From 87eb51a0899026d155de6b8c76290b4ded4352fc Mon Sep 17 00:00:00 2001
From: dotCooCoo <RobertLeeLW@gmail.com>
Date: Tue, 27 Oct 2026 09:22:14 -0700
Subject: [PATCH] Include alpha interpretation in frame-blend cache keys

---
 crates/engine/src/tests/proxy.rs | 43 ++++++++++++++++++++++++++++++++
 crates/render/src/pipeline.rs    |  4 +++
 2 files changed, 47 insertions(+)

diff --git a/crates/engine/src/tests/proxy.rs b/crates/engine/src/tests/proxy.rs
index 0e57e5fa1..941a9a96b 100644
--- a/crates/engine/src/tests/proxy.rs
+++ b/crates/engine/src/tests/proxy.rs
@@ -246,6 +246,49 @@ fn comp_proxy_frames_blend() {
     assert!(blue(px(&s, outer, 0.1, o, 1, 1)));
 }
 
+#[test]
+fn comp_proxy_frame_blend_cache_tracks_alpha_interpretation() {
+    struct Interpreted(std::sync::atomic::AtomicUsize);
+    impl FootageSource for Interpreted {
+        fn frame(&self, _: ItemId, f: &Footage, _: Tick) -> Option<Arc<Image>> {
+            self.0.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
+            let pixel = match f.alpha {
+                AlphaMode::Straight => [0.4, 0.2, 0.1, 0.5],
+                AlphaMode::Premultiplied => [f.premul_color[0] * 0.5, 0.1, 0.0, 0.5],
+                AlphaMode::Ignore => [0.8, 0.4, 0.2, 1.0],
+            };
+            Some(Arc::new(Image::filled(4, 4, pixel)))
+        }
+    }
+    for mode in ["frameMix", "pixelMotion"] {
+        let mut s = session();
+        let footage = Arc::new(Interpreted(std::sync::atomic::AtomicUsize::new(0)));
+        s.footage = footage.clone();
+        let (inner, outer) = nested(&mut s);
+        s.execute("file.setProxy", json!({"item": inner.0, "path": "/m/alpha.mov"})).unwrap();
+        s.execute("file.interpretProxy", json!({"item": inner.0, "alpha": "straight"})).unwrap();
+        s.execute("layer.frameBlending", json!({"mode": mode})).unwrap();
+        s.execute("comp.setSwitch", json!({"switch": "frameBlending", "value": true})).unwrap();
+        let opts = RenderOpts::default();
+        let first = px(&s, outer, 0.05, opts, 1, 1);
+        let calls = footage.0.load(std::sync::atomic::Ordering::Relaxed);
+        assert_eq!(px(&s, outer, 0.05, opts, 1, 1), first);
+        assert_eq!(footage.0.load(std::sync::atomic::Ordering::Relaxed), calls);
+        for params in [
+            json!({"item": inner.0, "alpha": "ignore"}),
+            json!({"item": inner.0, "alpha": "premultiplied", "premulColor": [0.0, 0.0, 0.0]}),
+            json!({"item": inner.0, "alpha": "premultiplied", "premulColor": [1.0, 0.0, 0.0]}),
+        ] {
+            s.execute("file.interpretProxy", params.clone()).unwrap();
+            let mut fresh = s.renderer(opts);
+            fresh.cache = None;
+            let want = fresh.comp_frame(outer, Tick::from_seconds_f64(0.05)).get(1, 1);
+            let actual = px(&s, outer, 0.05, opts, 1, 1);
+            assert_eq!(actual, want, "{mode} after {params}");
+        }
+    }
+}
+
 #[test]
 fn interpret_proxy_settings_apply_to_the_proxy() {
     let mut s = session();
diff --git a/crates/render/src/pipeline.rs b/crates/render/src/pipeline.rs
index faa21294e..84e4fec0d 100644
--- a/crates/render/src/pipeline.rs
+++ b/crates/render/src/pipeline.rs
@@ -740,6 +740,10 @@ impl<'a> Renderer<'a> {
                     use std::hash::{Hash, Hasher};
                     let mut h = std::collections::hash_map::DefaultHasher::new();
                     (0x00f8_a3e5_u64, item, i, (w as f32).to_bits(), mode as u8, f.frame_rate.num, f.frame_rate.den, &f.path, float).hash(&mut h);
+                    (f.alpha as u8).hash(&mut h);
+                    if f.alpha == effectcraft_project::AlphaMode::Premultiplied {
+                        f.premul_color.map(f32::to_bits).hash(&mut h);
+                    }
                     h.finish()
                 });
                 if let (Some(c), Some(k)) = (self.cache, key)