brep_render/engine_state/

transform_gizmo.rs

use super::*;

/// Which of the two gizmos is currently armed for the feature. `Transform` shows
/// the move/rotate gizmo; `Dimension` shows the on-canvas draggable dimension
/// annotations (feature-dimensions FD-1). Expanding a feature arms `Dimension`;
/// the viewport sphere/center toggle flips to `Transform` and back. The two modes
/// are EXCLUSIVE — the transform gizmo never renders in `Dimension` mode and
/// vice-versa.
#[derive(Default, Clone, Copy, PartialEq, Eq, Debug)]
pub enum GizmoMode {
    /// Neither gizmo armed (`feature_id` is `None`).
    #[default]
    None,
    /// The move/rotate transform gizmo is armed.
    Transform,
    /// The dimension-annotation gizmo is armed (FD-1).
    Dimension,
}

/// The transform-controls gizmo controller state (see the impl block below).
#[derive(Default)]
pub struct TransformArm {
    /// The feature id whose gizmo is armed (for EITHER mode), or `None`
    /// (disarmed → `mode == None`).
    pub(super) feature_id: Option<String>,
    /// Which gizmo is armed for `feature_id` (transform vs dimension). `None`
    /// exactly when `feature_id` is `None`.
    pub(super) mode: GizmoMode,
    /// The live handle drag, captured on pointer-down over a gizmo handle.
    pub(super) drag: Option<TransformDrag>,
    /// When the armed subject is ONE SPLINE ANCHOR rather than the feature's
    /// `transform` param: the anchor index into `persistentData.spline.points`
    /// of `feature_id` (an SP feature). The same gizmo, press / drag / release
    /// and live-follow apply; only the pose read and write-back differ (see
    /// `spline_edit.rs`).
    pub(super) anchor: Option<usize>,
}

/// A grab snapshot for an in-flight transform-gizmo drag: the grabbed handle,
/// the grab screen point, and the feature's pose AT GRAB. Every drag move
/// resolves an absolute delta from this grab (against the pinned grab-time
/// frame) and re-applies it to `start`, so the drag never accumulates error.
#[derive(Clone, Copy)]
pub(super) struct TransformDrag {
    handle: u32,
    sx: f32,
    sy: f32,
    start: TransformPose,
}

/// A TRS pose read from / written to a feature's `inputParams.transform`
/// (`rotation` in DEGREES, intrinsic XYZ Euler order — the kernel `transform_bake`
/// convention, `M = T·R·S`).
#[derive(Clone, Copy, PartialEq, Debug)]
struct TransformPose {
    position: [f64; 3],
    rotation_deg: [f64; 3],
    scale: [f64; 3],
}

/// A world-space delta shared by feature and component gizmo controllers.
#[derive(Clone, Copy, PartialEq, Debug)]
pub(super) enum TransformDelta {
    /// World-space translation, added to `position`.
    Translate([f64; 3]),
    /// World-axis rotation, pre-multiplied onto the pose's orientation.
    Rotate { axis: [f64; 3], radians: f64 },
}

/// Decode widget drag JSON; unknown kinds and invalid JSON produce no delta.
pub(super) fn parse_drag_delta(json: &str) -> Option<TransformDelta> {
    let value: serde_json::Value = serde_json::from_str(json).ok()?;
    match value.get("kind").and_then(|k| k.as_str()) {
        Some("translate") => Some(TransformDelta::Translate(
            crate::json_support::vec3_or(value.get("world"), [0.0; 3]),
        )),
        Some("rotate") => Some(TransformDelta::Rotate {
            axis: crate::json_support::vec3_or(value.get("axisWorld"), [0.0; 3]),
            radians: value.get("radians").and_then(|n| n.as_f64()).unwrap_or(0.0),
        }),
        _ => None,
    }
}

impl EngineState {
    /// Whether the TRANSFORM gizmo (move/rotate) is armed for ANY feature. False
    /// in dimension mode — the two ◎ modes are exclusive, so the transform gizmo
    /// arms/handles never render while dimensions are shown.
    pub fn transform_armed(&self) -> bool {
        matches!(self.transform_gizmo.mode, GizmoMode::Transform)
    }

    /// The transform-gizmo-armed feature id (empty unless in transform mode).
    pub fn transform_armed_feature(&self) -> String {
        if self.transform_armed() {
            self.transform_gizmo.feature_id.clone().unwrap_or_default()
        } else {
            String::new()
        }
    }

    /// The gizmo as the headed verifier sees it: the mode, the armed feature,
    /// the spline anchor index when the gizmo sits on one, and `origin` — the
    /// DRAWN move/rotate widget's frame origin (`null` when no widget is
    /// drawn), which is the proof a handle is on screen, unlike any
    /// params-derived pose.
    pub fn gizmo_state_json(&self) -> String {
        let mode = match self.transform_gizmo.mode {
            GizmoMode::None => "none",
            GizmoMode::Transform => "transform",
            GizmoMode::Dimension => "dimension",
        };
        serde_json::json!({
            "mode": mode,
            "armed": self.transform_armed(),
            "feature": self.transform_gizmo.feature_id,
            "anchor": self.transform_gizmo.anchor,
            "origin": self.widgets.transform_origin(),
        })
        .to_string()
    }

    /// Whether the TRANSFORM gizmo is armed for THIS feature.
    pub fn transform_armed_for(&self, feature_id: &str) -> bool {
        self.transform_armed() && self.transform_gizmo.feature_id.as_deref() == Some(feature_id)
    }

    /// Arm the TRANSFORM gizmo for `feature_id` and feed it at the feature's
    /// transform frame. Re-arming a different feature moves the gizmo to it.
    /// Clears any dimension overlay (the modes are exclusive).
    ///
    /// An ACOMP (assembly component) feature ROUTES to the component Move gizmo
    /// instead: its `transform` is the component pose (`{translate,
    /// rotateEulerDeg}`, a different shape), its gizmo attaches at the member
    /// bbox center, commits on release, and refuses fixed instances — the
    /// generic position/rotationEuler gizmo must never write its keys into an
    /// ACOMP's params. This covers the history panel's arm-on-expand path too.
    pub fn arm_transform(&mut self, feature_id: &str) {
        let is_acomp = self
            .history
            .index_of(feature_id)
            .and_then(|index| self.history.feature_type(index))
            .is_some_and(|ty| super::components::is_acomp_feature_type(&ty));
        if is_acomp {
            self.component_move_arm(feature_id);
            return;
        }
        self.component_move_reset();
        self.transform_gizmo.feature_id = Some(feature_id.to_string());
        self.transform_gizmo.mode = GizmoMode::Transform;
        self.transform_gizmo.drag = None;
        self.transform_gizmo.anchor = None;
        self.clear_feature_dimension_overlay();
        self.sync_transform_gizmo();
    }

    /// Disarm: hide BOTH gizmos + drop any in-flight drag. Also resets the
    /// component Move gizmo (the widget slot is shared, so a disarm clears
    /// whichever controller was feeding it).
    pub fn disarm_transform(&mut self) {
        self.component_move_reset();
        self.transform_gizmo.feature_id = None;
        self.transform_gizmo.mode = GizmoMode::None;
        self.transform_gizmo.drag = None;
        self.transform_gizmo.anchor = None;
        let _ = self.widgets.set_transform_json("null");
        self.clear_feature_dimension_overlay();
        self.dirty = true;
    }

    /// The armed feature's current TRS pose (from its `inputParams.transform`),
    /// or `None` when disarmed / the feature vanished.
    fn armed_pose(&self) -> Option<TransformPose> {
        let id = self.transform_gizmo.feature_id.as_deref()?;
        let index = self.history.index_of(id)?;
        if let Some(anchor) = self.transform_gizmo.anchor {
            // A spline anchor: its position + the intrinsic-XYZ Euler of its
            // stored axis triad (see `spline_edit.rs`).
            let (position, rotation_deg) = self.spline_anchor_pose(index, anchor)?;
            return Some(TransformPose {
                position,
                rotation_deg,
                scale: [1.0, 1.0, 1.0],
            });
        }
        let params = self.history.feature_params(index)?;
        let transform = params.get("transform");
        let pivot = if self.is_xform_feature(index) {
            self.xform_pivot(index, &params)
        } else {
            [0.0; 3]
        };
        // Build the history's expression environment ONCE for the three vectors:
        // a transform component may be an expression string.
        let env = brep_kernel::Env::build(&self.history.expressions(), &self.history.configurator())
            .ok();
        let env = env.as_ref();
        let position = read_pose_vec3(env, transform, "position", [0.0; 3]);
        Some(TransformPose {
            position: std::array::from_fn(|axis| position[axis] + pivot[axis]),
            rotation_deg: read_pose_vec3(env, transform, "rotationEuler", [0.0, 0.0, 0.0]),
            scale: read_pose_vec3(env, transform, "scale", [1.0, 1.0, 1.0]),
        })
    }

    fn is_xform_feature(&self, index: usize) -> bool {
        self.history.feature_type(index).is_some_and(|ty| {
            ty.eq_ignore_ascii_case("XFORM") || ty.eq_ignore_ascii_case("TRANSFORM")
        })
    }

    /// XFORM rotates each selected solid about its own source vertex-bbox center.
    /// Anchor the shared controls to the first resolved solid's pivot; the same
    /// translation/rotation delta still applies to every selected solid.
    fn xform_pivot(&self, index: usize, params: &serde_json::Value) -> [f64; 3] {
        if !params["pivot"]
            .as_str()
            .is_some_and(|p| p.eq_ignore_ascii_case("BBOX_CENTER"))
        {
            return [0.0; 3];
        }
        // Replay the warm current prefix, then fold only results BEFORE XFORM.
        // Using the transformed scene bbox would make the pivot drift on rotation.
        let Ok(request) = serde_json::from_value::<HistoryRequest>(self.history.prefix_request())
        else {
            return [0.0; 3];
        };
        let result = brep_kernel::execute_history(&request);
        let mut handles = HashMap::new();
        for feature in result.results.iter().take(index) {
            for name in &feature.removed {
                handles.remove(name);
            }
            for solid in &feature.added {
                handles.insert(solid.name.clone(), solid.handle);
            }
        }
        let Some(refs) = params["solids"].as_array() else {
            return [0.0; 3];
        };
        for reference in refs {
            let Some(name) = reference.as_str().or_else(|| reference["name"].as_str()) else {
                continue;
            };
            let Some(handle) = handles.get(name.trim()) else {
                continue;
            };
            if let Ok(center) = brep_kernel::transform_pivot_native(*handle) {
                return center;
            }
        }
        [0.0; 3]
    }

    /// (Re)feed the widget gizmo at the armed feature's frame: origin =
    /// `position`, axes = the feature's rotated basis (intrinsic XYZ Euler order, matching
    /// the kernel bake). Auto-disarms if the feature vanished. Called every drag
    /// frame from `transform_drag_to` so the widget tracks the moving pose live
    /// (Fix 3); the drag delta resolves against the frozen grab frame, so this
    /// re-sync never feeds back into the drag math.
    pub fn sync_transform_gizmo(&mut self) {
        // Only the TRANSFORM mode feeds the move/rotate widget; in dimension mode
        // the widget stays hidden (the annotations render as an overlay instead).
        if !matches!(self.transform_gizmo.mode, GizmoMode::Transform) {
            return;
        }
        let Some(pose) = self.armed_pose() else {
            self.disarm_transform();
            return;
        };
        let _ = self
            .widgets
            .set_transform_json(&transform_frame_json(&pose));
        self.dirty = true;
    }

    /// Whether the feature schema exposes the shared Transform controls.
    /// Capability belongs to the schema, not to which default-valued fields
    /// happen to have been serialized in the model.
    pub fn feature_has_transform(&self, feature_id: &str) -> bool {
        self.history
            .index_of(feature_id)
            .and_then(|i| self.history.feature_type(i))
            .and_then(|ty| crate::features::feature_schema(&ty))
            .is_some_and(|schema| schema["inputParamsSchema"]["transform"]["type"] == "transform")
    }

    /// The armed gizmo origin projected to VIEWPORT-LOCAL px (the center handle
    /// sits here). The history panel publishes it so the headed verifier can
    /// locate + drag the gizmo. `None` when disarmed / not projectable (the ONE
    /// [`crate::view::ViewCamera::projectable`] policy — ortho always projects).
    pub fn transform_gizmo_anchor(&self) -> Option<(f64, f64)> {
        let pose = self.armed_pose()?;
        let (sx, sy, _) = self.camera.project(pose.position);
        self.camera.projectable(pose.position).then_some((sx, sy))
    }

    /// The transform gizmo's axis-end labels as JSON:
    /// `[{ text:"XC"|"YC"|"ZC", rgb:[r,g,b], world:[x,y,z] }]`. The app projects
    /// each `world` point and draws the colored egui label just past the matching
    /// cone tip (X=red, Y=green, Z=blue). `[]` unless the TRANSFORM gizmo is armed.
    pub fn transform_axis_labels_json(&self) -> String {
        if !matches!(self.transform_gizmo.mode, GizmoMode::Transform) {
            return "[]".to_string();
        }
        let Some(pose) = self.armed_pose() else {
            return "[]".to_string();
        };
        let euler = [
            pose.rotation_deg[0].to_radians(),
            pose.rotation_deg[1].to_radians(),
            pose.rotation_deg[2].to_radians(),
        ];
        let axes = [
            normalize3(rotate_euler_xyz_f64([1.0, 0.0, 0.0], euler)),
            normalize3(rotate_euler_xyz_f64([0.0, 1.0, 0.0], euler)),
            normalize3(rotate_euler_xyz_f64([0.0, 0.0, 1.0], euler)),
        ];
        // Just past the cone tip, screen-constant.
        let gap_px = 12.0_f64;
        let dist =
            (brep_gizmos::transform::PX_AXIS_LEN as f64 + gap_px) * self.camera.world_per_pixel();
        let labels: [(&str, [f32; 3]); 3] = [
            ("XC", [0.92, 0.26, 0.28]), // red
            ("YC", [0.30, 0.78, 0.36]), // green
            ("ZC", [0.30, 0.52, 0.98]), // blue
        ];
        let out: Vec<serde_json::Value> = (0..3)
            .map(|i| {
                let o = pose.position;
                let a = axes[i];
                serde_json::json!({
                    "text": labels[i].0,
                    "rgb": labels[i].1,
                    "world": [o[0] + a[0] * dist, o[1] + a[1] * dist, o[2] + a[2] * dist],
                })
            })
            .collect();
        serde_json::to_string(&out).unwrap_or_else(|_| "[]".to_string())
    }

    /// Viewport-local pick regions for the debug overlay, shared by feature and
    /// component controllers. The widget feed determines visibility; hidden
    /// widgets return `[]`. The app offsets these circles/capsules by `rect.min`.
    pub fn transform_hit_areas_json(&self) -> String {
        let cam = gizmo_camera(&self.camera);
        let regions = self.widgets.transform_hit_regions(&cam);
        super::camera_widgets::hit_shapes_json(regions.iter().map(|(_, shape)| shape))
    }

    /// Begin a gizmo drag at viewport px `(x, y)` when the gizmo is armed AND a
    /// handle is under the pointer. Returns whether a handle was grabbed — the
    /// viewport routes the drag to the gizmo (not the camera) when `true`; a press
    /// on empty space returns `false` and still orbits.
    pub fn transform_press(&mut self, x: f64, y: f64) -> bool {
        // Only grabbable in TRANSFORM mode — in dimension mode the dimension
        // handles own the pointer (routed by the app), and disarmed grabs nothing.
        if !matches!(self.transform_gizmo.mode, GizmoMode::Transform) {
            return false;
        }
        let handle = self.transform_pick(x, y);
        if handle == 0 {
            return false;
        }
        let Some(pose) = self.armed_pose() else {
            return false;
        };
        self.widgets.set_transform_active(handle);
        self.transform_gizmo.drag = Some(TransformDrag {
            handle,
            sx: x as f32,
            sy: y as f32,
            start: pose,
        });
        self.dirty = true;
        true
    }

    /// Whether a gizmo handle drag is in flight.
    pub fn transform_dragging(&self) -> bool {
        self.transform_gizmo.drag.is_some()
    }

    /// Continue the in-flight gizmo drag to viewport px `(cx, cy)`: resolve the
    /// world delta from the grab (against the frozen grab-time frame), apply it to
    /// the grab pose, write it back into the feature's `transform`, and re-run so
    /// the model follows live. Then re-sync the VISIBLE gizmo to the moved pose so
    /// the widget tracks the pointer in real time (Fix 3) — the delta stays
    /// anchored to `drag.start`, so this visual sync never feeds back on itself.
    pub fn transform_drag_to(&mut self, cx: f64, cy: f64) {
        let Some(drag) = self.transform_gizmo.drag else {
            return;
        };
        let Some(delta) = self.resolve_transform_delta(&drag, cx, cy) else {
            return;
        };
        let pose = apply_transform_delta(&drag.start, &delta);
        self.write_armed_pose(&pose);
        // Live-follow: re-feed the widget frame to the just-written pose. NB
        // `finish_apply` skips this while a drag is in flight (drag.is_some()), so
        // the sync happens here. The active-handle gold highlight survives (the
        // widget only clears it on a `null` feed).
        self.sync_transform_gizmo();
    }

    /// End the drag: clear the active-handle highlight + re-sync the gizmo to the
    /// feature's final (moved) pose (unpin the frame).
    pub fn transform_release(&mut self) {
        if self.transform_gizmo.drag.take().is_some() {
            self.widgets.set_transform_active(0);
            self.sync_transform_gizmo();
        }
    }

    /// Resolve against the grab-time frame so live widget updates cannot
    /// feed back into the drag calculation.
    fn resolve_transform_delta(
        &self,
        drag: &TransformDrag,
        cx: f64,
        cy: f64,
    ) -> Option<TransformDelta> {
        let cam = gizmo_camera(&self.camera);
        let frame_json = transform_frame_json(&drag.start);
        let json = self.widgets.transform_drag_json_with_frame(
            &cam,
            &frame_json,
            drag.handle,
            drag.sx,
            drag.sy,
            cx as f32,
            cy as f32,
        );
        parse_drag_delta(&json)
    }

    /// Write `pose` into the armed feature's `inputParams.transform.{position,
    /// rotationEuler}` (preserving every other field, incl. `scale`) and re-run.
    fn write_armed_pose(&mut self, pose: &TransformPose) {
        let Some(id) = self.transform_gizmo.feature_id.clone() else {
            return;
        };
        let Some(index) = self.history.index_of(&id) else {
            return;
        };
        if let Some(anchor) = self.transform_gizmo.anchor {
            self.write_spline_anchor_pose(&id, anchor, pose.position, pose.rotation_deg);
            return;
        }
        let mut params = self
            .history
            .feature_params(index)
            .unwrap_or_else(|| serde_json::json!({}));
        let pivot = if self.is_xform_feature(index) {
            self.xform_pivot(index, &params)
        } else {
            [0.0; 3]
        };
        let position: [f64; 3] = std::array::from_fn(|axis| pose.position[axis] - pivot[axis]);
        // Ensure `transform` is an object, then set the two edited vectors.
        if !params
            .get("transform")
            .map(|t| t.is_object())
            .unwrap_or(false)
        {
            if let Some(object) = params.as_object_mut() {
                object.insert("transform".into(), serde_json::json!({}));
            }
        }
        if let Some(transform) = params.get_mut("transform").and_then(|t| t.as_object_mut()) {
            transform.insert("position".into(), serde_json::json!(position));
            transform.insert("rotationEuler".into(), serde_json::json!(pose.rotation_deg));
        }
        let _ = self.update_feature_params(&id, &params.to_string());
    }
}

/// Apply translation or world-axis rotation to the grab pose, retaining scale.
fn apply_transform_delta(start: &TransformPose, delta: &TransformDelta) -> TransformPose {
    match delta {
        TransformDelta::Translate(world) => TransformPose {
            position: [
                start.position[0] + world[0],
                start.position[1] + world[1],
                start.position[2] + world[2],
            ],
            ..*start
        },
        TransformDelta::Rotate { axis, radians } => {
            let q0 = quat_from_euler_xyz_deg(start.rotation_deg);
            let dq = quat_from_axis_angle(*axis, *radians);
            let nq = quat_mul(dq, q0);
            TransformPose {
                rotation_deg: euler_xyz_deg_from_quat(nq),
                ..*start
            }
        }
    }
}

/// Read a `[x, y, z]` from a transform sub-field (numbers only; missing / short
/// arrays keep the per-index default).
fn read_pose_vec3(
    env: Option<&brep_kernel::Env>,
    transform: Option<&serde_json::Value>,
    key: &str,
    default: [f64; 3],
) -> [f64; 3] {
    let array = transform
        .and_then(|t| t.get(key))
        .and_then(|v| v.as_array());
    let mut out = default;
    if let Some(array) = array {
        for (index, slot) in out.iter_mut().enumerate() {
            match array.get(index) {
                Some(serde_json::Value::Number(number)) => {
                    if let Some(number) = number.as_f64() {
                        *slot = number;
                    }
                }
                // A component may be an EXPRESSION (`"boxW/2"`) — the kernel
                // evaluates it when it builds, so the gizmo must arm at the same
                // place. Reading it as 0 parked the handles at the world origin
                // while the solid sat elsewhere, and the first drag wrote that
                // wrong origin back as a literal, teleporting the solid.
                Some(serde_json::Value::String(source)) => {
                    if let Some(number) = env
                        .and_then(|env| env.eval(source).ok())
                        .filter(|number| number.is_finite())
                    {
                        *slot = number;
                    }
                }
                _ => {}
            }
        }
    }
    out
}

/// The gizmo frame feed (`set_transform_json` shape) for a pose: origin =
/// `position`, axes = the feature's rotated basis (intrinsic XYZ Euler order, matching
/// the kernel bake), with the center free-move handle shown.
fn transform_frame_json(pose: &TransformPose) -> String {
    let euler = [
        pose.rotation_deg[0].to_radians(),
        pose.rotation_deg[1].to_radians(),
        pose.rotation_deg[2].to_radians(),
    ];
    let x = normalize3(rotate_euler_xyz_f64([1.0, 0.0, 0.0], euler));
    let y = normalize3(rotate_euler_xyz_f64([0.0, 1.0, 0.0], euler));
    let z = normalize3(rotate_euler_xyz_f64([0.0, 0.0, 1.0], euler));
    serde_json::json!({
        "origin": pose.position,
        "x": x,
        "y": y,
        "z": z,
        "showCenter": true,
    })
    .to_string()
}

pub(super) fn normalize3(v: [f64; 3]) -> [f64; 3] {
    let length = (v[0] * v[0] + v[1] * v[1] + v[2] * v[2]).sqrt();
    if length < 1e-12 {
        [0.0, 0.0, 1.0]
    } else {
        [v[0] / length, v[1] / length, v[2] / length]
    }
}

/// Apply an intrinsic XYZ Euler (radians) to a vector — the EXACT matrix the kernel
/// bake (`transform_bake` / `datum::rotate_euler_xyz`) uses, so the fed gizmo
/// frame aligns with the baked solid.
pub(crate) fn rotate_euler_xyz_f64(v: [f64; 3], euler: [f64; 3]) -> [f64; 3] {
    let (c1, s1) = (euler[0].cos(), euler[0].sin());
    let (c2, s2) = (euler[1].cos(), euler[1].sin());
    let (c3, s3) = (euler[2].cos(), euler[2].sin());
    let m00 = c2 * c3;
    let m01 = -c2 * s3;
    let m02 = s2;
    let m10 = c1 * s3 + c3 * s1 * s2;
    let m11 = c1 * c3 - s1 * s2 * s3;
    let m12 = -c2 * s1;
    let m20 = s1 * s3 - c1 * c3 * s2;
    let m21 = c3 * s1 + c1 * s2 * s3;
    let m22 = c1 * c2;
    [
        m00 * v[0] + m01 * v[1] + m02 * v[2],
        m10 * v[0] + m11 * v[1] + m12 * v[2],
        m20 * v[0] + m21 * v[1] + m22 * v[2],
    ]
}

// --- quaternion helpers (ported from CombinedTransformControls) -----

pub(super) type Quat = [f64; 4]; // [x, y, z, w]

pub(super) fn quat_from_axis_angle(axis: [f64; 3], angle: f64) -> Quat {
    let n = normalize3(axis);
    let half = angle * 0.5;
    let s = half.sin();
    [n[0] * s, n[1] * s, n[2] * s, half.cos()]
}

/// Quaternion from an intrinsic XYZ Euler (degrees in).
pub(super) fn quat_from_euler_xyz_deg(deg: [f64; 3]) -> Quat {
    let (c1, s1) = (
        (deg[0].to_radians() * 0.5).cos(),
        (deg[0].to_radians() * 0.5).sin(),
    );
    let (c2, s2) = (
        (deg[1].to_radians() * 0.5).cos(),
        (deg[1].to_radians() * 0.5).sin(),
    );
    let (c3, s3) = (
        (deg[2].to_radians() * 0.5).cos(),
        (deg[2].to_radians() * 0.5).sin(),
    );
    [
        s1 * c2 * c3 + c1 * s2 * s3,
        c1 * s2 * c3 - s1 * c2 * s3,
        c1 * c2 * s3 + s1 * s2 * c3,
        c1 * c2 * c3 - s1 * s2 * s3,
    ]
}

/// Quaternion product `a * b`.
pub(super) fn quat_mul(a: Quat, b: Quat) -> Quat {
    [
        a[3] * b[0] + a[0] * b[3] + a[1] * b[2] - a[2] * b[1],
        a[3] * b[1] - a[0] * b[2] + a[1] * b[3] + a[2] * b[0],
        a[3] * b[2] + a[0] * b[1] - a[1] * b[0] + a[2] * b[3],
        a[3] * b[3] - a[0] * b[0] - a[1] * b[1] - a[2] * b[2],
    ]
}

/// Intrinsic XYZ Euler from a quaternion (via the rotation matrix) → the
/// 'XYZ' Euler in DEGREES. Uses the SAME matrix element naming as
/// `rotate_euler_xyz_f64`, so the round-trip is consistent with the kernel bake.
pub(super) fn euler_xyz_deg_from_quat(q: Quat) -> [f64; 3] {
    let [x, y, z, w] = q;
    let (x2, y2, z2) = (x + x, y + y, z + z);
    let (xx, xy, xz) = (x * x2, x * y2, x * z2);
    let (yy, yz, zz) = (y * y2, y * z2, z * z2);
    let (wx, wy, wz) = (w * x2, w * y2, w * z2);
    // Rotation matrix elements (m<row><col> naming).
    let m11 = 1.0 - (yy + zz);
    let m12 = xy - wz;
    let m13 = xz + wy;
    let m22 = 1.0 - (xx + zz);
    let m23 = yz - wx;
    let m32 = yz + wx;
    let m33 = 1.0 - (xx + yy);
    let ey = m13.clamp(-1.0, 1.0).asin();
    let (ex, ez) = if m13.abs() < 0.9999999 {
        ((-m23).atan2(m33), (-m12).atan2(m11))
    } else {
        (m32.atan2(m22), 0.0)
    };
    [ex.to_degrees(), ey.to_degrees(), ez.to_degrees()]
}

// BREP private tests: a433bd9d8292ab45