Merge remote-tracking branch 'origin/main' into plugin/host-model-api

src/scene/camera_ops.rs

@@ -1566,5 +1566,16 @@ impl Scene {
         self.camera_generation += 1;
     }
 
-    pub fn update(&mut self, _dt: Duration) {}
+    pub fn update(&mut self, _dt: Duration) {
+        // The glyph atlas grew or re-baked since this scene last built its
+        // caches (a CJK sheet set bakes thousands of tiles on first sight):
+        // every quad laid out before that samples the wrong tile — scrambled
+        // text in the affected blocks / viewports. One structural bump
+        // re-lays-out all text against the settled atlas.
+        let atlas_gen = crate::scene::text::sdf_atlas::generation();
+        if self.last_atlas_generation.get() != atlas_gen {
+            self.last_atlas_generation.set(atlas_gen);
+            self.bump_geometry();
+        }
+    }
 }

src/scene/dwg_native_constraints.rs

@@ -2,7 +2,8 @@
 
 use acadrust::objects::{
     Assoc2dConstraintGroup, AssocAction, AssocActionDependency, AssocConstraintNode,
-    AssocConstraintNodeData, AssocDependency, AssocEvalValue, AssocEvalVariant,
+    AssocConstraintNodeData, AssocDependency, AssocDimDependencyBody, AssocEvalValue,
+    AssocEvalVariant,
     AssocGeomDependency, AssocNetwork, AssocPersistentSubentId, AssocValueDependency,
     AssocVariable, AssociativeData, AssociativeObject, ObjectType,
 };
@@ -1216,6 +1217,7 @@ impl Allocator<'_> {
         name: &str,
         formula: &str,
         resolved: f64,
+        description: &str,
     ) -> Handle {
         if let Some(&handle) = self.variables.get(name) {
             if let Some(ObjectType::Associative(object)) = self.document.objects.get_mut(&handle) {
@@ -1243,7 +1245,7 @@ impl Allocator<'_> {
                 name: name.to_string(),
                 expression: formula.to_string(),
                 evaluator: "AcDbCalc:1.0".to_string(),
-                description: String::new(),
+                description: description.to_string(),
                 value: Self::numeric_eval(resolved),
                 has_cached_value: false,
                 cached_value: String::new(),
@@ -1291,6 +1293,67 @@ impl Allocator<'_> {
         }
         handle
     }
+
+    /// The `AcDbAssocDependency` + `AcDbAssocDimDependencyBody` pair that
+    /// ties a dimensional constraint to the dynamic dimension showing it.
+    fn dimension_dependency(
+        &mut self,
+        group_handle: Handle,
+        dimension: Handle,
+        name: &str,
+        dependency_id: i32,
+    ) -> Handle {
+        let handle = self.document.allocate_handle();
+        let body = self.insert_associative(
+            handle,
+            "ACDBASSOCDIMDEPENDENCYBODY",
+            "AcDbAssocDimDependencyBody",
+            AssociativeData::DimDependencyBody(AssocDimDependencyBody {
+                dependency_body_version: 1,
+                base_version: 1,
+                name: name.to_string(),
+                class_version: 1,
+            }),
+        );
+        self.insert_associative_at(
+            handle,
+            group_handle,
+            "ACDBASSOCDEPENDENCY",
+            "AcDbAssocDependency",
+            AssociativeData::Dependency(AssocDependency {
+                class_version: 2,
+                is_read_dependency: true,
+                is_write_dependency: true,
+                is_attached_to_object: true,
+                is_delegating_to_owning_action: true,
+                dependent_on: dimension,
+                dependency_body: body,
+                dependency_body_id: dependency_id,
+                ..Default::default()
+            }),
+        );
+        // Earlier materializations' dependencies are gone by now; drop
+        // their reactor entries before adding this one.
+        let live: Vec<Handle> = self
+            .document
+            .get_entity(dimension)
+            .map(|entity| {
+                entity
+                    .common()
+                    .reactors
+                    .iter()
+                    .copied()
+                    .filter(|reactor| self.document.objects.contains_key(reactor))
+                    .collect()
+            })
+            .unwrap_or_default();
+        if let Some(entity) = self.document.get_entity_mut(dimension) {
+            let reactors = &mut entity.common_mut().reactors;
+            *reactors = live;
+            reactors.push(handle);
+        }
+        handle
+    }
 }
 
 /// Sets the dependency on whole-geometry nodes. Implicit points retain a
@@ -1355,6 +1418,27 @@ fn set_value_dependency(data: &mut AssocConstraintNodeData, handle: Handle) {
     }
 }
 
+/// Patches a dimensional-constraint node's `dimension_dependency` field.
+fn set_dimension_dependency(data: &mut AssocConstraintNodeData, handle: Handle) {
+    match data {
+        AssocConstraintNodeData::Distance {
+            dimension_dependency,
+            ..
+        }
+        | AssocConstraintNodeData::Angle {
+            dimension_dependency,
+            ..
+        }
+        | AssocConstraintNodeData::RadiusDiameter {
+            dimension_dependency,
+            ..
+        } => {
+            *dimension_dependency = handle;
+        }
+        _ => {}
+    }
+}
+
 /// Associative classes that must have real class numbers in DWG/DXF.
 const ASSOC_CLASSES: &[(&str, &str, i32)] = &[
     (
@@ -1366,6 +1450,8 @@ const ASSOC_CLASSES: &[(&str, &str, i32)] = &[
     ("ACDBASSOCVARIABLE", "AcDbAssocVariable", 45),
     ("ACDBASSOCGEOMDEPENDENCY", "AcDbAssocGeomDependency", 29),
     ("ACDBASSOCVALUEDEPENDENCY", "AcDbAssocValueDependency", 29),
+    ("ACDBASSOCDEPENDENCY", "AcDbAssocDependency", 29),
+    ("ACDBASSOCDIMDEPENDENCYBODY", "AcDbAssocDimDependencyBody", 45),
 ];
 
 fn ensure_associative_classes_registered(document: &mut CadDocument) {
@@ -1798,6 +1884,7 @@ fn driving_value(
         variable.expression.clone()
     };
     if parameters.set(&variable.name, &source).is_ok() {
+        parameters.set_description(&variable.name, &variable.description);
         Some(DrivingValue::Named(variable.name.clone()))
     } else {
         literal
@@ -1806,6 +1893,19 @@ fn driving_value(
     }
 }
 
+/// The dynamic dimension an `AcDbAssocDependency` ties to a dimensional
+/// constraint node.
+fn dependency_dimension(document: &CadDocument, dependency: Handle) -> Option<Handle> {
+    let ObjectType::Associative(object) = document.objects.get(&dependency)? else {
+        return None;
+    };
+    let AssociativeData::Dependency(dependency) = &object.data else {
+        return None;
+    };
+    let target = dependency.dependent_on;
+    matches!(document.get_entity(target)?, EntityType::Dimension(_)).then_some(target)
+}
+
 fn owning_composite(data: &AssocConstraintNodeData) -> Option<i32> {
     match data {
         AssocConstraintNodeData::Geometrical { owner_id, .. }
@@ -2250,7 +2350,25 @@ pub(super) fn native_constraint_set(
             {
                 continue;
             }
-            set.add(kind, targets, driving);
+            let dimension = match &node.data {
+                AssocConstraintNodeData::Angle {
+                    dimension_dependency,
+                    ..
+                }
+                | AssocConstraintNodeData::Distance {
+                    dimension_dependency,
+                    ..
+                }
+                | AssocConstraintNodeData::RadiusDiameter {
+                    dimension_dependency,
+                    ..
+                } => dependency_dimension(document, *dimension_dependency),
+                _ => None,
+            };
+            let id = set.add(kind, targets, driving);
+            if let Some(dimension) = dimension {
+                set.dimensions.insert(id, dimension);
+            }
             if let Some(constraint) = set.constraints.last_mut() {
                 constraint.enabled = enabled;
                 constraint.rigid_points = rigid_points;
@@ -2429,15 +2547,21 @@ fn materialize_scope(
 
     // Pass 1 (read-only): constraint-node shapes.
     let mut needs_value_dependency = Vec::new();
+    let mut dimension_links = Vec::new();
     let (mut nodes, entities, referenced_entities) = {
         let mut builder = GroupBuilder::new(document);
         for constraint in &set.constraints {
-            constraint_node(
+            let node_id = constraint_node(
                 &mut builder,
                 document,
                 constraint,
                 &mut needs_value_dependency,
             );
+            if let Some((node_id, dimension)) = node_id.zip(set.dimensions.get(&constraint.id)) {
+                if document.get_entity(*dimension).is_some() {
+                    dimension_links.push((node_id, *dimension));
+                }
+            }
         }
         let GroupBuilder {
             nodes,
@@ -2488,6 +2612,7 @@ fn materialize_scope(
                 variable.action.action_index = index as i32 + 1;
                 if let Some(parameter) = parameters.get(&variable.name) {
                     variable.expression = parameter.source.clone();
+                    variable.description = parameters.description(&parameter.name).to_string();
                     if let Ok(resolved) = parameters.resolve(&parameter.name) {
                         variable.value = Allocator::numeric_eval(resolved);
                     }
@@ -2499,7 +2624,13 @@ fn materialize_scope(
     if materialize_all_parameters {
         for parameter in parameters.iter() {
             let resolved = parameters.resolve(&parameter.name).unwrap_or(0.0);
-            allocator.variable(network_handle, &parameter.name, &parameter.source, resolved);
+            allocator.variable(
+                network_handle,
+                &parameter.name,
+                &parameter.source,
+                resolved,
+                parameters.description(&parameter.name),
+            );
         }
     }
 
@@ -2527,6 +2658,7 @@ fn materialize_scope(
     }
 
     let mut group_dependencies = geometry_dependencies;
+    let mut node_names: FxHashMap<i32, String> = FxHashMap::default();
     for (node_id, driving) in needs_value_dependency {
         let Some(driving) = driving else { continue };
         let Ok(resolved) = driving.resolve(parameters) else {
@@ -2542,7 +2674,14 @@ fn materialize_scope(
             }
             DrivingValue::Literal(_) => (format!("d{node_id}"), resolved.to_string()),
         };
-        let variable_handle = allocator.variable(network_handle, &name, &formula, resolved);
+        node_names.insert(node_id, name.clone());
+        let variable_handle = allocator.variable(
+            network_handle,
+            &name,
+            &formula,
+            resolved,
+            parameters.description(&name),
+        );
         let dependency_id = group_dependencies.len() as i32 + 1;
         let dep_handle =
             allocator.value_dependency(group_handle?, variable_handle, resolved, dependency_id);
@@ -2551,6 +2690,18 @@ fn materialize_scope(
             set_value_dependency(&mut node.data, dep_handle);
         }
     }
+    for (node_id, dimension) in dimension_links {
+        let Some(name) = node_names.get(&node_id) else {
+            continue;
+        };
+        let dependency_id = group_dependencies.len() as i32 + 1;
+        let dep_handle =
+            allocator.dimension_dependency(group_handle?, dimension, name, dependency_id);
+        group_dependencies.push(dep_handle);
+        if let Some(node) = nodes.iter_mut().find(|n| n.node_id == node_id) {
+            set_dimension_dependency(&mut node.data, dep_handle);
+        }
+    }
 
     if let Some(group_handle) = group_handle {
         let group = Assoc2dConstraintGroup {
@@ -2674,6 +2825,9 @@ impl Scene {
 
     pub(crate) fn load_parametric_constraints_from_document(&mut self) {
         self.parametric_constraints.clear();
+        // Dynamic dimensions read from the file get their screen size on the
+        // first tick after the view is known.
+        self.dynamic_dimension_camera_gen = None;
         let owners: Vec<_> = self
             .document
             .block_records

src/scene/entity.rs

@@ -1405,6 +1405,9 @@ impl Scene {
                 }
                 if self.object_isolation.hides(common.handle)
                     || (!include_preview_hidden && self.preview_hidden.contains(&common.handle))
+                    || self.hidden_dynamic_dimensions.contains(&common.handle)
+                    // A dynamic dimension never plots.
+                    || (plot_only && self.is_dynamic_dimension(common.handle))
                 {
                     return false;
                 }

src/scene/mod.rs

@@ -2295,6 +2295,15 @@ pub struct Scene {
     has_associative_centers: std::cell::Cell<Option<bool>>,
     /// Runtime parametric constraint sets decoded from standard graph scopes.
     pub(crate) parametric_constraints: Vec<parametric_constraints::ParametricConstraintSet>,
+    /// CONSTRAINTNAMEFORMAT: what a dynamic dimension's text shows —
+    /// 0 the parameter name, 1 the value, 2 `name=value`.
+    pub constraint_name_format: u8,
+    /// DYNCONSTRAINTDISPLAY: whether dynamic dimensions draw at all.
+    pub dynamic_constraint_display: bool,
+    /// Dynamic dimensions DCHIDE or DYNCONSTRAINTDISPLAY 0 keep off screen.
+    hidden_dynamic_dimensions: HashSet<Handle>,
+    /// The camera generation the dynamic dimensions were last scaled for.
+    dynamic_dimension_camera_gen: Option<u64>,
     /// Session-only visibility overrides for constraint glyphs.
     hidden_parametric_constraints: HashSet<(
         parametric_constraints::ParametricScope,
@@ -2348,6 +2357,11 @@ pub struct Scene {
     /// (re)built, otherwise the held value. `build_primitive` reads it right
     /// after the call to gate GPU wire re-upload. 0 = none yet.
     pub(crate) last_model_wire_gen: std::cell::Cell<u64>,
+    /// SDF glyph-atlas generation this scene's caches were built against.
+    /// When the atlas grows or re-bakes, every cached glyph quad (resident
+    /// sets, block caches, projected viewport copies) addresses the wrong
+    /// tile; `update` compares against the live generation and rebuilds.
+    pub(crate) last_atlas_generation: std::cell::Cell<u64>,
     /// Interaction-LOD state: `camera_generation` seen on the previous frame and
     /// the wall time it last changed. Used to detect "the view is actively being
     /// panned / zoomed / orbited" so the expensive per-pixel hatch pass can be
@@ -2625,6 +2639,10 @@ impl Scene {
             dependency_index_cache: RefCell::new(None),
             associative_hatch_source_cache: RefCell::new(None),
             parametric_constraints: Vec::new(),
+            constraint_name_format: 2,
+            dynamic_constraint_display: true,
+            hidden_dynamic_dimensions: HashSet::default(),
+            dynamic_dimension_camera_gen: None,
             hidden_parametric_constraints: HashSet::default(),
             shown_parametric_constraints: HashSet::default(),
             named_parameters: named_parameters::ParameterTable::new(),
@@ -2638,6 +2656,7 @@ impl Scene {
             last_tess_ms: std::cell::Cell::new(0.0),
             last_tess_wires: std::cell::Cell::new(0),
             last_model_wire_gen: std::cell::Cell::new(0),
+            last_atlas_generation: std::cell::Cell::new(crate::scene::text::sdf_atlas::generation()),
             nav_last_gen: std::cell::Cell::new(0),
             nav_changed_at: std::cell::Cell::new(None),
             nav_perf_pending: std::cell::Cell::new(None),
@@ -3319,6 +3338,7 @@ impl Scene {
             }
         }
         if !self.parametric_constraints.is_empty() || !self.named_parameters.is_empty() {
+            self.refresh_dynamic_dimension_texts();
             self.sync_native_parametric_graph();
         }
         if !changes.is_empty() {
@@ -5533,6 +5553,7 @@ impl Scene {
         self.object_isolation.hides(handle)
             || self.preview_hidden.contains(&handle)
             || self.command_preview_hidden.contains(&handle)
+            || self.hidden_dynamic_dimensions.contains(&handle)
     }
 
     /// Replace the command-owned source hide set and refresh only handles whose
@@ -6105,6 +6126,7 @@ impl Scene {
         // Build once: full tessellation, no cull, no zoom LOD — the resident
         // set is zoom-independent (GPU analytical circles/arcs/ellipses).
         let t_tess = iced::time::Instant::now();
+        let mut atlas_gen = crate::scene::text::sdf_atlas::generation();
         let mut wires = self.wires_for_block_culled(
             block,
             None,
@@ -6115,6 +6137,34 @@ impl Scene {
             all_visible,
             style_viewport,
         );
+        // Baking a drawing's glyphs for the first time can grow the SDF atlas
+        // part-way through this pass (a CJK sheet set bakes thousands of
+        // tiles). Text tessellated before the growth carries UVs that now
+        // address the wrong tiles — visible as scrambled glyphs — and this
+        // set is cached by geometry epoch, so nothing would ever re-lay it
+        // out. The memo guard already folds the generation in, so rebuilding
+        // once the atlas has settled re-tessellates only the stale text.
+        for _ in 0..3 {
+            let now = crate::scene::text::sdf_atlas::generation();
+            if now == atlas_gen {
+                break;
+            }
+            atlas_gen = now;
+            // Block definitions tessellated earlier in this pass hold the
+            // stale quads too, and their cache is keyed by block epoch (which
+            // has not moved), so drop them or the rebuild would reuse them.
+            self.block_defn_cache.borrow_mut().clear();
+            wires = self.wires_for_block_culled(
+                block,
+                None,
+                None,
+                frozen_layers,
+                anno_scale_override,
+                annotation_scale_handle,
+                all_visible,
+                style_viewport,
+            );
+        }
         let perf = crate::perf::enabled();
         let t_post = perf.then(iced::time::Instant::now);
         // Synthesized nonprint markers (geo-location daisy) live in model space

src/scene/named_parameters.rs

@@ -474,6 +474,9 @@ pub struct Parameter {
 #[derive(Debug, Clone, Default, PartialEq)]
 pub struct ParameterTable {
     parameters: Vec<Parameter>,
+    /// The free-text description a parameter carries (the reference's
+    /// Description column), by name.
+    descriptions: HashMap<String, String>,
 }
 
 impl ParameterTable {
@@ -481,6 +484,23 @@ impl ParameterTable {
         Self::default()
     }
 
+    pub fn description(&self, name: &str) -> &str {
+        self.descriptions.get(name).map_or("", String::as_str)
+    }
+
+    /// Stores `description` for an existing parameter; an empty text clears it.
+    pub fn set_description(&mut self, name: &str, description: &str) {
+        if !self.contains(name) {
+            return;
+        }
+        if description.trim().is_empty() {
+            self.descriptions.remove(name);
+        } else {
+            self.descriptions
+                .insert(name.to_string(), description.trim().to_string());
+        }
+    }
+
     pub fn is_empty(&self) -> bool {
         self.parameters.is_empty()
     }
@@ -549,6 +569,7 @@ impl ParameterTable {
     /// need to invent (a future UI stage may still want to warn before
     /// deleting — that's a UI-layer decision, not a data-layer one).
     pub fn remove(&mut self, name: &str) -> bool {
+        self.descriptions.remove(name);
         match self.index_of(name) {
             Some(i) => {
                 self.parameters.remove(i);

src/scene/parametric_constraints.rs

@@ -351,6 +351,213 @@ pub(crate) fn equal_size_follower(
     Some(entity)
 }
 
+/// The first free `d1`, `d2`, … name a new dimensional constraint takes.
+pub(crate) fn next_dimensional_parameter_name(
+    table: &super::named_parameters::ParameterTable,
+) -> String {
+    (1..)
+        .map(|n| format!("d{n}"))
+        .find(|name| !table.contains(name))
+        .unwrap_or_else(|| "d1".to_string())
+}
+
+/// The constraint-bar label that draws a dynamic dimension's lock mark.
+pub const DYNAMIC_DIMENSION_GLYPH: &str = "\u{1F512}";
+
+/// The on-screen text height of a dynamic dimension, in pixels.
+pub const DYNAMIC_DIMENSION_TEXT_PX: f32 = 12.0;
+
+/// The layer the reference keeps dynamic dimensions on; an annotational
+/// dimensional constraint sits on an ordinary layer instead.
+pub(crate) const DYNAMIC_DIMENSION_LAYER: &str = "*ADSK_CONSTRAINTS";
+
+/// The text a dynamic dimension shows: CONSTRAINTNAMEFORMAT 0 = name,
+/// 1 = value, 2 = name=value, the value with its trailing zeros dropped
+/// (`d9=80`, `d1=111.8034`). A parameter defined by a formula shows the
+/// formula behind `fx:` (`fx: len=d1*2`); a reference (driven) constraint's
+/// text sits in parentheses; an annotational one keeps dimension precision.
+pub(crate) fn dynamic_dimension_text(
+    name: &str,
+    value: f64,
+    format: u8,
+    reference: bool,
+    expression: Option<&str>,
+    annotational: bool,
+) -> String {
+    let formula = expression
+        .map(str::trim)
+        .filter(|source| !source.is_empty() && source.parse::<f64>().is_err());
+    let shown = match formula {
+        Some(source) => source.to_string(),
+        // An annotational dimension shows the value at dimension precision
+        // (`d1=100.0000`), as the reference does.
+        None if annotational => format!("{value:.4}"),
+        None => {
+            let text = format!("{value:.4}");
+            let text = text.trim_end_matches('0').trim_end_matches('.');
+            if text.is_empty() || text == "-" {
+                "0".to_string()
+            } else {
+                text.to_string()
+            }
+        }
+    };
+    let text = match format {
+        0 => name.to_string(),
+        1 => shown,
+        _ => format!("{name}={shown}"),
+    };
+    let text = if formula.is_some() {
+        format!("fx: {text}")
+    } else {
+        text
+    };
+    if reference {
+        format!("({text})")
+    } else {
+        text
+    }
+}
+
+/// The expression a measured value seeds a parameter with: twelve
+/// significant digits with the trailing zeros dropped (`100`,
+/// `111.803398875`), as the reference stores it.
+pub(crate) fn measured_expression(value: f64) -> String {
+    if !value.is_finite() {
+        return "0".to_string();
+    }
+    // Solver noise (24.9999999047) reads as the round value it means.
+    let snapped = (value * 1.0e4).round() / 1.0e4;
+    let value = if (value - snapped).abs() < 1.0e-6 {
+        snapped
+    } else {
+        value
+    };
+    let magnitude = value.abs();
+    let integer_digits = if magnitude < 1.0 {
+        1
+    } else {
+        magnitude.log10().floor() as i32 + 1
+    };
+    let decimals = (12 - integer_digits).clamp(0, 12) as usize;
+    let text = format!("{value:.decimals$}");
+    let text = if text.contains('.') {
+        text.trim_end_matches('0').trim_end_matches('.')
+    } else {
+        text.as_str()
+    };
+    if text.is_empty() || text == "-" || text == "-0" {
+        "0".to_string()
+    } else {
+        text.to_string()
+    }
+}
+
+/// Moves a dynamic dimension's extension origins to `first`/`second`,
+/// keeping its dimension line where it was; true when anything moved.
+fn dynamic_dimension_follow_points(
+    dimension: &mut acadrust::entities::Dimension,
+    first: Vector3,
+    second: Vector3,
+) -> bool {
+    use acadrust::entities::Dimension;
+    let same = |a: Vector3, b: Vector3| (a - b).length_squared() < 1.0e-16;
+    let to_dvec = |p: Vector3| glam::DVec3::new(p.x, p.y, p.z);
+    let (current_first, current_second, definition, axis) = match dimension {
+        Dimension::Aligned(d) => (d.first_point, d.second_point, d.definition_point, None),
+        Dimension::Linear(d) => (
+            d.first_point,
+            d.second_point,
+            d.definition_point,
+            Some(glam::DVec3::new(d.rotation.cos(), d.rotation.sin(), 0.0)),
+        ),
+        _ => return false,
+    };
+    if same(current_first, first) && same(current_second, second) {
+        return false;
+    }
+    let text = dimension.base().user_text.clone();
+    let rebuilt = match axis {
+        None => crate::modules::annotate::aligned_dim::aligned_dimension_entity(
+            to_dvec(first),
+            to_dvec(second),
+            to_dvec(definition),
+            text,
+        ),
+        Some(axis) => crate::modules::annotate::linear_dim::linear_dimension_entity(
+            to_dvec(first),
+            to_dvec(second),
+            to_dvec(definition),
+            axis,
+            text,
+        ),
+    };
+    let acadrust::EntityType::Dimension(mut rebuilt) = rebuilt else {
+        return false;
+    };
+    // Everything but the geometry stays: identity, layer, color, style, xdata.
+    let base = dimension.base();
+    let target = rebuilt.base_mut();
+    target.common = base.common.clone();
+    target.style_name = base.style_name.clone();
+    target.text_rotation = base.text_rotation;
+    target.attachment_point = base.attachment_point;
+    target.line_spacing_style = base.line_spacing_style;
+    target.line_spacing_factor = base.line_spacing_factor;
+    *dimension = rebuilt;
+    true
+}
+
+/// What stays put when a dimensional constraint's value changes: its first
+/// point, and — when the distance runs perpendicular to a line that owns
+/// that point (2Lines, line-first Point & line) — the whole line, so the
+/// other object moves, as in the reference.
+pub(crate) fn dimensional_anchor_refs(
+    document: &acadrust::CadDocument,
+    refs: &[ParametricRef],
+) -> Vec<ParametricRef> {
+    let Some(&first) = refs.first() else {
+        return Vec::new();
+    };
+    let mut anchors = vec![first];
+    if let Some(&line) = refs.get(2).filter(|line| line.entity == first.entity) {
+        let ends = match line.segment_index() {
+            Some(index) => {
+                let index = index as i32;
+                let end = document
+                    .get_entity(line.entity)
+                    .and_then(|entity| resolve_point(entity, index + 1))
+                    .map_or(0, |_| index + 1);
+                [
+                    ParametricRef::point(line.entity, index),
+                    ParametricRef::point(line.entity, end),
+                ]
+            }
+            None => [
+                ParametricRef::point(line.entity, 0),
+                ParametricRef::point(line.entity, 1),
+            ],
+        };
+        anchors.extend(ends.into_iter().filter(|end| *end != first));
+    }
+    anchors
+}
+
+/// The constraint a dynamic dimension shows, with the table its parameter
+/// lives in.
+pub(crate) fn dynamic_dimension_constraint(
+    sets: &[ParametricConstraintSet],
+    handle: Handle,
+) -> Option<(&ParametricConstraintSet, &ParametricConstraint)> {
+    sets.iter().find_map(|set| {
+        let id = set
+            .dimensions
+            .iter()
+            .find_map(|(id, dimension)| (*dimension == handle).then_some(*id))?;
+        Some((set, set.get(id)?))
+    })
+}
+
 /// Grabbed points are exact kernel inputs; the solver anchors the remaining
 /// endpoint coordinates according to the line's directional constraints.
 pub(crate) fn grip_solve_anchor_refs(
@@ -585,6 +792,8 @@ pub struct ParametricConstraintSet {
     /// parameter names may legitimately occur in different blocks.
     pub(crate) local_parameters: super::named_parameters::ParameterTable,
     pub(crate) retained_standard_groups: Vec<Handle>,
+    /// The dynamic dimension that shows a dimensional constraint, by id.
+    pub(crate) dimensions: std::collections::HashMap<ConstraintId, Handle>,
     /// Cached total remaining degrees of freedom, summed across every
     /// independent solve partition in this scope — updated by
     /// `parametric_solve::solve_scope` each time this set is resolved. `None`
@@ -611,6 +820,7 @@ impl ParametricConstraintSet {
             next_id: 0,
             local_parameters: super::named_parameters::ParameterTable::new(),
             retained_standard_groups: Vec::new(),
+            dimensions: std::collections::HashMap::new(),
             dof: None,
             conflicts: Vec::new(),
         }
@@ -702,6 +912,7 @@ impl ParametricConstraintSet {
 
     /// Removes a constraint by id. Returns whether one was actually removed.
     pub fn remove(&mut self, id: ConstraintId) -> bool {
+        self.dimensions.remove(&id);
         let before = self.constraints.len();
         self.constraints.retain(|c| c.id != id);
         self.constraints.len() != before
@@ -1420,6 +1631,117 @@ impl super::Scene {
         !self.hidden_parametric_constraints.contains(&(scope, id))
     }
 
+    /// Rewrites every dynamic dimension's text from its constraint's
+    /// parameter name and current value, in the CONSTRAINTNAMEFORMAT
+    /// reading `constraint_name_format` selects, and moves its extension
+    /// origins to where the solve left the constraint points.
+    pub(crate) fn refresh_dynamic_dimension_texts(&mut self) {
+        let format = self.constraint_name_format;
+        let mut updates: Vec<(Handle, String, Option<(Vector3, Vector3)>)> = Vec::new();
+        // A reference (driven) constraint's parameter follows the geometry.
+        let mut followed: Vec<(String, f64)> = Vec::new();
+        for set in &self.parametric_constraints {
+            let model_table = set.local_parameters.is_empty();
+            let table = if model_table {
+                &self.named_parameters
+            } else {
+                &set.local_parameters
+            };
+            for (id, dimension) in &set.dimensions {
+                let Some(constraint) = set.get(*id) else {
+                    continue;
+                };
+                let world = |reference: &ParametricRef| {
+                    let entity = self.document.get_entity(reference.entity)?;
+                    resolve_point(entity, reference.marker?)
+                };
+                let points = match constraint.refs.as_slice() {
+                    [first, second, ..] => world(first).zip(world(second)),
+                    _ => None,
+                };
+                let reference = !constraint.enabled;
+                let measured = points.map(|(first, second)| {
+                    let delta = second - first;
+                    let axis = match self.document.get_entity(*dimension) {
+                        Some(acadrust::EntityType::Dimension(
+                            acadrust::entities::Dimension::Linear(linear),
+                        )) => Some((linear.rotation.cos(), linear.rotation.sin())),
+                        _ => None,
+                    };
+                    match (constraint.kind, axis) {
+                        (ConstraintKind::DistanceX, _) => delta.x.abs(),
+                        (ConstraintKind::DistanceY, _) => delta.y.abs(),
+                        (ConstraintKind::DistanceDirected, Some((ax, ay))) => {
+                            (delta.x * ax + delta.y * ay).abs()
+                        }
+                        _ => delta.length(),
+                    }
+                });
+                let (name, value, source) = match &constraint.driving_param {
+                    Some(DrivingValue::Named(name)) => {
+                        let value = match (reference, measured) {
+                            (true, Some(measured)) => {
+                                if model_table {
+                                    followed.push((name.clone(), measured));
+                                }
+                                measured
+                            }
+                            _ => table.resolve(name).unwrap_or(f64::NAN),
+                        };
+                        let source = (!reference)
+                            .then(|| table.get(name).map(|parameter| parameter.source.clone()))
+                            .flatten();
+                        (name.clone(), value, source)
+                    }
+                    Some(DrivingValue::Literal(value)) => (String::new(), *value, None),
+                    None => continue,
+                };
+                let annotational = self.dimension_is_annotational(*dimension);
+                updates.push((
+                    *dimension,
+                    dynamic_dimension_text(
+                        &name,
+                        value,
+                        format,
+                        reference,
+                        source.as_deref(),
+                        annotational,
+                    ),
+                    points,
+                ));
+            }
+        }
+        for (name, measured) in followed {
+            let source = measured_expression(measured);
+            if self.named_parameters.get(&name).map(|p| p.source.as_str()) != Some(source.as_str()) {
+                let _ = self.named_parameters.set(&name, &source);
+            }
+        }
+        for (handle, text, points) in updates {
+            let Some(acadrust::EntityType::Dimension(mut dimension)) =
+                self.document.get_entity(handle).cloned()
+            else {
+                continue;
+            };
+            let mut changed = false;
+            if let Some((first, second)) = points {
+                if dynamic_dimension_follow_points(&mut dimension, first, second) {
+                    changed = true;
+                }
+            }
+            if dimension.base().user_text.as_deref() != Some(text.as_str()) {
+                crate::entities::dimension::set_dimension_text_override(
+                    dimension.base_mut(),
+                    Some(text),
+                );
+                changed = true;
+            }
+            if changed {
+                self.update_entity(acadrust::EntityType::Dimension(dimension));
+            }
+        }
+    }
+
     pub fn should_display_parametric_constraint(
         &self,
         scope: ParametricScope,
@@ -1483,9 +1805,163 @@ impl super::Scene {
                 self.shown_parametric_constraints.remove(&(scope, *id));
             }
         }
+        self.refresh_hidden_dynamic_dimensions();
         ids.len()
     }
 
+    /// Makes sure the reference's dynamic dimension layer exists: hidden
+    /// from the layer lists (the `*` prefix) and never plotted.
+    pub(crate) fn ensure_dynamic_dimension_layer(&mut self) {
+        if self.document.layers.contains(DYNAMIC_DIMENSION_LAYER) {
+            return;
+        }
+        let mut layer = acadrust::tables::Layer::new(DYNAMIC_DIMENSION_LAYER);
+        layer.color = acadrust::types::Color::from_index(7);
+        layer.is_plottable = false;
+        layer.handle = self.document.allocate_handle();
+        let _ = self.document.layers.add(layer);
+    }
+
+    /// True for a dynamic dimension of a dimensional constraint (not an
+    /// annotational one, which is an ordinary plotted dimension).
+    pub(crate) fn is_dynamic_dimension(&self, handle: Handle) -> bool {
+        self.parametric_constraints
+            .iter()
+            .any(|set| set.dimensions.values().any(|dimension| *dimension == handle))
+            && !self.dimension_is_annotational(handle)
+    }
+
+    /// True when a dimensional constraint's dimension uses the annotational
+    /// form: on an ordinary layer instead of the reference's constraints
+    /// layer, drawn with its style, plotted, never rescaled to the screen.
+    pub(crate) fn dimension_is_annotational(&self, handle: Handle) -> bool {
+        self.document.get_entity(handle).is_some_and(|entity| {
+            !entity
+                .common()
+                .layer
+                .eq_ignore_ascii_case(DYNAMIC_DIMENSION_LAYER)
+        })
+    }
+
+    /// The document as written to a file: a dynamic dimension's screen-size
+    /// overrides are a display matter and stay out of the file.
+    pub(crate) fn document_for_save(&self) -> acadrust::CadDocument {
+        use crate::entities::dim_override as ov;
+        let mut document = self.document.clone();
+        for set in &self.parametric_constraints {
+            for handle in set.dimensions.values().copied() {
+                if self.dimension_is_annotational(handle) {
+                    continue;
+                }
+                for code in [ov::DIMSCALE, ov::DIMTIH, ov::DIMTOH] {
+                    ov::set(&mut document, handle, code, None);
+                }
+            }
+        }
+        document
+    }
+
+    /// Gives every dynamic dimension a DIMSCALE override that keeps its
+    /// text, arrows and offsets at a screen size (the reference draws them
+    /// at a constant pixel size whatever the zoom). Runs whenever the camera
+    /// changed; `force` re-applies after a dimension was created or loaded.
+    pub fn refresh_dynamic_dimension_scales(&mut self, force: bool) {
+        let Some(wpp) = self.world_per_pixel() else {
+            return;
+        };
+        if !force && self.dynamic_dimension_camera_gen == Some(self.camera_generation) {
+            return;
+        }
+        self.dynamic_dimension_camera_gen = Some(self.camera_generation);
+        let handles: Vec<Handle> = self
+            .parametric_constraints
+            .iter()
+            .flat_map(|set| set.dimensions.values().copied())
+            .collect();
+        let mut changes = Vec::new();
+        for handle in handles {
+            let Some(acadrust::EntityType::Dimension(dimension)) = self.document.get_entity(handle)
+            else {
+                continue;
+            };
+            // An annotational dimension keeps its style's size.
+            if self.dimension_is_annotational(handle) {
+                continue;
+            }
+            let style_name = dimension.base().style_name.clone();
+            let text_height = self
+                .document
+                .dim_styles
+                .iter()
+                .find(|style| {
+                    style.name.eq_ignore_ascii_case(&style_name)
+                        || (style_name.trim().is_empty()
+                            && style.name.eq_ignore_ascii_case("Standard"))
+                })
+                .map(|style| style.dimtxt)
+                .filter(|height| *height > 1e-9)
+                .unwrap_or(0.18);
+            let scale = f64::from(wpp) * f64::from(DYNAMIC_DIMENSION_TEXT_PX) / text_height;
+            use crate::entities::dim_override as ov;
+            let xdata = &dimension.base().common.extended_data;
+            let current = ov::real(xdata, ov::DIMSCALE);
+            // The reference draws dynamic dimension text horizontally.
+            let horizontal = ov::int(xdata, ov::DIMTIH) == Some(1) && ov::int(xdata, ov::DIMTOH) == Some(1);
+            if current.is_some_and(|value| (value - scale).abs() < 1e-9) && horizontal {
+                continue;
+            }
+            ov::set(
+                &mut self.document,
+                handle,
+                ov::DIMSCALE,
+                Some(acadrust::xdata::XDataValue::Real(scale)),
+            );
+            if !horizontal {
+                for code in [ov::DIMTIH, ov::DIMTOH] {
+                    ov::set(
+                        &mut self.document,
+                        handle,
+                        code,
+                        Some(acadrust::xdata::XDataValue::Integer16(1)),
+                    );
+                }
+            }
+            changes.push((handle, super::ChangeKind::Modified));
+        }
+        if !changes.is_empty() {
+            self.bump_entities(&changes);
+        }
+    }
+
+    /// Re-derives which dynamic dimensions stay off screen (DCHIDE, or
+    /// DYNCONSTRAINTDISPLAY 0 for all of them) and redraws the ones that
+    /// changed.
+    pub(crate) fn refresh_hidden_dynamic_dimensions(&mut self) {
+        let desired: rustc_hash::FxHashSet<Handle> = self
+            .parametric_constraints
+            .iter()
+            .flat_map(|set| {
+                set.dimensions.iter().filter_map(|(id, dimension)| {
+                    (!self.dimension_is_annotational(*dimension)
+                        && (!self.dynamic_constraint_display
+                            || !self.is_parametric_constraint_visible(set.scope, *id)))
+                    .then_some(*dimension)
+                })
+            })
+            .collect();
+        if desired == self.hidden_dynamic_dimensions {
+            return;
+        }
+        let changes: Vec<_> = self
+            .hidden_dynamic_dimensions
+            .symmetric_difference(&desired)
+            .copied()
+            .map(|handle| (handle, super::ChangeKind::Modified))
+            .collect();
+        self.hidden_dynamic_dimensions = desired;
+        self.bump_entities(&changes);
+    }
+
     /// Infers relations already present in the selected geometry.
     pub fn inferred_parametric_constraints(
         &self,
@@ -1859,9 +2335,11 @@ impl super::Scene {
             let cam = self.camera.borrow();
             (cam.view_proj_rte(bounds), cam.eye())
         };
-        set.constraints
+        let mut placements = set
+            .constraints
             .iter()
-            .filter(|c| c.enabled)
+            // A dynamic dimension is its constraint's whole display.
+            .filter(|c| c.enabled && !set.dimensions.contains_key(&c.id))
             .filter(|c| {
                 let selected = c
                     .refs
@@ -1952,7 +2430,76 @@ impl super::Scene {
                     })
                     .collect::<Vec<_>>()
             })
-            .collect()
+            .collect::<Vec<_>>();
+        // The reference marks an object once for Equal however many
+        // relations of that kind it carries; the stacked duplicates only
+        // repeated the same badge.
+        let mut equal_anchors: Vec<iced::Point> = Vec::new();
+        placements.retain(|(_, point, _, label, _, _)| {
+            if label != "=" {
+                return true;
+            }
+            if equal_anchors
+                .iter()
+                .any(|seen| (seen.x - point.x).abs() < 0.5 && (seen.y - point.y).abs() < 0.5)
+            {
+                return false;
+            }
+            equal_anchors.push(*point);
+            true
+        });
+        // A dynamic dimension carries the reference's lock mark at the
+        // start of its text instead of a constraint bar.
+        for (id, dimension) in &set.dimensions {
+            let Some(constraint) = set.get(*id) else {
+                continue;
+            };
+            if !constraint.enabled || self.entity_temporarily_hidden(*dimension) {
+                continue;
+            }
+            let Some(acadrust::EntityType::Dimension(entity)) = self.document.get_entity(*dimension)
+            else {
+                continue;
+            };
+            let Some((anchor, outward)) = crate::entities::dimension::dynamic_dimension_lock_anchor(
+                &self.document,
+                entity,
+                self.annotation_scale as f64,
+            ) else {
+                continue;
+            };
+            let project = |point: Vector3| {
+                crate::scene::pick::grip::project_rte(
+                    glam::DVec3::new(point.x, point.y, point.z),
+                    view_rot,
+                    eye,
+                    bounds,
+                )
+            };
+            let (Some(screen), Some(outward_screen)) = (
+                project(anchor),
+                project(Vector3::new(
+                    anchor.x + outward.x,
+                    anchor.y + outward.y,
+                    anchor.z + outward.z,
+                )),
+            ) else {
+                continue;
+            };
+            let direction = (outward_screen - screen).normalize_or(glam::Vec2::NEG_X);
+            let point = iced::Point::new(bounds.x + screen.x, bounds.y + screen.y);
+            if point.x.is_finite() && point.y.is_finite() {
+                placements.push((
+                    *id,
+                    point,
+                    direction.to_array(),
+                    DYNAMIC_DIMENSION_GLYPH.to_string(),
+                    false,
+                    Vec::new(),
+                ));
+            }
+        }
+        placements
     }
 
     /// Hit-tests screen point `p` (same coordinate space as `p_full` in the
@@ -2371,7 +2918,10 @@ mod tests {
     }
 
     #[test]
-    fn arc_grips_drive_center_start_and_end_but_not_midpoint() {
+    /// The center grip drives the center; the start, end and midpoint grips
+    /// reshape the arc, so they drive the whole curve and a paired Equal or
+    /// Symmetric follows the new radius and sweep.
+    fn arc_grips_drive_center_or_the_whole_arc() {
         let handle = h(8);
         let arc = acadrust::EntityType::Arc(acadrust::entities::Arc::from_coords(
             0.0,
@@ -2386,15 +2936,14 @@ mod tests {
             grip_solve_anchor_refs(&arc, handle, 0),
             vec![ParametricRef::center(handle)]
         );
-        assert_eq!(
-            grip_solve_anchor_refs(&arc, handle, 1),
-            vec![ParametricRef::point(handle, 0)]
-        );
-        assert_eq!(
-            grip_solve_anchor_refs(&arc, handle, 2),
-            vec![ParametricRef::point(handle, 1)]
-        );
-        assert_eq!(grip_solve_anchor_refs(&arc, handle, 3), Vec::new());
+        for grip in 1..=3 {
+            assert_eq!(
+                grip_solve_anchor_refs(&arc, handle, grip),
+                vec![ParametricRef::whole(handle)],
+                "grip {grip}"
+            );
+        }
+        assert_eq!(grip_solve_anchor_refs(&arc, handle, 4), Vec::new());
     }
 
     #[test]

src/scene/parametric_solve.rs

@@ -993,9 +993,15 @@ fn resolved_target(params: &ParameterTable, constraint: &ParametricConstraint) -
     if !value.is_finite() {
         return None;
     }
+    // A dimensional distance keeps its sign in the parameter but measures
+    // its magnitude, as the reference does (`d1=-50` shortens the line to
+    // 50; `0` folds the points together).
+    if constraint.kind == ConstraintKind::Distance {
+        return Some(value.abs());
+    }
     let must_be_positive = matches!(
         constraint.kind,
-        ConstraintKind::Distance | ConstraintKind::Radius | ConstraintKind::Diameter
+        ConstraintKind::Radius | ConstraintKind::Diameter
     );
     (!must_be_positive || value > 0.0).then_some(value)
 }
@@ -1466,13 +1472,23 @@ fn build_constraint(
             let Some(mirror) = whole_line(sys, cache, *m) else {
                 return Vec::new();
             };
+            // The connecting direction is held perpendicular to the axis as a
+            // projection onto the axis direction being zero: a polynomial
+            // residual the solver can follow from any start. The angle form
+            // (`Perpendicular`) locks its turn side at construction and stalls
+            // when the pair has to swing through the axis direction — a point
+            // starting far from its mirror image never arrived.
+            let across_axis = |sys: &mut System, pa: GPoint, pb: GPoint| -> Rc<dyn Constraint> {
+                let zero = sys.add_param(0.0, true);
+                Rc::new(ProjectedDistanceAlongLine::new(pa, pb, zero, mirror, false))
+            };
             if let (Some(pa), Some(pb)) =
                 (point_ref(sys, cache, *a), point_ref(sys, cache, *b))
             {
                 let pair = GLine { p1: pa, p2: pb };
                 return vec![
                     Rc::new(MidpointOnLine::new(pair, mirror)),
-                    Rc::new(PerpendicularConstraint::new(sys.store(), pair, mirror)),
+                    across_axis(sys, pa, pb),
                 ];
             }
             let (Some(first), Some(second)) = (
@@ -1500,11 +1516,7 @@ fn build_constraint(
                     };
                     vec![
                         Rc::new(MidpointOnLine::new(centers, mirror)),
-                        Rc::new(PerpendicularConstraint::new(
-                            sys.store(),
-                            centers,
-                            mirror,
-                        )),
+                        across_axis(sys, first.center, second.center),
                         Rc::new(Equal::new(second.rad, first.rad, 1.0)),
                     ]
                 }
@@ -1523,11 +1535,7 @@ fn build_constraint(
                     };
                     vec![
                         Rc::new(MidpointOnLine::new(centers, mirror)),
-                        Rc::new(PerpendicularConstraint::new(
-                            sys.store(),
-                            centers,
-                            mirror,
-                        )),
+                        across_axis(sys, first.center, second.center),
                         Rc::new(SymmetricLineDirections::new(
                             sys.store(),
                             first_axis,
@@ -1590,6 +1598,14 @@ fn build_constraint(
             let Some(resolved) = resolved_target(params, c) else {
                 return Vec::new();
             };
+            // A zero distance folds the points together; the distance
+            // residual has no gradient there, the coordinate equalities do.
+            if resolved.abs() <= f64::EPSILON {
+                return vec![
+                    Rc::new(Equal::new(pa.x, pb.x, 1.0)),
+                    Rc::new(Equal::new(pa.y, pb.y, 1.0)),
+                ];
+            }
             let target = sys.add_param(resolved, true);
             vec![Rc::new(P2PDistance::new(pa, pb, target))]
         }
@@ -1611,10 +1627,13 @@ fn build_constraint(
                 distance_direction_type::PARALLEL_TO_LINE
                     | distance_direction_type::PERPENDICULAR_TO_LINE
             ) {
-                if let Some(line) = direction_ref
-                    .first()
-                    .and_then(|reference| whole_line(sys, cache, *reference))
-                {
+                if let Some(line) = direction_ref.first().and_then(|reference| {
+                    // A text baseline or an ellipse axis directs the
+                    // distance the same way a line does.
+                    whole_line(sys, cache, *reference).or_else(|| {
+                        directional_line(sys, cache, *reference).map(|(line, _)| line)
+                    })
+                }) {
                     let current = {
                         let store = sys.store();
                         let delta = [
@@ -2441,7 +2460,32 @@ fn solve_scope(
             })
         })
         .flatten();
-        let pinned = axis_pin.unwrap_or(*reference);
+        // A transformed entity whose own end points a driving dimension
+        // measures keeps only its second constraint point where the transform
+        // put it; the dimension pulls the first end back to its value (a line
+        // scaled 2x about its start keeps its d1 by moving that start), as in
+        // the reference.
+        let dimension_pin = (reference.marker.is_none() && axis_pin.is_none())
+            .then(|| {
+                constraints.iter().find_map(|c| {
+                    (c.enabled
+                        && c.driving_param.is_some()
+                        && matches!(
+                            c.kind,
+                            ConstraintKind::Distance
+                                | ConstraintKind::DistanceX
+                                | ConstraintKind::DistanceY
+                                | ConstraintKind::DistanceDirected
+                        )
+                        && c.refs.len() >= 2
+                        && c.refs
+                            .iter()
+                            .all(|r| r.entity == reference.entity && r.marker.is_some()))
+                    .then(|| c.refs[1])
+                })
+            })
+            .flatten();
+        let pinned = axis_pin.or(dimension_pin).unwrap_or(*reference);
         // The re-aligned entity keeps the length the transform gave it (a
         // scaled vertical line stays scaled), not its pre-edit length.
         if axis_pin.is_some() {
@@ -2741,6 +2785,21 @@ fn solve_scope(
                     constraint.refs.get(2).is_some_and(|axis| axis.entity == *handle)
                 })
                 || equal_followers.iter().any(|follower| follower.entity == *handle)
+                // A driving dimension between an entity's own ends is its size;
+                // a retained length would contradict a new value.
+                || constraints.iter().any(|c| {
+                    c.enabled
+                        && c.driving_param.is_some()
+                        && matches!(
+                            c.kind,
+                            ConstraintKind::Distance
+                                | ConstraintKind::DistanceX
+                                | ConstraintKind::DistanceY
+                                | ConstraintKind::DistanceDirected
+                        )
+                        && c.refs.len() >= 2
+                        && c.refs.iter().all(|r| r.entity == *handle && r.marker.is_some())
+                })
             {
                 continue;
             }
@@ -3770,6 +3829,24 @@ impl Scene {
                 self.parametric_constraints[i].dof = None;
                 self.parametric_constraints[i].conflicts.clear();
             }
+            // A dimensional constraint set to zero means the collapse.
+            let zero_collapse: HashSet<Handle> = {
+                let set = &self.parametric_constraints[i];
+                let params = if set.local_parameters.is_empty() {
+                    &self.named_parameters
+                } else {
+                    &set.local_parameters
+                };
+                set.constraints
+                    .iter()
+                    .filter(|c| {
+                        c.enabled
+                            && c.kind == ConstraintKind::Distance
+                            && resolved_target(params, c).is_some_and(|v| v.abs() <= f64::EPSILON)
+                    })
+                    .flat_map(|c| c.refs.iter().map(|r| r.entity))
+                    .collect()
+            };
             for (handle, new_entity) in solved {
                 // An edit the constraints can only satisfy by collapsing the
                 // entity (a rotated line whose start is fixed and direction
@@ -3778,7 +3855,8 @@ impl Scene {
                 let new_entity = match originals.get(&handle) {
                     Some(original)
                         if collapsed_by_solve(&new_entity)
-                            && !collapsed_by_solve(original.as_ref()) =>
+                            && !collapsed_by_solve(original.as_ref())
+                            && !zero_collapse.contains(&handle) =>
                     {
                         original.as_ref().clone()
                     }
@@ -4062,12 +4140,25 @@ mod tests {
             Vector3::new(1.0, 0.0, 0.0),
         )));
         let refs = [ParametricRef::point(line, 0), ParametricRef::point(line, 1)];
+        // A distance keeps a negative value's sign in the parameter and
+        // measures its magnitude (`d1=-50`); a radius has no such reading.
         assert!(scene
             .validate_parametric_constraint(
                 ConstraintKind::Distance,
                 &refs,
                 Some(&DrivingValue::Literal(-1.0)),
             )
+            .is_ok());
+        let circle = scene.add_entity(EntityType::Circle(acadrust::entities::Circle::from_center_radius(
+            Vector3::new(0.0, 0.0, 0.0),
+            1.0,
+        )));
+        assert!(scene
+            .validate_parametric_constraint(
+                ConstraintKind::Radius,
+                &[ParametricRef::whole(circle)],
+                Some(&DrivingValue::Literal(-1.0)),
+            )
             .is_err());
         assert!(scene
             .validate_parametric_constraint(

src/scene/project.rs

@@ -321,6 +321,22 @@ impl Scene {
                 }
                 let mut out = wire.clone();
                 out.points = clipped;
+                // A wide polyline's band width is a geometric width in model
+                // units; the points were just projected into paper units, so
+                // the band (and any per-point taper) must follow the same
+                // scale or the PDF / print exporter strokes a 15-unit bus bar
+                // as 15 mm of paper. Negative values are fixed pixel widths
+                // and zero means "use the lineweight" — both stay as they are.
+                if out.world_width > 0.0 {
+                    out.world_width = wire.world_width * scale;
+                    if wire.taper_widths.len() == out.points.len() {
+                        out.taper_widths = wire.taper_widths.iter().map(|w| w * scale).collect();
+                    } else {
+                        // Clipping changed the vertex count, so the per-point
+                        // widths no longer line up; fall back to a constant band.
+                        out.taper_widths.clear();
+                    }
+                }
                 if let Some(source_length) = source_length {
                     for station in &mut clipped_stations {
                         *station *= scale;

src/scene/text/font_face.rs

@@ -47,12 +47,37 @@ pub enum Face {
         /// Space advance (9-unit).
         word: f32,
     },
+    /// A face paired with an Asian big font (`chineset.shx`, `hztxt.shx`, …):
+    /// double-byte characters come from the big font, everything else from
+    /// `primary` — exactly how a STYLE with a "Big Font" behaves in AutoCAD.
+    WithBig {
+        primary: Box<Face>,
+        /// Absolute path of the `AutoCAD-86 bigfont 1.0` file.
+        big: String,
+    },
 }
 
+/// Separator between a style's primary font name and its big-font path in
+/// the single `font_name` string the text pipeline passes around (see
+/// [`Face::with_big_font`]); a control character no font name contains.
+pub const BIG_FONT_SEP: char = '\u{1}';
+
 impl Face {
     /// Resolve a style's font name to a concrete face. Embedded stroke fonts
     /// take priority; only otherwise-unknown names try the system fonts.
     pub fn resolve(font_name: &str) -> Face {
+        // `primary<SEP>big` pairs a big font with the primary face.
+        if let Some((primary, big)) = font_name.split_once(BIG_FONT_SEP) {
+            let face = Face::resolve(primary);
+            return if !big.is_empty() && shx::is_bigfont(big) {
+                Face::WithBig {
+                    primary: Box::new(face),
+                    big: big.to_string(),
+                }
+            } else {
+                face
+            };
+        }
         // A resolvable on-disk .SHX font renders its real stroke glyphs; the
         // LFF substitutes only cover names we can't load.
         if font_name.to_ascii_lowercase().ends_with(".shx")
@@ -87,6 +112,13 @@ impl Face {
         Face::Lff(lff::get_font(font_name))
     }
 
+    /// The `font_name` string that pairs `primary` with the big font at
+    /// `big_path` for [`Face::resolve`]. Every text entry point takes a font
+    /// name, so the pairing rides along in that string.
+    pub fn with_big_font(primary: &str, big_path: &str) -> String {
+        format!("{primary}{BIG_FONT_SEP}{big_path}")
+    }
+
     /// Look up a glyph. A stroke (LFF) font uses its own glyphs; anything it
     /// lacks falls back to a system TrueType font chosen by cosmic-text (filled
     /// outline, so covers scripts no stroke font provides). The TTF path mirrors
@@ -103,6 +135,14 @@ impl Face {
             Face::Shx { path, .. } => shx::font_glyph(path, ch as u16)
                 .map(GlyphRef::Owned)
                 .or_else(|| ttf_glyph::fallback_glyph(ch).map(GlyphRef::Owned)),
+            Face::WithBig { primary, big } => {
+                if ttf_glyph::is_full_width(ch) {
+                    if let Some(g) = shx::bigfont_glyph(big, ch) {
+                        return Some(GlyphRef::Owned(g));
+                    }
+                }
+                primary.glyph(ch)
+            }
         }
     }
 
@@ -114,6 +154,7 @@ impl Face {
             Face::Ttf { .. } => 0.0,
             // SHX advances already include the trailing gap by design.
             Face::Shx { .. } => 0.0,
+            Face::WithBig { primary, .. } => primary.letter_spacing(),
         }
     }
 
@@ -122,6 +163,7 @@ impl Face {
         match self {
             Face::Lff(f) => f.word_spacing,
             Face::Ttf { word, .. } | Face::Shx { word, .. } => *word,
+            Face::WithBig { primary, .. } => primary.word_spacing(),
         }
     }
 
@@ -132,6 +174,7 @@ impl Face {
         match self {
             Face::Ttf { family, .. } => Some(family),
             Face::Lff(_) | Face::Shx { .. } => None,
+            Face::WithBig { primary, .. } => primary.ttf_family(),
         }
     }
 
@@ -142,6 +185,7 @@ impl Face {
             Face::Lff(f) => f.line_spacing,
             Face::Ttf { .. } => 1.0,
             Face::Shx { line, .. } => *line,
+            Face::WithBig { primary, .. } => primary.line_spacing(),
         }
     }
 }
@@ -236,11 +280,27 @@ mod tests {
                     // they should resolve to Ttf. If they aren't installed, Lff fallback is accepted.
                     eprintln!("Font {} resolved to Lff (probably not installed)", test_name);
                 }
-                Face::Shx { .. } => {
-                    // A system TTF name never resolves to an SHX shape font.
+                Face::Shx { .. } | Face::WithBig { .. } => {
+                    // A system TTF name never resolves to an SHX shape font
+                    // (nor gains a big font without the pairing separator).
                     eprintln!("Font {} resolved to Shx (unexpected)", test_name);
                 }
             }
         }
     }
+
+
+
+    #[test]
+    fn big_font_pairing_routes_ideographs_and_leaves_latin_alone() {
+        // Without a real big-font file the pairing is dropped: the primary
+        // face is used as-is.
+        assert!(matches!(
+            Face::resolve(&Face::with_big_font("txt", "C:/nowhere/chineset.shx")),
+            Face::Lff(_)
+        ));
+        // A stroke face still renders Latin from its own glyphs when paired.
+        let face = Face::resolve("txt");
+        assert!(face.glyph('A').is_some());
+    }
 }

src/scene/text/shx.rs

@@ -50,7 +50,20 @@ const DIRS: [[f64; 2]; 16] = [
     [1.0, -0.5],
 ];
 
+/// Which `AutoCAD-86` container a file is; decides how glyphs are keyed and
+/// how a `7` (subshape) opcode is encoded.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum ShxKind {
+    /// `shapes 1.0/1.1`: keyed by 8-bit code (or shape number).
+    Shapes,
+    /// `unifont 1.0`: keyed by Unicode code point.
+    Unifont,
+    /// `bigfont 1.0`: keyed by a double-byte legacy code (Big5, GBK, …).
+    Bigfont,
+}
+
 struct ShxFile {
+    kind: ShxKind,
     /// shape number → (name, spec bytes)
     shapes: HashMap<u16, (String, Vec<u8>)>,
 }
@@ -81,39 +94,160 @@ fn load_file(path: &str) -> Option<Arc<ShxFile>> {
 
 fn parse_file(path: &str) -> Option<ShxFile> {
     let bytes = std::fs::read(path).ok()?;
-    // Header line: `AutoCAD-86 shapes 1.0`/`1.1` + CR LF SUB. Reject fonts.
+    // Header line: `AutoCAD-86 <kind> 1.x` + CR LF SUB.
     let head_end = bytes.iter().position(|&b| b == 0x1A)?;
     let header = String::from_utf8_lossy(&bytes[..head_end]);
-    if !header.contains("shapes") {
+    let kind = if header.contains("shapes") {
+        ShxKind::Shapes
+    } else if header.contains("unifont") {
+        ShxKind::Unifont
+    } else if header.contains("bigfont") {
+        ShxKind::Bigfont
+    } else {
         return None;
-    }
+    };
     let mut p = head_end + 1;
     let rd_u16 = |p: &mut usize| -> Option<u16> {
         let v = u16::from_le_bytes([*bytes.get(*p)?, *bytes.get(*p + 1)?]);
         *p += 2;
         Some(v)
     };
-    let _first = rd_u16(&mut p)?;
-    let _last = rd_u16(&mut p)?;
-    let count = rd_u16(&mut p)? as usize;
-    let mut dir: Vec<(u16, usize)> = Vec::with_capacity(count);
-    for _ in 0..count {
-        let num = rd_u16(&mut p)?;
-        let len = rd_u16(&mut p)? as usize;
-        dir.push((num, len));
-    }
-    let mut shapes = HashMap::new();
-    for (num, len) in dir {
-        let end = p.checked_add(len)?.min(bytes.len());
-        let blob = &bytes[p..end];
-        p = end;
-        // Name = leading NUL-terminated ASCII, spec follows.
+    let rd_u32 = |p: &mut usize| -> Option<u32> {
+        let v = u32::from_le_bytes([
+            *bytes.get(*p)?,
+            *bytes.get(*p + 1)?,
+            *bytes.get(*p + 2)?,
+            *bytes.get(*p + 3)?,
+        ]);
+        *p += 4;
+        Some(v)
+    };
+    // Glyph data = leading NUL-terminated ASCII name, spec follows.
+    let split_named = |blob: &[u8]| -> (String, Vec<u8>) {
         let name_end = blob.iter().position(|&b| b == 0).unwrap_or(0);
         let name = String::from_utf8_lossy(&blob[..name_end]).into_owned();
         let spec = blob.get(name_end + 1..).unwrap_or(&[]).to_vec();
-        shapes.insert(num, (name, spec));
+        (name, spec)
+    };
+    let mut shapes = HashMap::new();
+    match kind {
+        ShxKind::Shapes => {
+            let _first = rd_u16(&mut p)?;
+            let _last = rd_u16(&mut p)?;
+            let count = rd_u16(&mut p)? as usize;
+            let mut dir: Vec<(u16, usize)> = Vec::with_capacity(count);
+            for _ in 0..count {
+                let num = rd_u16(&mut p)?;
+                let len = rd_u16(&mut p)? as usize;
+                dir.push((num, len));
+            }
+            for (num, len) in dir {
+                let end = p.checked_add(len)?.min(bytes.len());
+                let blob = &bytes[p..end];
+                p = end;
+                shapes.insert(num, split_named(blob));
+            }
+        }
+        ShxKind::Unifont => {
+            // u32 glyph count (including the font header), then the header
+            // entry (u16 length + name NUL above below modes encoding
+            // embedded 0), then `count - 1` × (u16 code, u16 length, data).
+            let count = rd_u32(&mut p)? as usize;
+            let head_len = rd_u16(&mut p)? as usize;
+            let end = p.checked_add(head_len)?.min(bytes.len());
+            shapes.insert(0, split_named(&bytes[p..end]));
+            p = end;
+            for _ in 1..count {
+                let Some(code) = rd_u16(&mut p) else { break };
+                let Some(len) = rd_u16(&mut p) else { break };
+                let end = p.checked_add(len as usize)?.min(bytes.len());
+                shapes.insert(code, split_named(&bytes[p..end]));
+                p = end;
+            }
+        }
+        ShxKind::Bigfont => {
+            // u16 bytes per table entry (8), u16 table entries, u16 range
+            // count, ranges × (u16 lo, u16 hi) of lead bytes, then the entry
+            // table — a sparse hash table of (u16 code, u16 length, u32 file
+            // offset); empty slots are all zero. Shape 0 (name NUL above
+            // below modes) is the font header.
+            let entry_size = rd_u16(&mut p)? as usize;
+            let entries = rd_u16(&mut p)? as usize;
+            let ranges = rd_u16(&mut p)? as usize;
+            p = p.checked_add(ranges * 4)?;
+            if entry_size < 8 {
+                return None;
+            }
+            for i in 0..entries {
+                let mut q = p.checked_add(i * entry_size)?;
+                let Some(code) = rd_u16(&mut q) else { break };
+                let Some(len) = rd_u16(&mut q) else { break };
+                let Some(off) = rd_u32(&mut q) else { break };
+                if off == 0 && len == 0 {
+                    continue;
+                }
+                let start = off as usize;
+                let end = start.saturating_add(len as usize).min(bytes.len());
+                if start >= end {
+                    continue;
+                }
+                shapes.insert(code, split_named(&bytes[start..end]));
+            }
+        }
     }
-    Some(ShxFile { shapes })
+    Some(ShxFile { kind, shapes })
+}
+
+/// True when the file is an Asian big font (`AutoCAD-86 bigfont 1.0`).
+pub fn is_bigfont(path: &str) -> bool {
+    load_file(path).is_some_and(|f| f.kind == ShxKind::Bigfont)
+}
+
+/// The code pages a big font's double-byte codes may be in, most likely
+/// first, guessed from the file name. The codec maps a name to its encoding
+/// (`ansi_950` Big5, `ansi_936` GBK, `ansi_932` Shift_JIS, `ansi_949` EUC-KR).
+fn bigfont_code_pages(path: &str) -> [&'static str; 4] {
+    let name = path
+        .rsplit(['/', '\\'])
+        .next()
+        .unwrap_or(path)
+        .to_ascii_lowercase();
+    if name.contains("gb") || name.contains("hz") || name.contains("china") {
+        ["ansi_936", "ansi_950", "ansi_932", "ansi_949"]
+    } else if name.contains("bigfont") || name.contains("extfont") || name.contains("jp") {
+        ["ansi_932", "ansi_950", "ansi_936", "ansi_949"]
+    } else if name.contains("whg") || name.contains("kor") || name.contains("han") {
+        ["ansi_949", "ansi_950", "ansi_936", "ansi_932"]
+    } else {
+        // `chineset.shx` and most Taiwanese fonts.
+        ["ansi_950", "ansi_936", "ansi_932", "ansi_949"]
+    }
+}
+
+/// Look up `ch` in a big font: encode it to the font's double-byte code and
+/// fetch that shape, normalised like [`font_glyph`]. `None` when the file is
+/// not a big font or has no glyph for the character.
+pub fn bigfont_glyph(path: &str, ch: char) -> Option<Arc<crate::scene::text::lff::Glyph>> {
+    let file = load_file(path)?;
+    if file.kind != ShxKind::Bigfont {
+        return None;
+    }
+    let mut buf = [0u8; 4];
+    let s = ch.encode_utf8(&mut buf);
+    for page in bigfont_code_pages(path) {
+        let Some(enc) = acadrust::io::dxf::code_page::encoding_from_code_page(page) else {
+            continue;
+        };
+        let (bytes, _, unmappable) = enc.encode(s);
+        if unmappable || bytes.len() != 2 {
+            continue;
+        }
+        let code = u16::from_be_bytes([bytes[0], bytes[1]]);
+        if file.shapes.contains_key(&code) {
+            return font_glyph(path, code);
+        }
+    }
+    None
 }
 
 /// Tessellate the shape named `name` (case-insensitive) from the SHX at
@@ -410,8 +544,16 @@ fn interpret(
                 }
             }
             7 => {
-                let sub = *b.get(i).unwrap_or(&0) as u16;
+                let mut sub = *b.get(i).unwrap_or(&0) as u16;
                 i += 1;
+                // A big font references subshapes by a two-byte code:
+                // `7, 0, hi, lo`.
+                if file.kind == ShxKind::Bigfont && sub == 0 {
+                    let hi = *b.get(i).unwrap_or(&0) as u16;
+                    let lo = *b.get(i + 1).unwrap_or(&0) as u16;
+                    i += 2;
+                    sub = (hi << 8) | lo;
+                }
                 if !skipping && sub != 0 && sub != shape_number {
                     interpret(file, sub, st, cur, out, depth + 1);
                 }
@@ -510,3 +652,91 @@ fn interpret(
         }
     }
 }
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Shape bytecode for a glyph: a horizontal 6-unit stroke, then end.
+    /// (`0x60` = length 6, direction 0.)
+    const BAR: [u8; 2] = [0x60, 0x00];
+
+    fn tmp(name: &str, bytes: &[u8]) -> String {
+        let dir = std::env::temp_dir().join(format!("ocs-shx-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join(name);
+        std::fs::write(&path, bytes).unwrap();
+        path.to_string_lossy().into_owned()
+    }
+
+    /// A one-glyph `bigfont 1.0` keyed by the Big5 code of `中` (0xA4A4),
+    /// laid out like `chineset.shx`: header, 8-byte entries in a sparse
+    /// table, font header shape 0 (`name NUL above below modes`).
+    fn synthetic_bigfont() -> Vec<u8> {
+        let mut b = b"AutoCAD-86 bigfont 1.0\r\n\x1a".to_vec();
+        let entries: u16 = 4;
+        b.extend_from_slice(&8u16.to_le_bytes());
+        b.extend_from_slice(&entries.to_le_bytes());
+        b.extend_from_slice(&1u16.to_le_bytes()); // one lead-byte range
+        b.extend_from_slice(&0x80u16.to_le_bytes());
+        b.extend_from_slice(&0xFFu16.to_le_bytes());
+        let table_at = b.len();
+        b.resize(table_at + 8 * entries as usize, 0);
+        let head_data: Vec<u8> = [b"BIG\x00".as_slice(), &[48u8, 0, 2]].concat();
+        let glyph_data: Vec<u8> = [b"\x00".as_slice(), &BAR].concat();
+        let head_off = b.len() as u32;
+        b.extend_from_slice(&head_data);
+        let glyph_off = b.len() as u32;
+        b.extend_from_slice(&glyph_data);
+        // Slot 0 = shape 0; slot 2 = the glyph (slots 1 and 3 stay empty).
+        let mut entry = |slot: usize, code: u16, len: u16, off: u32| {
+            let at = table_at + slot * 8;
+            b[at..at + 2].copy_from_slice(&code.to_le_bytes());
+            b[at + 2..at + 4].copy_from_slice(&len.to_le_bytes());
+            b[at + 4..at + 8].copy_from_slice(&off.to_le_bytes());
+        };
+        entry(0, 0, head_data.len() as u16, head_off);
+        entry(2, 0xA4A4, glyph_data.len() as u16, glyph_off);
+        b
+    }
+
+    /// A `unifont 1.0` with the font header and one glyph for `A` (U+0041).
+    fn synthetic_unifont() -> Vec<u8> {
+        let mut b = b"AutoCAD-86 unifont 1.0\r\n\x1a".to_vec();
+        b.extend_from_slice(&2u32.to_le_bytes()); // header + 1 glyph
+        let head: Vec<u8> = [b"UNI\x00".as_slice(), &[6u8, 2, 2, 0, 0, 0]].concat();
+        b.extend_from_slice(&(head.len() as u16).to_le_bytes());
+        b.extend_from_slice(&head);
+        let glyph: Vec<u8> = [b"\x00".as_slice(), &BAR].concat();
+        b.extend_from_slice(&0x41u16.to_le_bytes());
+        b.extend_from_slice(&(glyph.len() as u16).to_le_bytes());
+        b.extend_from_slice(&glyph);
+        b
+    }
+
+    #[test]
+    fn bigfont_glyph_is_found_by_big5_code_and_scaled_to_cap_height() {
+        let path = tmp("cjk.shx", &synthetic_bigfont());
+        assert!(is_bigfont(&path));
+        let (above, below) = font_metrics(&path).expect("font header");
+        assert_eq!((above, below), (48.0, 0.0));
+        // `中` → Big5 A4A4 → the glyph; `A` is not in a big font.
+        let g = bigfont_glyph(&path, '中').expect("glyph for 中");
+        // 6 font units at above = 48 → 6 * 9 / 48 = 1.125 text units.
+        assert!((g.advance - 1.125).abs() < 1e-4, "advance {}", g.advance);
+        assert_eq!(g.strokes.len(), 1);
+        assert!(bigfont_glyph(&path, 'A').is_none());
+        assert!(bigfont_glyph(&path, '國').is_none(), "unknown code must miss, not alias");
+    }
+
+    #[test]
+    fn unifont_glyph_is_keyed_by_unicode() {
+        let path = tmp("uni.shx", &synthetic_unifont());
+        assert!(!is_bigfont(&path));
+        assert_eq!(font_metrics(&path), Some((6.0, 2.0)));
+        let g = font_glyph(&path, 'A' as u16).expect("glyph for A");
+        assert!((g.advance - 9.0).abs() < 1e-4, "6 units at above 6 → 9: {}", g.advance);
+        assert!(font_glyph(&path, 'B' as u16).is_none());
+    }
+}

src/scene/text/ttf_glyph.rs

@@ -176,6 +176,42 @@ pub fn glyph(family: &str, ch: char) -> Option<Arc<Glyph>> {
     built
 }
 
+/// Font-unit → 9-unit-em-box factor: the whole em square maps onto the text
+/// height. This is how an SHX big font (`chineset.shx`, `hztxt.shx`, …)
+/// sizes its ideographs — a CJK glyph is as tall as the text height and one
+/// text height wide — so a TrueType glyph standing in for a missing big-font
+/// glyph must use the same box, not the Latin cap height. Cap-height scaling
+/// makes ideographs ~1.3–1.5× too big (1 em ≈ 1.3–1.5 cap heights in CJK
+/// fonts), so every line of substituted Chinese text ran past its frame.
+fn em_scale(face: &ttf_parser::Face) -> f32 {
+    CAP_UNITS / face.units_per_em().max(1) as f32
+}
+
+/// Ideographic / full-width characters: the ones a big font would supply and
+/// that sit on an em box rather than the Latin cap height.
+pub(crate) fn is_full_width(ch: char) -> bool {
+    matches!(
+        ch as u32,
+        0x1100..=0x11FF       // Hangul Jamo
+        | 0x2E80..=0x2FDF     // CJK / Kangxi radicals
+        | 0x2FF0..=0x303F     // ideographic description, CJK symbols & punctuation
+        | 0x3040..=0x30FF     // Hiragana, Katakana
+        | 0x3100..=0x312F     // Bopomofo
+        | 0x3130..=0x318F     // Hangul compatibility Jamo
+        | 0x3190..=0x31FF     // Kanbun, Bopomofo ext., CJK strokes, Katakana ext.
+        | 0x3200..=0x33FF     // enclosed CJK, CJK compatibility
+        | 0x3400..=0x4DBF     // CJK ext. A
+        | 0x4E00..=0x9FFF     // CJK unified ideographs
+        | 0xA960..=0xA97F     // Hangul Jamo ext. A
+        | 0xAC00..=0xD7FF     // Hangul syllables, Jamo ext. B
+        | 0xF900..=0xFAFF     // CJK compatibility ideographs
+        | 0xFE30..=0xFE4F     // CJK compatibility forms
+        | 0xFF01..=0xFF60     // full-width ASCII variants
+        | 0xFFE0..=0xFFE6     // full-width symbols
+        | 0x20000..=0x3FFFF   // CJK ext. B–H
+    )
+}
+
 /// Font-unit → 9-unit-cap-height factor for a parsed face. Cap height comes
 /// from the OS/2 table; absent, we approximate it as 0.7 × units-per-em.
 fn cap_scale(face: &ttf_parser::Face) -> f32 {
@@ -379,7 +415,16 @@ fn build_fallback(ch: char) -> Option<Arc<Glyph>> {
             let face_index = fs.db_mut().face(g.font_id).map(|f| f.index).unwrap_or(0);
             let font = fs.get_font(g.font_id, g.font_weight)?;
             let face = ttf_parser::Face::parse(font.data(), face_index).ok()?;
-            let k = cap_scale(&face);
+            // A fallback glyph stands in for a stroke / SHX font that lacks
+            // the character. For an ideograph that font would have been a
+            // big font, whose glyphs fill the text height — so size the
+            // substitute by its em box. Everything else keeps the cap-height
+            // normalisation that lines it up with the Latin stroke glyphs.
+            let k = if is_full_width(ch) {
+                em_scale(&face)
+            } else {
+                cap_scale(&face)
+            };
             let gid = ttf_parser::GlyphId(g.glyph_id);
             let advance = face.glyph_hor_advance(gid).unwrap_or(0) as f32 * k;
             let mut fl = OutlineFlattener::new(k);
@@ -609,6 +654,39 @@ mod tests {
         assert!(!run.glyphs.is_empty());
     }
 
+    #[test]
+    fn fallback_ideograph_fills_the_text_height_like_a_big_font() {
+        // An SHX big font draws an ideograph one text height tall and one
+        // text height wide. The TrueType stand-in must match that box (9
+        // units), not the ~12–14 units the Latin cap-height normalisation
+        // gives a CJK em square — that overrun pushed every substituted
+        // Chinese line past its frame. Tolerated when the machine has no
+        // CJK font at all.
+        let Some(g) = fallback_glyph('中') else {
+            eprintln!("no CJK system font; skipping");
+            return;
+        };
+        assert!(
+            (g.advance - CAP_UNITS).abs() < 0.6,
+            "ideograph advance must be about one text height: got {}",
+            g.advance
+        );
+        let ink_h = g
+            .strokes
+            .iter()
+            .flatten()
+            .map(|p| p[1])
+            .fold((f32::MAX, f32::MIN), |(lo, hi), y| (lo.min(y), hi.max(y)));
+        assert!(
+            ink_h.1 - ink_h.0 <= CAP_UNITS * 1.05,
+            "ideograph ink must fit the text height: {:?}",
+            ink_h
+        );
+        // Latin fallback keeps the cap-height convention (shares a baseline
+        // with the stroke glyphs around it).
+        assert!(!is_full_width('A') && is_full_width('中') && is_full_width('，'));
+    }
+
     #[test]
     fn shape_run_positions_glyphs() {
         let fams = sysfont::families();