Export: an HP-GL plot of the art's bounds leaves out images in symbol art

The bounds of a plot of the art's bounds no longer count the objects a
plot leaves out (placed images, objects at 0% opacity, unpainted paths)
when they sit in the art of a symbol. An instance whose symbol holds
nothing else is left out, so a document with only such instances is
refused with "nothing to export". The art of a dynamic symbol, and of a
group with effects, fills or strokes of its own, is measured whole.

crates/engine/src/cmd/fileio/encode.rs

@@ -2,6 +2,7 @@
 //! (unknown keys are ignored, so one params object can carry the options of several formats).
 
 use std::borrow::Cow;
+use std::collections::HashSet;
 use std::sync::Arc;
 
 use serde::Deserialize;
@@ -447,14 +448,94 @@ pub fn export_art_bounds(doc: &Document, format: &str) -> Option<Rect> {
 }
 
 /// The bounds of the visible art of `doc` with the objects that `left_out` picks hidden
-/// ([`hidden_nodes`]).
+/// ([`hidden_nodes`]) and the ones in the art of the symbols that instances show taken out
+/// ([`without_nodes`]: symbol art is measured with its hidden objects). An instance of a symbol
+/// whose art is all picked or hidden is hidden too. The art of a dynamic symbol is measured whole:
+/// an instance can paint its objects, and finds them by their places in the art.
 fn bounds_without(doc: &Document, left_out: &dyn Fn(&Node) -> bool) -> Option<Rect> {
-    let drawn = hidden_nodes(&doc.layers, left_out).map(|layers| {
-        let mut d = doc.clone();
+    // The symbols instances show (the first of each name) that aren't dynamic.
+    let mut names = HashSet::new();
+    let shown: Vec<(usize, &vectorcraft_doc::Symbol)> =
+        doc.symbols.iter().enumerate().filter(|(_, s)| names.insert(s.name.as_str())).filter(|(_, s)| !s.dynamic).collect();
+    // The symbols whose art `left_out` leaves nothing of, those that only hold instances of such
+    // symbols included.
+    let mut empty: HashSet<&str> = HashSet::new();
+    while let Some((_, s)) = shown.iter().find(|(_, s)| !empty.contains(s.name.as_str()) && all_left_out(&s.art, left_out, &empty)) {
+        empty.insert(&s.name);
+    }
+    let left_out =
+        &|n: &Node| left_out(n) || matches!(&n.kind, NodeKind::SymbolInstance { symbol, .. } if empty.contains(symbol.as_str()) && !has_effects(n));
+    let layers = hidden_nodes(&doc.layers, left_out);
+    let symbols: Vec<(usize, Arc<Node>)> = shown
+        .iter()
+        .filter(|(_, s)| !empty.contains(s.name.as_str()))
+        .filter_map(|(i, s)| without_nodes(&s.art, left_out).map(|art| (*i, art)))
+        .collect();
+    if layers.is_none() && symbols.is_empty() {
+        return vectorcraft_render::encode::art_bounds(doc);
+    }
+    let mut d = doc.clone();
+    if let Some(layers) = layers {
         d.layers = layers;
-        d
-    });
-    vectorcraft_render::encode::art_bounds(drawn.as_ref().unwrap_or(doc))
+    }
+    for (i, art) in symbols {
+        if let Some(s) = d.symbols.get_mut(i) {
+            s.art = art;
+        }
+    }
+    vectorcraft_render::encode::art_bounds(&d)
+}
+
+/// Whether `n` is hidden, picked by `left_out`, an instance of one of the `empty` symbols, or a
+/// layer or a group holding only such objects (its clipping path among them when it clips). A
+/// Shaper group, or a layer, group or instance with effects, fills or strokes of its own, is none
+/// of these unless it is hidden or picked.
+fn all_left_out(n: &Node, left_out: &dyn Fn(&Node) -> bool, empty: &HashSet<&str>) -> bool {
+    !n.visible
+        || left_out(n)
+        || !has_effects(n)
+            && n.extras().shaper.is_none()
+            && match &n.kind {
+                NodeKind::Layer { children, .. } | NodeKind::Group { children, .. } => children.iter().all(|c| all_left_out(c, left_out, empty)),
+                NodeKind::SymbolInstance { symbol, .. } => empty.contains(symbol.as_str()),
+                _ => false,
+            }
+}
+
+/// Whether `n` has a visible effect, fill or stroke of its own, which the objects it holds can
+/// take part in.
+fn has_effects(n: &Node) -> bool {
+    n.appearance.effects.iter().any(|e| e.visible) || n.appearance.items.iter().any(|i| i.visible())
+}
+
+/// `n` without the objects that `left_out` picks in it, when it is a layer or a group, and in the
+/// layers and groups in it at any depth; `None` when it picks none of them. A clipping layer or
+/// group keeps its clipping path, its first object, and a Shaper group and a layer or group with
+/// effects, fills or strokes of its own keep all they hold.
+fn without_nodes(n: &Arc<Node>, left_out: &dyn Fn(&Node) -> bool) -> Option<Arc<Node>> {
+    let (NodeKind::Layer { children, clip, .. } | NodeKind::Group { children, clip }) = &n.kind else { return None };
+    if has_effects(n) || n.extras().shaper.is_some() {
+        return None;
+    }
+    let mut changed = false;
+    let kept: Vec<Arc<Node>> = children
+        .iter()
+        .enumerate()
+        .filter_map(|(i, c)| {
+            if left_out(c) && !(*clip && i == 0) {
+                changed = true;
+                return None;
+            }
+            Some(without_nodes(c, left_out).inspect(|_| changed = true).unwrap_or_else(|| c.clone()))
+        })
+        .collect();
+    changed.then(|| {
+        let mut new = (**n).clone();
+        if let NodeKind::Layer { children, .. } | NodeKind::Group { children, .. } = &mut new.kind {
+            *children = kept;
+        }
+        Arc::new(new)
+    })
 }
 
 /// The `rect` param of a raster export: `[x, y, width, height]` in points, y down. `None` when

crates/engine/src/cmd/fileio/tests_hpgl.rs

@@ -221,6 +221,39 @@ fn a_plot_of_the_arts_bounds_leaves_out_the_layers_it_does_not_plot() {
     assert!(e.contains("no visible art"), "{e}");
 }
 
+/// A placed image in a symbol's art doesn't move a plot of the art's bounds either, and a
+/// document whose only other visible art is an instance of that symbol is refused.
+#[test]
+fn a_plot_of_the_arts_bounds_leaves_out_images_in_symbol_art() {
+    let mut s = two_boards();
+    let plot = |s: &mut Session| s.execute("document.export", &json!({"format": "hpgl", "useArtboards": false})).map(|v| bytes(&v));
+    let alone = plot(&mut s).unwrap();
+    let printing = s.doc().unwrap().doc.layers[0].id;
+    s.execute("layer.new", &json!({})).unwrap();
+    let mut png = vec![];
+    image::DynamicImage::new_rgb8(4, 4).write_to(&mut std::io::Cursor::new(&mut png), image::ImageFormat::Png).unwrap();
+    s.execute("file.place", &json!({"name": "far.png", "dataBase64": b64(&png), "at": [-600, 800]})).unwrap();
+    s.execute("symbol.new", &json!({"name": "Far"})).unwrap();
+    assert!(s.doc().unwrap().doc.symbols.iter().any(|sym| sym.name == "Far"));
+    assert_eq!(plot(&mut s).unwrap(), alone, "an image in symbol art");
+
+    s.execute("layer.setProps", &json!({"id": printing, "visible": false})).unwrap();
+    let e = plot(&mut s).unwrap_err().to_string();
+    assert!(e.contains("no visible art"), "{e}");
+
+    // A symbol of a square and an image is measured by its square.
+    let bounds = |s: &Session| super::export_art_bounds(&s.doc().unwrap().doc, "hpgl").unwrap();
+    let square = s.execute("shape.rectangle", &json!({"x": 200, "y": 200, "width": 20, "height": 20})).unwrap()["id"].clone();
+    let before = bounds(&s);
+    let image = s.execute("file.place", &json!({"name": "near.png", "dataBase64": b64(&png), "at": [400, 600]})).unwrap()["ids"][0].clone();
+    s.execute("symbol.new", &json!({"name": "Both", "ids": [square, image]})).unwrap();
+    assert_eq!(s.doc().unwrap().doc.symbols.len(), 2);
+    let after = bounds(&s);
+    for (a, b) in [(before.x0, after.x0), (before.y0, after.y0), (before.x1, after.x1), (before.y1, after.y1)] {
+        assert!((a - b).abs() < 1e-6, "{before:?} {after:?}");
+    }
+}
+
 #[test]
 fn export_options_are_checked() {
     let mut s = two_boards();

docs/mcp.md

@@ -1089,6 +1089,8 @@ way. `document.exportPdf {useArtboards: false}` writes that one page as well, an
 (unless `includeNonPrinting` or `createLayers` keeps them; a `.ai` file keeps layers by default). An HP-GL plot of the
 art's bounds is measured without what the plot leaves out: non-printing layers, objects at 0% opacity, placed images,
 gradient meshes whose every point is at 0% opacity, and paths without effects whose fills and strokes paint nothing.
+Such objects in the art of a symbol that is not dynamic are left out of its instances too, and an instance whose
+symbol holds nothing else is left out.
 A document whose only visible art is left out is refused, and Export As refuses an HP-GL plot of it before the save
 dialog. A PDF of that page, from either command, carries no Preserve Editing data; when Preserve Editing is on (as it
 is in VectorCraft Default), the export comes back with a warning that says so. A `.ai` export with