feat(hatch): editable gradient colors + background color

Gradient Type (One/Two color), Color 1 and Color 2 editable via a generic field-keyed colour picker path. Background colour editable and stored as HATCHBACKGROUNDCOLOR extended data (group 1071 true colour), rendered in OCS as a solid backdrop drawn behind the pattern. Hide Origin X/Y for gradients (pattern-only concept) and drop the redundant gradient rows from the pattern branch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -1558,6 +1558,12 @@ pub enum Message {
     /// User picked an MTEXT background fill colour — sets `background_color`
     /// and switches the background mode to Fill so it shows immediately.
     PropBgColorChanged(AcadColor),
+    /// Toggle the generic per-field colour picker (e.g. a hatch gradient colour)
+    /// identified by its property field name.
+    PropColorFieldToggle(String),
+    /// User picked a colour for a generic per-field colour row (hatch gradient
+    /// `Color 1` / `Color 2`), routed by the field name.
+    PropColorFieldChanged { field: String, color: AcadColor },
     /// Collapse the inline color picker dropdown. Fired when another
     /// properties-panel dropdown (a combo_box) opens, so at most one panel
     /// dropdown is open at a time and they can't overlap. (#235)

src/app/update/mod.rs

@@ -2279,13 +2279,18 @@ impl OpenCADStudio {
                 if !handles.is_empty() {
                     self.push_undo_snapshot(i, "CHPROP");
                     for &handle in &handles {
-                        if let Some(acadrust::EntityType::MText(m)) =
-                            self.tabs[i].scene.document.get_entity_mut(handle)
-                        {
-                            m.background_color = color.clone();
-                            // Picking a colour turns the background on in Fill
-                            // mode (specific colour), preserving the frame bit.
-                            m.background_fill_flags = (m.background_fill_flags & !0x02) | 0x01;
+                        match self.tabs[i].scene.document.get_entity_mut(handle) {
+                            Some(acadrust::EntityType::MText(m)) => {
+                                m.background_color = color.clone();
+                                // Picking a colour turns the background on in Fill
+                                // mode (specific colour), preserving the frame bit.
+                                m.background_fill_flags =
+                                    (m.background_fill_flags & !0x02) | 0x01;
+                            }
+                            Some(acadrust::EntityType::Hatch(h)) => {
+                                crate::entities::hatch::set_background_color(h, &color);
+                            }
+                            _ => {}
                         }
                     }
                     self.invalidate_property_targets(i, &handles);
@@ -2296,6 +2301,54 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::PropColorFieldToggle(field) => {
+                let i = self.active_tab;
+                let p = &mut self.tabs[i].properties;
+                p.open_color_field = if p.open_color_field.as_deref() == Some(field.as_str()) {
+                    None
+                } else {
+                    Some(field)
+                };
+                Task::none()
+            }
+
+            Message::PropColorFieldChanged { field, color } => {
+                let i = self.active_tab;
+                let handles = self.property_target_handles(i);
+                if !handles.is_empty() {
+                    self.push_undo_snapshot(i, "CHPROP");
+                    let idx = if field == "gradient_color_2" { 1 } else { 0 };
+                    for &handle in &handles {
+                        if let Some(acadrust::EntityType::Hatch(h)) =
+                            self.tabs[i].scene.document.get_entity_mut(handle)
+                        {
+                            while h.gradient_color.colors.len() <= idx {
+                                let value = if h.gradient_color.colors.is_empty() {
+                                    0.0
+                                } else {
+                                    1.0
+                                };
+                                h.gradient_color.colors.push(
+                                    acadrust::entities::hatch::GradientColorEntry {
+                                        value,
+                                        color: acadrust::types::Color::Index(7),
+                                    },
+                                );
+                            }
+                            h.gradient_color.colors[idx].color = color.clone();
+                        }
+                    }
+                    // Rebuild hatch seeds so the gradient fill picks up the new
+                    // colour (synced_hatch_models only patches the main colour).
+                    self.tabs[i].scene.populate_hatches_from_document();
+                    self.invalidate_property_targets(i, &handles);
+                    self.tabs[i].properties.open_color_field = None;
+                    self.tabs[i].dirty = true;
+                    self.refresh_properties();
+                }
+                Task::none()
+            }
+
             Message::PropColorPickerClose => {
                 let i = self.active_tab;
                 self.tabs[i].properties.color_picker_open = false;

src/entities/hatch.rs

@@ -99,9 +99,51 @@ fn boundary_centroid(h: &Hatch) -> Option<(f64, f64)> {
     (n > 0.0).then(|| (sx / n, sy / n))
 }
 
-/// Format a color for a read-only row (`ByLayer` / `ByBlock` / index / RGB).
-fn color_str(c: acadrust::types::Color) -> String {
-    c.to_string()
+/// Read the hatch background colour from its `HATCHBACKGROUNDCOLOR` extended
+/// data (group 1071, packed true colour: high byte = colour method, low three =
+/// RGB). `None` when unset or not a true-colour value.
+pub fn background_color(h: &Hatch) -> Option<acadrust::types::Color> {
+    let rec = h.common.extended_data.get_record("HATCHBACKGROUNDCOLOR")?;
+    let raw = rec.values.iter().find_map(|v| match v {
+        acadrust::xdata::XDataValue::Integer32(n) => Some(*n as u32),
+        _ => None,
+    })?;
+    match (raw >> 24) & 0xFF {
+        0xC2 | 0xC3 => Some(acadrust::types::Color::Rgb {
+            r: ((raw >> 16) & 0xFF) as u8,
+            g: ((raw >> 8) & 0xFF) as u8,
+            b: (raw & 0xFF) as u8,
+        }),
+        _ => None,
+    }
+}
+
+/// Pack an RGB colour into a `HATCHBACKGROUNDCOLOR` group-1071 true-colour word.
+pub fn pack_background_color(c: &acadrust::types::Color) -> i32 {
+    let (r, g, b) = c.rgb().unwrap_or((255, 255, 255));
+    (0xC2000000u32 | ((r as u32) << 16) | ((g as u32) << 8) | (b as u32)) as i32
+}
+
+/// Replace (or insert) the hatch's `HATCHBACKGROUNDCOLOR` extended-data record,
+/// preserving every other application's records.
+pub fn set_background_color(h: &mut Hatch, c: &acadrust::types::Color) {
+    use acadrust::xdata::{ExtendedDataRecord, XDataValue};
+    const APP: &str = "HATCHBACKGROUNDCOLOR";
+    let kept: Vec<ExtendedDataRecord> = h
+        .common
+        .extended_data
+        .records()
+        .iter()
+        .filter(|r| r.application_name != APP)
+        .cloned()
+        .collect();
+    h.common.extended_data.clear();
+    for r in kept {
+        h.common.extended_data.add_record(r);
+    }
+    let mut rec = ExtendedDataRecord::new(APP);
+    rec.add_value(XDataValue::Integer32(pack_background_color(c)));
+    h.common.extended_data.add_record(rec);
 }
 
 fn properties(h: &Hatch) -> Vec<PropSection> {
@@ -117,8 +159,10 @@ fn properties(h: &Hatch) -> Vec<PropSection> {
     };
     let area = boundary_area(h);
     let g = &h.gradient_color;
-    let grad_c1 = g.colors.first().map(|e| color_str(e.color)).unwrap_or_default();
-    let grad_c2 = g.colors.get(1).map(|e| color_str(e.color)).unwrap_or_default();
+    let default_col = acadrust::types::Color::Index(7);
+    let grad_c1 = g.colors.first().map(|e| e.color).unwrap_or(default_col);
+    let grad_c2 = g.colors.get(1).map(|e| e.color).unwrap_or(default_col);
+    let bg_col = background_color(h).unwrap_or(default_col);
 
     if g.enabled {
         // ── Gradient fill ──────────────────────────────────────────────────
@@ -128,10 +172,25 @@ fn properties(h: &Hatch) -> Vec<PropSection> {
             PropSection {
                 title: "Pattern".into(),
                 props: vec![
-                    ro("Type", "fill_type", grad_type),
+                    Property {
+                        label: "Type".into(),
+                        field: "fill_type",
+                        value: PropValue::Choice {
+                            selected: grad_type.to_string(),
+                            options: vec!["Two color".into(), "One color".into()],
+                        },
+                    },
                     ro("Gradient name", "gradient_name", g.name.clone()),
-                    ro("Color 1", "gradient_color_1", grad_c1),
-                    ro("Color 2", "gradient_color_2", grad_c2),
+                    Property {
+                        label: "Color 1".into(),
+                        field: "gradient_color_1",
+                        value: PropValue::ColorChoice(grad_c1),
+                    },
+                    Property {
+                        label: "Color 2".into(),
+                        field: "gradient_color_2",
+                        value: PropValue::ColorChoice(grad_c2),
+                    },
                     edit("Angle", "pattern_angle", g.angle.to_degrees()),
                     ro("Centered", "gradient_centered", centered),
                 ],
@@ -140,8 +199,6 @@ fn properties(h: &Hatch) -> Vec<PropSection> {
                 title: "Geometry".into(),
                 props: vec![
                     edit("Elevation", "elevation", h.elevation),
-                    ro("Origin X", "origin_x", String::new()),
-                    ro("Origin Y", "origin_y", String::new()),
                     ro("Area", "area", format!("{:.4}", area)),
                     ro("Cumulative area", "cumulative_area", format!("{:.4}", area)),
                 ],
@@ -156,7 +213,11 @@ fn properties(h: &Hatch) -> Vec<PropSection> {
                     ),
                     ro("Annotative", "annotative", String::new()),
                     ro("Island detection style", "style", style),
-                    ro("Background color", "background_color", String::new()),
+                    Property {
+                    label: "Background color".into(),
+                    field: "background_color",
+                    value: PropValue::ColorChoice(bg_col),
+                },
                 ],
             },
         ];
@@ -234,12 +295,11 @@ fn properties(h: &Hatch) -> Vec<PropSection> {
                 double_row,
                 associative_row,
                 island_row,
-                ro("Background color", "background_color", String::new()),
-                // ── Gradient info (read-only) ──────────────────────────────
-                ro("Gradient colors", "gradient_colors", g.colors.len().to_string()),
-                ro("Gradient tint", "gradient_tint", format!("{:.4}", g.color_tint)),
-                ro("Gradient color 1", "gradient_color_1", grad_c1),
-                ro("Gradient color 2", "gradient_color_2", grad_c2),
+                Property {
+                    label: "Background color".into(),
+                    field: "background_color",
+                    value: PropValue::ColorChoice(bg_col),
+                },
             ],
         },
         PropSection {
@@ -292,6 +352,10 @@ fn apply_geom_prop(h: &mut Hatch, field: &str, value: &str) {
             };
             return;
         }
+        "fill_type" => {
+            h.gradient_color.is_single_color = value == "One color";
+            return;
+        }
         _ => {}
     }
     let Some(v) = parse_f64(value) else {

src/scene/entity.rs

@@ -483,12 +483,23 @@ impl Scene {
                         self.model_space_block_handle(),
                     )
             })
-            .map(|(&handle, model)| {
+            .flat_map(|(&handle, model)| {
                 let entity = self.document.get_entity(handle);
                 let mut m = model.clone();
+                // Optional solid backdrop drawn behind the pattern/gradient when
+                // the hatch carries a HATCHBACKGROUNDCOLOR. Same draw_depth +
+                // emitted first so LessEqual layering keeps it underneath.
+                let mut backdrop: Option<HatchModel> = None;
                 if let Some(e) = entity {
                     m.color = self.render_style(e).0;
                     if let EntityType::Hatch(dxf) = e {
+                        if let Some(bg) = crate::entities::hatch::background_color(dxf) {
+                            let mut b = m.clone();
+                            b.pattern = model::hatch_model::HatchPattern::Solid;
+                            b.color = crate::scene::convert::tess_util::aci_to_rgba(&bg);
+                            b.name = "SOLID".into();
+                            backdrop = Some(b);
+                        }
                         match &mut m.pattern {
                             // Pattern built from the hatch's own stored lines is
                             // already final (scale 1 / angle 0) — don't re-apply
@@ -516,8 +527,12 @@ impl Scene {
                 if self.selected.contains(&handle) {
                     m.color = [0.15, 0.55, 1.00, m.color[3]];
                 }
-                m.draw_depth = depth_map.get(&handle.value()).copied().unwrap_or(0.0);
-                m
+                let d = depth_map.get(&handle.value()).copied().unwrap_or(0.0);
+                m.draw_depth = d;
+                if let Some(b) = &mut backdrop {
+                    b.draw_depth = d;
+                }
+                backdrop.into_iter().chain(std::iter::once(m))
             })
             .collect();
 

src/ui/properties.rs

@@ -149,6 +149,9 @@ pub struct PropertiesPanel {
     /// from `color_picker_open` so the entity colour and the background colour
     /// pickers are independent.
     pub bg_color_picker_open: bool,
+    /// Field name of the generic per-field colour picker currently open (e.g. a
+    /// hatch gradient colour), or `None`. Keeps each field's picker independent.
+    pub open_color_field: Option<String>,
     /// Which vertex a multi-vertex entity (polyline) is focused on — driven by
     /// the Current Vertex ◀ / ▶ stepper. Reset to 0 when the selection changes.
     pub prop_vertex: usize,
@@ -173,6 +176,7 @@ impl Default for PropertiesPanel {
             color_picker_open: false,
             color_palette_open: false,
             bg_color_picker_open: false,
+            open_color_field: None,
             prop_vertex: 0,
         }
     }
@@ -430,6 +434,27 @@ 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" {
+            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,
+                crate::ui::color_select::ColorExtras {
+                    by_layer: false,
+                    by_block: false,
+                },
+                move |c| Message::PropColorFieldChanged {
+                    field: fsel.clone(),
+                    color: c,
+                },
+                Message::PropColorFieldToggle(field.to_string()),
+                Message::PropColorFieldToggle(field.to_string()),
+            );
+            return prop_row_widget(label, selector);
+        }
         let selector = crate::ui::color_select::color_selector(
             color,
             self.color_picker_open,