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 <[email protected]>

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;