Components: occurrences with transforms (instances and Paste New copies), world placement of the model (Session::world_state for display, measure, export), active component authoring frame, move/ground/capture/revert positions, move bodies and sketches between components, rename/delete, migration of older designs

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/doc/src/assembly.rs

@@ -0,0 +1,285 @@
+//! Components and occurrences: the design as a tree.
+//!
+//! The root component (id 0) is the design. Every other component lives in a parent component
+//! through one or more occurrences, each with a rigid transform (instances share the component's
+//! contents; a "Paste New" copy is a separate component). A component's sketches, construction
+//! geometry and features are authored in its own frame (its origin); the model is evaluated in
+//! those frames and placed in the world through the occurrence transforms when bodies are
+//! gathered for display, measuring and export (`world_bodies`). Commands take world coordinates
+//! and the engine maps a new feature's geometry into the active component's frame.
+
+use serde::{Deserialize, Serialize};
+use solvecraft_geom::{Plane, Vec3};
+
+use crate::{AxisRef, DocError, Document, FeatureKind, PatternKind, PlaneRef, Result};
+
+/// Column-major 4×4 affine transform (`m[col][row]`).
+pub type Mat = [[f64; 4]; 4];
+
+pub const IDENTITY: Mat = [[1.0, 0.0, 0.0, 0.0], [0.0, 1.0, 0.0, 0.0], [0.0, 0.0, 1.0, 0.0], [0.0, 0.0, 0.0, 1.0]];
+
+pub fn mat_mul(a: &Mat, b: &Mat) -> Mat {
+    let mut r = [[0.0; 4]; 4];
+    for (c, col) in r.iter_mut().enumerate() {
+        for (row, cell) in col.iter_mut().enumerate() {
+            *cell = (0..4).map(|k| a[k][row] * b[c][k]).sum();
+        }
+    }
+    r
+}
+
+pub fn apply_point(m: &Mat, p: Vec3) -> Vec3 {
+    Vec3::new(
+        m[0][0] * p.x + m[1][0] * p.y + m[2][0] * p.z + m[3][0],
+        m[0][1] * p.x + m[1][1] * p.y + m[2][1] * p.z + m[3][1],
+        m[0][2] * p.x + m[1][2] * p.y + m[2][2] * p.z + m[3][2],
+    )
+}
+
+pub fn apply_vector(m: &Mat, v: Vec3) -> Vec3 {
+    Vec3::new(
+        m[0][0] * v.x + m[1][0] * v.y + m[2][0] * v.z,
+        m[0][1] * v.x + m[1][1] * v.y + m[2][1] * v.z,
+        m[0][2] * v.x + m[1][2] * v.y + m[2][2] * v.z,
+    )
+}
+
+pub fn is_identity(m: &Mat) -> bool {
+    m.iter().flatten().zip(IDENTITY.iter().flatten()).all(|(a, b)| (a - b).abs() < 1e-12)
+}
+
+/// Inverse of an affine transform.
+pub fn mat_inverse(m: &Mat) -> Option<Mat> {
+    let a = |r: usize, c: usize| m[c][r];
+    let det = a(0, 0) * (a(1, 1) * a(2, 2) - a(1, 2) * a(2, 1)) - a(0, 1) * (a(1, 0) * a(2, 2) - a(1, 2) * a(2, 0))
+        + a(0, 2) * (a(1, 0) * a(2, 1) - a(1, 1) * a(2, 0));
+    if det.abs() < 1e-14 || !det.is_finite() {
+        return None;
+    }
+    let inv = |r: usize, c: usize| -> f64 {
+        // Cofactor of (c, r) / det.
+        let (r0, r1) = match c {
+            0 => (1, 2),
+            1 => (0, 2),
+            _ => (0, 1),
+        };
+        let (c0, c1) = match r {
+            0 => (1, 2),
+            1 => (0, 2),
+            _ => (0, 1),
+        };
+        let minor = a(r0, c0) * a(r1, c1) - a(r0, c1) * a(r1, c0);
+        let sign = if (r + c) % 2 == 0 { 1.0 } else { -1.0 };
+        sign * minor / det
+    };
+    let mut out = IDENTITY;
+    for r in 0..3 {
+        for c in 0..3 {
+            out[c][r] = inv(r, c);
+        }
+    }
+    let t = Vec3::new(m[3][0], m[3][1], m[3][2]);
+    let it = apply_vector(&out, t);
+    out[3] = [-it.x, -it.y, -it.z, 1.0];
+    Some(out)
+}
+
+/// A rigid transform: rotation by `angle` about `axis` through `origin`, then a translation.
+pub fn rigid(translate: Vec3, origin: Vec3, axis: Vec3, angle: f64) -> Mat {
+    let k = axis.normalized().unwrap_or(Vec3::Z);
+    let (s, c) = angle.sin_cos();
+    let t = 1.0 - c;
+    let r = [
+        [t * k.x * k.x + c, t * k.x * k.y + s * k.z, t * k.x * k.z - s * k.y],
+        [t * k.x * k.y - s * k.z, t * k.y * k.y + c, t * k.y * k.z + s * k.x],
+        [t * k.x * k.z + s * k.y, t * k.y * k.z - s * k.x, t * k.z * k.z + c],
+    ];
+    let mut m = IDENTITY;
+    for col in 0..3 {
+        for row in 0..3 {
+            m[col][row] = r[col][row];
+        }
+    }
+    let ro = apply_vector(&m, origin);
+    let tr = origin - ro + translate;
+    m[3] = [tr.x, tr.y, tr.z, 1.0];
+    m
+}
+
+/// A placement of a component inside a parent component.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Occurrence {
+    pub id: u64,
+    pub component: u64,
+    /// The component it sits in (0 = the root).
+    #[serde(default)]
+    pub parent: u64,
+    pub name: String,
+    #[serde(default = "identity")]
+    pub transform: Mat,
+    /// Grounded occurrences don't move.
+    #[serde(default)]
+    pub grounded: bool,
+}
+
+fn identity() -> Mat {
+    IDENTITY
+}
+
+fn map_plane(m: &Mat, p: &Plane) -> Plane {
+    let (o, x, y) = (apply_point(m, p.origin), apply_vector(m, p.x), apply_vector(m, p.y));
+    Plane::new(o, x, y).unwrap_or(*p)
+}
+
+fn map_plane_ref(m: &Mat, p: &mut PlaneRef) {
+    match p {
+        PlaneRef::Custom { plane } => *plane = map_plane(m, plane),
+        PlaneRef::Offset { base, .. } => map_plane_ref(m, base),
+        PlaneRef::AtAngle { base, axis_origin, axis_dir, .. } => {
+            map_plane_ref(m, base);
+            *axis_origin = apply_point(m, *axis_origin);
+            *axis_dir = apply_vector(m, *axis_dir);
+        }
+        // Named origin planes and construction planes are the component's own.
+        PlaneRef::Origin { .. } | PlaneRef::Construction { .. } => {}
+    }
+}
+
+impl FeatureKind {
+    /// Map the feature's world geometry (points, directions, explicit planes) by `m`.
+    pub fn transform_geometry(&mut self, m: &Mat) {
+        let pt = |p: &mut Vec3| *p = apply_point(m, *p);
+        let dir = |v: &mut Vec3| *v = apply_vector(m, *v);
+        match self {
+            FeatureKind::Sketch { plane, .. }
+            | FeatureKind::ConstructionPlane { plane }
+            | FeatureKind::Split { plane, .. }
+            | FeatureKind::Mirror { plane, .. } => map_plane_ref(m, plane),
+            FeatureKind::Revolve { axis: AxisRef::Line { origin, dir: d }, .. } => {
+                pt(origin);
+                dir(d);
+            }
+            FeatureKind::Fillet { edges, .. } | FeatureKind::Chamfer { edges, .. } => edges.iter_mut().for_each(pt),
+            FeatureKind::Shell { faces, .. } | FeatureKind::OffsetFace { faces, .. } => faces.iter_mut().for_each(pt),
+            FeatureKind::Draft { faces, neutral, pull, .. } => {
+                faces.iter_mut().for_each(pt);
+                map_plane_ref(m, neutral);
+                dir(pull);
+            }
+            FeatureKind::Box { corner, .. } => pt(corner),
+            FeatureKind::Cylinder { base, axis, .. } => {
+                pt(base);
+                dir(axis);
+            }
+            FeatureKind::Sphere { center, .. } | FeatureKind::Torus { center, .. } => pt(center),
+            FeatureKind::Pattern { pattern: PatternKind::Rectangular { dir1, dir2, .. }, .. } => {
+                dir(dir1);
+                if let Some(d) = dir2 {
+                    dir(d);
+                }
+            }
+            FeatureKind::Pattern { pattern: PatternKind::Circular { origin, axis, .. }, .. } => {
+                pt(origin);
+                dir(axis);
+            }
+            FeatureKind::Hole { position, direction, .. } => {
+                pt(position);
+                dir(direction);
+            }
+            FeatureKind::Thread { face, .. } => pt(face),
+            FeatureKind::Scale { origin, .. } => pt(origin),
+            FeatureKind::Move { rotate_axis, .. } => {
+                if let Some(a) = rotate_axis {
+                    dir(a);
+                }
+            }
+            FeatureKind::Revolve { .. }
+            | FeatureKind::Extrude { .. }
+            | FeatureKind::Combine { .. }
+            | FeatureKind::Loft { .. }
+            | FeatureKind::Sweep { .. }
+            | FeatureKind::BoundingSolid { .. }
+            | FeatureKind::Pipe { .. }
+            | FeatureKind::Import { .. }
+            | FeatureKind::MeshImport { .. } => {}
+        }
+    }
+}
+
+impl Document {
+    /// The first occurrence of a component (its placement for authoring).
+    pub fn occurrence_of(&self, component: u64) -> Option<&crate::Occurrence> {
+        self.occurrences.iter().find(|o| o.component == component)
+    }
+
+    /// World transform of a component's frame (through its first occurrence and its parents').
+    pub fn component_transform(&self, component: u64) -> Mat {
+        let mut m = IDENTITY;
+        let mut c = component;
+        for _ in 0..1000 {
+            if c == 0 {
+                break;
+            }
+            let Some(o) = self.occurrence_of(c) else { break };
+            m = mat_mul(&o.transform, &m);
+            c = o.parent;
+        }
+        m
+    }
+
+    /// Every placement of each component: (component, occurrence path ids, world transform).
+    pub fn placements(&self) -> Vec<(u64, Vec<u64>, Mat)> {
+        let mut out = vec![(0, Vec::new(), IDENTITY)];
+        let mut stack: Vec<(u64, Vec<u64>, Mat)> = vec![(0, Vec::new(), IDENTITY)];
+        while let Some((comp, path, m)) = stack.pop() {
+            if path.len() > 64 || out.len() > 100_000 {
+                break;
+            }
+            for o in self.occurrences.iter().filter(|o| o.parent == comp) {
+                let mut p = path.clone();
+                p.push(o.id);
+                let w = mat_mul(&m, &o.transform);
+                out.push((o.component, p.clone(), w));
+                stack.push((o.component, p, w));
+            }
+        }
+        out
+    }
+
+    /// Is `a` inside `b` (or `b` itself)?
+    pub fn component_within(&self, a: u64, b: u64) -> bool {
+        let mut c = a;
+        for _ in 0..1000 {
+            if c == b {
+                return true;
+            }
+            if c == 0 {
+                return false;
+            }
+            match self.components.iter().find(|x| x.id == c) {
+                Some(x) => c = x.parent,
+                None => return false,
+            }
+        }
+        false
+    }
+
+    /// Add an occurrence of an existing component into `parent`.
+    pub fn add_occurrence(&mut self, component: u64, parent: u64, transform: Mat) -> Result<u64> {
+        if component == 0 || !self.components.iter().any(|c| c.id == component) {
+            return Err(DocError::Unknown(format!("component {component}")));
+        }
+        if self.component_within(parent, component) {
+            return Err(DocError::Invalid("a component can't contain itself".into()));
+        }
+        if self.occurrences.len() >= 100_000 {
+            return Err(DocError::Invalid("too many occurrences".into()));
+        }
+        let id = self.next_id.max(1);
+        self.next_id = id + 1;
+        let cname = self.components.iter().find(|c| c.id == component).map(|c| c.name.clone()).unwrap_or_default();
+        let k = self.occurrences.iter().filter(|o| o.component == component).count() + 1;
+        self.occurrences.push(crate::Occurrence { id, component, parent, name: format!("{cname}:{k}"), transform, grounded: false });
+        Ok(id)
+    }
+}

crates/doc/src/document.rs

@@ -638,6 +638,9 @@ pub struct Document {
     /// Components below the root, as a tree (by parent).
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub components: Vec<Component>,
+    /// Placements of components in their parents (each non-root component has at least one).
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub occurrences: Vec<crate::Occurrence>,
     /// Physical material per body (by body name); others use the default.
     #[serde(default, skip_serializing_if = "std::collections::BTreeMap::is_empty")]
     pub materials: std::collections::BTreeMap<String, String>,
@@ -670,6 +673,7 @@ impl Document {
             marker: None,
             next_id: 1,
             components: Vec::new(),
+            occurrences: Vec::new(),
             body_components: Default::default(),
             materials: Default::default(),
         }
@@ -706,6 +710,7 @@ impl Document {
             }
         };
         self.components.push(Component { id, name, parent });
+        self.add_occurrence(id, parent, crate::IDENTITY)?;
         Ok(id)
     }
 
@@ -719,6 +724,13 @@ impl Document {
 
     pub fn from_json(s: &str) -> Result<Document> {
         let d: Document = serde_json::from_str(s).map_err(|e| DocError::Invalid(format!("document: {e}")))?;
+        // Designs from before occurrences: every component gets one, in place.
+        let mut d = d;
+        let missing: Vec<(u64, u64)> =
+            d.components.iter().filter(|c| !d.occurrences.iter().any(|o| o.component == c.id)).map(|c| (c.id, c.parent)).collect();
+        for (c, p) in missing {
+            d.add_occurrence(c, p, crate::IDENTITY)?;
+        }
         if d.features.len() > MAX_FEATURES || d.params.len() > MAX_PARAMS {
             return Err(DocError::Invalid("document too large".into()));
         }

crates/doc/src/eval.rs

@@ -1443,3 +1443,58 @@ fn unique_body_name(st: &ModelState, base: &str) -> String {
     }
     (2..).map(|i| format!("{base} ({i})")).find(|n| st.body(n).is_none()).unwrap_or_else(|| base.to_string())
 }
+
+/// The model placed in the world: each component's bodies, sketches and threads through every
+/// occurrence of it (bodies of the first placement keep their names; further instances get the
+/// occurrence path in brackets). Without components this is the model itself.
+pub fn world_state(doc: &Document, st: &ModelState) -> ModelState {
+    if doc.occurrences.is_empty() {
+        return st.clone();
+    }
+    let comp_of_feature = |id: u64| doc.feature(id).map(|f| f.component).unwrap_or(0);
+    let first_path = |comp: u64| -> Vec<u64> {
+        let mut path = Vec::new();
+        let mut c = comp;
+        for _ in 0..1000 {
+            if c == 0 {
+                break;
+            }
+            let Some(o) = doc.occurrence_of(c) else { break };
+            path.insert(0, o.id);
+            c = o.parent;
+        }
+        path
+    };
+    let mut out = ModelState { body_counter: st.body_counter, ..Default::default() };
+    for (comp, path, m) in doc.placements() {
+        let primary = path == first_path(comp);
+        let label = || -> String {
+            path.iter().filter_map(|id| doc.occurrences.iter().find(|o| o.id == *id)).map(|o| o.name.as_str()).collect::<Vec<_>>().join("/")
+        };
+        let ident = crate::is_identity(&m);
+        for b in st.bodies.iter().filter(|b| doc.body_component(&b.name, b.feature) == comp) {
+            let name = if primary { b.name.clone() } else { format!("{} ({})", b.name, label()) };
+            let body = if ident { b.body.clone() } else { kernel::transform_matrix(&b.body, m).unwrap_or_else(|_| b.body.clone()) };
+            out.bodies.push(ModelBody::new(name, body, b.feature));
+        }
+        if primary {
+            for s in st.sketches.iter().filter(|s| comp_of_feature(s.feature) == comp) {
+                let mut s2 = s.clone();
+                if !ident {
+                    let p = &s.plane;
+                    if let Some(np) = Plane::new(crate::apply_point(&m, p.origin), crate::apply_vector(&m, p.x), crate::apply_vector(&m, p.y)) {
+                        s2.plane = np;
+                    }
+                }
+                out.sketches.push(s2);
+            }
+            for t in st.threads.iter().filter(|t| comp_of_feature(t.feature) == comp) {
+                let mut t2 = t.clone();
+                t2.axis_point = crate::apply_point(&m, t.axis_point);
+                t2.axis = crate::apply_vector(&m, t.axis);
+                out.threads.push(t2);
+            }
+        }
+    }
+    out
+}

crates/doc/src/lib.rs

@@ -5,13 +5,15 @@
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 #![forbid(unsafe_code)]
 
+mod assembly;
 mod document;
 mod eval;
 pub mod expr;
 pub mod project;
 
+pub use assembly::{IDENTITY, Mat, Occurrence, apply_point, apply_vector, is_identity, mat_inverse, mat_mul, rigid};
 pub use document::*;
-pub use eval::{FeatureResult, Model, ModelBody, ModelState, SolvedSketch, ThreadInfo, parse_metric_thread};
+pub use eval::{FeatureResult, Model, ModelBody, ModelState, SolvedSketch, ThreadInfo, parse_metric_thread, world_state};
 pub use solvecraft_kernel as kernel;
 pub use solvecraft_sketch as sketch;
 

crates/engine/src/cmd/component.rs

@@ -1,11 +1,14 @@
-//! Components: the design as a tree. New sketches and features go into the active component;
-//! bodies belong to their feature's component unless moved. (Groundwork for assemblies:
-//! occurrences, joints and per-component physical properties build on this.)
+//! Components and occurrences: the design as a tree (see `solvecraft_doc` assembly docs).
+//! New sketches and features go into the active component, authored in its frame; bodies
+//! belong to their feature's component unless moved; occurrences place components (instances
+//! share contents, "paste new" copies them) and can be grounded and moved.
 
 use serde_json::{Value, json};
+use solvecraft_doc::{FeatureKind, Mat, Occurrence};
+use solvecraft_geom::Vec3;
 
 use super::CommandSpec;
-use crate::params::{bad, str_, string_list};
+use crate::params::{bad, bool_, num, str_, string_list, vec3};
 use crate::{Result, Session};
 
 pub static COMMANDS: &[CommandSpec] = &[
@@ -18,9 +21,21 @@ pub static COMMANDS: &[CommandSpec] = &[
         .params("bodies: [names] → one new component per body, named after it"),
     CommandSpec::new("component.activate", "Activate Component", activate).noundo().params("component: id or name (0 or \"root\" for the design)"),
     CommandSpec::new("component.list", "List Components", list).noundo(),
+    CommandSpec::new("component.rename", "Rename Component", rename).params("component, name"),
+    CommandSpec::new("component.delete", "Delete Component", delete).params("component: deletes it, its subcomponents, occurrences and features"),
+    CommandSpec::new("component.move_bodies", "Move Bodies to Component", move_bodies).params("bodies: [names], component"),
+    CommandSpec::new("component.move_sketches", "Move Sketches to Component", move_sketches).params("sketches: [ids or names], component"),
+    CommandSpec::new("occurrence.copy", "Paste (Instance)", copy_occurrence)
+        .params("component (or occurrence): what to place again; parent?: component (default: the same parent); translate?: [x,y,z]"),
+    CommandSpec::new("component.paste_new", "Paste New", paste_new).params("component: copied with its features into a new, independent component; translate?: [x,y,z]"),
+    CommandSpec::new("occurrence.move", "Move Occurrence", move_occurrence)
+        .params("occurrence; translate?: [x,y,z]; axis?: [x,y,z], angle?: radians or \"30 deg\", origin?: [x,y,z]; capture?: bool (default true; false keeps it pending until Capture Position)"),
+    CommandSpec::new("occurrence.ground", "Ground", ground).params("occurrence; grounded?: bool (default toggles)"),
+    CommandSpec::new("SnapshotCmd", "Capture Position", capture).at("SOLID", "POSITION").icon("capture").params("keeps pending occurrence moves"),
+    CommandSpec::new("AsBuiltPositionsCmd", "Revert Position", revert).at("SOLID", "POSITION").icon("revert").noundo().params("drops pending occurrence moves"),
 ];
 
-fn component_key(v: Option<&Value>) -> Option<String> {
+fn key(v: Option<&Value>) -> Option<String> {
     match v {
         Some(Value::Number(n)) => Some(n.to_string()),
         Some(Value::String(s)) => Some(s.clone()),
@@ -28,18 +43,30 @@ fn component_key(v: Option<&Value>) -> Option<String> {
     }
 }
 
+fn component(s: &Session, p: &Value, k: &str, cmd: &str) -> Result<u64> {
+    let kk = key(p.get(k)).ok_or_else(|| bad(cmd, format!("`{k}` must be a component id or name")))?;
+    s.doc.find_component(&kk).ok_or_else(|| bad(cmd, format!("no component `{kk}`")))
+}
+
+fn occurrence(s: &Session, p: &Value, cmd: &str) -> Result<u64> {
+    let kk = key(p.get("occurrence")).ok_or_else(|| bad(cmd, "`occurrence` must be an id or name"))?;
+    s.doc.occurrences.iter().find(|o| o.id.to_string() == kk || o.name == kk).map(|o| o.id).ok_or_else(|| bad(cmd, format!("no occurrence `{kk}`")))
+}
+
+fn translation(t: Vec3) -> Mat {
+    solvecraft_doc::rigid(t, Vec3::ZERO, Vec3::Z, 0.0)
+}
+
 fn new_component(s: &mut Session, p: &Value) -> Result<Value> {
     let cmd = "FusionCreateNewComponentCommand";
-    let parent = match component_key(p.get("parent")) {
-        Some(k) => s.doc.find_component(&k).ok_or_else(|| bad(cmd, format!("no component `{k}`")))?,
-        None => s.active_component,
-    };
+    let parent = if p.get("parent").is_some() { component(s, p, "parent", cmd)? } else { s.active_component };
     let id = s.doc_mut().add_component(str_(p, "name"), parent)?;
     if p.get("activate").and_then(Value::as_bool).unwrap_or(true) {
         s.active_component = id;
     }
     let name = s.doc.components.iter().find(|c| c.id == id).map(|c| c.name.clone()).unwrap_or_default();
-    Ok(json!({"component": id, "name": name, "parent": parent}))
+    let occ = s.doc.occurrence_of(id).map(|o| o.id);
+    Ok(json!({"component": id, "name": name, "parent": parent, "occurrence": occ}))
 }
 
 fn from_bodies(s: &mut Session, p: &Value) -> Result<Value> {
@@ -65,9 +92,7 @@ fn from_bodies(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 fn activate(s: &mut Session, p: &Value) -> Result<Value> {
-    let cmd = "component.activate";
-    let k = component_key(p.get("component")).ok_or_else(|| bad(cmd, "`component` must be an id or name"))?;
-    let id = s.doc.find_component(&k).ok_or_else(|| bad(cmd, format!("no component `{k}`")))?;
+    let id = component(s, p, "component", "component.activate")?;
     s.active_component = id;
     s.revision += 1;
     Ok(json!({ "active": id }))
@@ -78,12 +103,266 @@ fn list(s: &mut Session, _p: &Value) -> Result<Value> {
     let doc = &s.doc;
     let node = |id: u64, name: &str, parent: Option<u64>| {
         let bodies: Vec<&str> = st.bodies.iter().filter(|b| doc.body_component(&b.name, b.feature) == id).map(|b| b.name.as_str()).collect();
-        let features: Vec<&str> = doc.features.iter().filter(|f| f.component == id).map(|f| f.name.as_str()).collect();
-        json!({"id": id, "name": name, "parent": parent, "bodies": bodies, "features": features})
+        let features: Vec<&str> = doc
+            .features
+            .iter()
+            .filter(|f| f.component == id && !matches!(f.kind, FeatureKind::Sketch { .. } | FeatureKind::ConstructionPlane { .. }))
+            .map(|f| f.name.as_str())
+            .collect();
+        let sketches: Vec<&str> =
+            doc.features.iter().filter(|f| f.component == id && matches!(f.kind, FeatureKind::Sketch { .. })).map(|f| f.name.as_str()).collect();
+        let construction: Vec<&str> = doc
+            .features
+            .iter()
+            .filter(|f| f.component == id && matches!(f.kind, FeatureKind::ConstructionPlane { .. }))
+            .map(|f| f.name.as_str())
+            .collect();
+        let occurrences: Vec<&Occurrence> = doc.occurrences.iter().filter(|o| o.component == id).collect();
+        let children: Vec<&Occurrence> = doc.occurrences.iter().filter(|o| o.parent == id).collect();
+        json!({"id": id, "name": name, "parent": parent, "bodies": bodies, "features": features, "sketches": sketches,
+            "construction": construction, "occurrences": occurrences, "children": children})
     };
     let mut out = vec![node(0, &doc.name, None)];
     for c in &doc.components {
         out.push(node(c.id, &c.name, Some(c.parent)));
     }
-    Ok(json!({"active": s.active_component, "components": out}))
+    Ok(json!({"active": s.active_component, "components": out, "pending_moves": s.pending_moves.keys().collect::<Vec<_>>()}))
+}
+
+fn rename(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "component.rename";
+    let id = component(s, p, "component", cmd)?;
+    let name =
+        str_(p, "name").map(str::trim).filter(|n| !n.is_empty() && n.len() <= 128).ok_or_else(|| bad(cmd, "`name` must be 1…128 characters"))?;
+    if id == 0 {
+        s.doc_mut().name = name.to_string();
+    } else if let Some(c) = s.doc_mut().components.iter_mut().find(|c| c.id == id) {
+        c.name = name.to_string();
+    }
+    Ok(json!({"component": id, "name": name}))
+}
+
+fn delete(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "component.delete";
+    let id = component(s, p, "component", cmd)?;
+    if id == 0 {
+        return Err(bad(cmd, "the design itself can't be deleted"));
+    }
+    let gone: Vec<u64> = s.doc.components.iter().filter(|c| s.doc.component_within(c.id, id)).map(|c| c.id).collect();
+    let feats: Vec<u64> = s.doc.features.iter().filter(|f| gone.contains(&f.component)).map(|f| f.id).collect();
+    let d = s.doc_mut();
+    for f in &feats {
+        let _ = d.delete_feature(*f);
+    }
+    d.components.retain(|c| !gone.contains(&c.id));
+    d.occurrences.retain(|o| !gone.contains(&o.component) && !gone.contains(&o.parent));
+    d.body_components.retain(|_, c| !gone.contains(c));
+    if gone.contains(&s.active_component) {
+        s.active_component = 0;
+    }
+    Ok(json!({"deleted": gone, "features": feats}))
+}
+
+fn move_bodies(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "component.move_bodies";
+    let to = component(s, p, "component", cmd)?;
+    let bodies = string_list(p, "bodies");
+    let st = s.model.state();
+    if bodies.is_empty() || bodies.iter().any(|b| st.body(b).is_none()) {
+        return Err(bad(cmd, "`bodies` must list existing bodies"));
+    }
+    for b in &bodies {
+        let feature = st.body(b).map(|x| x.feature).unwrap_or(0);
+        let own = s.doc.feature(feature).map(|f| f.component).unwrap_or(0);
+        if own == to {
+            s.doc_mut().body_components.remove(b);
+        } else {
+            s.doc_mut().body_components.insert(b.clone(), to);
+        }
+    }
+    Ok(json!({"bodies": bodies, "component": to}))
+}
+
+fn move_sketches(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "component.move_sketches";
+    let to = component(s, p, "component", cmd)?;
+    let keys = string_list(p, "sketches");
+    let mut ids = Vec::new();
+    for k in &keys {
+        match s.doc.find_feature(k) {
+            Some(f) if matches!(f.kind, FeatureKind::Sketch { .. }) => ids.push(f.id),
+            _ => return Err(bad(cmd, format!("no sketch `{k}`"))),
+        }
+    }
+    if ids.is_empty() {
+        return Err(bad(cmd, "`sketches` must list sketches"));
+    }
+    for id in &ids {
+        if let Some(f) = s.doc_mut().feature_mut(*id) {
+            f.component = to;
+        }
+    }
+    Ok(json!({"sketches": ids, "component": to}))
+}
+
+fn copy_occurrence(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "occurrence.copy";
+    let comp = if p.get("occurrence").is_some() {
+        let o = occurrence(s, p, cmd)?;
+        s.doc.occurrences.iter().find(|x| x.id == o).map(|x| x.component).unwrap_or(0)
+    } else {
+        component(s, p, "component", cmd)?
+    };
+    let src = s.doc.occurrence_of(comp).cloned().ok_or_else(|| bad(cmd, "that component has no occurrence"))?;
+    let parent = if p.get("parent").is_some() { component(s, p, "parent", cmd)? } else { src.parent };
+    let t = p.get("translate").and_then(vec3).unwrap_or(Vec3::ZERO);
+    let m = solvecraft_doc::mat_mul(&translation(t), &src.transform);
+    let id = s.doc_mut().add_occurrence(comp, parent, m)?;
+    Ok(json!({"occurrence": id, "component": comp}))
+}
+
+fn paste_new(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "component.paste_new";
+    let comp = component(s, p, "component", cmd)?;
+    if comp == 0 {
+        return Err(bad(cmd, "pick a component, not the design"));
+    }
+    let src = s.doc.components.iter().find(|c| c.id == comp).cloned().ok_or_else(|| bad(cmd, "component"))?;
+    let occ = s.doc.occurrence_of(comp).cloned();
+    let new_id = s.doc_mut().add_component(Some(&format!("{} (copy)", src.name)), src.parent)?;
+    // Copy the component's features with fresh ids and names; references between them follow.
+    let feats: Vec<solvecraft_doc::Feature> = s.doc.features.iter().filter(|f| f.component == comp).cloned().collect();
+    let mut idmap: std::collections::HashMap<u64, u64> = Default::default();
+    let mut namemap: std::collections::HashMap<String, String> = Default::default();
+    let mut new_ids = Vec::new();
+    for f in &feats {
+        let nid = s.doc_mut().add_feature(f.kind.clone(), Some(&format!("{} (copy)", f.name)))?;
+        idmap.insert(f.id, nid);
+        let nname = s.doc.feature(nid).map(|x| x.name.clone()).unwrap_or_default();
+        namemap.insert(f.name.clone(), nname);
+        new_ids.push(nid);
+    }
+    for nid in &new_ids {
+        let Some(f) = s.doc.feature(*nid).cloned() else { continue };
+        let mut v = serde_json::to_value(&f.kind).map_err(|e| bad(cmd, e.to_string()))?;
+        remap(&mut v, &idmap, &namemap, 0);
+        let kind: FeatureKind = serde_json::from_value(v).map_err(|e| bad(cmd, e.to_string()))?;
+        if let Some(slot) = s.doc_mut().feature_mut(*nid) {
+            slot.kind = kind;
+            slot.component = new_id;
+        }
+    }
+    let t = p.get("translate").and_then(vec3).unwrap_or(Vec3::ZERO);
+    let base = occ.map(|o| o.transform).unwrap_or(solvecraft_doc::IDENTITY);
+    if let Some(o) = s.doc_mut().occurrences.iter_mut().find(|o| o.component == new_id) {
+        o.transform = solvecraft_doc::mat_mul(&translation(t), &base);
+    }
+    Ok(json!({"component": new_id, "features": new_ids}))
+}
+
+/// Point copied features at their copied sketches and features.
+fn remap(v: &mut Value, ids: &std::collections::HashMap<u64, u64>, names: &std::collections::HashMap<String, String>, depth: usize) {
+    if depth > 32 {
+        return;
+    }
+    match v {
+        Value::Object(o) => {
+            for (k, x) in o.iter_mut() {
+                match (k.as_str(), &*x) {
+                    ("sketch" | "path_sketch", Value::Number(n)) => {
+                        if let Some(m) = n.as_u64().and_then(|i| ids.get(&i)) {
+                            *x = json!(m);
+                        }
+                    }
+                    ("features", Value::Array(_)) => {
+                        if let Value::Array(a) = x {
+                            for e in a.iter_mut() {
+                                if let Some(m) = e.as_str().and_then(|n| names.get(n)) {
+                                    *e = json!(m);
+                                }
+                            }
+                        }
+                    }
+                    _ => remap(x, ids, names, depth + 1),
+                }
+            }
+        }
+        Value::Array(a) => a.iter_mut().for_each(|x| remap(x, ids, names, depth + 1)),
+        _ => {}
+    }
+}
+
+fn move_occurrence(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "occurrence.move";
+    let id = occurrence(s, p, cmd)?;
+    let o = s.doc.occurrences.iter().find(|o| o.id == id).cloned().ok_or_else(|| bad(cmd, "occurrence"))?;
+    if o.grounded {
+        return Err(bad(cmd, format!("{} is grounded", o.name)));
+    }
+    let t = p.get("translate").and_then(vec3).unwrap_or(Vec3::ZERO);
+    let axis = p.get("axis").and_then(vec3).unwrap_or(Vec3::Z);
+    let angle = match p.get("angle") {
+        Some(Value::String(e)) => s.doc.eval(e, solvecraft_doc::expr::Kind::Angle).map_err(|e| bad(cmd, e.to_string()))?,
+        _ => num(p, "angle").unwrap_or(0.0),
+    };
+    if !(t.is_finite() && angle.is_finite()) {
+        return Err(bad(cmd, "non-finite move"));
+    }
+    let origin = p.get("origin").and_then(vec3).unwrap_or(Vec3::ZERO);
+    let delta = solvecraft_doc::rigid(t, origin, axis, angle);
+    let cur = s.pending_moves.get(&id).copied().unwrap_or(o.transform);
+    let next = solvecraft_doc::mat_mul(&delta, &cur);
+    if bool_(p, "capture").unwrap_or(true) {
+        s.pending_moves.remove(&id);
+        if let Some(x) = s.doc_mut().occurrences.iter_mut().find(|x| x.id == id) {
+            x.transform = next;
+        }
+    } else {
+        s.pending_moves.insert(id, next);
+        s.revision += 1;
+    }
+    Ok(json!({"occurrence": id, "transform": next, "pending": !bool_(p, "capture").unwrap_or(true)}))
+}
+
+fn ground(s: &mut Session, p: &Value) -> Result<Value> {
+    let cmd = "occurrence.ground";
+    let id = occurrence(s, p, cmd)?;
+    let want = bool_(p, "grounded");
+    let o = s.doc_mut().occurrences.iter_mut().find(|o| o.id == id).ok_or_else(|| bad(cmd, "occurrence"))?;
+    o.grounded = want.unwrap_or(!o.grounded);
+    let g = o.grounded;
+    Ok(json!({"occurrence": id, "grounded": g}))
+}
+
+fn capture(s: &mut Session, _p: &Value) -> Result<Value> {
+    let moves = std::mem::take(&mut s.pending_moves);
+    let n = moves.len();
+    for (id, m) in moves {
+        if let Some(o) = s.doc_mut().occurrences.iter_mut().find(|o| o.id == id) {
+            o.transform = m;
+        }
+    }
+    s.revision += 1;
+    Ok(json!({ "captured": n }))
+}
+
+fn revert(s: &mut Session, _p: &Value) -> Result<Value> {
+    let n = s.pending_moves.len();
+    s.pending_moves.clear();
+    s.revision += 1;
+    Ok(json!({ "reverted": n }))
+}
+
+/// The active component's frame from world coordinates (for new features' geometry).
+pub fn to_active_frame(s: &Session, kind: &mut FeatureKind) {
+    if s.active_component == 0 {
+        return;
+    }
+    let m = s.doc.component_transform(s.active_component);
+    if solvecraft_doc::is_identity(&m) {
+        return;
+    }
+    if let Some(inv) = solvecraft_doc::mat_inverse(&m) {
+        kind.transform_geometry(&inv);
+    }
 }

crates/engine/src/cmd/features.rs

@@ -236,6 +236,9 @@ fn check_expr(s: &Session, e: &str, kind: Kind, cmd: &str, what: &str) -> Result
 /// Add a feature, evaluate, and report its result (an evaluation error fails the command).
 fn add_feature(s: &mut Session, p: &Value, kind: FeatureKind) -> Result<Value> {
     let name = str_(p, "name");
+    // Commands speak world coordinates; the feature is authored in the active component.
+    let mut kind = kind;
+    super::component::to_active_frame(s, &mut kind);
     let id = s.doc_mut().add_feature(kind, name)?;
     let comp = s.active_component;
     if comp != 0

crates/engine/src/cmd/file.rs

@@ -160,7 +160,7 @@ fn save_as(s: &mut Session, p: &Value) -> Result<Value> {
 
 fn export_to(s: &Session, path: &str, format: Format, bodies: &[String]) -> Result<Value> {
     let name = std::path::Path::new(path).file_stem().map(|x| x.to_string_lossy().to_string()).unwrap_or_else(|| s.doc.name.clone());
-    let bytes = solvecraft_io::export(&s.model.state(), bodies, format, &name)?;
+    let bytes = solvecraft_io::export(&s.world_state(), bodies, format, &name)?;
     std::fs::write(path, &bytes).map_err(|e| EngineError::Other(format!("{path}: {e}")))?;
     Ok(json!({"path": path, "bytes": bytes.len(), "format": format!("{format:?}")}))
 }

crates/engine/src/cmd/inspect.rs

@@ -47,7 +47,7 @@ pub fn measure_json(b: &solvecraft_doc::ModelBody) -> Value {
 
 fn measure(s: &mut Session, p: &Value) -> Result<Value> {
     let want = string_list(p, "bodies");
-    let st = s.model.state();
+    let st = s.world_state();
     let mut bodies: Vec<Value> = st.bodies.iter().filter(|b| want.is_empty() || want.contains(&b.name)).map(measure_json).collect();
     // Mass from each body's material.
     for b in &mut bodies {
@@ -197,7 +197,7 @@ fn body_of<'a>(st: &'a solvecraft_doc::ModelState, p: &Value, cmd: &str) -> Resu
 }
 
 fn model_edges(s: &mut Session, p: &Value) -> Result<Value> {
-    let st = s.model.state();
+    let st = s.world_state();
     let b = body_of(&st, p, "model.edges")?;
     let tol = (b.body.size() * 2e-3).max(1e-3);
     let edges: Vec<Value> = b
@@ -210,7 +210,7 @@ fn model_edges(s: &mut Session, p: &Value) -> Result<Value> {
 }
 
 fn model_faces(s: &mut Session, p: &Value) -> Result<Value> {
-    let st = s.model.state();
+    let st = s.world_state();
     let b = body_of(&st, p, "model.faces")?;
     let tol = (b.body.size() * 2e-3).max(1e-3);
     let faces: Vec<Value> = b
@@ -227,7 +227,7 @@ fn commands(s: &mut Session, _p: &Value) -> Result<Value> {
 }
 
 fn model_threads(s: &mut Session, _p: &Value) -> Result<Value> {
-    let st = s.model.state();
+    let st = s.world_state();
     Ok(json!({ "threads": st.threads }))
 }
 

crates/engine/src/cmd/sketch.rs

@@ -354,7 +354,9 @@ fn create_sketch(s: &mut Session, p: &Value) -> Result<Value> {
     let (vals, _) = s.doc.param_values();
     s.doc.resolve_plane(&vals, &plane, 0)?;
     let name = str_(p, "name");
-    let id = s.doc_mut().add_feature(FeatureKind::Sketch { plane, sketch: Sketch::new() }, name)?;
+    let mut kind = FeatureKind::Sketch { plane, sketch: Sketch::new() };
+    super::component::to_active_frame(s, &mut kind);
+    let id = s.doc_mut().add_feature(kind, name)?;
     let comp = s.active_component;
     if let Some(f) = s.doc_mut().feature_mut(id) {
         f.component = comp;

crates/engine/src/lib.rs

@@ -151,6 +151,9 @@ pub struct Session {
     pub auto_project: bool,
     /// The component new sketches and features go into (0 = the root).
     pub active_component: u64,
+    /// Occurrence moves not captured yet (Capture Position keeps them, a recompute drops them).
+    pub pending_moves: std::collections::BTreeMap<u64, solvecraft_doc::Mat>,
+    world_cache: std::sync::Mutex<Option<(u64, Arc<solvecraft_doc::ModelState>)>>,
 }
 
 const MAX_UNDO: usize = 200;
@@ -180,6 +183,8 @@ impl Session {
             revision: 1,
             auto_project: true,
             active_component: 0,
+            pending_moves: Default::default(),
+            world_cache: Default::default(),
         }
     }
 
@@ -204,6 +209,37 @@ impl Session {
     }
 
     /// Re-evaluate the model after a document change.
+    /// The model placed in the world through component occurrences (and uncaptured moves): what
+    /// to display, measure, pick and export. The same as `model.state()` without components.
+    pub fn world_state(&self) -> Arc<solvecraft_doc::ModelState> {
+        let st = self.model.state();
+        if self.doc.occurrences.is_empty() {
+            return st;
+        }
+        if let Ok(c) = self.world_cache.lock()
+            && let Some((rev, w)) = c.as_ref()
+            && *rev == self.revision
+        {
+            return w.clone();
+        }
+        let w = if self.pending_moves.is_empty() {
+            solvecraft_doc::world_state(&self.doc, &st)
+        } else {
+            let mut d = (*self.doc).clone();
+            for o in &mut d.occurrences {
+                if let Some(m) = self.pending_moves.get(&o.id) {
+                    o.transform = *m;
+                }
+            }
+            solvecraft_doc::world_state(&d, &st)
+        };
+        let w = Arc::new(w);
+        if let Ok(mut c) = self.world_cache.lock() {
+            *c = Some((self.revision, w.clone()));
+        }
+        w
+    }
+
     pub fn refresh(&mut self) {
         self.model.evaluate(&self.doc);
         self.revision += 1;
@@ -272,6 +308,8 @@ impl Session {
             revision: self.revision,
             auto_project: self.auto_project,
             active_component: self.active_component,
+            pending_moves: self.pending_moves.clone(),
+            world_cache: Default::default(),
         }
     }
 

crates/engine/src/tests.rs

@@ -733,3 +733,69 @@ fn pipe_scale_offset_bounding_and_materials() {
     assert_eq!(m["bodies"][0]["material"], "Aluminum");
     assert!(s.execute("PhysicalMaterialCommand", &json!({"bodies": ["Cube"], "material": "unobtainium"})).is_err());
 }
+
+#[test]
+fn components_occurrences_and_world_placement() {
+    let mut s = Session::default();
+    run(&mut s, "PrimitiveBox", json!({"length": 10, "width": 10, "height": 10, "body_name": "Base"}));
+    // A component, active: its box is authored in its frame.
+    let c = run(&mut s, "FusionCreateNewComponentCommand", json!({"name": "Arm"}));
+    let (cid, occ) = (c["component"].as_u64().unwrap(), c["occurrence"].as_u64().unwrap());
+    run(&mut s, "PrimitiveBox", json!({"corner": [20, 0, 0], "length": 10, "width": 4, "height": 4, "body_name": "ArmBody"}));
+    run(&mut s, "component.activate", json!({"component": 0}));
+    let bbox = |s: &mut Session, b: &str| run(s, "MeasureCommand", json!({ "bodies": [b] }))["bodies"][0]["bbox"].clone();
+    assert_eq!(bbox(&mut s, "ArmBody")["min"][0], 20.0);
+    // Move the occurrence: the world placement follows, the authoring model doesn't change.
+    run(&mut s, "occurrence.move", json!({"occurrence": occ, "translate": [0, 50, 0]}));
+    assert!((bbox(&mut s, "ArmBody")["min"][1].as_f64().unwrap() - 50.0).abs() < 1e-9);
+    assert_eq!(s.model.state().body("ArmBody").unwrap().mesh().bounds().min.y, 0.0);
+    // A fillet picked in the world, while the component is active, lands on its edge.
+    run(&mut s, "component.activate", json!({"component": "Arm"}));
+    run(&mut s, "FusionFilletEdgesCommand", json!({"edges": [[25, 54, 4]], "radius": 1}));
+    let v = run(&mut s, "MeasureCommand", json!({"bodies": ["ArmBody"]}))["total"]["volume_mm3"].as_f64().unwrap();
+    assert!(rel(v, 160.0 - (1.0 - PI / 4.0) * 10.0) < 1e-4, "{v}");
+    run(&mut s, "component.activate", json!({"component": 0}));
+    // Instances share the contents; a copy is independent.
+    run(&mut s, "occurrence.copy", json!({"component": cid, "translate": [0, 20, 0]}));
+    let w = s.world_state();
+    assert_eq!(w.bodies.len(), 3, "{:?}", w.bodies.iter().map(|b| &b.name).collect::<Vec<_>>());
+    let pn = run(&mut s, "component.paste_new", json!({"component": cid, "translate": [0, -30, 0]}));
+    assert_eq!(pn["features"].as_array().map(|a| a.len()), Some(2));
+    assert_eq!(s.world_state().bodies.len(), 4);
+    // Ground stops moves; pending moves show until captured or reverted.
+    run(&mut s, "occurrence.ground", json!({"occurrence": occ}));
+    assert!(s.execute("occurrence.move", &json!({"occurrence": occ, "translate": [1, 0, 0]})).is_err());
+    run(&mut s, "occurrence.ground", json!({"occurrence": occ, "grounded": false}));
+    run(&mut s, "occurrence.move", json!({"occurrence": occ, "translate": [0, 0, 5], "capture": false}));
+    assert!((bbox(&mut s, "ArmBody")["min"][2].as_f64().unwrap() - 5.0).abs() < 1e-9);
+    run(&mut s, "AsBuiltPositionsCmd", json!({}));
+    assert!(bbox(&mut s, "ArmBody")["min"][2].as_f64().unwrap().abs() < 1e-9);
+    run(&mut s, "occurrence.move", json!({"occurrence": occ, "translate": [0, 0, 5], "capture": false}));
+    run(&mut s, "SnapshotCmd", json!({}));
+    assert!(s.pending_moves.is_empty());
+    assert!((bbox(&mut s, "ArmBody")["min"][2].as_f64().unwrap() - 5.0).abs() < 1e-9);
+    // Bodies and sketches move between components.
+    run(&mut s, "component.move_bodies", json!({"bodies": ["Base"], "component": "Arm"}));
+    let l = run(&mut s, "component.list", json!({}));
+    let arm = l["components"].as_array().unwrap().iter().find(|x| x["id"] == cid).unwrap().clone();
+    assert!(arm["bodies"].as_array().unwrap().iter().any(|b| b == "Base"), "{arm}");
+    run(&mut s, "SketchCreate", json!({"plane": "XY", "name": "S1"}));
+    run(&mut s, "SketchStop", json!({}));
+    run(&mut s, "component.move_sketches", json!({"sketches": ["S1"], "component": cid}));
+    assert_eq!(s.doc.find_feature("S1").unwrap().component, cid);
+    // Undo/redo and the timeline work with features in components.
+    run(&mut s, "UndoCommand", json!({}));
+    assert_eq!(s.doc.find_feature("S1").unwrap().component, 0);
+    run(&mut s, "RedoCommand", json!({}));
+    run(&mut s, "timeline.rollTo", json!({"position": 1}));
+    // Only Base is left; it now lives in Arm, which is placed twice (original and instance).
+    assert_eq!(s.world_state().bodies.len(), 2);
+    run(&mut s, "timeline.rollTo", json!({}));
+    // Saved and loaded; older designs get occurrences.
+    let back = solvecraft_doc::Document::from_json(&s.doc.to_json()).unwrap();
+    assert_eq!(back.occurrences.len(), s.doc.occurrences.len());
+    let mut old: serde_json::Value = serde_json::from_str(&s.doc.to_json()).unwrap();
+    old.as_object_mut().unwrap().remove("occurrences");
+    let migrated = solvecraft_doc::Document::from_json(&old.to_string()).unwrap();
+    assert_eq!(migrated.occurrences.len(), migrated.components.len());
+}

crates/engine/src/view.rs

@@ -37,7 +37,7 @@ pub mod colors {
 
 /// Bounds of everything visible.
 pub fn bounds(s: &Session) -> Aabb3 {
-    let st = s.model.state();
+    let st = s.world_state();
     let mut b = Aabb3::EMPTY;
     for body in &st.bodies {
         b = b.union(&body.mesh().bounds());
@@ -92,7 +92,7 @@ pub fn sketch_lines(sk: &Sketch, plane: &Plane, active: bool, determined: &[bool
 
 /// The scene for a headless render.
 pub fn scene(s: &Session, cam: &Camera) -> Scene {
-    let st = s.model.state();
+    let st = s.world_state();
     let mut sc = Scene { background: Some((colors::BG_TOP, colors::BG_BOTTOM)), ..Default::default() };
     let b = bounds(s);
     sc.radius = (b.diagonal() * 0.5).max(cam.half_height()).max(10.0) + b.center().dist(cam.target);