Roto Brush: keep frozen mattes in a session without their model (#2833)

The frozen key hashes the chain keys, whose seed holds the session's
model, so mattes frozen with SAM 2.1 didn't match in a session on
Classic, such as a fresh effectcraft-cli render, and the frame was
segmented again with Classic. Accept the key under any Roto Brush model
too, as Object Matte has done since #1852. frozen_key is unchanged for
projects frozen today, and editing a stroke or a matte setting still
makes the frozen mattes stale.

crates/effects/src/roto.rs

@@ -9,7 +9,8 @@
 //! neighbouring frames with [`crate::EffectHost::self_at`]). Undo, redo and reopening a project
 //! therefore never see stale mattes. Behind the memory cache an optional [`SegStore`] (the
 //! persistent disk cache, set by the engine) keeps computed segmentations across restarts. **Freeze** stores the final mattes in the hidden **Frozen**
-//! parameter ([`FrozenCache`]); they are used while their key still matches.
+//! parameter ([`FrozenCache`]); they are used while their key still matches, whichever model the
+//! session has (a session without the model that froze them uses them as they are).
 //!
 //! Rendering: binary segmentation → Roto Brush Matte (Shift Edge, Reduce Chatter, Feather,
 //! Contrast) → Refine Edge matting inside the Refine Edge band (guided filter + closed-form
@@ -242,6 +243,11 @@ fn seed_with(params: &Params, layer_size: [f64; 2], fps: f64, model: &str) -> u6
     h
 }
 
+/// Show Object: 0 shows every object, N object N alone.
+fn show_object_of(params: &Params) -> u32 {
+    f(params, "rotoBrushMatte/object").round().clamp(0.0, 32.0) as u32
+}
+
 /// The layer frame shown at layer time `t` seconds.
 pub fn frame_of(t: f64, fps: f64) -> i64 {
     (t * fps + 1e-6).floor() as i64
@@ -415,7 +421,7 @@ impl Chain {
         let data = data(params);
         let keys = data.chain_keys(seed(params, layer_size, fps));
         let saved = saved_for(params, &data, layer_size, fps);
-        let show_object = f(params, "rotoBrushMatte/object").round().clamp(0.0, 32.0) as u32;
+        let show_object = show_object_of(params);
         Chain { refine_radius: data.refine_radius(), data, keys, opts: seg_opts(params, scale), model: model_for(params), saved, show_object }
     }
 
@@ -869,7 +875,8 @@ fn needs_neighbours(mp: &MatteParams) -> bool {
 // ------------------------------------------------------------------ Freeze
 
 /// Frozen mattes (Freeze): the final 8-bit alpha and the Refine Edge band of every frame of
-/// the span at full resolution, valid while `key` matches [`frozen_key`].
+/// the span at full resolution, valid while `key` matches [`frozen_key`] under the session's model or
+/// any other Roto Brush model.
 #[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
 #[serde(default, rename_all = "camelCase")]
 pub struct FrozenCache {
@@ -899,21 +906,35 @@ impl FrozenCache {
     }
 }
 
-/// What frozen mattes depend on: every chain key and the matte settings.
+/// What frozen mattes depend on: every chain key (the session's model is in their seed) and the matte settings.
 pub fn frozen_key(params: &Params, layer_size: [f64; 2], fps: f64) -> String {
-    let ch = Chain::new(params, layer_size, fps, 1.0);
+    frozen_key_with(params, layer_size, fps, model_for(params).map_or(effectcraft_segment::CLASSICAL, |m| m.info().id))
+}
+
+/// [`frozen_key`] for the model with id `model` ([`effectcraft_segment::CLASSICAL`]: none).
+fn frozen_key_with(params: &Params, layer_size: [f64; 2], fps: f64, model: &str) -> String {
     let mut h = 0xcbf2_9ce4_8422_2325;
-    for (f, k) in &ch.keys {
+    for (f, k) in &data(params).chain_keys(seed_with(params, layer_size, fps, model)) {
         fnv(&mut h, &f.to_le_bytes());
         fnv(&mut h, &k.to_le_bytes());
     }
     fnv(&mut h, format!("{:?}", matte_params(params)).as_bytes());
-    if ch.show_object != 0 {
-        fnv(&mut h, &ch.show_object.to_le_bytes());
+    let show_object = show_object_of(params);
+    if show_object != 0 {
+        fnv(&mut h, &show_object.to_le_bytes());
     }
     format!("{h:016x}")
 }
 
+/// Whether frozen mattes still apply: their key matches under the session's model, or under the model that froze
+/// them, which this session may not have loaded (a fresh headless render). Frozen mattes need no segmentation.
+fn frozen_applies(fc: &FrozenCache, params: &Params, layer_size: [f64; 2], fps: f64) -> bool {
+    fc.key == frozen_key(params, layer_size, fps)
+        || std::iter::once(effectcraft_segment::CLASSICAL)
+            .chain(effectcraft_segment::MODELS.iter().filter(|m| m.task == effectcraft_segment::Task::Mask).map(|m| m.id))
+            .any(|id| fc.key == frozen_key_with(params, layer_size, fps, id))
+}
+
 /// Whether the instance is frozen (has frozen mattes).
 pub fn is_frozen(params: &Params) -> bool {
     !s(params, FROZEN).is_empty()
@@ -1132,7 +1153,7 @@ fn matte_for(ctx: &EffectCtx, f: i64, img: &Arc<Image>, scale: f64) -> Option<(V
     let (w, h) = (img.width as usize, img.height as usize);
     // Frozen mattes.
     if let Some(fc) = frozen(ctx.params)
-        && fc.key == frozen_key(ctx.params, ctx.layer_size, ctx.fps())
+        && frozen_applies(&fc, ctx.params, ctx.layer_size, ctx.fps())
         && let Some(fr) = fc.frames.get(&f)
     {
         let [fw, fh] = fc.size;
@@ -1351,6 +1372,42 @@ mod tests {
         assert!(o.data.iter().all(|p| p[3] == 0.0));
     }
 
+    /// Mattes frozen with a model render as frozen in a session that has another model or none (a fresh headless
+    /// render), instead of being segmented again with the classic engine.
+    #[test]
+    fn frozen_mattes_survive_a_session_without_their_model() {
+        let mut d = RotoData::default();
+        d.add(Stroke { kind: StrokeKind::Fg, frame: 0, radius: 3.0, points: vec![[35.0, 40.0], [45.0, 40.0]], object: 0 }, 2, [0, 5]);
+        let mut params = params_with(&d);
+        params.values.insert(INPUT_KEY.into(), Value::Str("frozen-without-the-model".into()));
+        let size = [100.0, 80.0];
+        assert!(model_for(&params).is_none(), "this session has no model");
+        // the frozen matte is the left half of the layer: no segmentation of the disk gives it
+        let alpha: Vec<f32> = (0..100 * 80).map(|i| f32::from(u8::from(i % 100 < 50))).collect();
+        let mut fc = FrozenCache { key: frozen_key_with(&params, size, 25.0, effectcraft_segment::SAM2_TINY.id), size: [100, 80], ..Default::default() };
+        fc.frames.insert(0, freeze_frame(&alpha, &[0; 100 * 80]));
+        assert_ne!(fc.key, frozen_key(&params, size, 25.0));
+        params.values.insert(FROZEN.into(), Value::Str(fc.to_json()));
+        let host = Seq;
+        let ctx = EffectCtx {
+            params: &params,
+            time: 0.001,
+            layer_size: size,
+            seed: 1,
+            adjustment: false,
+            env: EffectEnv { host: Some(&host), frame_rate: 25.0, ..Default::default() },
+        };
+        let out = crate::apply(&specs()[0], &ctx, Buf { img: frame(0.0), offset: [0.0; 2], scale: 1.0 }).img;
+        let a = |x: usize, y: usize| out.data[y * 100 + x][3];
+        assert!(a(10, 70) > 0.99 && a(90, 10) < 0.01, "the frozen matte is used: {} at (10, 70), {} at (90, 10)", a(10, 70), a(90, 10));
+        // a stroke edited after the freeze still makes it stale, whatever the model
+        let mut moved = d.clone();
+        moved.strokes[0].points[0] = [36.0, 40.0];
+        let mut edited = params.clone();
+        edited.values.insert(STROKES.into(), Value::Str(moved.to_json()));
+        assert!(!frozen_applies(&fc, &edited, size, 25.0));
+    }
+
     /// A stand-in tracker for two objects: object 0 is the moving disk, object 1 a fixed square. It records how many
     /// objects (and prompts per object) it was asked for.
     struct TwoObjects(std::sync::Mutex<Vec<Vec<usize>>>);