vectorcraft/crates/engine/src/cmd/draw2/cut.rs

use super::common::{
    dist_to_polyline, ids_json, path_mut, path_of, points_param, poly_bounds, replace_with_pieces, sibling_with, target_paths, usize_opt,
};
use super::*;

/// Split a filled path into connected pieces (each outer contour with its holes).
pub(in super::super) fn components(pd: &PathData) -> Vec<PathData> {
    let subs: Vec<&SubPath> = pd.subpaths.iter().filter(|s| s.closed && s.anchors.len() >= 2).collect();
    if subs.len() <= 1 {
        return if pd.is_empty() { vec![] } else { vec![pd.clone()] };
    }
    let bps: Vec<BezPath> = subs
        .iter()
        .map(|s| {
            let mut b = BezPath::new();
            s.to_bezpath_into(&mut b);
            b
        })
        .collect();
    let samples: Vec<Point> = subs.iter().map(|s| s.segment(0).eval(0.5)).collect();
    let n = subs.len();
    let inside = |j: usize, i: usize| fill_contains(&bps[j], FillRule::NonZero, samples[i]);
    let depth: Vec<usize> = (0..n).map(|i| (0..n).filter(|&j| j != i && inside(j, i)).count()).collect();
    let areas: Vec<f64> = subs.iter().map(|s| s.area().abs()).collect();
    let outers: Vec<usize> = (0..n).filter(|&i| depth[i].is_multiple_of(2)).collect();
    let mut groups: Vec<Vec<SubPath>> = outers.iter().map(|&o| vec![subs[o].clone()]).collect();
    for h in (0..n).filter(|&i| !depth[i].is_multiple_of(2)) {
        let best = outers
            .iter()
            .enumerate()
            .filter(|(_, o)| depth[**o] + 1 == depth[h] && inside(**o, h))
            .min_by(|a, b| areas[*a.1].total_cmp(&areas[*b.1]));
        if let Some((k, _)) = best {
            groups[k].push(subs[h].clone());
        }
    }
    groups.into_iter().map(PathData::new).collect()
}

/// The pieces of `sp` where `remove(point)` is false. `None` when nothing is removed. Each segment
/// is sampled at least every `step` pt (and at least 24 times), so a removed stretch at least
/// `step` long is found.
fn cut_subpath(sp: &SubPath, step: f64, remove: &dyn Fn(Point) -> bool) -> Option<Vec<SubPath>> {
    let nseg = sp.segment_count();
    if nseg == 0 {
        return sp.anchors.first().filter(|a| remove(a.p)).map(|_| vec![]);
    }
    const K: usize = 24;
    const MAX_SAMPLES: usize = 4096;
    let mut runs: Vec<Vec<(usize, f64, f64)>> = vec![];
    let mut cur: Vec<(usize, f64, f64)> = vec![];
    let mut any = false;
    for i in 0..nseg {
        let c = sp.segment(i);
        // The curve moves at most 3 times its longest control-polygon edge per unit of t, so with
        // n samples, neighboring samples are at most 3 · edge / n apart.
        let edge = (c.p1 - c.p0).hypot().max((c.p2 - c.p1).hypot()).max((c.p3 - c.p2).hypot());
        let wanted = (3.0 * edge / step).ceil();
        let samples = if wanted.is_finite() && wanted > K as f64 { (wanted as usize).min(MAX_SAMPLES) } else { K };
        let mut prev_t = 0.0;
        let mut prev_rm = remove(c.eval(0.0));
        let mut start = if prev_rm { None } else { Some(0.0) };
        if prev_rm {
            any = true;
            if !cur.is_empty() {
                runs.push(std::mem::take(&mut cur));
            }
        }
        for k in 1..=samples {
            let t = k as f64 / samples as f64;
            let rm = remove(c.eval(t));
            if rm != prev_rm {
                let (mut lo, mut hi) = (prev_t, t);
                for _ in 0..30 {
                    let m = 0.5 * (lo + hi);
                    if remove(c.eval(m)) == prev_rm { lo = m } else { hi = m }
                }
                let b = 0.5 * (lo + hi);
                if prev_rm {
                    start = Some(b);
                } else {
                    any = true;
                    if let Some(s) = start.take() {
                        cur.push((i, s, b));
                    }
                    runs.push(std::mem::take(&mut cur));
                }
            }
            prev_t = t;
            prev_rm = rm;
        }
        if let Some(s) = start {
            cur.push((i, s, 1.0));
        }
    }
    if !cur.is_empty() {
        runs.push(cur);
    }
    runs.retain(|r| !r.is_empty());
    if !any {
        return None;
    }
    // A closed path's last and first runs meet at anchor 0.
    if sp.closed && runs.len() >= 2 {
        let first_starts = runs.first().and_then(|r| r.first()).is_some_and(|s| s.0 == 0 && s.1 == 0.0);
        let last_ends = runs.last().and_then(|r| r.last()).is_some_and(|s| s.0 + 1 == nseg && s.2 == 1.0);
        if first_starts && last_ends {
            let first = runs.remove(0);
            if let Some(last) = runs.last_mut() {
                last.extend(first);
            }
        }
    }
    let out = runs
        .iter()
        .filter(|r| r.len() > 1 || r[0].2 - r[0].1 > 1e-4)
        .map(|r| {
            let mut anchors: Vec<Anchor> = vec![];
            for &(i, t0, t1) in r {
                let c = sp.segment(i).subsegment(t0..t1);
                let (h1, h2) = if sp.segment_is_line(i) { (c.p0, c.p3) } else { (c.p1, c.p2) };
                match anchors.last_mut() {
                    Some(a) => a.h_out = h1,
                    None => anchors.push(Anchor { h_out: h1, ..Anchor::corner(c.p0) }),
                }
                anchors.push(Anchor { p: c.p3, h_in: h2, h_out: c.p3, kind: AnchorKind::Corner });
            }
            for a in &mut anchors {
                *a = Anchor::with_handles(a.p, a.h_in, a.h_out);
            }
            SubPath::new(anchors, false)
        })
        .filter(|s| s.anchors.len() >= 2)
        .collect();
    Some(out)
}

/// Erase from an outline path (open or closed) where `remove` holds, sampling each segment at least
/// every `step` pt (`f64::INFINITY` for the fixed sampling). Returns the new geometry per output
/// object (one object per piece when the path had a single subpath), or None if unchanged.
pub(in super::super) fn erase_outline(pd: &PathData, step: f64, remove: &dyn Fn(Point) -> bool) -> Option<Vec<PathData>> {
    let mut changed = false;
    let mut subs = vec![];
    for sp in &pd.subpaths {
        match cut_subpath(sp, step, remove) {
            Some(pieces) => {
                changed = true;
                subs.extend(pieces);
            }
            None => subs.push(sp.clone()),
        }
    }
    if !changed {
        return None;
    }
    Some(if pd.subpaths.len() == 1 {
        subs.into_iter().map(PathData::single).collect()
    } else if subs.is_empty() {
        vec![]
    } else {
        vec![PathData::new(subs)]
    })
}

// ---------- Scissors ----------

pub(super) fn split(s: &mut Session, p: &Value) -> Result<Value> {
    const C: &str = "path.split";
    let id = id_param(p, "id").ok_or_else(|| bad(C, "missing id"))?;
    let si = usize_opt(p, "subpath", C)?.unwrap_or(0);
    let anchor = usize_opt(p, "anchor", C)?;
    let seg = usize_opt(p, "segment", C)?;
    if anchor.is_none() && seg.is_none() {
        return Err(bad(C, "need `anchor` or `segment` + `t`"));
    }
    let t = f64_or(p, "t", 0.5);
    if !t.is_finite() || p.get("t").is_some_and(|v| !v.is_f64() && !v.is_i64() && !v.is_u64()) {
        return Err(bad(C, "invalid t"));
    }
    let ids = s.edit("Split Path", |d, sel| {
        let path = path_mut(d, id)?;
        let mut sp = path.subpaths.get(si).cloned().ok_or_else(|| EngineError::Other("no such subpath".into()))?;
        let n = sp.anchors.len();
        let k = match (anchor, seg) {
            (Some(a), _) if a < n => a,
            (Some(_), _) => return Err(EngineError::Other("no such anchor".into())),
            (None, Some(g)) if g < sp.segment_count() => {
                if t <= 1e-6 {
                    g
                } else if t >= 1.0 - 1e-6 {
                    (g + 1) % n
                } else {
                    sp.insert_anchor(g, t)
                }
            }
            _ => return Err(EngineError::Other("no such segment".into())),
        };
        let mut pieces = sp.cut_at(&std::collections::BTreeSet::from([k]));
        if sp.closed {
            path.subpaths[si] = pieces.pop().ok_or_else(|| EngineError::Other("no such anchor".into()))?;
            sel.set([id]);
            return Ok(vec![id]);
        }
        let [left, right] = <[SubPath; 2]>::try_from(pieces).map_err(|_| EngineError::Other("cannot split an open path at its end point".into()))?;
        if path.subpaths.len() == 1 {
            path.subpaths[0] = left;
            let node = sibling_with(d, id, PathData::single(right))?;
            let (parent, idx, _) = d.position(id).ok_or(EngineError::NoNode(id))?;
            let nid = d.insert(parent, idx + 1, node)?;
            sel.set([id, nid]);
            Ok(vec![id, nid])
        } else {
            path.subpaths[si] = left;
            path.subpaths.insert(si + 1, right);
            sel.set([id]);
            Ok(vec![id])
        }
    })?;
    Ok(ids_json(&ids))
}

// ---------- Knife / Eraser ----------

/// Width of the slit the knife leaves between pieces.
const KNIFE_GAP: f64 = 0.05;

pub(super) fn knife(s: &mut Session, p: &Value) -> Result<Value> {
    const C: &str = "path.knife";
    let pts = points_param(p, "points", C)?;
    if pts.len() < 2 {
        return Err(bad(C, "need at least two points"));
    }
    let st = s.doc()?;
    let strip = po::outline_stroke(&PathData::single(SubPath::polyline(&pts, false)), KNIFE_GAP, Cap::Butt, Join::Round, 4.0);
    let mut plan: Vec<(NodeId, Vec<PathData>)> = vec![];
    for id in target_paths(&st.doc, &st.selection, poly_bounds(&pts, 1.0)) {
        let (pd, rule) = path_of(&st.doc, id)?;
        if !pd.is_closed() {
            continue;
        }
        let pieces = components(&po::boolean(&pd, rule, &strip, FillRule::NonZero, BoolOp::Difference));
        if pieces.len() >= 2 {
            plan.push((id, pieces));
        }
    }
    if plan.is_empty() {
        return Ok(json!({ "ids": [] }));
    }
    let ids = s.edit("Knife", |d, sel| {
        let mut all = vec![];
        let mut cut = Beside::replacing(d, &plan.iter().map(|(id, _)| *id).collect::<Vec<_>>());
        for (id, pieces) in plan {
            all.extend(replace_with_pieces(d, &mut cut, id, pieces)?);
        }
        cut.finish(d)?;
        sel.set(all.iter().copied());
        Ok(all)
    })?;
    Ok(ids_json(&ids))
}

pub(super) fn erase_region(s: &mut Session, p: &Value) -> Result<Value> {
    const C: &str = "path.eraseRegion";
    let pts = points_param(p, "points", C)?;
    let size = number_or(p, "size", 10.0, C)?;
    if !(size.is_finite() && size > 0.0) {
        return Err(bad(C, "size must be positive"));
    }
    let angle = number_or(p, "angle", 0.0, C)?;
    let roundness = number_or(p, "roundness", 100.0, C)?;
    let r = size / 2.0;
    // The tip's short axis: an open path is sampled at least every half of it.
    let short = size * roundness.clamp(1.0, 100.0) / 100.0;
    let st = s.doc()?;
    let region = eraser_area(&pts, size, angle, roundness);
    // A point is under the tip when, with the tip squashed back into a circle, it is within the
    // circle's radius of the squashed drag.
    let squash = eraser_tip(angle, roundness).inverse();
    let round: Vec<Point> = pts.iter().map(|q| squash * *q).collect();
    let mut plan: Vec<(NodeId, Vec<PathData>)> = vec![];
    for id in target_paths(&st.doc, &st.selection, poly_bounds(&pts, r)) {
        let (pd, rule) = path_of(&st.doc, id)?;
        if pd.is_closed() {
            if po::area(&po::boolean(&pd, rule, &region, FillRule::NonZero, BoolOp::Intersect), FillRule::NonZero) <= 1e-6 {
                continue;
            }
            plan.push((id, components(&po::boolean(&pd, rule, &region, FillRule::NonZero, BoolOp::Difference))));
        } else if let Some(pieces) = erase_outline(&pd, short / 2.0, &|q| dist_to_polyline(&round, squash * q) <= r) {
            plan.push((id, pieces));
        }
    }
    apply_plan(s, "Eraser", plan)
}

fn apply_plan(s: &mut Session, label: &str, plan: Vec<(NodeId, Vec<PathData>)>) -> Result<Value> {
    if plan.is_empty() {
        return Ok(json!({ "ids": [] }));
    }
    let ids = s.edit(label, |d, sel| {
        let mut all = vec![];
        let mut cut = Beside::replacing(d, &plan.iter().map(|(id, _)| *id).collect::<Vec<_>>());
        for (id, pieces) in plan {
            all.extend(replace_with_pieces(d, &mut cut, id, pieces)?);
        }
        cut.finish(d)?;
        sel.set(all.iter().copied());
        Ok(all)
    })?;
    Ok(ids_json(&ids))
}

pub(super) fn erase_segments(s: &mut Session, p: &Value) -> Result<Value> {
    const C: &str = "path.eraseSegments";
    let pts = points_param(p, "points", C)?;
    let w = number_or(p, "width", 8.0, C)?;
    if !(w.is_finite() && w > 0.0) {
        return Err(bad(C, "width must be positive"));
    }
    let st = s.doc()?;
    let mut plan = vec![];
    for id in target_paths(&st.doc, &st.selection, poly_bounds(&pts, w)) {
        let (pd, _) = path_of(&st.doc, id)?;
        if let Some(pieces) = erase_outline(&pd, w / 2.0, &|q| dist_to_polyline(&pts, q) <= w / 2.0) {
            plan.push((id, pieces));
        }
    }
    apply_plan(s, "Path Eraser", plan)
}