From 8594cf0d4108398c5062549c936530b292c2fa99 Mon Sep 17 00:00:00 2001
From: "Dylan M. Taylor" <dylan@dylanmtaylor.com>
Date: Mon, 2 Nov 2026 20:33:36 -0500
Subject: [PATCH] Puppet: clamp an imported Expansion before padding the
 outline grid

---
 crates/effects/src/puppet/mesh.rs  | 24 ++++++++++++++++++++----
 crates/effects/src/puppet/tests.rs | 16 ++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/crates/effects/src/puppet/mesh.rs b/crates/effects/src/puppet/mesh.rs
index f01ee8f78..f783e9f4e 100644
--- a/crates/effects/src/puppet/mesh.rs
+++ b/crates/effects/src/puppet/mesh.rs
@@ -614,13 +614,29 @@ pub fn triangulate(outline: &[[f64; 2]], opts: &MeshOpts) -> Mesh {
     Mesh { verts, tris, outline: poly }
 }
 
+/// The Expansion range the outline honours, in layer pixels (the property's slider range). A
+/// project file can store any number; outside this range it is clamped, so the padded grid
+/// below stays a few hundred pixels larger than the buffer.
+pub const EXPANSION_RANGE: (f64, f64) = (-100.0, 200.0);
+/// Most buffer pixels of padding the outline grid takes on each side (Expansion × buffer scale).
+const MAX_PAD: f64 = 4096.0;
+
 /// The outline of the alpha region under `seed` (buffer pixels → layer space via `scale` and
-/// `offset`), expanded by `expansion` layer pixels.
+/// `offset`), expanded by `expansion` layer pixels (clamped to [`EXPANSION_RANGE`]).
 pub fn outline(alpha: &[f32], w: usize, h: usize, scale: f64, offset: [f64; 2], seed: [f64; 2], expansion: f64) -> Vec<[f64; 2]> {
+    let expansion = if expansion.is_finite() { expansion.clamp(EXPANSION_RANGE.0, EXPANSION_RANGE.1) } else { 0.0 };
     // Pad so expansion can grow past the buffer edge.
-    let pad = (expansion.max(0.0) * scale).ceil() as usize + 2;
-    let (pw, ph) = (w + 2 * pad, h + 2 * pad);
-    let mut on = vec![false; pw * ph];
+    let pad = (expansion.max(0.0) * scale).ceil();
+    if !pad.is_finite() || pad > MAX_PAD {
+        return vec![];
+    }
+    let pad = pad as usize + 2;
+    let Some((pw, ph)) = w.checked_add(2 * pad).zip(h.checked_add(2 * pad)) else { return vec![] };
+    let Some(cells) = pw.checked_mul(ph) else { return vec![] };
+    if alpha.len() < w.saturating_mul(h) {
+        return vec![];
+    }
+    let mut on = vec![false; cells];
     for y in 0..h {
         for x in 0..w {
             on[(y + pad) * pw + x + pad] = alpha[y * w + x] >= 0.5;
diff --git a/crates/effects/src/puppet/tests.rs b/crates/effects/src/puppet/tests.rs
index 10426d46c..ed528f6a9 100644
--- a/crates/effects/src/puppet/tests.rs
+++ b/crates/effects/src/puppet/tests.rs
@@ -106,6 +106,22 @@ fn expansion_grows_the_outline() {
     assert!((am - pi * 225.0).abs() < 60.0, "{am}");
 }
 
+/// An imported Expansion far past the property's range is clamped instead of padding the grid
+/// by that many pixels (a 1e12 expansion would ask for terabytes).
+#[test]
+fn hostile_expansion_is_clamped() {
+    let (w, h) = (40, 40);
+    let alpha = disc_alpha(w, h, [20.0, 20.0], 10.0);
+    let max = signed_area(&outline(&alpha, w, h, 1.0, [0.0; 2], [20.0, 20.0], EXPANSION_RANGE.1)).abs();
+    for e in [1e12, f64::MAX, f64::INFINITY] {
+        let a = signed_area(&outline(&alpha, w, h, 1.0, [0.0; 2], [20.0, 20.0], e)).abs();
+        assert!((a - max).abs() < 1.0 || e.is_infinite(), "{e}: {a} vs {max}");
+    }
+    assert!(outline(&alpha, w, h, 1.0, [0.0; 2], [20.0, 20.0], f64::NAN).len() >= 3);
+    assert!(outline(&alpha, w, h, 1e9, [0.0; 2], [20.0, 20.0], 100.0).is_empty());
+    let _ = outline(&alpha, w, h, 1.0, [0.0; 2], [20.0, 20.0], -1e12);
+}
+
 fn rect_mesh(w: f64, h: f64, tris: f64) -> Mesh {
     triangulate(&[[0.0, 0.0], [w, 0.0], [w, h], [0.0, h]], &MeshOpts { triangles: tris, density: 50.0, expansion: 0.0 })
 }