.0, 16384.0) as u32;
    let (width, height) = (px(sheet.size.x), px(sheet.size.y));
    let lineweights = o.lineweights.unwrap_or(match space {
        Space::Paper(_) => page.lineweights,
        Space::Model => true,
    });
    let table = cadcraft_doc::plot_style_table(d, &page.plot_style_table).map(Arc::new);
    // Paper units per drawing unit: 1 for a layout at 1:1, the fitted scale for model space.
    let fit = matches!(space, Space::Model) || o.fit == Some(true);
    let window = o.window.filter(|w| matches!(space, Space::Model) && !w.is_empty());
    let est = if fit { fit_scale(&window.unwrap_or_else(|| d.extents(space)), &sheet, &o) } else { 1.0 };
    // Chord tolerance: a fifth of a pixel.
    let tolerance = (0.2 / (k * est)).max(1e-9);
    let ropts = cadcraft_render::Options { tolerance, lineweights, plot_style_table: table, ..cadcraft_render::Options::default() };
    let mut list = cadcraft_render::build_plot(d, space, &ropts);
    let half = Vec2::new(f64::from(width), f64::from(height)) / (2.0 * k);
    let b = window.unwrap_or(list.bounds);
    let s = if fit { fit_scale(&b, &sheet, &o) } else { 1.0 };
    // Plot style ends, joins and fill patterns at the plot scale, as PDF draws them (a layout's
    // are already drawn).
    cadcraft_render::pen::apply(&mut list, s * sheet.unit_mm);
    let view = if fit {
        let from = if b.is_empty() { Vec2::ZERO } else { b.center() };
        // The world point at the image centre, with `from` on the printable area's centre.
        let center = from + (half - sheet.printable.center()) / s;
        raster::View { center, scale: k * s, width, height }
    } else {
        raster::View { center: half, scale: k, width, height }
    };
    let px_per_mm = if lineweights { (k / sheet.unit_mm) as f32 } else { 0.0 };
    let ro = raster::RasterOptions { background: Rgb(255, 255, 255), hairline: 1.0, px_per_mm, antialias: true };
    raster::render_png(&list, &view, &ro).ok_or_else(|| IoError::Format("render failed".into()))
}

fn svg(d: &Drawing, space: &Space, opts: &Value) -> Result<Vec<u8>> {
    let o = PdfOptions::from_json(opts);
    let Space::Model = space else {
        let window = sheet(d, space, &o)?.0.bounds();
        return Ok(crate::svg::export_window(d, space, Some(window)).into_bytes());
    };
    // Model space as plotted: the plot style table, lineweights, and the table's ends, joins and
    // fills at the scale that fits the window (or the extents) on the device's paper.
    let (sheet, page) = sheet(d, space, &o)?;
    let window = o.window.filter(|w| !w.is_empty());
    let table = cadcraft_doc::plot_style_table(d, &page.plot_style_table).map(Arc::new);
    let lineweights = o.lineweights.unwrap_or(true);
    let est = fit_scale(&window.unwrap_or_else(|| d.extents(space)), &sheet, &o);
    // Chord tolerance: about 0.05 mm on paper.
    let tolerance = (0.05 / (sheet.unit_mm * est)).max(1e-9);
    let tolerance = if tolerance.is_finite() { tolerance } else { cadcraft_render::Options::default().tolerance };
    let ropts = cadcraft_render::Options { tolerance, lineweights, plot_style_table: table, ..cadcraft_render::Options::default() };
    let mut list = cadcraft_render::build_plot(d, space, &ropts);
    let s = fit_scale(&window.unwrap_or(list.bounds), &sheet, &o);
    cadcraft_render::pen::apply(&mut list, s * sheet.unit_mm);
    Ok(crate::svg::export_list(&list, window).into_bytes())
}

#[cfg(test)]
mod tests {
    use super::*;
    use cadcraft_doc::{Common, EntityKind, Line};
    use cadcraft_geom::Vec3;
    use serde_json::json;

    /// Width and height from a PNG's header.
    fn png_size(b: &[u8]) -> (u32, u32) {
        let be = |i: usize| u32::from_be_bytes([b[i], b[i + 1], b[i + 2], b[i + 3]]);
        (be(16), be(20))
    }

    fn drawing() -> Drawing {
        let mut d = Drawing::new_metric();
        d.add(&Space::Model, Common::default(), EntityKind::Line(Line { a: Vec3::ZERO, b: Vec3::new(100.0, 50.0, 0.0) })).unwrap();
        d
    }

    #[test]
    fn png_and_svg_devices() {
        let d = drawing();
        let a4 = json!({"output": "png", "resolution": 100, "width": 210, "height": 297, "landscape": true, "margins": [5, 5, 5, 5]});
        let png = plot(&d, &Space::Model, &a4).unwrap();
        assert_eq!(png_size(&png), (1169, 827), "A4 landscape at 100 dpi");
        // Huge sheets at a high resolution are capped.
        let big = json!({"output": "png", "resolution": 2400, "width": 841, "height": 1189});
        let (w, h) = png_size(&plot(&d, &Space::Model, &big).unwrap());
        assert!(f64::from(w) * f64::from(h) <= MAX_PNG_PIXELS * 1.01 && w <= 16384 && h <= 16384);
        let layout = Space::Paper(d.layouts[0].name.clone());
        let svg = String::from_utf8(plot(&d, &layout, &json!({"output": "svg"})).unwrap()).unwrap();
        assert!(svg.starts_with("<svg"));
        assert!(plot(&d, &layout, &json!({"output": "png", "resolution": f64::NAN, "margins": [1, 2, 3]})).is_ok());
        assert!(plot(&d, &Space::Model, &json!({"output": "dwf"})).is_err());
        assert!(plot(&d, &Space::Model, &json!({})).unwrap().starts_with(b"%PDF"));
    }
}