Shape Builder: the gaps closed paths enclose are regions (#1691)

With Separations Preview on, the renderer copied every node of the
document in every frame and separated each of its colors again. With
Overprint Preview on, it copied each object with an overprinting fill
or stroke in every frame, with the groups and layers that hold it. The
copies were new Arcs, so the geometry, stroke outline and raster
caches missed for each of them in every frame. In a release build,
drawing a 2880x1800 frame of a 50,000-path document again with the
same view and Separations Preview took 795 to 908 ms.

The renderer now keeps the art it prepared and what it was made from,
and in the next frame it uses that art again for each layer, symbol
art and member that has not changed. Only the objects that changed are
prepared again, with the layers and groups that hold them. All of the
art is prepared again when Discard White Overprint changes and, with
Separations Preview, when the plates shown, the proof setup, the
swatches, the Spot Colors option or the color settings change or a
profile is registered (cms::profiles_generation). The renderer now
draws that frame again in 98 to 107 ms, with the same pixels.

Docs: docs/target-app-parity.md.

Cargo.lock

@@ -4976,6 +4976,7 @@ dependencies = [
  "vectorcraft-three-d",
  "vectorcraft-tools",
  "wat",
+ "web-time",
 ]
 
 [[package]]

crates/color/src/cms/mod.rs

@@ -13,7 +13,7 @@ pub mod generic;
 pub mod icc;
 pub mod lab;
 
-use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex, OnceLock, RwLock};
 
 use serde::{Deserialize, Serialize};
@@ -165,6 +165,8 @@ fn generic() -> Arc<GenericCmyk> {
 }
 
 static USER: RwLock<Vec<Arc<IccProfile>>> = RwLock::new(Vec::new());
+/// Counts the profiles [`register_icc`] has registered ([`profiles_generation`]).
+static PROFILES_GENERATION: AtomicU64 = AtomicU64::new(0);
 
 fn builtin_rgb_cache(name: &str) -> Option<Arc<IccProfile>> {
     static CACHE: Mutex<Vec<Arc<IccProfile>>> = Mutex::new(Vec::new());
@@ -251,9 +253,17 @@ pub fn register_icc(bytes: &[u8], name: Option<String>) -> Result<ProfileInfo, C
     u.push(Arc::new(p));
     drop(u);
     clear_proof_cache();
+    PROFILES_GENERATION.fetch_add(1, Ordering::Relaxed);
     Ok(info)
 }
 
+/// A number that changes whenever [`register_icc`] registers a profile: conversions through a
+/// profile looked up by name, such as those of a [`ProofTarget::Cmyk`] proof, give the same colors
+/// as long as the number stays the same.
+pub fn profiles_generation() -> u64 {
+    PROFILES_GENERATION.load(Ordering::Relaxed)
+}
+
 /// Profile `name` as an ICC file to embed in an export: any RGB or CMYK profile of [`profiles`]
 /// (by its current or legacy name), or [`GRAY`]. Built-in profiles are written in code from the
 /// CMS: the RGB spaces from their primaries, the CMYK spaces as lookup tables sampled from their

crates/engine/src/cmd/shaper.rs

@@ -90,9 +90,13 @@ fn map_of(src: &[Arc<Node>]) -> Result<BuilderMap> {
     }
     let arrangement = po::shape_builder(&shapes, true);
     let bounded = |pieces: Vec<po::Shape>| pieces.into_iter().filter_map(|p| p.path.bounds().map(|b| (p, b))).collect();
+    // A Shaper Group's faces are what its shapes fill and what its open paths enclose: the gaps
+    // closed paths enclose are the Shape Builder's only.
+    let open = po::has_open_path(&shapes);
     let regions = arrangement
         .regions
         .into_iter()
+        .filter(|r| open || !r.sources.is_empty())
         .filter_map(|r| {
             let bounds = r.path.bounds()?;
             let path = r.path.to_bezpath();

crates/engine/src/tests_build.rs

@@ -152,6 +152,39 @@ fn shape_builder_regions_query() {
     assert!(regs.iter().any(|x| x["sources"].as_array().unwrap().len() == 2));
 }
 
+/// #1691: four circles in a 2×2 grid, each touching its neighbours, enclose a diamond nothing
+/// fills. It is a region, and a drag from a circle into it merges the two.
+#[test]
+fn shape_builder_merges_the_gap_touching_circles_enclose() {
+    let mut s = session();
+    let mut circles = vec![];
+    for (x, y) in [(0.0, 0.0), (100.0, 0.0), (0.0, 100.0), (100.0, 100.0)] {
+        let r = s.execute("shape.ellipse", &json!({"x": x, "y": y, "width": 100, "height": 100})).unwrap();
+        circles.push(NodeId(r["id"].as_u64().unwrap()));
+    }
+    set_fill(&mut s, circles[0], Color::rgb(1.0, 0.0, 0.0));
+    s.execute("select.set", &json!({"ids": circles.iter().map(|i| i.0).collect::<Vec<_>>()})).unwrap();
+    let r = s.execute("shapeBuilder.regions", &json!({})).unwrap();
+    let regs = r["regions"].as_array().unwrap();
+    assert_eq!(regs.len(), 5, "{regs:?}");
+    assert_eq!(regs.iter().filter(|x| x["sources"].as_array().unwrap().is_empty()).count(), 1, "the diamond");
+    let r = s.execute("shapeBuilder.merge", &json!({"points": [[50, 50], [100, 100]]})).unwrap();
+    assert_eq!(r["regions"], 2);
+    let out = ids(&r);
+    assert_eq!(out.len(), 4, "the merged shape and the three other circles");
+    let merged = NodeId(r["merged"].as_u64().unwrap());
+    // A circle (its Bézier outline: 7,854.9) and the diamond between the four (2,145.1).
+    assert!((area(&s, merged) - 10000.0).abs() < 10.0, "{}", area(&s, merged));
+    assert_eq!(node(&s, merged).appearance.fill_paint(), Paint::solid(Color::rgb(1.0, 0.0, 0.0)), "the look of the circle the drag began on");
+    assert_eq!(layer_children(&s), 4);
+    // A click in the diamond alone makes it a shape of its own.
+    s.execute("edit.undo", &json!({})).unwrap();
+    s.execute("select.set", &json!({"ids": circles.iter().map(|i| i.0).collect::<Vec<_>>()})).unwrap();
+    let r = s.execute("shapeBuilder.merge", &json!({"points": [[100, 100]]})).unwrap();
+    assert_eq!(ids(&r).len(), 5);
+    assert!((area(&s, NodeId(r["merged"].as_u64().unwrap())) - 2146.0).abs() < 10.0);
+}
+
 #[test]
 fn shape_builder_tool_drives_the_command() {
     let mut s = session();

crates/engine/tests/color_settings.rs

@@ -56,6 +56,48 @@ fn legacy_profile_name_resolves_in_commands_and_files() {
     cms::set_active(&before).unwrap();
 }
 
+/// Separations Preview follows the Color Settings and the profiles loaded: a renderer draws a gray
+/// square on the Black plate through the new working CMYK profile, and the four process plates
+/// through a proof profile loaded again under the same name, as a new renderer draws them.
+#[test]
+fn separations_preview_draws_through_new_color_settings() {
+    let _g = settings();
+    let mut s = session();
+    let gray = rect(&mut s, 20.0, 20.0, 160.0, 120.0);
+    exec(&mut s, "paint.setFill", json!({"ids": [gray.0], "color": "#808080"}));
+    // The proof and Overprint Preview options the canvas takes from the view state the
+    // commands set.
+    let canvas = || RenderOptions {
+        proof: vectorcraft_render::proof::active_proof(),
+        overprint_preview: vectorcraft_render::proof::overprint_preview_on(),
+        background: Some([255, 255, 255, 255]),
+        ..Default::default()
+    };
+    let frame = |r: &mut Renderer, s: &Session| r.render(&s.doc().unwrap().doc, 400, 300, Affine::IDENTITY, &canvas()).pixels;
+    exec(&mut s, "view.separationsPreview", json!({"only": "Black"}));
+    let mut r = Renderer::new();
+    let before = frame(&mut r, &s);
+    let old = cms::active_settings();
+    s.execute("edit.colorSettings", &json!({"cmyk": cms::DEVICE_CMYK})).unwrap();
+    let fresh = frame(&mut Renderer::new(), &s);
+    let warm = frame(&mut r, &s);
+    cms::set_active(&old).unwrap();
+    assert!(fresh != before, "the new profile changes the plate");
+    assert!(warm == fresh);
+    let name = "Separations Proof CMYK";
+    cms::register_icc(&cms::icc_bytes(cms::GENERIC_CMYK).unwrap(), Some(name.into())).unwrap();
+    exec(&mut s, "view.proofSetup", json!({"target": format!("cmyk:{name}")}));
+    exec(&mut s, "view.separationsPreview", json!({"plates": ["Cyan", "Magenta", "Yellow", "Black"]}));
+    let before = frame(&mut r, &s);
+    cms::register_icc(&cms::icc_bytes(cms::DEVICE_CMYK).unwrap(), Some(name.into())).unwrap();
+    let fresh = frame(&mut Renderer::new(), &s);
+    let warm = frame(&mut r, &s);
+    exec(&mut s, "view.proofSetup", json!({"target": "workingCmyk"}));
+    exec(&mut s, "view.separationsPreview", json!({"on": false}));
+    assert!(fresh != before, "the profile loaded again changes the plates");
+    assert!(warm == fresh);
+}
+
 /// Raster effects follow the Color Settings: a blurred CMYK fill, and a white square's drop shadow
 /// in a CMYK color, are drawn again through the new working CMYK profile, in a frame drawn while
 /// interacting (as during a dialog's preview) and after it.

crates/pathops/src/lib.rs

@@ -20,7 +20,7 @@ pub use edit::{
 };
 pub use offset::{Cap, Join, offset_path, outline_stroke, stroke_region};
 pub use pathfinder::{FaceMerger, PathfinderOp, Region, Shape, merge_regions, pathfinder, region_at, regions};
-pub use planar::{BuilderArrangement, SHAPE_BUILDER_MAX_SEGMENTS, cut_out, encloses_area, interior_point, live_paint, shape_builder};
+pub use planar::{BuilderArrangement, SHAPE_BUILDER_MAX_SEGMENTS, cut_out, encloses_area, has_open_path, interior_point, live_paint, shape_builder};
 
 /// Errors from fallible operations.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, thiserror::Error)]

crates/pathops/src/pathfinder.rs

@@ -102,7 +102,7 @@ pub fn pathfinder(op: PathfinderOp, shapes: &[Shape]) -> Vec<Shape> {
     }
     // Open paths are cutting edges for Divide; the filled-only operations keep their
     // implicit closure. Reuse Shape Builder's bounded planar map and its fallback.
-    if op == PathfinderOp::Divide && shapes.iter().flat_map(|s| &s.path.subpaths).any(|sp| !sp.closed && sp.anchors.len() >= 2) {
+    if op == PathfinderOp::Divide && crate::has_open_path(shapes) {
         return crate::shape_builder(shapes, false)
             .regions
             .into_iter()
@@ -298,21 +298,22 @@ pub fn merge_regions(regions: &[&Region]) -> PathData {
 /// outlines ([`merge_regions`]) could leave those edges in, as a hairline gap or a spur, where
 /// neighbouring faces' outlines had been refit apart. Shapes with open paths (faces lines cut, as
 /// [`shape_builder`](crate::shape_builder) gives them) merge in their planar map the same way
-/// (#893). Either falls back to [`merge_regions`] when it can't place a face.
+/// (#893), and so do faces with a gap closed paths enclose, which no shape covers (#1691). Either
+/// falls back to [`merge_regions`] when it can't place a face.
 pub struct FaceMerger {
     /// The arrangement (`None`: open paths, or the sweep failed) and the number of shapes.
     arr: Option<Arrangement>,
     shapes: usize,
-    /// With open paths, the shapes, and their planar map once a merge has needed it.
+    /// The shapes, and their planar map once a merge has needed it (open paths, or a gap).
     lines: Option<(Vec<Shape>, std::cell::OnceCell<Option<crate::planar::Map>>)>,
 }
 
 impl FaceMerger {
     pub fn new(shapes: &[Shape]) -> Self {
-        let has_open = shapes.iter().flat_map(|s| &s.path.subpaths).any(|sp| !sp.closed && sp.anchors.len() >= 2);
+        let has_open = crate::has_open_path(shapes);
         // The Shape Builder's faces come from the planar map only up to its cap.
         let segments: usize = shapes.iter().flat_map(|s| &s.path.subpaths).map(|sp| sp.segment_count()).sum();
-        let lines = (has_open && segments <= crate::SHAPE_BUILDER_MAX_SEGMENTS).then(|| (shapes.to_vec(), std::cell::OnceCell::new()));
+        let lines = (segments <= crate::SHAPE_BUILDER_MAX_SEGMENTS).then(|| (shapes.to_vec(), std::cell::OnceCell::new()));
         Self { arr: if has_open { None } else { arrangement(shapes) }, shapes: shapes.len(), lines }
     }
 
@@ -321,8 +322,8 @@ impl FaceMerger {
         self.exact(faces).or_else(|| self.planar(faces)).filter(|p| !p.is_empty()).unwrap_or_else(|| merge_regions(faces))
     }
 
-    /// `faces` merged in the planar map of shapes with open paths: each face found again by a
-    /// point inside it, and the result checked to cover what they cover.
+    /// `faces` merged in the planar map of the shapes: each face found again by a point inside
+    /// it, and the result checked to cover what they cover.
     fn planar(&self, faces: &[&Region]) -> Option<PathData> {
         let (shapes, map) = self.lines.as_ref()?;
         let map = map.get_or_init(|| crate::planar::map(shapes)).as_ref()?;
@@ -335,6 +336,10 @@ impl FaceMerger {
     }
 
     fn exact(&self, faces: &[&Region]) -> Option<PathData> {
+        // A gap no shape covers is no face of the arrangement: it merges in the planar map.
+        if faces.iter().any(|r| r.sources.is_empty()) {
+            return None;
+        }
         let arr = self.arr.as_ref()?;
         // Each face by its coverage and a point inside it.
         let mut picks: Vec<(Vec<bool>, Point)> = Vec::with_capacity(faces.len());

crates/pathops/src/planar.rs

@@ -307,8 +307,9 @@ pub fn live_paint(shapes: &[Shape]) -> (Vec<Region>, Vec<Shape>) {
     build(shapes).unwrap_or_default()
 }
 
-/// Most segments the Shape Builder sweeps with open paths as edges: the planar map costs far more
-/// than the filled areas' arrangement, so past this only the filled areas count.
+/// Most segments the Shape Builder sweeps into its planar map (open paths as edges, the gaps closed
+/// paths enclose, outline edges): the map costs far more than the filled areas' arrangement, so past
+/// this only the filled areas count.
 pub const SHAPE_BUILDER_MAX_SEGMENTS: usize = 4096;
 
 /// The Shape Builder's arrangement: see [`shape_builder`].
@@ -322,20 +323,26 @@ pub struct BuilderArrangement {
     pub edges: Vec<Shape>,
 }
 
+/// Does any of `shapes` have an open subpath (a cutting edge for the Shape Builder)?
+pub fn has_open_path(shapes: &[Shape]) -> bool {
+    shapes.iter().flat_map(|s| &s.path.subpaths).any(|sp| !sp.closed && sp.anchors.len() >= 2)
+}
+
 /// Shape Builder regions of `shapes` (back → front), the pieces of their open paths and, with
 /// `edges`, the pieces of their outlines (what erasing an edge deletes).
 ///
-/// Closed paths bound regions with their filled areas, as in [`regions`](crate::regions). Open
-/// paths (the caller closes the ones whose fill should count) are cutting edges: a line across a
-/// shape splits it, lines around an area enclose a region nothing fills (empty `sources`), and each
-/// path with no closed subpath comes back cut wherever another path meets it, as pieces keyed by
-/// its index in `shapes`. Outlines are cut the same way. With no open path, more than
+/// Closed paths bound regions with their filled areas, as in [`regions`](crate::regions), and the
+/// gaps they enclose that nothing fills are regions too (empty `sources`), such as the middle of
+/// four circles that touch (#1691). Open paths (the caller closes the ones whose fill should count)
+/// are cutting edges: a line across a shape splits it, lines around an area enclose a region
+/// nothing fills, and each path with no closed subpath comes back cut wherever another path meets
+/// it, as pieces keyed by its index in `shapes`. Outlines are cut the same way. With more than
 /// [`SHAPE_BUILDER_MAX_SEGMENTS`] segments or a map that can't be built, only the filled areas
 /// count and there are no pieces.
 pub fn shape_builder(shapes: &[Shape], edges: bool) -> BuilderArrangement {
-    let has_open = shapes.iter().flat_map(|s| &s.path.subpaths).any(|sp| !sp.closed && sp.anchors.len() >= 2);
+    let has_open = has_open_path(shapes);
     let segments: usize = shapes.iter().flat_map(|s| &s.path.subpaths).map(|sp| sp.segment_count()).sum();
-    let planar = ((has_open || edges) && segments <= SHAPE_BUILDER_MAX_SEGMENTS)
+    let planar = (segments <= SHAPE_BUILDER_MAX_SEGMENTS)
         .then(|| {
             let keyed: Vec<Shape> = shapes.iter().enumerate().map(|(i, s)| Shape::new(s.path.clone(), s.rule, i as u64)).collect();
             live_paint(&keyed)
@@ -346,11 +353,15 @@ pub fn shape_builder(shapes: &[Shape], edges: bool) -> BuilderArrangement {
     };
     let is_line = |i: u64| shapes.get(i as usize).is_some_and(|s| !s.path.subpaths.iter().any(|sp| sp.closed));
     let (lines, outline): (Vec<Shape>, Vec<Shape>) = pieces.into_iter().partition(|e| is_line(e.key));
-    BuilderArrangement {
-        regions: if has_open { faces } else { crate::regions(shapes) },
-        lines: if has_open { lines } else { Vec::new() },
-        edges: if edges { outline } else { Vec::new() },
-    }
+    let regions = if has_open {
+        faces
+    } else {
+        // The filled areas from their arrangement, whose faces merge exactly, then the gaps.
+        let mut regions = crate::regions(shapes);
+        regions.extend(faces.into_iter().filter(|f| f.sources.is_empty()));
+        regions
+    };
+    BuilderArrangement { regions, lines: if has_open { lines } else { Vec::new() }, edges: if edges { outline } else { Vec::new() } }
 }
 
 /// Does `sp`, closed, enclose an area (rather than retrace itself)? The Shape Builder closes the
@@ -1182,6 +1193,43 @@ mod tests {
         assert!((regions.iter().map(area).sum::<f64>() - 10000.0).abs() < 1e-6);
     }
 
+    fn circle(cx: f64, cy: f64, r: f64, key: u64) -> Shape {
+        Shape::new(shapes::ellipse(Rect::new(cx - r, cy - r, cx + r, cy + r)), FillRule::NonZero, key)
+    }
+
+    #[test]
+    fn shape_builder_offers_the_gaps_closed_shapes_enclose() {
+        // Four circles in a 2×2 grid, each touching its neighbours (#1691): the four circles and
+        // the diamond between them, which nothing fills.
+        let s = [circle(50.0, 50.0, 50.0, 0), circle(150.0, 50.0, 50.0, 1), circle(50.0, 150.0, 50.0, 2), circle(150.0, 150.0, 50.0, 3)];
+        let regions = shape_builder(&s, false).regions;
+        assert_eq!(regions.len(), 5, "{regions:?}");
+        let gaps: Vec<&Region> = regions.iter().filter(|r| r.sources.is_empty()).collect();
+        assert_eq!(gaps.len(), 1);
+        assert!(gaps[0].contains(Point::new(100.0, 100.0)) && !gaps[0].contains(Point::new(50.0, 50.0)));
+        let diamond = 10000.0 - std::f64::consts::PI * 2500.0;
+        assert!((area(gaps[0]).abs() - diamond).abs() < 0.01 * diamond, "{}", area(gaps[0]));
+        assert_eq!(shape_builder(&s, true).regions, regions, "the outline edges don't change them");
+        // A ring of four bars that overlap at the corners: the eight pieces of the bars and the
+        // square they enclose.
+        let s =
+            [rect(0.0, 0.0, 300.0, 100.0, 0), rect(200.0, 0.0, 300.0, 300.0, 1), rect(0.0, 200.0, 300.0, 300.0, 2), rect(0.0, 0.0, 100.0, 300.0, 3)];
+        let regions = shape_builder(&s, false).regions;
+        assert_eq!(regions.len(), 9, "{regions:?}");
+        let gaps: Vec<&Region> = regions.iter().filter(|r| r.sources.is_empty()).collect();
+        assert_eq!(gaps.len(), 1);
+        assert!((area(gaps[0]).abs() - 10000.0).abs() < 1e-6 && gaps[0].contains(Point::new(150.0, 150.0)));
+        // The gap merges with a bar in the planar map: the bar's piece and the square, no seam.
+        let merger = crate::FaceMerger::new(&s);
+        let bar = regions.iter().find(|r| r.sources == [0] && r.contains(Point::new(150.0, 50.0))).unwrap();
+        let merged = merger.merge(&[bar, gaps[0]]);
+        assert_eq!(merged.subpaths.len(), 1, "{merged:?}");
+        assert!((crate::area(&merged, FillRule::NonZero) - 20000.0).abs() < 1e-6);
+        // Shapes apart or overlapping without a hole enclose no gap.
+        let s = [circle(50.0, 50.0, 50.0, 0), circle(250.0, 50.0, 50.0, 1), rect(80.0, 0.0, 220.0, 60.0, 2)];
+        assert!(shape_builder(&s, false).regions.iter().all(|r| !r.sources.is_empty()));
+    }
+
     #[test]
     fn shape_builder_stays_quick_up_to_its_cap() {
         // A wavy ring of nearly the most segments the map takes, crossed by a few lines.
@@ -1194,6 +1242,10 @@ mod tests {
             })
             .collect();
         let mut s = vec![Shape::new(PathData::single(SubPath::polyline(&ring, true)), FillRule::NonZero, 0)];
+        // Closed paths alone are swept for the gaps they enclose.
+        let started = std::time::Instant::now();
+        assert_eq!(shape_builder(&s, false).regions.len(), 1, "the ring encloses no gap");
+        assert!(started.elapsed().as_secs_f64() < 5.0, "{:?}", started.elapsed());
         for k in 0..4 {
             let y = -60.0 + 40.0 * f64::from(k);
             s.push(line((-150.0, y), (150.0, y + 7.0), 1));

crates/render/src/lib.rs

@@ -490,6 +490,9 @@ pub struct Renderer {
     isolation: Option<(u64, usize, NodeId, Vec<NodeId>)>,
     /// Drawing inside the isolated container or a dimmed object: nothing further dims.
     isolation_settled: bool,
+    /// The art the last frame drew with Overprint Preview or Separations Preview: the next frame
+    /// draws it again for the objects that have not changed ([`proof::prepare`]).
+    proof_art: Option<proof::Prepared>,
 }
 
 /// How deep inline graphics nest (text in a symbol shown inline in text…) before they draw nothing.
@@ -592,6 +595,7 @@ impl Renderer {
             raster: vello_cpu::RasterizerSettings::default(),
             isolation: None,
             isolation_settled: false,
+            proof_art: None,
         }
     }
 
@@ -616,7 +620,7 @@ impl Renderer {
         }
         // The document's own symbols: proofing rewrites the colors and blend modes of their art.
         self.check_symbols(doc);
-        let prepared = proof::prepare(doc, opts);
+        let prepared = proof::prepare(doc, opts, &mut self.proof_art);
         let doc: &Document = &prepared;
         let w = width.clamp(1, u16::MAX as u32) as u16;
         let h = height.clamp(1, u16::MAX as u32) as u16;

crates/render/src/proof.rs

@@ -18,14 +18,15 @@
 //! [`crate::RenderOptions`] with [`active_proof`] and [`overprint_preview_on`].
 
 use std::borrow::Cow;
-use std::sync::RwLock;
+use std::collections::HashMap;
+use std::sync::{Arc, RwLock, Weak};
 
-use vectorcraft_color::Color;
 use vectorcraft_color::cms::{self, Cms, PROCESS_PLATES};
 pub use vectorcraft_color::cms::{Intent, ProofSetup, ProofTarget};
-use vectorcraft_doc::Document;
+use vectorcraft_color::{Color, Swatch, SwatchGroup};
 pub use vectorcraft_doc::inks::{Inks, Link, Plate, inks, map_document_colors, map_node_colors, plates, spot_color};
 use vectorcraft_doc::overprint::multiply_overprints;
+use vectorcraft_doc::{Document, Node, NodeId, Shared};
 
 use crate::RenderOptions;
 
@@ -63,29 +64,164 @@ fn plate_color(doc: &Document, c: &Cms, proof: &ProofSetup, visible: &[String],
     Color::Rgb { r, g, b }
 }
 
-/// The document as it should be drawn for these options (overprints, separations).
-pub(crate) fn prepare<'a>(doc: &'a Document, opts: &RenderOptions) -> Cow<'a, Document> {
-    let seps = opts.proof.as_ref().and_then(|p| p.separations.as_ref().map(|s| (p, s)));
-    let overprint = overprints(opts) && (doc.layers.iter().any(|l| l.has_overprint()) || doc.symbols.iter().any(|s| s.art.has_overprint()));
-    if !overprint && seps.is_none() {
+/// The art a renderer drew with Overprint Preview or Separations Preview, kept for its next frame
+/// ([`prepare`]): the document's layers and symbol art as they were, each beside the art drawn for
+/// it, and what that art was made with. The kept nodes keep their addresses: no other node gets
+/// one of them while they are kept.
+pub(crate) struct Prepared {
+    inputs: Inputs,
+    layers: (Vec<Arc<Node>>, Vec<Arc<Node>>),
+    art: (Vec<Arc<Node>>, Vec<Arc<Node>>),
+}
+
+/// What [`prepare`] reads besides the art.
+#[derive(PartialEq)]
+struct Inputs {
+    discard_white: bool,
+    plates: Option<Plates>,
+}
+
+/// What the colors of Separations Preview's plates are made from ([`plate_color`]).
+struct Plates {
+    /// The proof setup, with the visible plates.
+    proof: ProofSetup,
+    /// The document's swatches, swatch groups and Spot Colors option.
+    swatches: Shared<Vec<Swatch>>,
+    groups: Shared<Vec<SwatchGroup>>,
+    spot_use_lab: bool,
+    /// The color settings, held weakly: no other settings get their address while they are kept.
+    cms: Weak<Cms>,
+    /// [`cms::profiles_generation`].
+    profiles: u64,
+}
+
+impl PartialEq for Plates {
+    fn eq(&self, o: &Self) -> bool {
+        (&self.proof, &self.swatches, &self.groups, self.spot_use_lab, self.profiles)
+            == (&o.proof, &o.swatches, &o.groups, o.spot_use_lab, o.profiles)
+            && Weak::ptr_eq(&self.cms, &o.cms)
+    }
+}
+
+/// What [`prepare`] does to the fills and strokes of each node: overprinting ones multiply
+/// ([`multiply_overprints`]), and with Separations Preview every color shows as the visible plates
+/// print it ([`plate_color`]).
+struct How<'a> {
+    doc: &'a Document,
+    discard_white: bool,
+    /// Separations Preview: the color settings, the proof setup and the visible plates.
+    plates: Option<(&'a Cms, &'a ProofSetup, &'a [String])>,
+}
+
+impl How<'_> {
+    /// Whether [`Self::apply`] can change `n`: with Separations Preview any node, else a node with
+    /// an overprinting fill or stroke.
+    fn changes(&self, n: &Node) -> bool {
+        self.plates.is_some() || n.appearance.items.iter().any(|i| i.overprint())
+    }
+
+    /// Change the fills, strokes and other colors of node `a`, which holds no members.
+    fn apply(&self, a: &mut Arc<Node>) {
+        multiply_overprints(a, self.discard_white);
+        if let Some((c, proof, visible)) = self.plates {
+            map_node_colors(Arc::make_mut(a), &mut |col, sw| plate_color(self.doc, c, proof, visible, col, sw));
+        }
+    }
+}
+
+/// The document as it should be drawn for these options (overprints, separations). `kept` holds
+/// the art of an earlier frame ([`Prepared`]): when that frame's inputs were the same, each layer,
+/// symbol art and member that is still the node its kept art was made from is drawn from that art,
+/// with its `Arc`. `kept` then holds this frame's art, or nothing when neither preview is on.
+pub(crate) fn prepare<'a>(doc: &'a Document, opts: &RenderOptions, kept: &mut Option<Prepared>) -> Cow<'a, Document> {
+    if !overprints(opts) {
+        *kept = None;
         return Cow::Borrowed(doc);
     }
-    let mut d = doc.clone();
-    if overprint {
-        let discard_white = doc.setup.discard_white_overprint;
-        for l in &mut d.layers {
-            multiply_overprints(l, discard_white);
-        }
-        for s in &mut d.symbols {
-            multiply_overprints(&mut s.art, discard_white);
+    let seps = opts.proof.as_ref().and_then(|p| p.separations.as_ref().map(|s| (p, s)));
+    let c = cms::active();
+    let inputs = Inputs {
+        discard_white: doc.setup.discard_white_overprint,
+        plates: seps.map(|(proof, _)| Plates {
+            proof: proof.clone(),
+            swatches: doc.swatches.clone(),
+            groups: doc.swatch_groups.clone(),
+            spot_use_lab: doc.spot_use_lab,
+            cms: Arc::downgrade(&c),
+            profiles: cms::profiles_generation(),
+        }),
+    };
+    let earlier = kept.take().filter(|k| k.inputs == inputs);
+    let how = How { doc, discard_white: inputs.discard_white, plates: seps.map(|(proof, visible)| (&*c, proof, visible.as_slice())) };
+    let none = (vec![], vec![]);
+    let (layers, art) = earlier.as_ref().map_or((&none, &none), |k| (&k.layers, &k.art));
+    let made_layers = prepare_list(&doc.layers, &layers.0, &layers.1, &how);
+    let symbol_art: Vec<Arc<Node>> = doc.symbols.iter().map(|s| s.art.clone()).collect();
+    let made_art = prepare_list(&symbol_art, &art.0, &art.1, &how);
+    let same = |made: &[Arc<Node>], from: &[Arc<Node>]| made.iter().zip(from).all(|(a, b)| Arc::ptr_eq(a, b));
+    let out = if same(&made_layers, &doc.layers) && same(&made_art, &symbol_art) {
+        Cow::Borrowed(doc)
+    } else {
+        let mut d = doc.clone();
+        d.layers.clone_from(&made_layers);
+        for (s, a) in d.symbols.iter_mut().zip(&made_art) {
+            s.art = a.clone();
         }
+        Cow::Owned(d)
+    };
+    *kept = Some(Prepared { inputs, layers: (doc.layers.clone(), made_layers), art: (symbol_art, made_art) });
+    out
+}
+
+/// `nodes` as drawn with `how` ([`prepare_node`]), each against its earlier version in `was`: the
+/// node at its place when that node has its id, else the node with its id. `made` holds the art
+/// drawn for `was`, place by place.
+fn prepare_list(nodes: &[Arc<Node>], was: &[Arc<Node>], made: &[Arc<Node>], how: &How) -> Vec<Arc<Node>> {
+    let mut places: Option<HashMap<NodeId, usize>> = None;
+    nodes
+        .iter()
+        .enumerate()
+        .map(|(i, n)| {
+            let at = match was.get(i) {
+                Some(w) if w.id == n.id => Some(i),
+                _ => places.get_or_insert_with(|| was.iter().enumerate().map(|(j, w)| (w.id, j)).collect()).get(&n.id).copied(),
+            };
+            prepare_node(n, at.and_then(|j| Some((was.get(j)?, made.get(j)?))), how)
+        })
+        .collect()
+}
+
+/// `n` as drawn with `how`: the art of `earlier` (a node and the art drawn for it) when that art
+/// was made from `n` itself; else a copy of `n` with its own fills and strokes changed
+/// ([`How::apply`]) and its members prepared against those of `earlier` ([`prepare_list`]), or `n`
+/// itself when neither changes.
+fn prepare_node(n: &Arc<Node>, earlier: Option<(&Arc<Node>, &Arc<Node>)>, how: &How) -> Arc<Node> {
+    if let Some((was, made)) = earlier
+        && Arc::ptr_eq(was, n)
+    {
+        return made.clone();
     }
-    if let Some((proof, visible)) = seps {
-        let c = cms::active();
-        let src = doc.clone();
-        map_document_colors(&mut d, &mut |col, sw| plate_color(&src, &c, proof, visible, col, sw));
+    let members = n.children().map(|ch| {
+        let (was, made) = earlier.and_then(|(w, m)| Some((w.children()?.as_slice(), m.children()?.as_slice()))).unwrap_or_default();
+        prepare_list(ch, was, made, how)
+    });
+    let same_members = match (&members, n.children()) {
+        (Some(m), Some(ch)) => m.iter().zip(ch).all(|(a, b)| Arc::ptr_eq(a, b)),
+        _ => true,
+    };
+    if same_members && !how.changes(n) {
+        return n.clone();
     }
-    Cow::Owned(d)
+    let mut own = Node::clone(n);
+    if let Some(ch) = own.children_mut() {
+        ch.clear();
+    }
+    let mut a = Arc::new(own);
+    how.apply(&mut a);
+    if let (Some(m), Some(ch)) = (members, Arc::make_mut(&mut a).children_mut()) {
+        *ch = m;
+    }
+    a
 }
 
 /// Soft-proof the rendered (premultiplied RGBA8) pixels in place.

crates/render/src/tests_memory.rs

@@ -1136,6 +1136,149 @@ fn rasters_follow_the_view_options() {
     draws_as_new(&mut d, &isolated, &on_white, unchanged);
 }
 
+/// A document for the proof previews: a cyan square, a magenta circle over it whose black stroke
+/// overprints, a white square over the cyan one that overprints, a blurred rectangle in spot color
+/// `Spot`, and an instance of symbol `S`, a group holding a yellow square.
+fn proof_doc() -> Document {
+    use vectorcraft_geom::shapes::{ellipse, rectangle};
+    let mut d = Document::new(200.0, 100.0);
+    let orange = Color::cmyk(0.0, 0.6, 1.0, 0.0);
+    d.swatches.push(vectorcraft_color::Swatch { name: "Spot".into(), paint: Paint::solid(orange), global: true, spot: true });
+    let cyan = filled(&mut d, rectangle(Rect::new(10.0, 10.0, 90.0, 90.0)), Paint::solid(Color::cmyk(1.0, 0.0, 0.0, 0.0)), vec![]);
+    let black = Paint::solid(Color::cmyk(0.0, 0.0, 0.0, 1.0));
+    let ring = vectorcraft_doc::Appearance::basic(Paint::solid(Color::cmyk(0.0, 1.0, 0.0, 0.0)), black, 4.0);
+    let mut circle = Node::path(d.alloc_id(), ellipse(Rect::new(40.0, 20.0, 100.0, 80.0)), ring);
+    circle.appearance.stroke_mut().unwrap().overprint = true;
+    let mut white = filled(&mut d, rectangle(Rect::new(20.0, 30.0, 40.0, 50.0)), Paint::solid(Color::cmyk(0.0, 0.0, 0.0, 0.0)), vec![]);
+    white.appearance.fill_mut().unwrap().overprint = true;
+    let spot = Paint::Solid { color: orange, swatch: Some("Spot".into()), tint: 1.0 };
+    let blur = effect("blur.gaussian", serde_json::json!({"radius": 1.0}));
+    let spot = filled(&mut d, rectangle(Rect::new(110.0, 10.0, 150.0, 50.0)), spot, vec![blur]);
+    let yellow = filled(&mut d, rectangle(Rect::new(-10.0, -10.0, 10.0, 10.0)), Paint::solid(Color::cmyk(0.0, 0.0, 1.0, 0.0)), vec![]);
+    let art = Node::group(d.alloc_id(), vec![Arc::new(yellow)]);
+    d.symbols.push(vectorcraft_doc::Symbol { name: "S".into(), art: Arc::new(art) });
+    let instance = Node::new(d.alloc_id(), NodeKind::SymbolInstance { symbol: "S".into(), xf: Affine::translate((175.0, 75.0)) });
+    with_art(d, vec![cyan, circle, white, spot, instance])
+}
+
+/// Overprint Preview, and Separations Preview showing `plates`, which turns Overprint Preview on
+/// too (as the canvas draws them).
+fn proof_views(plates: &[&str]) -> (RenderOptions, RenderOptions) {
+    let overprint = RenderOptions { overprint_preview: true, ..Default::default() };
+    let proof = proof::ProofSetup { separations: Some(plates.iter().map(|p| p.to_string()).collect()), ..Default::default() };
+    (overprint.clone(), RenderOptions { proof: Some(proof), ..overprint })
+}
+
+/// [`proof_views`] with every plate of [`proof_doc`].
+fn every_plate() -> (RenderOptions, RenderOptions) {
+    proof_views(&["Cyan", "Magenta", "Yellow", "Black", "Spot"])
+}
+
+/// With Overprint Preview or Separations Preview on, a second frame of an unchanged document draws
+/// the art the first prepared for the preview: it makes no geometry entries. After an object
+/// moves, a frame makes them for the object and its layer only. A frame drawn with neither preview
+/// lets go of the art, and each frame drawn with a preview draws what a new renderer draws.
+#[test]
+fn proof_previews_keep_their_art_between_frames() {
+    let _fonts = fonts_steady();
+    let d = proof_doc();
+    let (overprint, separations) = every_plate();
+    let frame = |r: &mut Renderer, d: &Document, opts: &RenderOptions| r.render(d, 200, 100, Affine::IDENTITY, opts).pixels;
+    let geometry = |r: &Renderer| r.geom.keys().copied().collect::<std::collections::HashSet<_>>();
+    for opts in [&overprint, &separations] {
+        let mut r = Renderer::new();
+        let first = frame(&mut r, &d, opts);
+        let kept = geometry(&r);
+        assert!(frame(&mut r, &d, opts) == first);
+        assert_eq!(geometry(&r), kept, "the second frame makes no geometry entries");
+        // The cyan square moves 5 pt right.
+        let mut moved = d.clone();
+        let square = moved.layers[0].children().unwrap()[0].id;
+        moved.node_mut(square).unwrap().transform(Affine::translate((5.0, 0.0)), false);
+        assert!(frame(&mut r, &moved, opts) == frame(&mut Renderer::new(), &moved, opts));
+        assert_eq!(geometry(&r).difference(&kept).count(), 2, "the square and its layer");
+        frame(&mut r, &moved, &RenderOptions::default());
+        assert!(r.proof_art.is_none(), "drawn without the previews, the renderer keeps no art for them");
+    }
+}
+
+/// With Overprint Preview or Separations Preview on, a renderer draws what a new renderer draws
+/// after a change to the art or to what the previews read: an object recolored, Discard White
+/// Overprint turned off, a symbol's art recolored (its instance shows the plates of the new art),
+/// the spot color redefined, a spot color in a color group redefined, the Spot Colors option set
+/// to CMYK values, a plate hidden, Simulate Paper Color, another proof profile, and one preview
+/// after the other.
+#[test]
+fn proof_previews_draw_changes_as_a_new_renderer_does() {
+    let _fonts = fonts_steady();
+    let (overprint, separations) = every_plate();
+    let unchanged = |_: &mut Document| {};
+    let recolor_square = |d: &mut Document| {
+        let square = d.layers[0].children().unwrap()[0].id;
+        d.node_mut(square).unwrap().appearance.set_fill(Paint::solid(Color::cmyk(0.0, 0.0, 1.0, 0.0)));
+    };
+    let recolor_symbol = |d: &mut Document| {
+        let mut art = (*d.symbols[0].art).clone();
+        if let Some(square) = art.children_mut().and_then(|c| c.first_mut()) {
+            Arc::make_mut(square).appearance.set_fill(Paint::solid(Color::cmyk(1.0, 0.0, 0.0, 0.0)));
+        }
+        d.symbols[0].art = Arc::new(art);
+    };
+    for opts in [&overprint, &separations] {
+        draws_as_new(&mut proof_doc(), opts, opts, recolor_square);
+        draws_as_new(&mut proof_doc(), opts, opts, |d| d.setup.discard_white_overprint = false);
+    }
+    draws_as_new(&mut proof_doc(), &separations, &separations, recolor_symbol);
+    draws_as_new(&mut proof_doc(), &separations, &separations, |d| {
+        if let Some(s) = d.swatch_mut("Spot") {
+            s.paint = Paint::solid(Color::cmyk(1.0, 0.0, 0.0, 0.0));
+        }
+    });
+    // A square in spot color `Lab Spot`, defined in Lab in a color group, on its own plate.
+    let lab_doc = || {
+        let mut d = proof_doc();
+        let lab = Color::lab(50.0, 60.0, 40.0);
+        let swatch = vectorcraft_color::Swatch { name: "Lab Spot".into(), paint: Paint::solid(lab), global: true, spot: true };
+        d.swatch_groups.push(vectorcraft_color::SwatchGroup { name: "Lab".into(), swatches: vec![swatch] });
+        let fill = Paint::Solid { color: lab, swatch: Some("Lab Spot".into()), tint: 1.0 };
+        let square = filled(&mut d, vectorcraft_geom::shapes::rectangle(Rect::new(115.0, 60.0, 155.0, 95.0)), fill, vec![]);
+        with_art(d, vec![square])
+    };
+    let lab_plate = proof_views(&["Cyan", "Magenta", "Yellow", "Black", "Lab Spot"]).1;
+    draws_as_new(&mut lab_doc(), &lab_plate, &lab_plate, |d| {
+        if let Some(s) = d.swatch_mut("Lab Spot") {
+            s.paint = Paint::solid(Color::lab(70.0, -40.0, 30.0));
+        }
+    });
+    draws_as_new(&mut lab_doc(), &lab_plate, &lab_plate, |d| d.spot_use_lab = false);
+    let hidden = proof_views(&["Magenta", "Yellow", "Black", "Spot"]).1;
+    draws_as_new(&mut proof_doc(), &separations, &hidden, unchanged);
+    let with = |f: fn(&mut proof::ProofSetup)| {
+        let mut opts = separations.clone();
+        if let Some(p) = &mut opts.proof {
+            f(p);
+        }
+        opts
+    };
+    draws_as_new(&mut proof_doc(), &separations, &with(|p| p.simulate_paper = true), unchanged);
+    let device = with(|p| p.target = proof::ProofTarget::Cmyk(vectorcraft_color::cms::DEVICE_CMYK.into()));
+    draws_as_new(&mut proof_doc(), &separations, &device, unchanged);
+    let cyan = proof_views(&["Cyan"]).1;
+    draws_as_new(&mut proof_doc(), &overprint, &cyan, unchanged);
+    draws_as_new(&mut proof_doc(), &cyan, &overprint, unchanged);
+    // On the Yellow plate the instance is solid while its art is yellow, and blank once it is cyan.
+    let yellow = proof_views(&["Yellow"]).1;
+    let mut d = proof_doc();
+    let mut r = Renderer::new();
+    let instance = |r: &mut Renderer, d: &Document| {
+        let pixels = r.render(d, 200, 100, Affine::IDENTITY, &yellow).pixels;
+        Rendered { width: 200, height: 100, pixels }.pixel(175, 75)
+    };
+    assert_eq!(instance(&mut r, &d), [0, 0, 0, 255]);
+    recolor_symbol(&mut d);
+    assert_eq!(instance(&mut r, &d), [255, 255, 255, 255]);
+}
+
 /// A thumbnail of an object under a filter that treats color channels apart (Color Halftone) is
 /// made again when the document's color mode changes: CMYK documents screen ink channels, RGB
 /// documents light ones.

crates/ui-egui/Cargo.toml

@@ -33,6 +33,11 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 log = { workspace = true }
 
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+# `now_ms` (src/lib.rs) reads the page's `performance.now()` with this crate in the web build. It is
+# MIT OR Apache-2.0 and already in the build through eframe.
+web-time = "1"
+
 [dev-dependencies]
 egui_kittest = { workspace = true, features = ["wgpu", "snapshot"] }
 vectorcraft-testkit = { workspace = true }

crates/ui-egui/src/canvas.rs

@@ -153,6 +153,11 @@ pub fn fit(app: &mut VectorcraftApp, how: &str) {
 pub fn show(app: &mut VectorcraftApp, ui: &mut Ui) {
     let t = Tokens::get(ui.ctx());
     let full = ui.available_rect_before_wrap();
+    // `hidden_chars` holds the marks Show Hidden Characters kept and the text nodes they were laid
+    // out from. Only the assignment right before the overlay call below puts them back. A frame
+    // that does not draw the overlay drops them, for example with the option off, with the edges
+    // hidden, on the Home screen or with no document open.
+    let hidden_chars = std::mem::take(&mut app.canvas.hidden_chars);
     // A document that opened, closed or became active since Home was chosen replaces it.
     if app.ui.home.is_some_and(|k| k != crate::menus::home_key(app)) {
         app.ui.home = None;
@@ -438,6 +443,7 @@ pub fn show(app: &mut VectorcraftApp, ui: &mut Ui) {
             thread_overlay(app, &painter, &xf);
         }
         if app.ui.view.hidden_chars {
+            app.canvas.hidden_chars = hidden_chars;
             hidden_chars_overlay(app, &painter, &xf);
         }
     }
@@ -1530,8 +1536,8 @@ fn hidden_chars_overlay(app: &mut VectorcraftApp, p: &egui::Painter, xf: &Xf) {
     let color = Color32::from_rgb(0x4f, 0x9d, 0xff);
     let font = egui::FontId::proportional(((10.0 * xf.zoom) as f32).clamp(7.0, 18.0));
     let kept = &mut app.canvas.hidden_chars;
-    // `last` holds the marks of the last frame that showed them. The marks of the objects this
-    // frame doesn't draw are dropped at the end.
+    // `last` holds the marks of the last frame. The marks of the objects this frame doesn't draw
+    // are dropped at the end.
     let mut last = std::mem::take(&mut kept.marks);
     // The inputs are read before any layout: when fonts load during this frame, the next frame
     // lays all type out again.
@@ -1569,7 +1575,7 @@ fn hidden_chars_overlay(app: &mut VectorcraftApp, p: &egui::Painter, xf: &Xf) {
     });
 }
 
-/// The Show Hidden Characters marks of the text objects drawn in the last frame that showed them
+/// The Show Hidden Characters marks of the text objects drawn in the last frame
 /// ([`crate::CanvasCache::hidden_chars`]). Each is kept with the object it was laid out from: an
 /// edited object is a new `Arc` and is laid out again, and all type is laid out again when the
 /// fonts or the hyphenation exceptions change.
@@ -3763,6 +3769,66 @@ mod tests {
         assert_ne!(drawn(&mut app, &xf), zoomed, "set in the family that arrived");
     }
 
+    /// The shapes Type → Show Hidden Characters draws in one canvas frame ([`show`]).
+    fn hidden_char_marks(app: &mut VectorcraftApp, ctx: &egui::Context) -> Vec<Shape> {
+        let blue = Color32::from_rgb(0x4f, 0x9d, 0xff);
+        shapes(app, ctx)
+            .into_iter()
+            .filter(|s| matches!(s, Shape::Circle(c) if c.fill == blue) || matches!(s, Shape::Text(t) if t.fallback_color == blue))
+            .collect()
+    }
+
+    /// While Show Hidden Characters is on, a canvas frame keeps the marks of the frame before.
+    /// Turning it off drops the marks with their text nodes, and turning it on again draws the
+    /// same marks.
+    #[test]
+    fn show_hidden_characters_off_releases_the_text_nodes() {
+        let mut app = VectorcraftApp::new(Session::new(), Default::default());
+        app.session.execute("file.new", &json!({"width": 400, "height": 300})).unwrap();
+        let text = json!({"x": 20, "y": 60, "text": "one two\nthree four"});
+        let id = vectorcraft_doc::NodeId(app.session.execute("text.create", &text).unwrap()["id"].as_u64().unwrap());
+        let ctx = egui::Context::default();
+        app.run("type.hiddenCharacters", json!({})).unwrap();
+        let on = hidden_char_marks(&mut app, &ctx);
+        assert!(on.len() > 2, "{on:?}");
+        // Tests running alongside add fonts and set hyphenation exceptions, which lays all type out
+        // again: frames are drawn until neither changed between two of them.
+        let kept = (0..100).any(|_| {
+            let (inputs, marks) = (app.canvas.hidden_chars.inputs.clone(), app.canvas.hidden_chars.marks[&id].1.clone());
+            hidden_char_marks(&mut app, &ctx);
+            let after = &app.canvas.hidden_chars;
+            after.inputs == inputs && std::sync::Arc::ptr_eq(&after.marks[&id].1, &marks)
+        });
+        assert!(kept, "a frame keeps the marks of the frame before");
+        app.run("type.hiddenCharacters", json!({})).unwrap();
+        assert!(hidden_char_marks(&mut app, &ctx).is_empty(), "off");
+        assert!(app.canvas.hidden_chars.marks.is_empty(), "no node is kept");
+        app.run("type.hiddenCharacters", json!({})).unwrap();
+        assert_eq!(hidden_char_marks(&mut app, &ctx), on, "on again: the same marks");
+    }
+
+    /// Closing the document drops the marks Show Hidden Characters kept with its text nodes, and
+    /// the same type in a new document shows the same marks.
+    #[test]
+    fn show_hidden_characters_releases_the_text_nodes_of_a_closed_document() {
+        let mut app = VectorcraftApp::new(Session::new(), Default::default());
+        let ctx = egui::Context::default();
+        crate::theme::install_fonts(&ctx);
+        app.run("type.hiddenCharacters", json!({})).unwrap();
+        let open = |app: &mut VectorcraftApp| {
+            app.run("file.new", json!({"width": 400, "height": 300})).unwrap();
+            app.session.execute("text.create", &json!({"x": 20, "y": 60, "text": "one two\nthree four"})).unwrap();
+            hidden_char_marks(app, &ctx)
+        };
+        let first = open(&mut app);
+        assert!(first.len() > 2, "{first:?}");
+        assert_eq!(app.canvas.hidden_chars.marks.len(), 1, "the marks are kept with the text object's node");
+        app.session.execute("file.close", &json!({})).unwrap();
+        assert!(hidden_char_marks(&mut app, &ctx).is_empty(), "the Home screen");
+        assert!(app.canvas.hidden_chars.marks.is_empty(), "no node of the closed document is kept");
+        assert_eq!(open(&mut app), first, "the same type in a new document");
+    }
+
     /// General › Zoom with Mouse Wheel (#394), through the control channel's `ui.wheel`: off,
     /// the wheel scrolls and Cmd-wheel zooms; on, the wheel zooms about the pointer, Shift-wheel
     /// scrolls up and down and Cmd/Ctrl-wheel sideways. Alt-wheel (Option on the Mac) and a

crates/ui-egui/src/lib.rs

@@ -284,8 +284,8 @@ pub struct CanvasCache {
     pub slices: Option<SliceCache>,
     /// The print tiling's pages for (document uid, revision) (View → Show Print Tiling).
     pub print_tiling: Option<PrintTilingCache>,
-    /// The marks Type → Show Hidden Characters drew on each text object in the last frame that
-    /// showed them.
+    /// The marks Type → Show Hidden Characters drew on each text object in the last frame. A frame
+    /// that does not draw them drops them ([`canvas::show`]).
     pub hidden_chars: canvas::HiddenChars,
     /// [`VectorcraftApp::selection_box`] for (document uid, revision, Use Preview Bounds).
     pub selection_box: Option<((u64, u64, bool), Option<vectorcraft_doc::OrientedBox>)>,
@@ -964,6 +964,8 @@ impl VectorcraftApp {
     }
 }
 
+/// Returns the milliseconds since the Unix epoch, or in the web build the milliseconds since the
+/// first call, read from the page's `performance.now()`.
 pub fn now_ms() -> f64 {
     #[cfg(not(target_arch = "wasm32"))]
     {
@@ -972,7 +974,10 @@ pub fn now_ms() -> f64 {
     }
     #[cfg(target_arch = "wasm32")]
     {
-        0.0
+        use std::sync::LazyLock;
+        use web_time::Instant;
+        static START: LazyLock<Instant> = LazyLock::new(Instant::now);
+        START.elapsed().as_secs_f64() * 1000.0
     }
 }
 

docs/gaps.md

@@ -144,10 +144,10 @@ from G14 and the budget run of G15: **~170–270 h** one agent, ~50–80 h wall
   during a drag keeps the drag (#1856, #1719); a template layer dims its images by Dim Images instead of fading the
   whole layer (#1864, #1683); a failed save or export is reported in a dialog that names the file and stays until
   closed, the document left modified (#1865, #1685).
-- **Missing (noted for reporters, 2026-10-14):** the Shape Builder offers no region for an empty area enclosed
-  only by closed shapes, such as the middle of four circles that touch (#1691); deleting an interior anchor of an
-  open path joins across the gap, where the documented behaviour removes the point and its connecting segments.
-  Inside the estimate below.
+- **Done:** the Shape Builder offers the empty areas closed shapes enclose as regions, such as the middle of four
+  circles that touch, and merges them with the regions around them (#1691). Gap Detection is still missing.
+- **Missing (noted for reporters, 2026-10-14):** deleting an interior anchor of an open path joins across the gap,
+  where the documented behaviour removes the point and its connecting segments. Inside the estimate below.
 - **Missing:** Shape Builder misses planar regions and targets whole shapes (#937); Transform effect dialog's invisible checkboxes and missing options (#885);
   PDF text boxes moving on open (#722); SVG units reverting to points (#864); bezier drag preview freezing (#834).
 - **Impact:** wrong output in everyday work.

docs/target-app-parity.md

@@ -543,9 +543,11 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   actual OS display and Caps Lock remain unverified. Behaviour reference: [public tool-pointer documentation](https://helpx.adobe.com/illustrator/using/tools.html#change_tool_pointers). Tool cursors are painted into the window on Wayland (#1652; not run on Linux, #1645 stays open until confirmed). A Precise Cursors command toggles the preference and can take a shortcut (#1663).
 - **Performance:** 20k shapes + 1k texts render in 27 ms per full-retina frame (7.8 ms zoomed), 7× faster than the first version. The UI thread never blocks. The web build is 7.1 MB gzipped. Print-size images (more than 512 MB decoded, up to 2 GB) draw in the canvas and in raster exports and can be trimmed with Crop Image; an image with a side past 65,535 px is shrunk to fit, a raster export says when an image could not be decoded, and Crop Image's trim leaves CMYK images alone (#1517). On Windows `vectorcraft-cli perf` reports the cores busy and, with `--deep`, its working set, and warns on a busy machine as it does on macOS and Linux (#1502).
   The renderer composes the two ink planes of a CMYK document that shows transparency into screen colors on up to as many threads as it rasterizes with, instead of on one. At 2880 × 1800 on 8 threads, a page of 300 shapes at 20% to 90% opacity takes 30 ms a frame instead of 55 ms, and 50,000 paths with one at 99% opacity take 258 ms instead of 361 ms (`vectorcraft-cli bench`), with the same pixels.
+  With Overprint Preview or Separations Preview on, the renderer keeps the art it prepared for the preview from one frame to the next. It prepares again the objects that changed, and all of the art when Discard White Overprint changes or, with Separations Preview, when the plates shown, the proof setup, the swatches, the Spot Colors option or the color settings change or a profile is loaded. It draws the other objects from the art, geometry and stroke outlines it kept for them.
   The Pathfinder panel, Offset Path, Clean Up, Divide Objects Below, Make and Release Blend, Envelope Distort's Make and Release, Repeat (Radial, Grid, Mirror and Release), Vector Halftone, New and Redefine Symbol, Delete Symbol, erasing with the Symbol Sprayer, Rasterize, Convert to Artboards, Flatten Transparency, Clear Guides, Shape Builder, Live Paint, Release Image Trace, Make and Release Opacity Mask, Delete with direct-selected anchor points, Remove Anchor Points, Cut Path, and the Shaper, Knife, Eraser, Path Eraser, Line Cut, Rectangle Cut, Mirror & Cut and Blob Brush tools add and remove objects in one pass over each layer or group they change, and Outline Stroke and Expand write each new object in the place of the object it replaces (#1429).
   Type › Show Hidden Characters keeps the marks it places on each text object from one frame to the next. The canvas lays a text object out again when an edit changes it or its threaded story, or when the last frame that showed the marks did not draw it, and it lays out all type in view again when the fonts or the hyphenation exceptions change. With 1,000 two-line labels in view, drawing the marks takes 0.8 ms per frame in a release build instead of 19.7 ms.
   Delete, Cut, Group, Ungroup, Make and Release Compound Path, Make Clipping Mask, Send to Current Layer, Duplicate, Copy in the Move, Rotate, Scale, Reflect and Shear dialogs, Transform Each with Copy and each move of an Alt-drag take time in proportion to the size of the document (#1429).
+  In the web build the status bar's render and UI times are measured with the browser's `performance.now()`, and the Layers panel stops rendering row thumbnails in a frame once they have taken 8 ms.
   An Alt-drag with the Selection, Direct Selection, Group Selection, Rotate, Scale, Reflect or Shear tool copies the selection on its first move, and the moves after it transform those copies; the previews of the Move, Rotate, Scale, Reflect and Shear dialogs with Copy and Preview on copy the selection once in the same way (#1429).
   When the desktop app opens a document on a thread of its own (#1245), that thread also reads the document's linked files and lays out its type, and the UI thread only adds the finished document: in release builds, the step left on the UI thread takes 0.02 ms instead of 1.04 s for a document with 12 linked 3000 × 2000 TIFFs, and it takes 0.1 ms instead of 0.85 s for one with 300 Auto Size area type objects, every second one in three columns.
   The Layers panel's Delete Selection, Duplicate Selection, Collect in New Layer, Merge Selected, Flatten Artwork, Release to Layers (Sequence) and row drags also take time in proportion to the size of the document, and so do Cut Artboard and Duplicate Artboard with their art and each move of an Alt-drag of one artboard with the Artboard tool while Move/Copy Artwork with Artboard is on (#1429).