Linear dimensional constraints: point flow, dynamic dimension, driving parameter

DCLINEAR, DCHORIZONTAL, DCVERTICAL and DCALIGNED follow the reference flow:
`Specify first constraint point or [Object] <Object>:`, `Specify second
constraint point:`, `Specify dimension line location:`, then `Dimension
text = …` and `Enter value or name and value <d1=100>:`. Linear reads
horizontal or vertical from the dimension line location the way a linear
dimension does; Object takes a line's, an arc's or a polyline segment's
ends. A miss reports `No valid constraint point found.` / `No object
found.` and asks again; another object type reports `Invalid selection for
Linear. Select a line, polyline segment or arc.`.

Each constraint creates a drawing parameter (`d1`, `d2`, …, or the typed
`name=expression`), drives the constraint through it, and draws a dynamic
dimension in constraint gray whose text follows CONSTRAINTNAMEFORMAT
(`d1=100.0000`); the dimension is associated with the constrained objects
and its text is refreshed after every solve. A typed value other than the
measured one moves the second point while the first stays, and so does a
later parameter edit. Deleting the constraint removes its dimension and,
when nothing else reads it, its parameter.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/app/command_driver.rs

@@ -1103,6 +1103,50 @@ impl OpenCADStudio {
         TableCellEditStart::Started
     }
 
+    /// Reports a refused command-line value and shows the prompt again.
+    fn reprompt_active_command(&mut self, i: usize, message: &str) {
+        self.command_line.push_error(message);
+        if let Some(prompt) = self.tabs[i].active_cmd.as_ref().map(|command| command.prompt()) {
+            self.command_line.push_info(&prompt);
+        }
+    }
+
+    /// Drops what removed dimensional constraints leave behind: their dynamic
+    /// dimensions, and their parameters when no other constraint reads them.
+    pub(crate) fn purge_dimensional_extras(
+        &mut self,
+        i: usize,
+        dimensions: Vec<Handle>,
+        parameters: Vec<String>,
+    ) {
+        if !dimensions.is_empty() {
+            self.tabs[i].scene.erase_entities(&dimensions);
+        }
+        let unused: Vec<String> = parameters
+            .into_iter()
+            .filter(|name| {
+                !self.tabs[i]
+                    .scene
+                    .parametric_constraints
+                    .iter()
+                    .flat_map(|set| set.constraints.iter())
+                    .any(|constraint| {
+                        matches!(
+                            &constraint.driving_param,
+                            Some(crate::scene::named_parameters::DrivingValue::Named(used))
+                                if used == name
+                        )
+                    })
+            })
+            .collect();
+        if !unused.is_empty() {
+            self.tabs[i].scene.record_undo_named_parameters_before();
+            for name in &unused {
+                self.tabs[i].scene.named_parameters_mut().remove(name);
+            }
+        }
+    }
+
     fn remove_parametric_constraint(
         &mut self,
         id: crate::scene::parametric_constraints::ConstraintId,
@@ -1117,8 +1161,13 @@ impl OpenCADStudio {
             return false;
         };
         let touched: Vec<Handle> = constraint.refs.iter().map(|r| r.entity).collect();
+        let dimension = set.dimensions.get(&id).copied();
+        let parameter = match &constraint.driving_param {
+            Some(crate::scene::named_parameters::DrivingValue::Named(name)) => Some(name.clone()),
+            _ => None,
+        };
         let constraints_before = set.clone();
-        let pending = self.begin_undo(i, label, touched.len(), true);
+        let pending = self.begin_undo(i, label, touched.len(), dimension.is_none());
         self.tabs[i]
             .scene
             .record_undo_parametric_constraints_before(scope, constraints_before);
@@ -1126,6 +1175,11 @@ impl OpenCADStudio {
             .scene
             .parametric_constraint_set_mut(scope)
             .remove(id);
+        self.purge_dimensional_extras(
+            i,
+            dimension.into_iter().collect(),
+            parameter.into_iter().collect(),
+        );
         if self.tabs[i].scene.selected_constraint == Some(id) {
             self.tabs[i].scene.selected_constraint = None;
         }
@@ -1219,6 +1273,23 @@ impl OpenCADStudio {
             .flat_map(|c| c.refs.iter().map(|r| r.entity))
             .collect();
 
+        // A changed value moves a dimensional constraint's second point; its
+        // first point stays, as in the reference.
+        let anchors: Vec<crate::scene::parametric_constraints::ParametricRef> = self.tabs[i]
+            .scene
+            .parametric_constraints
+            .iter()
+            .flat_map(|set| set.constraints.iter())
+            .filter(|c| {
+                c.enabled
+                    && matches!(
+                        c.driving_param,
+                        Some(crate::scene::named_parameters::DrivingValue::Named(_))
+                    )
+            })
+            .filter_map(|c| c.refs.first().copied())
+            .filter(|reference| reference.marker.is_some())
+            .collect();
         let pending = self.begin_undo(i, "Apply named parameters", touched.len(), true);
         self.tabs[i].scene.record_undo_named_parameters_before();
         self.tabs[i].scene.named_parameters = table;
@@ -1228,10 +1299,15 @@ impl OpenCADStudio {
                 .into_iter()
                 .map(|h| (h, crate::scene::ChangeKind::Modified))
                 .collect();
-            self.tabs[i].scene.bump_entities(&changes);
+            self.tabs[i].scene.bump_entities_with_parametric_policy(
+                &changes,
+                &anchors,
+                self.constraint_solve_mode,
+            );
         } else {
             self.tabs[i].scene.sync_native_parametric_graph();
         }
+        self.tabs[i].scene.refresh_dynamic_dimension_texts();
         if let Some(pd) = pending {
             self.commit_undo_delta(i, pd);
         }
@@ -3450,6 +3526,174 @@ impl OpenCADStudio {
                     self.commit_undo_delta(i, pd);
                 }
             }
+            CmdResult::CheckConstraintPoint(pick) => {
+                use crate::scene::parametric_constraints::{
+                    nearest_parametric_point, nearest_parametric_point_on_entity, resolve_point,
+                };
+                let scope = self.tabs[i].current_parametric_scope();
+                let resolved = {
+                    let document = &self.tabs[i].scene.document;
+                    let world =
+                        acadrust::types::Vector3::new(pick.point.x, pick.point.y, pick.point.z);
+                    let reference = match pick.handle {
+                        Some(handle) => {
+                            nearest_parametric_point_on_entity(document, scope, handle, world)
+                        }
+                        None => nearest_parametric_point(document, scope, world, None),
+                    };
+                    reference.map(|reference| {
+                        let point = document
+                            .get_entity(reference.entity)
+                            .zip(reference.marker)
+                            .and_then(|(entity, marker)| resolve_point(entity, marker))
+                            .map_or(pick.point, |p| glam::DVec3::new(p.x, p.y, p.z));
+                        (reference, point)
+                    })
+                };
+                let Some((reference, point)) = resolved else {
+                    return self.apply_cmd_result(CmdResult::ReportError(
+                        crate::modules::parametric::DimConstraintCommand::NO_POINT.to_string(),
+                    ));
+                };
+                let result = self.tabs[i]
+                    .active_cmd
+                    .as_mut()
+                    .map(|command| command.accept_constraint_point(reference, point));
+                return match result {
+                    Some(result) => self.apply_cmd_result(result),
+                    None => Task::none(),
+                };
+            }
+            CmdResult::AddDimensionalConstraint {
+                kind,
+                first,
+                second,
+                first_point,
+                second_point,
+                location,
+                axis,
+                name,
+                expression,
+                label,
+            } => {
+                use crate::modules::annotate::{aligned_dim, linear_dim};
+                use crate::scene::named_parameters::{is_valid_name, DrivingValue};
+                use crate::scene::parametric_constraints::{dynamic_dimension_text, ConstraintKind};
+
+                let scope = self.tabs[i].current_parametric_scope();
+                let refs = vec![first, second];
+                // A refused value keeps the prompt open, as the reference's
+                // editor does.
+                if let Err(message) = self.tabs[i].scene.validate_parametric_constraint(
+                    kind,
+                    &refs,
+                    Some(&DrivingValue::Literal(1.0)),
+                ) {
+                    self.reprompt_active_command(i, message);
+                    return Task::none();
+                }
+                let name = name.trim().to_string();
+                if !is_valid_name(&name) {
+                    self.reprompt_active_command(i, "Invalid parameter name.");
+                    return Task::none();
+                }
+                let mut table = self.tabs[i].scene.named_parameters().clone();
+                if let Err(error) = table.set(&name, &expression) {
+                    self.reprompt_active_command(i, &error.to_string());
+                    return Task::none();
+                }
+                let value = match table.resolve(&name) {
+                    Ok(value) if value.is_finite() => value,
+                    _ => {
+                        self.reprompt_active_command(i, "Invalid expression.");
+                        return Task::none();
+                    }
+                };
+                let text = dynamic_dimension_text(
+                    &name,
+                    value,
+                    self.tabs[i].scene.constraint_name_format,
+                );
+                let mut entity = if kind == ConstraintKind::Distance {
+                    aligned_dim::aligned_dimension_entity(
+                        first_point,
+                        second_point,
+                        location,
+                        Some(text),
+                    )
+                } else {
+                    linear_dim::linear_dimension_entity(
+                        first_point,
+                        second_point,
+                        location,
+                        axis,
+                        Some(text),
+                    )
+                };
+                crate::scene::creation_style::apply_current_creation_styles(
+                    &self.tabs[i].scene.document,
+                    &mut entity,
+                );
+                let layer = self.tabs[i].active_layer.clone();
+                if layer != "0" {
+                    entity.as_entity_mut().set_layer(layer);
+                }
+                // A dynamic dimension draws in the constraint gray, not the
+                // current color.
+                entity.common_mut().color = acadrust::types::Color::Rgb {
+                    r: 103,
+                    g: 109,
+                    b: 118,
+                };
+                let constraints_before = self.tabs[i]
+                    .scene
+                    .parametric_constraint_set(scope)
+                    .cloned()
+                    .unwrap_or_else(|| {
+                        crate::scene::parametric_constraints::ParametricConstraintSet::new(scope)
+                    });
+                let mut touched = vec![first.entity];
+                if second.entity != first.entity {
+                    touched.push(second.entity);
+                }
+                let pending = self.begin_undo(i, label, touched.len() + 1, false);
+                self.tabs[i]
+                    .scene
+                    .record_undo_parametric_constraints_before(scope, constraints_before);
+                self.tabs[i].scene.record_undo_named_parameters_before();
+                self.tabs[i].scene.named_parameters = table;
+                let dimension = self.tabs[i].scene.add_entity(entity);
+                let set = self.tabs[i].scene.parametric_constraint_set_mut(scope);
+                let id = set.add(kind, refs, Some(DrivingValue::Named(name)));
+                set.dimensions.insert(id, dimension);
+                self.tabs[i].scene.note_parametric_constraint_applied(
+                    scope,
+                    id,
+                    self.constraint_bar_display,
+                );
+                self.tabs[i].scene.attach_dimension_association(
+                    dimension,
+                    vec![Some(first.entity), Some(second.entity)],
+                );
+                let changes: Vec<(Handle, crate::scene::ChangeKind)> = touched
+                    .into_iter()
+                    .map(|handle| (handle, crate::scene::ChangeKind::Modified))
+                    .collect();
+                // The first point stays; a value other than the measured one
+                // moves the second, as in the reference.
+                self.tabs[i].scene.bump_entities_with_parametric_policy(
+                    &changes,
+                    &[first],
+                    self.constraint_solve_mode,
+                );
+                self.tabs[i].dirty = true;
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.refresh_properties();
+                if let Some(pd) = pending {
+                    self.commit_undo_delta(i, pd);
+                }
+            }
             CmdResult::AddFixedConstraint(pick) => {
                 use crate::modules::parametric::FixConstraintCommand;
                 use crate::scene::parametric_constraints::{

src/app/commands/draw.rs

@@ -1131,7 +1131,26 @@ impl OpenCADStudio {
                         self.command_line.push_output("No constraints found.");
                         return None;
                     }
-                    let pending = self.begin_undo(i, "Delete constraints", handles.len(), true);
+                    let dimensions: Vec<acadrust::Handle> = ids
+                        .iter()
+                        .filter_map(|id| before.dimensions.get(id).copied())
+                        .collect();
+                    let parameters: Vec<String> = ids
+                        .iter()
+                        .filter_map(|id| before.get(*id))
+                        .filter_map(|constraint| match &constraint.driving_param {
+                            Some(crate::scene::named_parameters::DrivingValue::Named(name)) => {
+                                Some(name.clone())
+                            }
+                            _ => None,
+                        })
+                        .collect();
+                    let pending = self.begin_undo(
+                        i,
+                        "Delete constraints",
+                        handles.len(),
+                        dimensions.is_empty(),
+                    );
                     self.tabs[i]
                         .scene
                         .record_undo_parametric_constraints_before(scope, before);
@@ -1139,6 +1158,7 @@ impl OpenCADStudio {
                     for id in &ids {
                         set.remove(*id);
                     }
+                    self.purge_dimensional_extras(i, dimensions, parameters);
                     let changes: Vec<_> = handles
                         .iter()
                         .copied()
@@ -1726,8 +1746,24 @@ impl OpenCADStudio {
                 }
             }
 
-            "DCONSTRAINT" | "DCLINEAR" | "DCHORIZONTAL" | "DCVERTICAL" | "DCALIGNED"
-            | "DCRADIUS" | "DCDIAMETER" => {
+            "DCLINEAR" | "DCHORIZONTAL" | "DCVERTICAL" | "DCALIGNED" => {
+                use crate::modules::parametric::{DimConstraintAxis, DimConstraintCommand};
+                use crate::scene::parametric_constraints::next_dimensional_parameter_name;
+                let axis = match cmd {
+                    "DCHORIZONTAL" => DimConstraintAxis::Horizontal,
+                    "DCVERTICAL" => DimConstraintAxis::Vertical,
+                    "DCALIGNED" => DimConstraintAxis::Aligned,
+                    _ => DimConstraintAxis::Linear,
+                };
+                let name = next_dimensional_parameter_name(self.tabs[i].scene.named_parameters());
+                // Both constraint points are picked inside the command.
+                self.tabs[i].scene.deselect_all();
+                let command = DimConstraintCommand::new(axis, name);
+                self.command_line.push_info(&command.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(command));
+            }
+
+            "DCONSTRAINT" | "DCRADIUS" | "DCDIAMETER" => {
                 let handles = self.tabs[i].scene.selected_handles_in_order();
                 if handles.is_empty() {
                     use crate::modules::draw::select::SelectObjectsCommand;

src/command.rs

@@ -1610,6 +1610,25 @@ pub enum CmdResult {
         multiple: bool,
         label: &'static str,
     },
+    /// Resolves a constraint-point pick against the live document and hands
+    /// it back through `CadCommand::accept_constraint_point`; a miss reports
+    /// `No valid constraint point found.` and asks again.
+    CheckConstraintPoint(CoincidentPick),
+    /// Adds a dimensional constraint between two constraint points together
+    /// with the dynamic dimension that shows it and the parameter
+    /// (`name` = `expression`) that drives it.
+    AddDimensionalConstraint {
+        kind: crate::scene::parametric_constraints::ConstraintKind,
+        first: crate::scene::parametric_constraints::ParametricRef,
+        second: crate::scene::parametric_constraints::ParametricRef,
+        first_point: DVec3,
+        second_point: DVec3,
+        location: DVec3,
+        axis: DVec3,
+        name: String,
+        expression: String,
+        label: &'static str,
+    },
     /// Adds a point or object symmetry relation around a picked line. The
     /// first reference and axis remain fixed during initial placement.
     AddSymmetricConstraint {
@@ -2453,6 +2472,16 @@ pub trait CadCommand: Send {
         false
     }
 
+    /// A constraint point the host resolved for a `CheckConstraintPoint`
+    /// pick, with its world position.
+    fn accept_constraint_point(
+        &mut self,
+        _reference: crate::scene::parametric_constraints::ParametricRef,
+        _point: DVec3,
+    ) -> CmdResult {
+        CmdResult::NeedPoint
+    }
+
     /// Include filled hatch / DXF SOLID regions in the entity hit-test.
     ///
     /// Most entity-pick commands operate on curve geometry and intentionally

src/modules/annotate/aligned_dim.rs

@@ -67,26 +67,36 @@ impl AlignedDimensionCommand {
         let first = self.plane.to_local(first);
         let second = self.plane.to_local(second);
         let point = self.plane.to_local(point);
-        let mut dim = DimensionAligned::new(v3(first), v3(second));
-        // The placement point is stored so commit matches the preview.
-        dim.definition_point = v3(point);
-        dim.base.definition_point = v3(point);
-        let (d1, d2) = dim_line_endpoints(first, second, point);
-        dim.base.text_middle_point = v3((d1 + d2) * 0.5);
-        dim.base.insertion_point = dim.base.text_middle_point;
-        dim.base.actual_measurement = dim.measurement();
-        crate::entities::dimension::set_dimension_text_override(
-            &mut dim.base,
-            self.text_override.clone(),
-        );
+        let mut entity = aligned_dimension_entity(first, second, point, self.text_override.clone());
         // An explicit text angle overrides the default rotation.
-        if let Some(angle) = self.text_angle {
-            dim.base.text_rotation = angle;
+        if let (Some(angle), EntityType::Dimension(dimension)) = (self.text_angle, &mut entity) {
+            dimension.base_mut().text_rotation = angle;
         }
-        self.plane.place_entity(EntityType::Dimension(Dimension::Aligned(dim)))
+        self.plane.place_entity(entity)
     }
 }
 
+/// An aligned dimension between two points of the working plane, its
+/// dimension line through `point` — what DIMALIGNED places and what an
+/// aligned dimensional constraint draws.
+pub(crate) fn aligned_dimension_entity(
+    first: DVec3,
+    second: DVec3,
+    point: DVec3,
+    text_override: Option<String>,
+) -> EntityType {
+    let mut dim = DimensionAligned::new(v3(first), v3(second));
+    // The placement point is stored so commit matches the preview.
+    dim.definition_point = v3(point);
+    dim.base.definition_point = v3(point);
+    let (d1, d2) = dim_line_endpoints(first, second, point);
+    dim.base.text_middle_point = v3((d1 + d2) * 0.5);
+    dim.base.insertion_point = dim.base.text_middle_point;
+    dim.base.actual_measurement = dim.measurement();
+    crate::entities::dimension::set_dimension_text_override(&mut dim.base, text_override);
+    EntityType::Dimension(Dimension::Aligned(dim))
+}
+
 impl CadCommand for AlignedDimensionCommand {
     fn set_working_plane(&mut self, plane: WorkingPlane) {
         self.plane = plane;

src/modules/annotate/linear_dim.rs

@@ -15,7 +15,7 @@ use glam::DVec3;
 use crate::t;
 
 /// Select the measured axis from where the dimension line clears the points.
-fn measure_axis(first: DVec3, second: DVec3, def: DVec3) -> DVec3 {
+pub(crate) fn measure_axis(first: DVec3, second: DVec3, def: DVec3) -> DVec3 {
     let outside = |value: f64, a: f64, b: f64| {
         let (low, high) = if a <= b { (a, b) } else { (b, a) };
         (low - value).max(value - high).max(0.0)
@@ -113,26 +113,38 @@ impl LinearDimensionCommand {
         let first = self.plane.to_local(first);
         let second = self.plane.to_local(second);
         let point = self.plane.to_local(point);
-        let mut dim = DimensionLinear::new(v3(first), v3(second));
         let axis = self.axis_mode.axis(first, second, point);
-        dim.rotation = axis.y.atan2(axis.x);
-        dim.set_offset(dimension_line_offset(second, point, axis));
-        dim.base.definition_point = dim.definition_point;
-        dim.base.text_middle_point = v3(linear_text_pos(first, second, point, axis));
-        dim.base.insertion_point = dim.base.text_middle_point;
-        dim.base.actual_measurement = dim.measurement();
-        crate::entities::dimension::set_dimension_text_override(
-            &mut dim.base,
-            self.text_override.clone(),
-        );
+        let mut entity =
+            linear_dimension_entity(first, second, point, axis, self.text_override.clone());
         // An explicit text angle overrides the UCS-derived rotation.
-        if let Some(angle) = self.text_angle {
-            dim.base.text_rotation = angle;
+        if let (Some(angle), EntityType::Dimension(dimension)) = (self.text_angle, &mut entity) {
+            dimension.base_mut().text_rotation = angle;
         }
-        self.plane.place_entity(EntityType::Dimension(Dimension::Linear(dim)))
+        self.plane.place_entity(entity)
     }
 }
 
+/// A linear dimension between two points of the working plane, its
+/// dimension line through `point` along `axis` — what DIMLINEAR places and
+/// what a dynamic dimensional constraint draws.
+pub(crate) fn linear_dimension_entity(
+    first: DVec3,
+    second: DVec3,
+    point: DVec3,
+    axis: DVec3,
+    text_override: Option<String>,
+) -> EntityType {
+    let mut dim = DimensionLinear::new(v3(first), v3(second));
+    dim.rotation = axis.y.atan2(axis.x);
+    dim.set_offset(dimension_line_offset(second, point, axis));
+    dim.base.definition_point = dim.definition_point;
+    dim.base.text_middle_point = v3(linear_text_pos(first, second, point, axis));
+    dim.base.insertion_point = dim.base.text_middle_point;
+    dim.base.actual_measurement = dim.measurement();
+    crate::entities::dimension::set_dimension_text_override(&mut dim.base, text_override);
+    EntityType::Dimension(Dimension::Linear(dim))
+}
+
 impl CadCommand for LinearDimensionCommand {
     fn name(&self) -> &'static str {
         "DIMLINEAR"

src/modules/parametric/dim_constraint.rs

@@ -0,0 +1,445 @@
+use acadrust::{EntityType, Handle};
+use glam::DVec3;
+
+use crate::command::{CadCommand, CmdOption, CmdResult, CoincidentPick};
+use crate::scene::parametric_constraints::{
+    measured_expression, resolve_point, ConstraintKind, ParametricRef,
+};
+
+/// Which distance a dimensional constraint measures.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum DimConstraintAxis {
+    /// Horizontal or vertical, decided by where the dimension line goes.
+    Linear,
+    Horizontal,
+    Vertical,
+    Aligned,
+}
+
+#[derive(Clone, Copy)]
+enum Step {
+    /// `Specify first constraint point or [Object] <Object>:`
+    First,
+    /// `Select object:`
+    Object,
+    /// `Specify second constraint point:`
+    Second {
+        first: ParametricRef,
+        first_point: DVec3,
+    },
+    /// `Specify dimension line location:`
+    Location {
+        first: ParametricRef,
+        second: ParametricRef,
+        first_point: DVec3,
+        second_point: DVec3,
+    },
+    /// `Enter value or name and value <d1=100>:`
+    Value {
+        first: ParametricRef,
+        second: ParametricRef,
+        first_point: DVec3,
+        second_point: DVec3,
+        location: DVec3,
+        axis: DVec3,
+        kind: ConstraintKind,
+        measured: f64,
+    },
+}
+
+/// The reference's Linear/Horizontal/Vertical/Aligned dimensional constraint:
+/// two constraint points (or one object's ends), a dimension line location,
+/// then the parameter name and expression the dynamic dimension carries.
+pub struct DimConstraintCommand {
+    axis: DimConstraintAxis,
+    step: Step,
+    picked_entity: Option<EntityType>,
+    /// The next free `dN` the host reserved for this constraint.
+    default_name: String,
+}
+
+impl DimConstraintCommand {
+    pub const NO_OBJECT: &'static str = "No object found.";
+    pub const NO_POINT: &'static str = "No valid constraint point found.";
+    pub const SAME_POINT: &'static str =
+        "The object or point is already selected.  Select a different object or constraint point.";
+
+    pub fn new(axis: DimConstraintAxis, default_name: String) -> Self {
+        Self {
+            axis,
+            step: Step::First,
+            picked_entity: None,
+            default_name,
+        }
+    }
+
+    fn command_name(&self) -> &'static str {
+        match self.axis {
+            DimConstraintAxis::Linear => "DCLINEAR",
+            DimConstraintAxis::Horizontal => "DCHORIZONTAL",
+            DimConstraintAxis::Vertical => "DCVERTICAL",
+            DimConstraintAxis::Aligned => "DCALIGNED",
+        }
+    }
+
+    fn noun(&self) -> &'static str {
+        match self.axis {
+            DimConstraintAxis::Linear => "Linear",
+            DimConstraintAxis::Horizontal => "Horizontal",
+            DimConstraintAxis::Vertical => "Vertical",
+            DimConstraintAxis::Aligned => "Aligned",
+        }
+    }
+
+    fn report(message: &str) -> CmdResult {
+        CmdResult::ReportError(message.to_string())
+    }
+
+    /// The two end points an object pick constrains: a line's or an arc's
+    /// ends, the picked polyline segment's vertices.
+    fn object_ends(
+        entity: &EntityType,
+        handle: Handle,
+        point: DVec3,
+    ) -> Option<(ParametricRef, ParametricRef)> {
+        match entity {
+            EntityType::Line(_) | EntityType::Arc(_) => {
+                Some((ParametricRef::point(handle, 0), ParametricRef::point(handle, 1)))
+            }
+            EntityType::LwPolyline(_) | EntityType::Polyline2D(_) => {
+                let (source, _, _) =
+                    crate::scene::centerline::picked_source(entity, handle, point)?;
+                let index = source.segment_index;
+                // A closed polyline's last segment ends at the first vertex.
+                let end = if resolve_point(entity, index + 1).is_some() {
+                    index + 1
+                } else {
+                    0
+                };
+                Some((ParametricRef::point(handle, index), ParametricRef::point(handle, end)))
+            }
+            _ => None,
+        }
+    }
+
+    fn world(entity: &EntityType, reference: ParametricRef) -> Option<DVec3> {
+        let point = resolve_point(entity, reference.marker?)?;
+        Some(DVec3::new(point.x, point.y, point.z))
+    }
+
+    /// The measured kind and axis: Linear reads the dimension line location
+    /// the way a linear dimension does, the others are fixed.
+    fn decide(&self, first: DVec3, second: DVec3, location: DVec3) -> (ConstraintKind, DVec3) {
+        match self.axis {
+            DimConstraintAxis::Linear => {
+                let axis =
+                    crate::modules::annotate::linear_dim::measure_axis(first, second, location);
+                if axis.x.abs() > 0.5 {
+                    (ConstraintKind::DistanceX, DVec3::X)
+                } else {
+                    (ConstraintKind::DistanceY, DVec3::Y)
+                }
+            }
+            DimConstraintAxis::Horizontal => (ConstraintKind::DistanceX, DVec3::X),
+            DimConstraintAxis::Vertical => (ConstraintKind::DistanceY, DVec3::Y),
+            DimConstraintAxis::Aligned => (
+                ConstraintKind::Distance,
+                (second - first).normalize_or(DVec3::X),
+            ),
+        }
+    }
+
+    fn measured(kind: ConstraintKind, first: DVec3, second: DVec3) -> f64 {
+        match kind {
+            ConstraintKind::DistanceX => (second.x - first.x).abs(),
+            ConstraintKind::DistanceY => (second.y - first.y).abs(),
+            _ => (second - first).length(),
+        }
+    }
+
+    fn build(&self, name: String, expression: String) -> Option<CmdResult> {
+        let Step::Value {
+            first,
+            second,
+            first_point,
+            second_point,
+            location,
+            axis,
+            kind,
+            ..
+        } = self.step
+        else {
+            return None;
+        };
+        if expression.trim().is_empty() {
+            return None;
+        }
+        Some(CmdResult::AddDimensionalConstraint {
+            kind,
+            first,
+            second,
+            first_point,
+            second_point,
+            location,
+            axis,
+            name,
+            expression,
+            label: match self.axis {
+                DimConstraintAxis::Linear => "Linear constraint",
+                DimConstraintAxis::Horizontal => "Horizontal distance constraint",
+                DimConstraintAxis::Vertical => "Vertical distance constraint",
+                DimConstraintAxis::Aligned => "Aligned constraint",
+            },
+        })
+    }
+}
+
+impl CadCommand for DimConstraintCommand {
+    fn name(&self) -> &'static str {
+        self.command_name()
+    }
+
+    fn prompt(&self) -> String {
+        let name = self.command_name();
+        match self.step {
+            Step::First => {
+                format!("{name}  Specify first constraint point or [Object] <Object>:")
+            }
+            Step::Object => format!("{name}  Select object:"),
+            Step::Second { .. } => format!("{name}  Specify second constraint point:"),
+            Step::Location { .. } => format!("{name}  Specify dimension line location:"),
+            Step::Value { measured, .. } => format!(
+                "{name}  Enter value or name and value <{}={}>:",
+                self.default_name,
+                measured_expression(measured)
+            ),
+        }
+    }
+
+    fn options(&self) -> Vec<CmdOption> {
+        matches!(self.step, Step::First)
+            .then(|| vec![CmdOption::new("Object", "O")])
+            .unwrap_or_default()
+    }
+
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn point_step_accepts_keywords(&self) -> bool {
+        matches!(self.step, Step::First | Step::Value { .. })
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        match self.step {
+            Step::First => {
+                let keyword = text.trim().trim_start_matches('_').to_ascii_uppercase();
+                if matches!(keyword.as_str(), "O" | "OBJECT") {
+                    self.step = Step::Object;
+                    return Some(CmdResult::NeedPoint);
+                }
+                None
+            }
+            Step::Value { .. } => {
+                let text = text.trim();
+                let (name, expression) = match text.split_once('=') {
+                    Some((name, expression)) => (name.trim().to_string(), expression.trim().to_string()),
+                    None => (self.default_name.clone(), text.to_string()),
+                };
+                self.build(name, expression)
+            }
+            _ => None,
+        }
+    }
+
+    fn needs_entity_pick(&self) -> bool {
+        matches!(self.step, Step::First | Step::Object | Step::Second { .. })
+    }
+
+    fn entity_pick_accepts_points(&self) -> bool {
+        true
+    }
+
+    fn typed_point_picks_entity(&self) -> bool {
+        true
+    }
+
+    fn entity_pick_highlights_hover(&self) -> bool {
+        true
+    }
+
+    fn inject_before_entity_pick(&self) -> bool {
+        true
+    }
+
+    fn inject_picked_entity(&mut self, entity: EntityType) {
+        self.picked_entity = Some(entity);
+    }
+
+    fn on_entity_pick(&mut self, handle: Handle, point: DVec3) -> CmdResult {
+        match self.step {
+            // The host resolves the constraint point and hands it back
+            // through `accept_constraint_point`.
+            Step::First | Step::Second { .. } => CmdResult::CheckConstraintPoint(CoincidentPick {
+                handle: (!handle.is_null()).then_some(handle),
+                point,
+                whole_curve: false,
+            }),
+            Step::Object => {
+                if handle.is_null() {
+                    return Self::report(Self::NO_OBJECT);
+                }
+                let Some(entity) = self.picked_entity.take() else {
+                    return CmdResult::NeedPoint;
+                };
+                let Some((first, second)) = Self::object_ends(&entity, handle, point) else {
+                    return Self::report(&format!(
+                        "Invalid selection for {}. Select a line, polyline segment or arc.",
+                        self.noun()
+                    ));
+                };
+                let (Some(first_point), Some(second_point)) =
+                    (Self::world(&entity, first), Self::world(&entity, second))
+                else {
+                    return Self::report(Self::NO_POINT);
+                };
+                self.step = Step::Location {
+                    first,
+                    second,
+                    first_point,
+                    second_point,
+                };
+                CmdResult::NeedPoint
+            }
+            Step::Location { .. } | Step::Value { .. } => self.on_point(point),
+        }
+    }
+
+    fn accept_constraint_point(&mut self, reference: ParametricRef, point: DVec3) -> CmdResult {
+        match self.step {
+            Step::First => {
+                self.step = Step::Second {
+                    first: reference,
+                    first_point: point,
+                };
+                CmdResult::NeedPoint
+            }
+            Step::Second { first, first_point } => {
+                if first == reference {
+                    return Self::report(Self::SAME_POINT);
+                }
+                self.step = Step::Location {
+                    first,
+                    second: reference,
+                    first_point,
+                    second_point: point,
+                };
+                CmdResult::NeedPoint
+            }
+            _ => CmdResult::NeedPoint,
+        }
+    }
+
+    fn on_point(&mut self, point: DVec3) -> CmdResult {
+        match self.step {
+            Step::First | Step::Second { .. } => CmdResult::CheckConstraintPoint(CoincidentPick {
+                handle: None,
+                point,
+                whole_curve: false,
+            }),
+            Step::Object => Self::report(Self::NO_OBJECT),
+            Step::Location {
+                first,
+                second,
+                first_point,
+                second_point,
+            } => {
+                let (kind, axis) = self.decide(first_point, second_point, point);
+                let measured = Self::measured(kind, first_point, second_point);
+                self.step = Step::Value {
+                    first,
+                    second,
+                    first_point,
+                    second_point,
+                    location: point,
+                    axis,
+                    kind,
+                    measured,
+                };
+                CmdResult::ReportMeasurement(format!("Dimension text = {measured:.4}"))
+            }
+            Step::Value { .. } => CmdResult::NeedPoint,
+        }
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        match self.step {
+            Step::First => {
+                self.step = Step::Object;
+                CmdResult::NeedPoint
+            }
+            Step::Value { measured, .. } => self
+                .build(self.default_name.clone(), measured_expression(measured))
+                .unwrap_or(CmdResult::Cancel),
+            _ => CmdResult::Cancel,
+        }
+    }
+
+    fn on_escape(&mut self) -> CmdResult {
+        CmdResult::Cancel
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use acadrust::entities::Line;
+    use acadrust::types::Vector3;
+
+    #[test]
+    fn object_pick_takes_the_line_ends_then_asks_for_the_location() {
+        let mut command = DimConstraintCommand::new(DimConstraintAxis::Linear, "d1".into());
+        assert!(matches!(command.on_enter(), CmdResult::NeedPoint));
+        command.inject_picked_entity(EntityType::Line(Line::from_points(
+            Vector3::ZERO,
+            Vector3::new(100.0, 50.0, 0.0),
+        )));
+        assert!(matches!(
+            command.on_entity_pick(Handle::new(7), DVec3::new(50.0, 25.0, 0.0)),
+            CmdResult::NeedPoint
+        ));
+        // Below the pair: horizontal, so the measured value is the X span.
+        let CmdResult::ReportMeasurement(text) = command.on_point(DVec3::new(50.0, -30.0, 0.0))
+        else {
+            panic!("the location must report the dimension text");
+        };
+        assert_eq!(text, "Dimension text = 100.0000");
+        assert_eq!(
+            command.prompt(),
+            "DCLINEAR  Enter value or name and value <d1=100>:"
+        );
+        let CmdResult::AddDimensionalConstraint {
+            kind, name, expression, ..
+        } = command.on_text_input("w=d1*2").expect("a value builds the constraint")
+        else {
+            panic!("the value must build the constraint");
+        };
+        assert_eq!(kind, ConstraintKind::DistanceX);
+        assert_eq!(name, "w");
+        assert_eq!(expression, "d1*2");
+    }
+
+    #[test]
+    fn a_location_beside_the_pair_measures_vertically() {
+        let mut command = DimConstraintCommand::new(DimConstraintAxis::Linear, "d1".into());
+        let first = ParametricRef::point(Handle::new(7), 0);
+        let second = ParametricRef::point(Handle::new(7), 1);
+        command.accept_constraint_point(first, DVec3::ZERO);
+        command.accept_constraint_point(second, DVec3::new(100.0, 50.0, 0.0));
+        let CmdResult::ReportMeasurement(text) = command.on_point(DVec3::new(140.0, 25.0, 0.0))
+        else {
+            panic!("the location must report the dimension text");
+        };
+        assert_eq!(text, "Dimension text = 50.0000");
+    }
+}

src/modules/parametric/mod.rs

@@ -4,6 +4,7 @@
 
 mod coincident;
 mod concentric;
+mod dim_constraint;
 mod constraint_bar;
 mod equal_distance;
 #[path = "equal.rs"]
@@ -25,6 +26,7 @@ mod tools;
 mod value;
 pub use coincident::{coincident_tool, CoincidentConstraintCommand};
 pub use concentric::ConcentricConstraintCommand;
+pub use dim_constraint::{DimConstraintAxis, DimConstraintCommand};
 pub use constraint_bar::ConstraintBarOptionCommand;
 pub use equal_command::EqualConstraintCommand;
 pub use equal_distance::{equal_distance_tool, EqualDistanceConstraintCommand};

src/scene/mod.rs

@@ -2295,6 +2295,9 @@ 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,
     /// Session-only visibility overrides for constraint glyphs.
     hidden_parametric_constraints: HashSet<(
         parametric_constraints::ParametricScope,
@@ -2625,6 +2628,7 @@ impl Scene {
             dependency_index_cache: RefCell::new(None),
             associative_hatch_source_cache: RefCell::new(None),
             parametric_constraints: Vec::new(),
+            constraint_name_format: 2,
             hidden_parametric_constraints: HashSet::default(),
             shown_parametric_constraints: HashSet::default(),
             named_parameters: named_parameters::ParameterTable::new(),
@@ -3319,6 +3323,7 @@ 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() {

src/scene/parametric_constraints.rs

@@ -351,6 +351,37 @@ 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 text a dynamic dimension shows: CONSTRAINTNAMEFORMAT 0 = name,
+/// 1 = value, 2 = name=value.
+pub(crate) fn dynamic_dimension_text(name: &str, value: f64, format: u8) -> String {
+    match format {
+        0 => name.to_string(),
+        1 => format!("{value:.4}"),
+        _ => format!("{name}={value:.4}"),
+    }
+}
+
+/// The expression a measured value seeds a parameter with (`100`, `111.8034`).
+pub(crate) fn measured_expression(value: f64) -> String {
+    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()
+    }
+}
+
 /// 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 +616,8 @@ 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 +644,7 @@ 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 +736,7 @@ 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 +1455,49 @@ 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.
+    pub(crate) fn refresh_dynamic_dimension_texts(&mut self) {
+        let format = self.constraint_name_format;
+        let mut updates: Vec<(Handle, String)> = Vec::new();
+        for set in &self.parametric_constraints {
+            let table = if set.local_parameters.is_empty() {
+                &self.named_parameters
+            } else {
+                &set.local_parameters
+            };
+            for (id, dimension) in &set.dimensions {
+                let Some(constraint) = set.get(*id) else {
+                    continue;
+                };
+                let (name, value) = match &constraint.driving_param {
+                    Some(DrivingValue::Named(name)) => {
+                        (name.clone(), table.resolve(name).unwrap_or(f64::NAN))
+                    }
+                    Some(DrivingValue::Literal(value)) => (String::new(), *value),
+                    None => continue,
+                };
+                updates.push((*dimension, dynamic_dimension_text(&name, value, format)));
+            }
+        }
+        for (handle, text) in updates {
+            let Some(acadrust::EntityType::Dimension(mut dimension)) =
+                self.document.get_entity(handle).cloned()
+            else {
+                continue;
+            };
+            if dimension.base().user_text.as_deref() == Some(text.as_str()) {
+                continue;
+            }
+            crate::entities::dimension::set_dimension_text_override(
+                dimension.base_mut(),
+                Some(text),
+            );
+            self.update_entity(acadrust::EntityType::Dimension(dimension));
+        }
+    }
+
     pub fn should_display_parametric_constraint(
         &self,
         scope: ParametricScope,
@@ -1861,7 +1939,8 @@ impl super::Scene {
         };
         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