Merge pull request #7382 from ncic/pencil-alt-close-straight

Pencil: a closed stroke closes with a straight segment

crates/engine/src/cmd/draw2/freehand.rs

@@ -11,7 +11,9 @@ use super::{
 // ---------- Pencil / Paintbrush ----------
 
 /// Fit a freehand polyline: drop jitter, build a spline through the samples (sharp turns stay
-/// corners) and simplify it to `tol`.
+/// corners) and simplify it to `tol`. A closed stroke is fitted as the open one is and closed by a
+/// straight segment from its end back to its start: fitting round the gap would curve that segment
+/// on from both ends, past them and back.
 fn fit_freehand(pts: &[Point], tol: f64, closed: bool) -> SubPath {
     let min = (tol * 0.3).max(vectorcraft_tools::draw2::MIN_FIT_TOLERANCE * 0.3);
     let (Some(&p0), Some(&pn)) = (pts.first(), pts.last()) else { return SubPath::new(vec![], closed) };
@@ -41,15 +43,26 @@ fn fit_freehand(pts: &[Point], tol: f64, closed: bool) -> SubPath {
             (kept[i], corner)
         })
         .collect();
-    let sp = vectorcraft_tools::draw2::catmull_rom(&marked, closed);
+    let sp = vectorcraft_tools::draw2::catmull_rom(&marked, false);
     if sp.anchors.len() < 3 {
-        return sp;
+        // Two anchors closed would run back over the line itself.
+        return SubPath::new(sp.anchors, closed && n > 2);
     }
     let fitted = po::simplify_with(
         &PathData::single(sp.clone()),
         &SimplifyOptions { tolerance: tol, corner_angle_deg: 60.0, straight_lines: false, ..Default::default() },
     );
-    fitted.subpaths.into_iter().next().filter(|s| s.anchors.len() >= 2).unwrap_or(sp)
+    let mut anchors = fitted.subpaths.into_iter().next().filter(|s| s.anchors.len() >= 2).unwrap_or(sp).anchors;
+    if closed {
+        // No handle on either side of the closing segment.
+        if let Some(l) = anchors.last_mut() {
+            l.h_out = l.p;
+        }
+        if let Some(f) = anchors.first_mut() {
+            f.h_in = f.p;
+        }
+    }
+    SubPath::new(anchors, closed)
 }
 
 /// The path of a freehand stroke: fitted at `tol` ([`fit_freehand`]), or with no `tol` the points

crates/engine/src/tests/draw2.rs

@@ -184,6 +184,25 @@ fn pencil_alt_closes_path() {
     assert!(ps[0].1.is_closed());
 }
 
+/// A Pencil stroke drawn as a dome and closed with Alt at the release closes with a straight segment
+/// across the bottom, from where the stroke ends to where it starts: the path stays within where the
+/// pen went, rather than curving on past both ends and back like a hat's brim.
+#[test]
+fn pencil_alt_closes_a_stroke_straight_back_to_its_start() {
+    let mut s = session();
+    let pts: Vec<(f64, f64)> =
+        (0..=60).map(|i| f64::from(i) * std::f64::consts::PI / 60.0).map(|a| (300.0 - 150.0 * a.cos(), 400.0 - 200.0 * a.sin())).collect();
+    drag(&mut s, "pencil", &pts, Mods { alt: true, ..Default::default() });
+    let ps = paths(&s);
+    let sp = &ps[0].1.subpaths[0];
+    assert!(sp.closed);
+    let b = ps[0].1.bounds().unwrap();
+    assert!(b.x0 > 149.5 && b.x1 < 450.5 && b.y1 < 400.5, "within the stroke: {b:?}");
+    let (first, last) = (sp.anchors.first().unwrap(), sp.anchors.last().unwrap());
+    assert!(first.p.distance(Point::new(150.0, 400.0)) < 1e-6 && last.p.distance(Point::new(450.0, 400.0)) < 1e-6, "{first:?} {last:?}");
+    assert_eq!((last.h_out, first.h_in), (last.p, first.p), "a straight closing segment");
+}
+
 /// #3799: with Shift held, a wavy Pencil drag draws one straight segment at 45° steps from the
 /// Constrain Angle (here 30°: a drag at about 60° comes out at 75°).
 #[test]