feat(props): make dim-line colour editable for leaders and dimensions

The "Dim line color" row on Leader and Dimension entities was
read-only: an earlier attempt wired it to Leader.override_color, which
acadrust never serialises, so the pick was lost on save. Store it
instead as a standard ACAD_DSTYLE per-object dimension-style override
(DXF code 176, an ACI index) through the existing dim_override codec,
so it round-trips through both DWG and DXF like the other dim
overrides. RGB picks collapse to the nearest ACI, matching the rest of
the dim-colour stack (dimension styles are index-only through the file
layer). The renderer prefers the override over the style's DIMCLRD.

The write branch is guarded to leaders and dimensions so a mixed
selection cannot stamp the override onto other entity types.

Bumps acadrust to c9fe982, which carries parsed XDATA onto dimensions
on DXF read (it was dropping common.extended_data), so the dimension
override persists on DXF save as well as DWG.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/properties.rs

@@ -414,6 +414,20 @@ impl OpenCADStudio {
                             })
                         {
                             sections.extend(crate::entities::dimension::style_sections(style));
+
+                            // The style groups are a read-only mirror, but the
+                            // dim-line colour is an editable per-object override:
+                            // prefer the ACAD_DSTYLE code-176 (ACI) override, else
+                            // the style's DIMCLRD.
+                            use crate::entities::dim_override as dov;
+                            use crate::scene::model::object::PropValue;
+                            let dim_c = dov::color(&d.base().common.extended_data, dov::DIMCLRD)
+                                .unwrap_or_else(|| acadrust::types::Color::from_index(style.dimclrd));
+                            set_row_value(
+                                &mut sections,
+                                "dim_line_color",
+                                PropValue::ColorChoice(dim_c),
+                            );
                         }
                     }
 
@@ -561,14 +575,16 @@ impl OpenCADStudio {
                                     },
                                 );
 
-                                // Dim-line colour stays read-only: it lives in the
-                                // leader's override_color, which the file format
-                                // layer does not yet serialise, so making it
-                                // editable would silently lose the pick on save.
-                                set_row(
+                                // Dim-line colour: a per-object ACAD_DSTYLE
+                                // override (code 176, an ACI index) wins over the
+                                // style's DIMCLRD. Editable — the picked colour is
+                                // written back as that override so it round-trips.
+                                let dim_c = dov::color(xd, dov::DIMCLRD)
+                                    .unwrap_or_else(|| acadrust::types::Color::from_index(ds.dimclrd));
+                                set_row_value(
                                     &mut sections,
                                     "dim_line_color",
-                                    dim_color_label(ds.dimclrd, &ld.override_color),
+                                    PropValue::ColorChoice(dim_c),
                                 );
 
                                 let gap = dov::real(xd, dov::DIMGAP).unwrap_or(ds.dimgap);
@@ -1578,18 +1594,6 @@ fn dim_lineweight_label(dimlwd: i16) -> String {
     }
 }
 
-/// DIMCLRD color (ACI) → label; ByBlock falls back to the leader's override.
-fn dim_color_label(dimclrd: i16, override_color: &acadrust::types::Color) -> String {
-    match dimclrd {
-        0 => match override_color.rgb() {
-            Some((r, g, b)) => format!("RGB({r},{g},{b})"),
-            None => "ByBlock".to_string(),
-        },
-        256 => "ByLayer".to_string(),
-        n => format!("Color {n}"),
-    }
-}
-
 /// Human-readable INSUNITS name (DXF group 70 unit codes).
 fn insunits_name(code: i16) -> &'static str {
     match code {

src/app/update/mod.rs

@@ -2620,6 +2620,42 @@ impl OpenCADStudio {
             Message::PropColorFieldChanged { field, color } => {
                 let i = self.active_tab;
                 let handles = self.property_target_handles(i);
+                // Dim-line colour override (Leader / Dimension): write it as an
+                // ACAD_DSTYLE code-176 override (an ACI index) so it round-trips
+                // through DWG and DXF. RGB picks collapse to the nearest ACI, in
+                // line with the rest of the dim-colour stack (index-only through
+                // the file layer). Guarded to leaders / dimensions so a mixed
+                // selection can't stamp the override onto other entities.
+                if field == "dim_line_color" {
+                    let aci = color.approximate_index();
+                    let targets: Vec<acadrust::Handle> = handles
+                        .iter()
+                        .copied()
+                        .filter(|&h| {
+                            matches!(
+                                self.tabs[i].scene.document.get_entity(h),
+                                Some(acadrust::EntityType::Leader(_))
+                                    | Some(acadrust::EntityType::Dimension(_))
+                            )
+                        })
+                        .collect();
+                    if !targets.is_empty() {
+                        self.push_undo_snapshot(i, "CHPROP");
+                        for &handle in &targets {
+                            crate::entities::dim_override::set(
+                                &mut self.tabs[i].scene.document,
+                                handle,
+                                crate::entities::dim_override::DIMCLRD,
+                                Some(acadrust::xdata::XDataValue::Integer16(aci)),
+                            );
+                        }
+                        self.invalidate_property_targets(i, &targets);
+                        self.tabs[i].properties.open_color_field = None;
+                        self.tabs[i].dirty = true;
+                        self.refresh_properties();
+                    }
+                    return Task::none();
+                }
                 if !handles.is_empty() {
                     self.push_undo_snapshot(i, "CHPROP");
                     let idx = if field == "gradient_color_2" { 1 } else { 0 };

src/entities/dim_override.rs

@@ -6,6 +6,7 @@
 //! renderer and the properties panel prefer an override over the style default,
 //! so editing one of these rows writes here and the change round-trips to file.
 
+use acadrust::types::Color;
 use acadrust::xdata::{ExtendedData, XDataValue};
 use acadrust::{CadDocument, Handle};
 
@@ -13,6 +14,7 @@ use acadrust::{CadDocument, Handle};
 pub const DIMSCALE: i16 = 40; // overall scale       (real)
 pub const DIMASZ: i16 = 41; // arrow size          (real)
 pub const DIMTAD: i16 = 77; // text vertical pos   (int16)
+pub const DIMCLRD: i16 = 176; // dim line colour     (int16 = ACI index)
 pub const DIMGAP: i16 = 147; // text offset / gap   (real)
 pub const DIMLWD: i16 = 371; // dim line lineweight (int16)
 pub const DIMLDRBLK: i16 = 341; // leader arrow block  (handle)
@@ -58,6 +60,13 @@ pub fn int(xd: &ExtendedData, code: i16) -> Option<i16> {
         })
 }
 
+/// The colour override for `code`, if present. Dim-colour overrides are stored
+/// as an ACI index (the same `int16` slot the dimension style uses), so this
+/// decodes it back into a `Color` (0 = ByBlock, 256 = ByLayer, else indexed).
+pub fn color(xd: &ExtendedData, code: i16) -> Option<Color> {
+    int(xd, code).map(Color::from_index)
+}
+
 /// The handle-valued override for `code`, if present.
 pub fn handle(xd: &ExtendedData, code: i16) -> Option<Handle> {
     pairs(xd)

src/entities/dimension.rs

@@ -1290,11 +1290,18 @@ fn tessellate_dimension_inner(
     );
 
     // Per-spec colours: DIMCLRD (dim/arrows), DIMCLRE (ext), DIMCLRT (text).
-    // 0=ByBlock and 256=ByLayer fall through to entity_color.
+    // 0=ByBlock and 256=ByLayer fall through to entity_color. DIMCLRD also
+    // honours a per-object ACAD_DSTYLE override (code 176) so an edited
+    // dim-line colour renders even without touching the style.
     let dim_color = if selected {
         WireModel::SELECTED
     } else {
-        resolve_dim_color(style.map(|s| s.dimclrd).unwrap_or(0), entity_color)
+        let dim_clr = crate::entities::dim_override::int(
+            &dim.base().common.extended_data,
+            crate::entities::dim_override::DIMCLRD,
+        )
+        .unwrap_or_else(|| style.map(|s| s.dimclrd).unwrap_or(0));
+        resolve_dim_color(dim_clr, entity_color)
     };
     let ext_color = if selected {
         WireModel::SELECTED

src/entities/leader.rs

@@ -547,10 +547,29 @@ impl LeaderTess for Leader {
         use crate::entities::dim_override as dov;
         use crate::scene::model::wire_model::WireModel;
         let xd = &self.common.extended_data;
+        // Dim-line colour: a per-object ACAD_DSTYLE override (code 176, an ACI
+        // index) wins over the assigned dim style's DIMCLRD; ByLayer / ByBlock
+        // (0 / 256) and no setting fall through to the entity colour.
         let color = if selected {
             WireModel::SELECTED
         } else {
-            entity_color
+            let dim_clr = dov::int(xd, dov::DIMCLRD).or_else(|| {
+                document
+                    .dim_styles
+                    .iter()
+                    .find(|s| {
+                        s.name.eq_ignore_ascii_case(&self.dimension_style)
+                            || (self.dimension_style.trim().is_empty()
+                                && s.name.eq_ignore_ascii_case("Standard"))
+                    })
+                    .map(|s| s.dimclrd)
+            });
+            match dim_clr {
+                Some(idx) if idx != 0 && idx != 256 => crate::scene::convert::tess_util::aci_to_rgba(
+                    &acadrust::types::Color::from_index(idx),
+                ),
+                _ => entity_color,
+            }
         };
         // A concrete DIMLWD override sets the leader line's weight; ByLayer /
         // ByBlock / Default and no override keep the resolved weight passed in.

src/ui/properties.rs

@@ -434,18 +434,28 @@ impl PropertiesPanel {
             );
             return prop_row_widget(label, selector);
         }
-        // Generic per-field colour picker (hatch gradient colours) — routes to
-        // the field, not the entity's main colour.
-        if field == "gradient_color_1" || field == "gradient_color_2" {
+        // Generic per-field colour picker — routes to the named field, not the
+        // entity's main colour. Used by hatch gradient colours and the dim-line
+        // colour override (Leader / Dimension). Dim colours legitimately take
+        // ByLayer / ByBlock; gradient colours do not.
+        if field == "gradient_color_1" || field == "gradient_color_2" || field == "dim_line_color" {
             let open = self.open_color_field.as_deref() == Some(field);
             let fsel = field.to_string();
-            let selector = crate::ui::color_select::color_selector(
-                color,
-                open,
+            let extras = if field == "dim_line_color" {
+                crate::ui::color_select::ColorExtras {
+                    by_layer: true,
+                    by_block: true,
+                }
+            } else {
                 crate::ui::color_select::ColorExtras {
                     by_layer: false,
                     by_block: false,
-                },
+                }
+            };
+            let selector = crate::ui::color_select::color_selector(
+                color,
+                open,
+                extras,
                 move |c| Message::PropColorFieldChanged {
                     field: fsel.clone(),
                     color: c,