Merge #1841: Cryptomatte: pick the ID under a point into the Selection (effect.pickCryptomatte) (@MatejKozlovsky)

crates/engine/src/commands/effect.rs

@@ -186,6 +186,101 @@ fn pick_color(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(json!({"prop": uid, "color": color}))
 }
 
+/// What a Cryptomatte effect has at a layer-space point: the ID with the most coverage in its
+/// Cryptomatte layer, with the aux channels (for the manifest) and the effect's Selection.
+struct CryptoHit {
+    at: (effectcraft_project::ItemId, LayerId, Tick),
+    aux: std::sync::Arc<effectcraft_raster::AuxChannels>,
+    layer: String,
+    hash: u32,
+    selection: String,
+    prop: Uid,
+    /// The Selection has an expression: setting its value wouldn't change what it reads.
+    driven: bool,
+}
+
+impl CryptoHit {
+    fn manifest(&self) -> Option<&[(String, u32)]> {
+        self.aux.manifests.iter().find(|(l, _)| *l == self.layer).map(|(_, m)| m.as_slice())
+    }
+    fn reply(&self, sel: &str) -> Value {
+        let selected = effectcraft_effects::selection_hashes(sel, self.manifest()).contains(&self.hash);
+        let name = self.aux.manifest_name(&self.layer, self.hash);
+        json!({"name": name, "hash": format!("{:08x}", self.hash), "layer": self.layer, "selected": selected})
+    }
+}
+
+/// The ID under `{x, y}` (effect space, which is layer space on footage and precomp layers) for
+/// the Cryptomatte effect `{layer?, effect?}`, from the aux channels its render reads. The point
+/// snaps to the centre of the pixel the effect's input buffer samples in a render at `scale`
+/// (the viewer's resolution).
+fn crypto_hit(s: &Session, p: &Value, cmd: &str) -> Result<Option<CryptoHit>> {
+    let (cid, lid, fx_uid) = find_fx(s, p, cmd)?;
+    let (Some(x), Some(y)) = (f_p(p, "x"), f_p(p, "y")) else { return Err(bad(cmd, "missing `x` / `y` (layer pixels)")) };
+    let scale = f_p(p, "scale").unwrap_or(1.0);
+    if !(scale.is_finite() && scale > 0.0 && scale <= 1.0) {
+        return Err(bad(cmd, "`scale` is the preview's resolution factor, above 0 and at most 1"));
+    }
+    let comp = s.project.comp(cid).ok_or(EngineError::NoComp)?;
+    let layer = comp.layer(lid).ok_or(EngineError::NoComp)?;
+    let fx = layer.effects().ok_or_else(|| bad(cmd, "no effects"))?;
+    let pos = fx.groups().position(|g| g.uid == fx_uid).ok_or_else(|| bad(cmd, "no such effect"))?;
+    let g = fx.groups().nth(pos).ok_or_else(|| bad(cmd, "no such effect"))?;
+    let prop = g.prop("selection").filter(|_| g.match_id == "ec.3d.cryptomatte").ok_or_else(|| bad(cmd, "not a Cryptomatte effect"))?;
+    let t = super::time_p(s, p, Some(comp));
+    let ctx = effectcraft_render::EvalCtx { project: &s.project, comp_id: cid, comp, time: t, expr: s.expr.as_deref(), footage: None };
+    let params = effectcraft_effects::flatten_params(g, &mut |pr| ctx.value(layer, pr));
+    let r = s.renderer(effectcraft_render::RenderOpts { scale, ..Default::default() });
+    let aux = r.layer_aux(&ctx, layer);
+    let want = effectcraft_effects::CRYPTO_LAYERS.get(params.e("layer") as usize).copied().unwrap_or("CryptoAsset");
+    let Some((aux, layer_name)) = aux.and_then(|a| a.resolve_crypto_layer(want).map(|l| (a, l))) else {
+        return Err(bad(cmd, "this layer has no Cryptomatte channels (a multi-layer OpenEXR with Cryptomatte, or a 3D precomp)"));
+    };
+    // The grid of the effect's input buffer (footage keeps native pixels from 3/4 scale up,
+    // proxies have their own size, earlier effects can pad it), rendered and cached.
+    let b = r.layer_input(&ctx, layer, pos).ok_or_else(|| bad(cmd, "this layer has no pixels"))?;
+    let (bs, o) = (b.scale, b.offset);
+    // The centre of its pixel under the point, at the aux point the effect reads there.
+    let [ax, ay] = effectcraft_effects::aux_point(bs, o, [(x * bs + o[0]).floor() + 0.5, (y * bs + o[1]).floor() + 0.5]);
+    let Some(hash) = aux.index_at(ax, ay).and_then(|i| aux.crypto_id_at(&layer_name, i)) else { return Ok(None) };
+    let (selection, driven) = (params.s("selection").to_string(), prop.expr.as_ref().is_some_and(|e| e.enabled));
+    Ok(Some(CryptoHit { at: (cid, lid, t), aux, layer: layer_name, hash, selection, prop: prop.uid, driven }))
+}
+
+/// `effect.cryptomatteAt`: the ID under a point, for the viewer's hover hint. The first call per
+/// frame renders the effect's input to learn its pixel grid (cached afterwards).
+fn crypto_at(s: &mut Session, p: &Value) -> Result<Value> {
+    Ok(crypto_hit(s, p, "effect.cryptomatteAt")?.map_or(Value::Null, |h| h.reply(&h.selection)))
+}
+
+/// The Cryptomatte eyedropper: replace the effect's Selection with the ID under a point, add it
+/// or remove it, in one undo step at the time it was read (none when its meaning stays).
+fn pick_crypto(s: &mut Session, p: &Value) -> Result<Value> {
+    use effectcraft_effects::crypto_select::{PickMode, edit_selection, token_for};
+    let cmd = "effect.pickCryptomatte";
+    let mode = match str_p(p, "mode").unwrap_or("replace") {
+        "replace" => PickMode::Replace,
+        "add" => PickMode::Add,
+        "remove" => PickMode::Remove,
+        m => return Err(bad(cmd, format!("unknown `mode` {m:?} (replace, add or remove)"))),
+    };
+    let h = crypto_hit(s, p, cmd)?.ok_or_else(|| bad(cmd, "no Cryptomatte ID there (empty or outside the layer)"))?;
+    if h.driven {
+        return Err(bad(cmd, "the Selection is driven by an expression; disable it to pick"));
+    }
+    let m = h.manifest();
+    let sel = edit_selection(&h.selection, &token_for(h.aux.manifest_name(&h.layer, h.hash), h.hash, m), h.hash, mode, m);
+    let changed = sel != h.selection;
+    if changed {
+        let (cid, lid, t) = h.at;
+        s.execute("prop.set", json!({"comp": cid.0, "layer": lid.0, "prop": h.prop, "value": sel, "time": t.seconds(), "timeBase": "comp"}))?;
+    }
+    let mut out = h.reply(&sel);
+    out["selection"] = json!(sel);
+    out["changed"] = json!(changed);
+    Ok(out)
+}
+
 fn remove(s: &mut Session, p: &Value) -> Result<Value> {
     let cid = super::comp_id(s, p)?;
     let fx = effects_p(s, p, "effect.remove")?;
@@ -632,6 +727,21 @@ pub fn specs() -> Vec<CommandSpec> {
             has_layers,
             pick_color
         ),
+        cmd!(
+            "effect.pickCryptomatte",
+            "Pick Cryptomatte",
+            [],
+            None,
+            "{layer?, effect?: index|uid|name, x, y (effect space), mode?: replace|add|remove (default replace), scale? (preview resolution, default 1), time?} → {name, hash, layer, selection, changed, selected} — edits the Cryptomatte effect's Selection with the ID under the point",
+            has_layers,
+            pick_crypto
+        ),
+        crate::query!(
+            "effect.cryptomatteAt",
+            "Cryptomatte At",
+            "{layer?, effect?: index|uid|name, x, y (effect space), scale?, time?} → {name, hash, layer, selected} | null — the Cryptomatte ID under the point",
+            crypto_at
+        ),
         cmd!("effect.applyLast", "Last Effect", ["Effect"], Some("Cmd+Alt+Shift+E"), "{layers?}", has_layers, last),
         cmd!("effect.removeAll", "Remove All", ["Effect"], Some("Cmd+Shift+E"), "{layers?}", has_layers, remove_all),
         cmd!("effect.remove", "Remove Effect", [], None, "{layer?, effect: index|uid|name}", has_layers, remove),

crates/engine/src/lib.rs

@@ -1036,12 +1036,18 @@ impl Session {
 
     /// Render a comp frame with the session's footage + expression hosts.
     pub fn render(&self, comp: ItemId, t: Tick, opts: RenderOpts) -> Image {
+        self.renderer(opts).comp_frame(comp, t)
+    }
+
+    /// The renderer [`Session::render`] uses: the session's footage, expressions, layer cache and
+    /// accelerator, and the render prefs (nested switches, draft shadows) over `opts`.
+    pub fn renderer(&self, opts: RenderOpts) -> Renderer<'_> {
         let opts = RenderOpts { nested_switches: self.prefs.general.switches_affect_nested_comps, draft_shadows: self.prefs.three_d.realtime_shadows, ..opts };
         let mut r = Renderer::new(&self.project, self.footage.as_ref(), opts);
         r.expr = self.expr.as_deref();
         r.cache = Some(&self.layer_cache);
         r.accel = self.accel.as_deref();
-        r.comp_frame(comp, t)
+        r
     }
 
     /// Resolve a comp reference (item id number or name; `None`/null = the active comp).
@@ -1242,6 +1248,8 @@ mod tests_codec_options;
 #[cfg(test)]
 mod tests_color_view;
 #[cfg(test)]
+mod tests_crypto_pick;
+#[cfg(test)]
 mod tests_delete_keys;
 #[cfg(test)]
 mod tests_disk_cache;

crates/engine/src/tests_crypto_pick.rs

@@ -0,0 +1,336 @@
+//! `effect.pickCryptomatte` / `effect.cryptomatteAt` (#473): the Cryptomatte eyedropper reads the
+//! aux channels the effect renders from (footage at its source time, a 3D precomp's generated
+//! pass) and edits the Selection text in one undo step.
+
+use std::sync::Arc;
+
+use effectcraft_project::{Footage, FootageKind, ItemId};
+use effectcraft_raster::channels3d::{crypto_float, crypto_hash};
+use effectcraft_raster::{AuxChannels, Image};
+use effectcraft_time::{FrameRate, Tick};
+use serde_json::{Value, json};
+
+use crate::Session;
+use crate::render::FootageSource;
+
+const COMMA: &str = "Green, \"Glossy\"";
+
+/// 8 × 4 footage with a 16 × 8 Cryptomatte (two aux pixels per layer pixel). Layer pixels in x:
+/// 0-1 `left` (0.6) over `right` (0.4); 2-3 `left` (0.3) under the comma name (0.7), ranks out of
+/// order; 4-5 `star*`; 6 an ID missing from the manifest; 7 a 0.5 / 0.5 tie of `left` and
+/// `right`. Rows 3+ are empty. From 1 s of source time `late` replaces columns 0-1.
+struct Crypto;
+
+fn aux_at(t: Tick) -> AuxChannels {
+    let (w, h) = (16usize, 8usize);
+    let mut planes = vec![vec![0.0f32; w * h]; 4];
+    for (i, x) in (0..w * h).map(|i| (i, i % w)).filter(|(i, _)| i / w < 6) {
+        let late = if t >= Tick::from_seconds_f64(1.0) { "late" } else { "left" };
+        let (a, ca, b, cb) = match x {
+            0..4 => (late, 0.6, "right", 0.4),
+            4..8 => ("left", 0.3, COMMA, 0.7),
+            8..12 => ("star*", 1.0, "", 0.0),
+            12..14 => ("ghost", 1.0, "", 0.0),
+            _ => ("left", 0.5, "right", 0.5),
+        };
+        for (k, v) in [crypto_float(crypto_hash(a)), ca, crypto_float(crypto_hash(b)), cb].into_iter().enumerate() {
+            planes[k][i] = v;
+        }
+    }
+    let mut aux = AuxChannels::new(w as u32, h as u32, 1.0);
+    for (k, c) in ["R", "G", "B", "A"].iter().enumerate() {
+        aux.channels.push((format!("CryptoObject00.{c}"), planes[k].clone()));
+    }
+    aux.manifests = vec![("CryptoObject".into(), ["left", "right", "late", COMMA, "star*"].iter().map(|n| (n.to_string(), crypto_hash(n))).collect())];
+    aux
+}
+
+impl FootageSource for Crypto {
+    fn frame(&self, _: ItemId, f: &Footage, _: Tick) -> Option<Arc<Image>> {
+        Some(Arc::new(Image::new(f.width, f.height)))
+    }
+    fn aux(&self, _: ItemId, _: &Footage, t: Tick) -> Option<Arc<AuxChannels>> {
+        Some(Arc::new(aux_at(t)))
+    }
+}
+
+struct Probe;
+impl crate::Importer for Probe {
+    fn probe(&self, path: &str) -> Result<Footage, String> {
+        let duration = Tick::from_seconds_f64(2.0);
+        // A half-size proxy of the EXR.
+        let (width, height) = if path.contains("proxy") { (4, 2) } else { (8, 4) };
+        Ok(Footage {
+            path: path.into(),
+            kind: FootageKind::Video,
+            width,
+            height,
+            has_video: true,
+            frame_rate: FrameRate::from_f64(24.0),
+            duration,
+            ..Default::default()
+        })
+    }
+}
+
+fn session() -> Session {
+    let mut s = Session { footage: Arc::new(Crypto), importer: Some(Arc::new(Probe)), ..Default::default() };
+    let item = s.execute("file.import", json!({"paths": ["/renders/crypto.exr"]})).unwrap()["items"][0].clone();
+    s.execute("comp.new", json!({"name": "C", "width": 8, "height": 4, "frameRate": 24, "duration": 2})).unwrap();
+    s.execute("layer.addItem", json!({"item": item})).unwrap();
+    s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+    s
+}
+
+fn pick(s: &mut Session, x: f64, mode: &str) -> Value {
+    s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": x, "y": 1.5, "mode": mode})).unwrap()
+}
+
+fn selection(s: &Session) -> String {
+    let l = &s.active_comp().unwrap().layers[0];
+    let g = l.effects().unwrap().groups().next().unwrap();
+    match &g.prop("selection").unwrap().value {
+        effectcraft_keyframe::Value::Str(t) => t.clone(),
+        v => panic!("{v:?}"),
+    }
+}
+
+#[test]
+fn picks_replace_add_and_remove_in_one_undo_step_each() {
+    let mut s = session();
+    let steps = s.history.undo.len();
+    let r = pick(&mut s, 0.5, "replace");
+    assert_eq!((r["name"].as_str(), r["selection"].as_str(), r["changed"].as_bool()), (Some("left"), Some("left"), Some(true)), "{r}");
+    assert_eq!(r["hash"], format!("{:08x}", crypto_hash("left")));
+    assert_eq!(s.history.undo.len(), steps + 1);
+    // The highest coverage wins even when it is not rank 0; the name is quoted.
+    assert_eq!(pick(&mut s, 2.5, "add")["selection"], r#"left, "Green, \"Glossy\"""#);
+    // Adding it again changes nothing and leaves no undo step.
+    let again = pick(&mut s, 3.5, "add");
+    assert_eq!((again["changed"].as_bool(), s.history.undo.len()), (Some(false), steps + 2));
+    // A `*` name and an unnamed ID go in as hashes; a tie goes to rank 0.
+    pick(&mut s, 4.5, "add");
+    assert_eq!(pick(&mut s, 6.5, "add")["selection"], format!(r#"left, "Green, \"Glossy\"", <{:08x}>, <{:08x}>"#, crypto_hash("star*"), crypto_hash("ghost")));
+    assert_eq!(s.execute("effect.cryptomatteAt", json!({"effect": 1, "x": 7.5, "y": 0.5})).unwrap()["name"], "left");
+    let r = pick(&mut s, 0.0, "remove");
+    assert_eq!(r["selection"], format!(r#""Green, \"Glossy\"", <{:08x}>, <{:08x}>"#, crypto_hash("star*"), crypto_hash("ghost")));
+    assert_eq!(r["selected"], false);
+    // The text parses back to exactly the picked IDs.
+    let manifest = aux_at(Tick::ZERO).manifests[0].1.clone();
+    let got = effectcraft_effects::selection_hashes(&selection(&s), Some(&manifest));
+    assert_eq!(got, [COMMA, "star*", "ghost"].map(crypto_hash));
+    assert_eq!(s.history.undo.len(), steps + 5);
+    s.execute("edit.undo", json!({})).unwrap();
+    assert!(selection(&s).starts_with("left, "), "{}", selection(&s));
+    pick(&mut s, 2.0, "replace");
+    assert_eq!(selection(&s), r#""Green, \"Glossy\"""#);
+    // The same selection with other spacing: no change, no undo step.
+    s.execute_checked("prop.set", json!({"path": "effects/#1/selection", "value": " \"Green, \\\"Glossy\\\"\" "})).unwrap();
+    let n = s.history.undo.len();
+    assert_eq!((pick(&mut s, 2.0, "replace")["changed"].as_bool(), s.history.undo.len()), (Some(false), n));
+}
+
+#[test]
+fn bad_points_layers_and_modes_are_errors_and_change_nothing() {
+    let mut s = session();
+    let at = |s: &mut Session, x: f64, y: f64| s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": x, "y": y}));
+    for (x, y) in [(-0.1, 1.0), (8.0, 1.0), (1.0, 4.0), (1.0, 3.5), (1e300, -1e300)] {
+        assert!(at(&mut s, x, y).is_err(), "{x},{y}");
+        assert_eq!(s.execute("effect.cryptomatteAt", json!({"effect": 1, "x": x, "y": y})).unwrap(), Value::Null);
+    }
+    assert!(s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 1, "y": 1, "mode": "toggle"})).is_err());
+    assert!(s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 1})).is_err());
+    for scale in [0.0, -1.0, 2.0] {
+        assert!(s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 1, "y": 1, "scale": scale})).is_err(), "{scale}");
+    }
+    s.execute_checked("effect.apply", json!({"effect": "Gaussian Blur"})).unwrap();
+    assert!(s.execute_checked("effect.pickCryptomatte", json!({"effect": 2, "x": 1, "y": 1})).is_err(), "not a Cryptomatte effect");
+    assert_eq!(selection(&s), "");
+    // A layer without aux channels.
+    s.execute("layer.newSolid", json!({"name": "S"})).unwrap();
+    s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+    let e = s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 1, "y": 1})).unwrap_err().to_string();
+    assert!(e.contains("no Cryptomatte channels"), "{e}");
+    // An expression-driven Selection would ignore the edit.
+    let mut s = session();
+    s.execute_checked("prop.setExpression", json!({"path": "effects/#1/selection", "expression": "\"right\""})).unwrap();
+    assert!(s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 1, "y": 1})).is_err());
+    assert_eq!(s.execute("effect.cryptomatteAt", json!({"effect": 1, "x": 1, "y": 1})).unwrap()["selected"], false);
+}
+
+/// The pick reads the frame the render shows: Time Remap's source time, not the layer time.
+#[test]
+fn time_remap_picks_the_shown_source_frame() {
+    let mut s = session();
+    assert_eq!(pick(&mut s, 0.5, "replace")["name"], "left");
+    s.execute_checked("layer.enableTimeRemap", json!({})).unwrap();
+    s.execute_checked("prop.set", json!({"path": "timeRemap", "value": 1.5})).unwrap();
+    assert_eq!(pick(&mut s, 0.5, "replace")["name"], "late");
+}
+
+/// A precomp of a 3D comp: the generated CryptoObject pass names its layers.
+#[test]
+fn picks_on_a_precomp_of_a_3d_comp() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Outer", "width": 40, "height": 20, "frameRate": 24, "duration": 1})).unwrap();
+    let l = s.execute("layer.newSolid", json!({"name": "Red, Ball", "width": 40, "height": 20})).unwrap()["layer"].clone();
+    s.execute("layer.setSwitch", json!({"layers": [l], "switch": "threeD", "value": true})).unwrap();
+    s.execute("layer.precompose", json!({"layers": [l], "name": "Inner"})).unwrap();
+    s.execute("layer.select", json!({"layers": [s.active_comp().unwrap().layers[0].id.0]})).ok();
+    s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+    let r = s.execute_checked("effect.pickCryptomatte", json!({"effect": 1, "x": 20, "y": 10})).unwrap();
+    assert_eq!((r["name"].as_str(), r["selection"].as_str()), (Some("Red, Ball"), Some("\"Red, Ball\"")), "{r}");
+}
+
+/// The matte the rendered Cryptomatte effect gives the picked ID at the buffer pixel under
+/// `{x, y}`: the pick has to name the ID the effect's own input buffer samples there.
+fn rendered_matte_of_pick(s: &mut Session, x: f64, y: f64, scale: f64) -> (String, f32) {
+    let r = s.execute_checked("effect.pickCryptomatte", json!({"effect": "Cryptomatte", "x": x, "y": y, "scale": scale, "mode": "replace"})).unwrap();
+    let fx = s.active_comp().unwrap().layers[0].effects().unwrap().groups().position(|g| g.match_id == "ec.3d.cryptomatte").unwrap() + 1;
+    s.execute_checked("prop.set", json!({"path": format!("effects/#{fx}/matteOnly"), "value": true})).unwrap();
+    let (cid, comp) = (s.active_comp_id().unwrap(), s.active_comp().unwrap());
+    let layer = &comp.layers[0];
+    let ctx = effectcraft_render::EvalCtx { project: &s.project, comp_id: cid, comp, time: Tick::ZERO, expr: None, footage: None };
+    let buf = s.renderer(effectcraft_render::RenderOpts { scale, ..Default::default() }).content_buf(&ctx, layer).unwrap();
+    let (px, py) = buf.to_px([x, y]);
+    let m = buf.img.get(px.floor() as i64, py.floor() as i64)[0];
+    (r["name"].as_str().unwrap_or("?").to_string(), m)
+}
+
+/// Between 3/4 and full resolution footage keeps its native pixels: at 0.8 the effect samples
+/// layer pixel 2 (the comma name, 0.7) at x = 2.2, not the 0.8-grid pixel snapped back to 1.
+#[test]
+fn pick_at_scale_0_8_matches_the_native_buffer_the_effect_renders() {
+    let mut s = session();
+    let (name, m) = rendered_matte_of_pick(&mut s, 2.2, 1.5, 0.8);
+    assert!(m >= 0.5, "picked {name:?}, but the render gives it matte {m} there");
+    assert_eq!(name, COMMA);
+}
+
+/// A half-size proxy renders a buffer at 0.5 layer pixels per pixel even at full resolution:
+/// x = 6.5 lies in buffer pixel 3, which samples layer x = 7 (the `left` / `right` tie).
+#[test]
+fn pick_on_a_proxy_matches_the_proxy_sized_buffer() {
+    let mut s = session();
+    let item = *s.project.items.iter().find(|(_, i)| matches!(i.kind, effectcraft_project::ItemKind::Footage(_))).unwrap().0;
+    s.execute("file.setProxy", json!({"item": item.0, "path": "/renders/crypto_proxy.exr"})).unwrap();
+    let (name, m) = rendered_matte_of_pick(&mut s, 6.5, 1.5, 1.0);
+    assert!(m >= 0.5, "picked {name:?}, but the render gives it matte {m} there");
+    assert_eq!(name, "left");
+}
+
+/// 1920-px footage with `left` up to x = 120 and `right` after it, and a 104-px proxy.
+struct Edge;
+impl FootageSource for Edge {
+    fn frame(&self, _: ItemId, f: &Footage, _: Tick) -> Option<Arc<Image>> {
+        Some(Arc::new(Image::new(f.width, f.height)))
+    }
+    fn aux(&self, _: ItemId, _: &Footage, _: Tick) -> Option<Arc<AuxChannels>> {
+        let (w, h) = (1920usize, 40usize);
+        let mut aux = AuxChannels::new(w as u32, h as u32, 1.0);
+        let ids = (0..w * h).map(|i| crypto_float(crypto_hash(if i % w < 120 { "left" } else { "right" }))).collect();
+        aux.channels = vec![("CryptoObject00.R".into(), ids), ("CryptoObject00.G".into(), vec![1.0; w * h])];
+        aux.manifests = vec![("CryptoObject".into(), ["left", "right"].iter().map(|n| (n.to_string(), crypto_hash(n))).collect())];
+        Some(Arc::new(aux))
+    }
+}
+
+/// Proxy buffer pixel 6's centre maps to layer x = 6.5 / (104 / 1920): 120.0 by division, but
+/// 119.99999999999999 by the reciprocal the effect multiplies with. The pick must agree.
+#[test]
+fn pick_maps_pixel_centres_bit_exactly_as_the_effect() {
+    let mut s = Session { footage: Arc::new(Edge), ..Default::default() };
+    let at = |path: &str, width| Footage {
+        path: path.into(),
+        kind: FootageKind::Video,
+        width,
+        height: 40,
+        has_video: true,
+        frame_rate: FrameRate::from_f64(24.0),
+        duration: Tick::from_seconds_f64(2.0),
+        ..Default::default()
+    };
+    s.importer = Some(Arc::new(EdgeProbe(at("/renders/edge.exr", 1920), at("/renders/edge_proxy.exr", 104))));
+    let item = s.execute("file.import", json!({"paths": ["/renders/edge.exr"]})).unwrap()["items"][0].clone();
+    s.execute("comp.new", json!({"name": "C", "width": 1920, "height": 40, "frameRate": 24, "duration": 2})).unwrap();
+    s.execute("layer.addItem", json!({"item": item})).unwrap();
+    s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+    s.execute("file.setProxy", json!({"item": item, "path": "/renders/edge_proxy.exr"})).unwrap();
+    let (name, m) = rendered_matte_of_pick(&mut s, 118.0, 5.0, 1.0);
+    assert_eq!((name.as_str(), m), ("left", 1.0));
+}
+
+struct EdgeProbe(Footage, Footage);
+impl crate::Importer for EdgeProbe {
+    fn probe(&self, path: &str) -> Result<Footage, String> {
+        Ok(if path.contains("proxy") { self.1.clone() } else { self.0.clone() })
+    }
+}
+
+/// Footage whose decoded frames are `num / den` of the probed size (a file re-rendered at another
+/// resolution, a relinked file): the render stretches them over the layer.
+struct OffNominal(u32, u32);
+impl FootageSource for OffNominal {
+    fn frame(&self, _: ItemId, f: &Footage, _: Tick) -> Option<Arc<Image>> {
+        Some(Arc::new(Image::new(f.width * self.0 / self.1, f.height * self.0 / self.1)))
+    }
+    fn aux(&self, _: ItemId, _: &Footage, t: Tick) -> Option<Arc<AuxChannels>> {
+        Some(Arc::new(aux_at(t)))
+    }
+}
+
+/// Points along rows `ys` where the picked ID isn't lit in the rendered matte under the point.
+fn mismatches(s: &mut Session, scales: &[f64], xs: impl Iterator<Item = f64> + Clone, ys: &[f64]) -> Vec<String> {
+    let mut bad = vec![];
+    for &scale in scales {
+        for (x, &y) in ys.iter().flat_map(|y| xs.clone().map(move |x| (x, y))) {
+            if s.execute("effect.cryptomatteAt", json!({"effect": "Cryptomatte", "x": x, "y": y, "scale": scale})).unwrap().is_null() {
+                continue;
+            }
+            let (name, m) = rendered_matte_of_pick(s, x, y, scale);
+            if m < 0.5 {
+                bad.push(format!("scale {scale} ({x:.2}, {y}): picked {name:?}, matte {m}"));
+            }
+        }
+    }
+    bad
+}
+
+const PREVIEW_SCALES: [f64; 7] = [1.0, 0.8, 0.75, 0.74, 0.5, 0.33, 0.25];
+
+/// The pick follows the decoded frame's real size, not the footage's nominal one.
+#[test]
+fn pick_matches_the_render_when_frames_decode_off_nominal_size() {
+    for (num, den) in [(2, 1), (1, 2), (3, 4)] {
+        let mut s = Session { footage: Arc::new(OffNominal(num, den)), importer: Some(Arc::new(Probe)), ..Default::default() };
+        let item = s.execute("file.import", json!({"paths": ["/renders/crypto.exr"]})).unwrap()["items"][0].clone();
+        s.execute("comp.new", json!({"name": "C", "width": 8, "height": 4, "frameRate": 24, "duration": 2})).unwrap();
+        s.execute("layer.addItem", json!({"item": item})).unwrap();
+        s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+        let bad = mismatches(&mut s, &PREVIEW_SCALES, (0..80).map(|i| i as f64 * 0.1 + 0.05), &[0.3, 1.7, 2.6]);
+        assert!(bad.is_empty(), "decode {num}/{den}: {} mismatches:\n{}", bad.len(), bad.join("\n"));
+    }
+}
+
+/// A precomp of a 3D comp, with and without Preserve Resolution (drawn at full size below full
+/// resolution), behind a disabled effect: the pick names the ID the rendered matte shows.
+#[test]
+fn pick_matches_the_render_on_precomps_with_and_without_preserve_resolution() {
+    for preserve in [false, true] {
+        let mut s = Session::default();
+        s.execute("comp.new", json!({"name": "Outer", "width": 40, "height": 20, "frameRate": 24, "duration": 2})).unwrap();
+        let a = s.execute("layer.newSolid", json!({"name": "A", "width": 40, "height": 20})).unwrap()["layer"].clone();
+        let b = s.execute("layer.newSolid", json!({"name": "B", "width": 7, "height": 20})).unwrap()["layer"].clone();
+        s.execute_checked("prop.set", json!({"layer": b, "path": "transform/position", "value": [3.5, 10, -10]})).unwrap();
+        s.execute("layer.setSwitch", json!({"layers": [a, b], "switch": "threeD", "value": true})).unwrap();
+        s.execute("layer.precompose", json!({"layers": [a, b], "name": "Inner"})).unwrap();
+        let inner = *s.project.items.iter().find(|(_, i)| i.name == "Inner").unwrap().0;
+        s.execute_checked("comp.settings", json!({"comp": inner.0, "preserveResolution": preserve})).unwrap();
+        s.execute("layer.select", json!({"layers": [s.active_comp().unwrap().layers[0].id.0]})).ok();
+        s.execute_checked("effect.apply", json!({"effect": "Gaussian Blur"})).unwrap();
+        s.execute_checked("effect.toggle", json!({"effect": 1, "value": false})).unwrap();
+        s.execute_checked("effect.apply", json!({"effect": "Cryptomatte"})).unwrap();
+        let bad = mismatches(&mut s, &PREVIEW_SCALES, (0..93).map(|i| i as f64 * 0.15 + 0.05), &[10.0]);
+        assert!(bad.is_empty(), "preserve {preserve}: {} mismatches:\n{}", bad.len(), bad.join("\n"));
+    }
+}