jitter 0.1.0

Add natural handwriting-like variation to digital text
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use crate::font::{GlyphData, PathCommand};
use std::fmt::Write;

/// Generate an SVG string from jittered glyph data.
///
/// Converts from font coordinate space (Y-up) to SVG coordinate space (Y-down).
pub fn render_svg(
    glyphs: &[GlyphData],
    jittered_commands: &[Vec<PathCommand>],
    font_size: u32,
    units_per_em: u16,
) -> String {
    let scale = font_size as f64 / units_per_em as f64;

    // Calculate total width and height
    let total_advance: f64 = glyphs.iter().map(|g| g.advance_width as f64).sum();
    let svg_width = (total_advance * scale).ceil() as u32;
    // Use 1.5x font size for height to accommodate ascenders/descenders
    let svg_height = (font_size as f64 * 1.5).ceil() as u32;
    // Baseline at ~75% of the height
    let baseline_y = font_size as f64 * 1.1;

    let mut svg = String::new();
    writeln!(
        &mut svg,
        r#"<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 {svg_width} {svg_height}" width="{svg_width}" height="{svg_height}">"#,
    )
    .unwrap();

    let mut cursor_x: f64 = 0.0;

    for (i, (glyph, commands)) in glyphs.iter().zip(jittered_commands.iter()).enumerate() {
        if commands.is_empty() {
            // Space or glyph with no outline — just advance
            cursor_x += glyph.advance_width as f64;
            continue;
        }

        let path_d = commands_to_path_d(commands, scale, cursor_x * scale, baseline_y);
        if !path_d.is_empty() {
            writeln!(&mut svg, r#"  <path id="g{i}" d="{path_d}" fill="black"/>"#,).unwrap();
        }

        cursor_x += glyph.advance_width as f64;
    }

    writeln!(&mut svg, "</svg>").unwrap();
    svg
}

/// Convert path commands to an SVG path `d` attribute string.
///
/// Applies coordinate transformation: font (Y-up) -> SVG (Y-down).
fn commands_to_path_d(
    commands: &[PathCommand],
    scale: f64,
    offset_x: f64,
    baseline_y: f64,
) -> String {
    let mut d = String::new();

    for cmd in commands {
        match cmd {
            PathCommand::MoveTo(x, y) => {
                let sx = *x as f64 * scale + offset_x;
                let sy = -*y as f64 * scale + baseline_y;
                write!(&mut d, "M{sx:.2} {sy:.2} ").unwrap();
            }
            PathCommand::LineTo(x, y) => {
                let sx = *x as f64 * scale + offset_x;
                let sy = -*y as f64 * scale + baseline_y;
                write!(&mut d, "L{sx:.2} {sy:.2} ").unwrap();
            }
            PathCommand::QuadTo(cx, cy, x, y) => {
                let scx = *cx as f64 * scale + offset_x;
                let scy = -*cy as f64 * scale + baseline_y;
                let sx = *x as f64 * scale + offset_x;
                let sy = -*y as f64 * scale + baseline_y;
                write!(&mut d, "Q{scx:.2} {scy:.2} {sx:.2} {sy:.2} ").unwrap();
            }
            PathCommand::CurveTo(cx0, cy0, cx1, cy1, x, y) => {
                let scx0 = *cx0 as f64 * scale + offset_x;
                let scy0 = -*cy0 as f64 * scale + baseline_y;
                let scx1 = *cx1 as f64 * scale + offset_x;
                let scy1 = -*cy1 as f64 * scale + baseline_y;
                let sx = *x as f64 * scale + offset_x;
                let sy = -*y as f64 * scale + baseline_y;
                write!(
                    &mut d,
                    "C{scx0:.2} {scy0:.2} {scx1:.2} {scy1:.2} {sx:.2} {sy:.2} "
                )
                .unwrap();
            }
            PathCommand::Close => {
                write!(&mut d, "Z ").unwrap();
            }
        }
    }

    d.trim_end().to_string()
}