From d643e7f8f0babbf9c80aeba1fbd82dea7d9bd9f8 Mon Sep 17 00:00:00 2001
From: FredApps <FredApps@users.noreply.github.com>
Date: Mon, 9 Nov 2026 18:55:46 +0100
Subject: [PATCH] #1388: distinguish fine raster clips and update layer test
 fixtures

---
 crates/render/src/pipeline.rs          |  8 +++++++-
 crates/render/src/tests/raster_clip.rs | 15 +++++++++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/crates/render/src/pipeline.rs b/crates/render/src/pipeline.rs
index 5966ebf2e..029438cc5 100644
--- a/crates/render/src/pipeline.rs
+++ b/crates/render/src/pipeline.rs
@@ -499,7 +499,7 @@ impl<'a> Renderer<'a> {
     pub(crate) fn clipped_key(&self, ctx: &EvalCtx, layer: &Layer, key: Option<u64>) -> Option<u64> {
         let k = key?;
         Some(match self.raster_clip(ctx, layer) {
-            Some(c) => [c.x0, c.y0, c.x1, c.y1].iter().fold(cache::derive(k, 0xc11b), |d, v| cache::derive(d, (v * 16.0).round() as i64 as u64)),
+            Some(c) => raster_clip_key(k, c),
             None => k,
         })
     }
@@ -1209,3 +1209,9 @@ impl<'a> Renderer<'a> {
         Some(self.keep(key, Arc::new(buf?), &files).0)
     }
 }
+
+/// Snap cells can be finer than 1/16 unit: preserve every coordinate bit so visible
+/// clips cannot collide with another cell or the empty behind-camera raster.
+pub(crate) fn raster_clip_key(key: u64, clip: kurbo::Rect) -> u64 {
+    [clip.x0, clip.y0, clip.x1, clip.y1].iter().fold(cache::derive(key, 0xc11b), |key, coordinate| cache::derive(key, coordinate.to_bits()))
+}
diff --git a/crates/render/src/tests/raster_clip.rs b/crates/render/src/tests/raster_clip.rs
index 8bcadb7ee..f7227f634 100644
--- a/crates/render/src/tests/raster_clip.rs
+++ b/crates/render/src/tests/raster_clip.rs
@@ -190,7 +190,7 @@ fn moving(label: &str, pos: Keys, poi: Keys, text_pos: Keys, text_rot: &[(f64, f
     set(&mut cam, "cameraOptions/zoom", Value::Scalar(zoom()));
     keyed(&mut cam, "transform/position", pos);
     keyed(&mut cam, "transform/poi", poi);
-    p.comp_mut(cid).unwrap().layers = vec![cam, text];
+    p.comp_mut(cid).unwrap().layers = vec![cam, text].into();
     let cache = crate::LayerCache::default();
     let (mut exact, mut near, mut capped) = (0, 0, 0);
     for f in 0..30 {
@@ -286,7 +286,7 @@ fn layer_space_reads_get_the_whole_layer() {
     p.next_id = next;
     g.prop_mut("takeMatteFromLayer").unwrap().value = Value::Layer(Some(text_id.0));
     solid.props.sub_mut("effects").unwrap().children.push(g.into());
-    p.comp_mut(cid).unwrap().layers = vec![text, solid];
+    p.comp_mut(cid).unwrap().layers = vec![text, solid].into();
     assert_eq!(frame(&p, cid, false).data, frame(&p, cid, true).data, "Set Matte from the text");
     let r = Renderer::new(&p, &NoFootage, RenderOpts::default());
     let ctx = r.eval_ctx(cid, Tick::ZERO).unwrap();
@@ -321,3 +321,14 @@ fn layer_panel_input_reads_the_whole_layer_behind_the_camera() {
     assert!(expected.img.data.iter().any(|pixel| pixel[3] > 0.5));
     assert_eq!(r.layer_input(&ctx, layer, 0).unwrap().img, expected.img);
 }
+
+#[test]
+fn fine_clip_cells_have_distinct_cache_keys() {
+    let a = kurbo::Rect::new(0.0, 0.0, 1.0 / 128.0, 1.0 / 128.0);
+    let b = kurbo::Rect::new(1.0 / 128.0, 0.0, 2.0 / 128.0, 1.0 / 128.0);
+    let key = |clip| crate::pipeline::raster_clip_key(42, clip);
+    // All three clips rounded to identical coordinates in the old 1/16-unit key.
+    assert_ne!(key(a), key(b));
+    assert_ne!(key(a), key(kurbo::Rect::ZERO));
+    assert_ne!(key(b), key(kurbo::Rect::ZERO));
+}