From e0bb54e4c619470e3a93534fdaf69654b4761549 Mon Sep 17 00:00:00 2001
From: DWAA1660 <DWAA1660@users.noreply.github.com>
Date: Tue, 13 Oct 2026 18:05:48 -0600
Subject: [PATCH] render: hash the comp scene of selected layers that read it
 into the owner's cache key (#1252)

A layer selected by another layer's effect (Displacement Map, Blend...) had
its structure, values, matrix and time hashed into the owner's key, but not
the comp camera/lights its own scene-reading effects (Caustics, CC Particle
World...) see. The owner's key included the scene only when the owner itself
ran such an effect, and a cached owner never runs the selected layer's
effects, so moving the camera or a light reused stale owner pixels.

Dependencies::layer now hashes comp_scene for every selected (or nested)
layer that reads it, with the same policy as owner keys.

Fixes #1252

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N9kwMcw2pYQ5fSjKa3ZPnh
---
 crates/render/src/cache/dependencies.rs |  5 ++++
 crates/render/src/tests.rs              | 39 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/crates/render/src/cache/dependencies.rs b/crates/render/src/cache/dependencies.rs
index eaccd058..483b19da 100644
--- a/crates/render/src/cache/dependencies.rs
+++ b/crates/render/src/cache/dependencies.rs
@@ -78,6 +78,11 @@ impl Dependencies<'_> {
         hash_debug(self.h, layer);
         hash_values(self.h, ctx, layer, &layer.props);
         hash_debug(self.h, &ctx.world_matrix(layer));
+        // A cached owner never runs this layer's effects, so the comp camera and lights its
+        // scene-reading effects see belong in the owner's key too (#1252).
+        if super::reads_comp_scene(layer) {
+            hash_debug(self.h, &crate::comp_scene(ctx, layer));
+        }
         if super::time_dependent(layer, true) {
             layer.layer_time(ctx.time).0.hash(self.h);
         }
diff --git a/crates/render/src/tests.rs b/crates/render/src/tests.rs
index 39e022b0..78577fa9 100644
--- a/crates/render/src/tests.rs
+++ b/crates/render/src/tests.rs
@@ -953,3 +953,42 @@ fn shape_content_bounds_are_the_visual_edges() {
         assert!(b.iter().zip([-half, -half, half, half]).all(|(a, e)| (a - e).abs() < 1e-6), "{stroke:?}: {b:?}");
     }
 }
+
+/// #1252: a layer blended with a CC Particle World layer, under a camera panned by `pan` px.
+fn scene_reader_dependency(pan: f64) -> (Project, ItemId) {
+    let (mut p, cid, comp) = setup();
+    let mut source = solid(&mut p, &comp, [0.0, 0.0, 0.0], 200, 100);
+    let vals = [("birthRate", Value::Scalar(2.0)), ("particle/particleType", Value::Enum(2)), ("particle/birthSize", Value::Scalar(0.1))];
+    add_effect(&mut p, &mut source, "ec.sim.ccparticleworld", [200.0, 100.0], &vals);
+    source.switches.video = false;
+    let mut owner = solid(&mut p, &comp, [0.0, 0.0, 0.0], 200, 100);
+    add_effect_200(&mut p, &mut owner, "ec.channel.blend", &[("blendWithLayer", Value::Layer(Some(source.id.0))), ("blendWithOriginal", Value::Scalar(0.0))]);
+    let mut cam = build::layer(&mut p, &comp, "Camera", LayerSource::Camera, (200, 100), None);
+    for path in ["transform/position", "transform/poi"] {
+        let pr = cam.props.prop_mut(path).unwrap();
+        let Value::Vec3(v) = pr.value else { panic!("{path}: {:?}", pr.value) };
+        pr.value = Value::Vec3([v[0] + pan, v[1], v[2]]);
+    }
+    p.comp_mut(cid).unwrap().layers = vec![cam, owner, source];
+    (p, cid)
+}
+
+/// #1252: the owner's cache key covers the comp camera and lights that a layer it selects reads,
+/// though the owner itself runs no scene-reading effect.
+#[test]
+fn a_selected_layer_reading_the_comp_scene_invalidates_its_owner() {
+    let t = Tick::from_seconds_f64(1.0);
+    let (p, cid) = scene_reader_dependency(0.0);
+    let (q, _) = scene_reader_dependency(40.0);
+    let key = |p: &Project| {
+        let c = p.comp(cid).unwrap();
+        crate::cache::layer_key(&crate::EvalCtx::new(p, cid, c, t), &c.layers[1], 1.0, false, false).unwrap()
+    };
+    assert_ne!(key(&p), key(&q), "moving the camera changes the owner's key");
+    let cache = crate::LayerCache::default();
+    let here = render_cached(&p, cid, t, Some(&cache));
+    let panned = render_cached(&q, cid, t, Some(&cache));
+    assert_same(&panned, &render_cached(&q, cid, t, None), "cached render after the camera moved");
+    let (a, b) = (particles_x(&here), particles_x(&panned));
+    assert!(b < a - 20.0, "the blended particles follow the camera: {a} -> {b}");
+}