feat(dimension): styled placement previews for creation commands

Show the styled dimension and its value while placing a dimension, using
the same builder the command commits with. Each creation command
(DIMLINEAR, DIMALIGNED, DIMANGULAR, DIMRADIUS, DIMDIAMETER, DIMARC,
DIMJOGGED, DIMORDINATE, DIMCONTINUE, DIMBASELINE, QDIM) reports the
dimensions it would commit at the current stage through
`CadCommand::dimension_preview`. The application applies the current
creation style, or the base dimension's style for DIMCONTINUEMODE=1,
and the same viewport measurement scale as commit, then tessellates the
transient entity through the normal dimension renderer.

While the second definition point is being acquired, a hovered model
snap supplies a provisional viewport scale; once both points are fixed,
hovering another viewport does not change the value. Angular dimensions
never receive length compensation. Degenerate geometry, an invalid
scale, or conflicting viewports fall back to the plain rubber-band
preview so no misleading value is shown.

src/app/dim_viewport.rs

@@ -2,7 +2,7 @@
 //! supplies a viewport scale; sheet-only dimensions retain paper units.
 
 use super::OpenCADStudio;
-use crate::command::DimensionAssociationSource;
+use crate::command::{DimensionAssociationSource, DimensionPreview};
 use crate::entities::dim_override;
 use crate::scene::viewport_ref::{AcceptedSnap, MeasurementScale, SnapSourceRef, ViewportFrame};
 use acadrust::entities::Dimension;
@@ -27,12 +27,25 @@ impl OpenCADStudio {
     }
 
     pub(crate) fn dimension_measure_space(&self, i: usize) -> DimensionMeasureSpace {
+        self.dimension_measure_space_with_candidate(i, None)
+    }
+
+    fn dimension_measure_space_with_candidate(
+        &self,
+        i: usize,
+        candidate: Option<ViewportFrame>,
+    ) -> DimensionMeasureSpace {
         let scene = &self.tabs[i].scene;
         if scene.current_layout == "Model" || scene.active_viewport.is_some() {
             return DimensionMeasureSpace::Direct;
         }
         let mut frame: Option<ViewportFrame> = None;
-        for f in self.accepted_snaps().iter().filter_map(|snap| snap.frame) {
+        for f in self
+            .accepted_snaps()
+            .iter()
+            .filter_map(|snap| snap.frame)
+            .chain(candidate)
+        {
             match frame {
                 None => frame = Some(f),
                 Some(previous) if previous.viewport == f.viewport => {}
@@ -122,13 +135,10 @@ impl OpenCADStudio {
         i: usize,
         entity: &mut EntityType,
     ) -> bool {
-        let EntityType::Dimension(dimension) = entity else {
+        if !matches!(entity, EntityType::Dimension(_)) {
             return true;
-        };
-        let angular = matches!(
-            dimension,
-            Dimension::Angular2Ln(_) | Dimension::Angular3Pt(_)
-        );
+        }
+        let angular = is_angular_dimension(entity);
         let frame = match self.dimension_measure_space(i) {
             DimensionMeasureSpace::Direct => return true,
             DimensionMeasureSpace::ConflictingViewports => {
@@ -140,18 +150,106 @@ impl OpenCADStudio {
         if angular {
             return true;
         }
+        let Some(scale) = self.viewport_dimension_scale(i, entity, frame) else {
+            return false;
+        };
+        // Owner is needed even by DIMASSOC=0's explode path, before insertion.
+        entity.common_mut().owner_handle = self.tabs[i].scene.current_layout_block_handle_pub();
+        scale.write_to_entity(entity);
+        true
+    }
+
+    fn viewport_dimension_scale(
+        &self,
+        i: usize,
+        entity: &EntityType,
+        frame: ViewportFrame,
+    ) -> Option<MeasurementScale> {
         let dimlfac = self.pending_dimension_style_dimlfac(i, entity);
         let scale = MeasurementScale {
             user_lfac: MeasurementScale::user_lfac_for_space(dimlfac, true),
             viewport_compensation: frame.paper_to_model_length_factor(),
         };
-        if !scale.paper_factor().is_finite() || scale.paper_factor() <= 0.0 {
-            return false;
+        (scale.paper_factor().is_finite() && scale.paper_factor() > 0.0).then_some(scale)
+    }
+
+    /// Styled dimensions for the placement preview at `cursor`, carrying the
+    /// same style and viewport measurement the commit path would apply.
+    /// `None` when the active command has no committable dimension at this
+    /// stage; an empty list when the candidate geometry or scale is invalid.
+    pub(crate) fn dimension_preview_entities(
+        &self,
+        i: usize,
+        cursor: DVec3,
+    ) -> Option<Vec<EntityType>> {
+        let command = self.tabs[i].active_cmd.as_ref()?;
+        let previews = command.dimension_preview(cursor)?;
+        let scene = &self.tabs[i].scene;
+        let measure_space = if command.measures_through_viewports() {
+            // The hovered model snap supplies a provisional viewport only while
+            // the second definition point is still being acquired.
+            let candidate = if command.dimension_placement_pending() {
+                None
+            } else {
+                self.vp_snap_frame.filter(|frame| {
+                    self.tabs[i]
+                        .snap_result
+                        .is_some_and(|hit| hit.viewport == Some(frame.viewport))
+                })
+            };
+            self.dimension_measure_space_with_candidate(i, candidate)
+        } else {
+            DimensionMeasureSpace::Direct
+        };
+        if matches!(measure_space, DimensionMeasureSpace::ConflictingViewports) {
+            return Some(Vec::new());
         }
-        // Owner is needed even by DIMASSOC=0's explode path, before insertion.
-        entity.common_mut().owner_handle = self.tabs[i].scene.current_layout_block_handle_pub();
-        scale.write_to_entity(entity);
-        true
+        let mut entities = Vec::with_capacity(previews.len());
+        for DimensionPreview {
+            mut entity,
+            preserve_base_style,
+        } in previews
+        {
+            if !preserve_base_style {
+                crate::scene::creation_style::apply_current_creation_styles(
+                    &scene.document,
+                    &mut entity,
+                );
+            }
+            entity.common_mut().owner_handle = scene.current_layout_block_handle_pub();
+            if let DimensionMeasureSpace::Viewport(frame) = measure_space {
+                if !is_angular_dimension(&entity) {
+                    let Some(scale) = self.viewport_dimension_scale(i, &entity, frame) else {
+                        return Some(Vec::new());
+                    };
+                    scale.write_to_entity(&mut entity);
+                }
+            }
+            entities.push(entity);
+        }
+        Some(entities)
+    }
+
+    pub(crate) fn dimension_preview_wires(
+        &self,
+        i: usize,
+        cursor: DVec3,
+    ) -> Option<Vec<crate::scene::WireModel>> {
+        let entities = self.dimension_preview_entities(i, cursor)?;
+        // Degenerate geometry, an invalid scale, or conflicting viewports
+        // produce no styled dimension. Returning None lets the command's
+        // plain rubber-band preview run, which shows no value to mistrust.
+        if entities.is_empty() {
+            return None;
+        }
+        let mut wires = self.tabs[i].scene.wires_for_entities(&entities);
+        for wire in &mut wires {
+            wire.color = crate::scene::WireModel::CYAN;
+            for vertex in &mut wire.text_verts {
+                vertex.color = crate::scene::WireModel::CYAN;
+            }
+        }
+        Some(wires)
     }
 
     pub(crate) fn try_dimension_viewport_entity_pick(
@@ -254,3 +352,10 @@ impl OpenCADStudio {
             .bump_entities(&[(dimension, crate::scene::ChangeKind::Modified)]);
     }
 }
+
+fn is_angular_dimension(entity: &EntityType) -> bool {
+    matches!(
+        entity,
+        EntityType::Dimension(Dimension::Angular2Ln(_) | Dimension::Angular3Pt(_))
+    )
+}

src/app/dimension_preview_tests.rs

@@ -0,0 +1,225 @@
+//! Styled placement previews must show the text and geometry the command
+//! commits at the same stage. Viewport measurement cases live in
+//! `viewport_dimension_tests`; these cover the remaining creation commands
+//! in model space, style inheritance, batches, and degenerate stages.
+
+use super::viewport_dimension_tests::preview_text as text;
+use super::OpenCADStudio;
+use crate::command::StepInput;
+use acadrust::entities::{Arc, Circle, Line};
+use acadrust::types::{Handle, Vector3};
+use acadrust::EntityType;
+use glam::DVec3;
+
+fn app() -> (OpenCADStudio, usize) {
+    let mut app = OpenCADStudio::new_for_test();
+    app.automation_op(r#"{"op":"new"}"#);
+    let i = app.active_tab;
+    (app, i)
+}
+
+fn style_name(entity: &EntityType) -> String {
+    let EntityType::Dimension(dimension) = entity else {
+        panic!("expected dimension")
+    };
+    dimension.base().style_name.clone()
+}
+
+fn committed(app: &OpenCADStudio) -> Vec<EntityType> {
+    app.tabs[app.active_tab]
+        .scene
+        .document
+        .entities()
+        .filter(|entity| matches!(entity, EntityType::Dimension(_)))
+        .cloned()
+        .collect()
+}
+
+/// Styled preview entities at `cursor`, asserting they also tessellate.
+fn preview(app: &OpenCADStudio, i: usize, cursor: DVec3) -> Vec<EntityType> {
+    let entities = app.dimension_preview_entities(i, cursor).unwrap();
+    assert!(!entities.is_empty(), "no styled preview at {cursor}");
+    assert!(!app.dimension_preview_wires(i, cursor).unwrap().is_empty());
+    entities
+}
+
+fn commit_and_compare(app: &mut OpenCADStudio, i: usize, cursor: DVec3) -> EntityType {
+    let previewed = preview(app, i, cursor);
+    assert_eq!(previewed.len(), 1);
+    let before = committed(app).len();
+    let _ = app.feed_command(StepInput::Point(cursor));
+    let after = committed(app);
+    assert_eq!(after.len(), before + 1, "commit did not add one dimension");
+    let entity = after.last().unwrap().clone();
+    assert_eq!(text(app, &entity), text(app, &previewed[0]));
+    assert_eq!(style_name(&entity), style_name(&previewed[0]));
+    entity
+}
+
+#[test]
+fn ordinate_preview_matches_commit() {
+    let (mut app, i) = app();
+    let _ = app.dispatch_command("DIMORDINATE");
+    assert!(app.dimension_preview_entities(i, DVec3::ZERO).is_none());
+    let _ = app.feed_command(StepInput::Point(DVec3::new(12.5, 40.0, 0.0)));
+    let entity = commit_and_compare(&mut app, i, DVec3::new(12.5, 90.0, 0.0));
+    assert_eq!(text(&app, &entity), "12.5");
+}
+
+#[test]
+fn arc_length_preview_matches_commit_for_full_and_partial_arcs() {
+    let (mut app, i) = app();
+    let mut arc = Arc::new();
+    arc.center = Vector3::ZERO;
+    arc.radius = 50.0;
+    arc.start_angle = 0.0;
+    arc.end_angle = std::f64::consts::FRAC_PI_2;
+    let handle = app.tabs[i].scene.add_entity(EntityType::Arc(arc));
+    let on_arc = |degrees: f64| {
+        let radians = degrees.to_radians();
+        DVec3::new(50.0 * radians.cos(), 50.0 * radians.sin(), 0.0)
+    };
+
+    let _ = app.dispatch_command("DIMARC");
+    let _ = app.feed_command(StepInput::EntityPick(handle, on_arc(45.0)));
+    let full = commit_and_compare(&mut app, i, DVec3::new(60.0, 60.0, 0.0));
+
+    let _ = app.dispatch_command("DIMARC");
+    let _ = app.feed_command(StepInput::EntityPick(handle, on_arc(45.0)));
+    let _ = app.feed_command(StepInput::Text("P".into()));
+    let _ = app.feed_command(StepInput::Point(on_arc(10.0)));
+    // While the second partial point is acquired the command has no
+    // committable dimension; the plain arc preview stays in charge.
+    assert!(app.dimension_preview_entities(i, on_arc(80.0)).is_none());
+    let _ = app.feed_command(StepInput::Point(on_arc(80.0)));
+    let partial = commit_and_compare(&mut app, i, DVec3::new(60.0, 60.0, 0.0));
+    assert_ne!(text(&app, &full), text(&app, &partial));
+}
+
+#[test]
+fn jogged_radius_preview_matches_commit_at_text_and_jog_stages() {
+    let (mut app, i) = app();
+    let mut circle = Circle::new();
+    circle.center = Vector3::ZERO;
+    circle.radius = 100.0;
+    let handle = app.tabs[i].scene.add_entity(EntityType::Circle(circle));
+    let _ = app.dispatch_command("DIMJOGGED");
+    let _ = app.feed_command(StepInput::EntityPick(handle, DVec3::new(100.0, 0.0, 0.0)));
+    assert!(app
+        .dimension_preview_entities(i, DVec3::new(30.0, 0.0, 0.0))
+        .is_none());
+    let _ = app.feed_command(StepInput::Point(DVec3::new(30.0, 0.0, 0.0)));
+    let text_position = DVec3::new(150.0, 40.0, 0.0);
+    let staged = preview(&app, i, text_position);
+    assert_eq!(staged.len(), 1);
+    let _ = app.feed_command(StepInput::Point(text_position));
+    let entity = commit_and_compare(&mut app, i, DVec3::new(90.0, 20.0, 0.0));
+    assert_eq!(text(&app, &entity), text(&app, &staged[0]));
+    assert_eq!(text(&app, &entity), "R100");
+}
+
+#[test]
+fn angular_three_point_preview_matches_commit() {
+    let (mut app, i) = app();
+    let _ = app.dispatch_command("DIMANGULAR");
+    let _ = app.feed_command(StepInput::Point(DVec3::ZERO));
+    let _ = app.feed_command(StepInput::Point(DVec3::new(100.0, 0.0, 0.0)));
+    assert!(app
+        .dimension_preview_entities(i, DVec3::new(0.0, 100.0, 0.0))
+        .is_none());
+    let _ = app.feed_command(StepInput::Point(DVec3::new(0.0, 100.0, 0.0)));
+    let entity = commit_and_compare(&mut app, i, DVec3::new(70.0, 70.0, 0.0));
+    assert_eq!(text(&app, &entity), "90°");
+}
+
+fn place_linear(app: &mut OpenCADStudio, first: DVec3, second: DVec3, line: DVec3) -> Handle {
+    let _ = app.dispatch_command("DIMLINEAR");
+    let _ = app.feed_command(StepInput::Point(first));
+    let _ = app.feed_command(StepInput::Point(second));
+    let _ = app.feed_command(StepInput::Point(line));
+    committed(app).last().unwrap().common().handle
+}
+
+#[test]
+fn continue_and_baseline_previews_follow_style_inheritance() {
+    let (mut app, i) = app();
+    let default_style = app.tabs[i]
+        .scene
+        .document
+        .header
+        .current_dimstyle_name
+        .clone();
+    let mut style = acadrust::tables::DimStyle::new("Inherit");
+    style.dimlfac = 2.0;
+    app.tabs[i].scene.document.dim_styles.add(style).unwrap();
+    app.tabs[i].scene.document.header.current_dimstyle_name = "Inherit".into();
+    let base = place_linear(
+        &mut app,
+        DVec3::ZERO,
+        DVec3::new(100.0, 0.0, 0.0),
+        DVec3::new(50.0, -20.0, 0.0),
+    );
+    assert_eq!(text(&app, committed(&app).last().unwrap()), "200");
+    app.tabs[i].scene.document.header.current_dimstyle_name = default_style;
+
+    // DIMCONTINUEMODE=1 keeps the base dimension's style in the preview.
+    app.dimension_continue_mode = 1;
+    app.tabs[i].scene.last_created_dimension = Some(base);
+    let _ = app.dispatch_command("DIMCONTINUE");
+    let inherited = commit_and_compare(&mut app, i, DVec3::new(250.0, 0.0, 0.0));
+    assert_eq!(style_name(&inherited), "Inherit");
+    assert_eq!(text(&app, &inherited), "300");
+
+    // DIMCONTINUEMODE=0 runs the current creation defaults over the built
+    // dimension instead; preview and commit must still agree.
+    app.dimension_continue_mode = 0;
+    app.tabs[i].scene.last_created_dimension = Some(inherited.common().handle);
+    let _ = app.dispatch_command("DIMCONTINUE");
+    commit_and_compare(&mut app, i, DVec3::new(350.0, 0.0, 0.0));
+
+    app.dimension_continue_mode = 1;
+    app.tabs[i].scene.last_created_dimension = Some(base);
+    let _ = app.dispatch_command("DIMBASELINE");
+    let baseline = commit_and_compare(&mut app, i, DVec3::new(300.0, 0.0, 0.0));
+    assert_eq!(style_name(&baseline), "Inherit");
+    assert_eq!(text(&app, &baseline), "600");
+}
+
+#[test]
+fn qdim_preview_matches_the_committed_batch() {
+    let (mut app, i) = app();
+    let segments = [(0.0, 40.0), (40.0, 100.0), (100.0, 130.0)];
+    for (start, end) in segments {
+        let line = Line::from_points(Vector3::new(start, 0.0, 0.0), Vector3::new(end, 0.0, 0.0));
+        let handle = app.tabs[i].scene.add_entity(EntityType::Line(line));
+        app.tabs[i].scene.select_entity(handle, false);
+    }
+    let _ = app.dispatch_command("QDIM");
+    let cursor = DVec3::new(60.0, 40.0, 0.0);
+    let previewed = preview(&app, i, cursor);
+    assert_eq!(previewed.len(), segments.len());
+    let mut preview_texts: Vec<String> = previewed.iter().map(|e| text(&app, e)).collect();
+    let _ = app.feed_command(StepInput::Point(cursor));
+    let mut committed_texts: Vec<String> = committed(&app).iter().map(|e| text(&app, e)).collect();
+    preview_texts.sort();
+    committed_texts.sort();
+    assert_eq!(committed_texts, preview_texts);
+    assert_eq!(committed_texts, ["30", "40", "60"]);
+}
+
+#[test]
+fn degenerate_linear_preview_defers_to_plain_rubber_band() {
+    let (mut app, i) = app();
+    let _ = app.dispatch_command("DIMLINEAR");
+    assert!(app.dimension_preview_entities(i, DVec3::ZERO).is_none());
+    let _ = app.feed_command(StepInput::Point(DVec3::ZERO));
+    assert!(app
+        .dimension_preview_entities(i, DVec3::ZERO)
+        .is_some_and(|entities| entities.is_empty()));
+    assert!(app.dimension_preview_wires(i, DVec3::ZERO).is_none());
+    assert!(committed(&app).is_empty());
+    let cursor = DVec3::new(80.0, 0.0, 0.0);
+    let styled = preview(&app, i, cursor);
+    assert_eq!(text(&app, &styled[0]), "80");
+    assert!(committed(&app).is_empty(), "hover must not commit");
+}

src/app/mod.rs

@@ -13,6 +13,8 @@ pub(crate) mod commands;
 pub(crate) mod dim_viewport;
 #[cfg(test)]
 mod viewport_dimension_tests;
+#[cfg(test)]
+mod dimension_preview_tests;
 mod document;
 mod drafting_settings;
 pub(crate) mod expr_eval;

src/app/update/viewport.rs

@@ -2547,6 +2547,8 @@ impl OpenCADStudio {
                     }
                 }
                 p
+            } else if let Some(wires) = self.dimension_preview_wires(i, effective) {
+                wires
             } else {
                 self.tabs[i]
                     .active_cmd

src/app/viewport_dimension_tests.rs

@@ -87,6 +87,14 @@ fn displayed(doc: &CadDocument) -> f64 {
     dim.measurement() * MeasurementScale::user_lfac_for_space(factor, true)
 }
 
+pub(super) fn preview_text(app: &OpenCADStudio, entity: &EntityType) -> String {
+    let EntityType::Dimension(dimension) = entity else { panic!("expected dimension") };
+    let doc = &app.tabs[app.active_tab].scene.document;
+    let source = doc.dim_styles.get(&dimension.base().style_name).unwrap();
+    let style = crate::entities::dimension::resolved_dimension_style(source, dimension, doc);
+    crate::entities::dimension::dimension_text_value(dimension, Some(&style)).unwrap()
+}
+
 fn finish_aligned(app: &mut OpenCADStudio, line: Handle, frame: ViewportFrame) {
     let _ = app.dispatch_command("DIMALIGNED");
     point(app, frame, line, DVec3::ZERO);
@@ -300,7 +308,13 @@ fn viewport_dimension_linear_aligned_and_radial_object_picks() {
             if radial { 1 } else { 2 },
             "{name}"
         );
-        let _ = app.feed_command(StepInput::Point(DVec3::new(55.0, 80.0, 0.0)));
+        let place = DVec3::new(55.0, 80.0, 0.0);
+        let preview = app.dimension_preview_entities(i, place).unwrap();
+        assert_eq!(preview.len(), 1, "{name}");
+        let value = preview_text(&app, &preview[0]);
+        assert!(!app.dimension_preview_wires(i, place).unwrap().is_empty(), "{name}");
+        let _ = app.feed_command(StepInput::Point(place));
+        assert_eq!(preview_text(&app, &EntityType::Dimension(dimension(&app.tabs[i].scene.document).clone())), value, "{name}");
         assert!(
             (displayed(&app.tabs[i].scene.document) - expected).abs() < 1e-4,
             "{name}: {}",
@@ -326,12 +340,45 @@ fn viewport_dimension_angular_preserves_angle_without_length_factor() {
     point(&mut app, frame, line, DVec3::ZERO);
     point(&mut app, frame, line, DVec3::X * 100.0);
     point(&mut app, frame, vertical, DVec3::Y * 100.0);
-    let _ = app.feed_command(StepInput::Point(DVec3::new(70.0, 70.0, 0.0)));
+    let place = DVec3::new(70.0, 70.0, 0.0);
+    let preview = app.dimension_preview_entities(i, place).unwrap();
+    assert_eq!(preview.len(), 1);
+    assert!(MeasurementScale::read(&preview[0].common().extended_data).is_none());
+    let value = preview_text(&app, &preview[0]);
+    let _ = app.feed_command(StepInput::Point(place));
     let doc = &app.tabs[app.active_tab].scene.document;
+    assert_eq!(preview_text(&app, &EntityType::Dimension(dimension(doc).clone())), value);
     assert!((dimension(doc).measurement() - 90.0).abs() < 1e-5);
     assert!(MeasurementScale::read(&dimension(doc).base().common.extended_data).is_none());
 }
 
+#[test]
+fn viewport_dimension_preview_uses_candidate_scale_only_before_second_pick() {
+    for command in ["DIMLINEAR", "DIMALIGNED"] {
+        let (mut app, model, frame) = fixture();
+        let i = app.active_tab;
+        let mut style = acadrust::tables::DimStyle::new("PreviewUnits");
+        style.dimlfac = 25.4;
+        app.tabs[i].scene.document.dim_styles.add(style).unwrap();
+        app.tabs[i].scene.document.header.current_dimstyle_name = "PreviewUnits".into();
+        let _ = app.dispatch_command(command);
+        let _ = app.feed_command(StepInput::Point(DVec3::new(55.0, 50.0, 0.0)));
+        let target = hit(frame, model, DVec3::X * 100.0);
+        let sheet = app.dimension_preview_entities(i, target.world).unwrap();
+        assert_eq!(preview_text(&app, &sheet[0]), "127");
+        app.vp_snap_frame = Some(frame);
+        app.tabs[i].snap_result = Some(target);
+        let model_preview = app.dimension_preview_entities(i, target.world).unwrap();
+        assert_eq!(preview_text(&app, &model_preview[0]), "1270");
+        point(&mut app, frame, model, DVec3::X * 100.0);
+        let other = ViewportFrame { viewport: Handle::new(0xFFFF), scale: frame.scale * 2.0, ..frame };
+        app.vp_snap_frame = Some(other);
+        app.tabs[i].snap_result = Some(hit(other, model, DVec3::X * 100.0));
+        let placement = app.dimension_preview_entities(i, DVec3::new(60.0, 80.0, 0.0)).unwrap();
+        assert_eq!(preview_text(&app, &placement[0]), "1270");
+    }
+}
+
 #[test]
 fn viewport_dimension_snap_query_matches_pan_scale_and_twist() {
     for (height, twist, target) in [