Cap stroke width in the outliner so huge weights don't panic

Found while testing crates/engine/src/cmd/props.rs:361 (strokeWeight is only clamped with .max(0.0)); the panic is raised when the renderer draws the stroke (render crate / tiny-skia stroker)

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/engine/src/huge_stroke_tests.rs

@@ -0,0 +1,28 @@
+//! An absurd stroke weight must not take the renderer down with it: saving (thumbnail) and exporting still work.
+
+use serde_json::{Value, json};
+
+use crate::Session;
+use crate::params::id_of;
+use figcraft_doc::NodeId;
+
+fn id(v: Value) -> NodeId {
+    id_of(&v["id"]).unwrap()
+}
+
+#[test]
+fn huge_stroke_weight_with_round_caps_still_saves_and_exports() {
+    for weight in [1e6, 1e7, 1e10, 1e30] {
+        let mut s = Session::new();
+        let f = id(s.execute("frame.create", &json!({"x": 0, "y": 0, "width": 100, "height": 100})).unwrap());
+        let v = id(s.execute("vector.create", &json!({"parent": f, "path": "M0 0.8333 L7.5 6.25 L15 0.8333"})).unwrap());
+        s.execute("node.set", &json!({"id": v, "props": {"stroke": "#ff0000", "strokeWeight": weight, "strokeCap": "round", "strokeJoin": "round"}}))
+            .unwrap();
+        let path = std::env::temp_dir().join(format!("figcraft-huge-stroke-{}-{weight}.figcraft", std::process::id()));
+        let saved = s.execute("file.saveAs", &json!({"path": path.to_string_lossy()}));
+        let _ = std::fs::remove_file(&path);
+        assert!(saved.is_ok(), "saveAs at weight {weight}: {:?}", saved.err());
+        let exported = s.execute("file.export", &json!({"ids": [f], "format": "png"}));
+        assert!(exported.is_ok(), "export at weight {weight}: {:?}", exported.err());
+    }
+}

crates/engine/src/lib.rs

@@ -1548,6 +1548,8 @@ mod history_behaviour_tests;
 #[cfg(test)]
 mod html_codegen_tests;
 #[cfg(test)]
+mod huge_stroke_tests;
+#[cfg(test)]
 mod import_export_tests;
 #[cfg(test)]
 mod inspect_behaviour_tests;

crates/pathops/src/lib.rs

@@ -258,11 +258,16 @@ pub(crate) fn kjoin(j: StrokeJoin) -> Join {
     }
 }
 
-/// Plain centred stroke of `path` at `width`.
+/// The widest stroke outlined: past this the rasteriser's fixed-point maths overflows and panics,
+/// and nothing visible changes (a stroke this wide covers any canvas already).
+pub const MAX_STROKE_WIDTH: f64 = 1e6;
+
+/// Plain centred stroke of `path` at `width` (capped at [`MAX_STROKE_WIDTH`]).
 pub fn stroke_center(path: &BezPath, width: f64, props: &StrokeProps) -> BezPath {
     if !(width.is_finite() && width > 0.0 && finite(path)) {
         return BezPath::new();
     }
+    let width = width.min(MAX_STROKE_WIDTH);
     let mut style = kurbo::Stroke::new(width)
         .with_join(kjoin(props.join))
         .with_miter_limit(props.miter_limit.clamp(1.0, 100.0))
@@ -284,10 +289,17 @@ pub fn stroke_outline(path: &BezPath, props: &StrokeProps, closed_shape: bool) -
 /// [`stroke_outline`] of a shape whose stroke follows vector network `net` (`path` is its stroke
 /// path): points with a cap or join of their own draw them there.
 pub fn stroke_outline_of(path: &BezPath, props: &StrokeProps, closed_shape: bool, net: Option<&VectorNetwork>) -> BezPath {
-    let w = props.weight;
-    if !(w.is_finite() && w > 0.0) {
+    if !(props.weight.is_finite() && props.weight > 0.0) {
         return BezPath::new();
     }
+    let capped;
+    let props = if props.weight > MAX_STROKE_WIDTH {
+        capped = StrokeProps { weight: MAX_STROKE_WIDTH, ..props.clone() };
+        &capped
+    } else {
+        props
+    };
+    let w = props.weight;
     let styled = net.and_then(|n| points::Styled::new(n, props));
     // Centred at `width` (twice the weight for Inside/Outside, which clip half of it away).
     let centred = |width: f64| match (&styled, &props.brush, props.profile()) {