DWF and DGN underlays: attach, display, snaps, frames and references

DWFATTACH / -DWFATTACH and DGNATTACH / -DGNATTACH attach a DWF / DWFx sheet
or a DGN (V7 or V8) model with the reference's prompts; ATTACH routes the
file types to them. The sheet or model is read into vector paths, drawn as a
transparent underlay raster (contrast, fade, monochrome and background
adjustment apply) and offers its geometry to object snaps. Definitions are
kept in ACAD_DWFDEFINITIONS / ACAD_DGNDEFINITIONS, the External References
palette lists and reloads them, and image textures get line-keeping mip
levels so thin underlay lines stay visible when zoomed out.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/update/dialog.rs

@@ -867,8 +867,7 @@ pub(super) fn on_ribbon_tool_click(&mut self, tool_id: String, event: ModuleEven
                     Some(entity.common().handle)
                 }
                 codec::EntityType::Underlay(underlay)
-                    if matches!(underlay.underlay_type, codec::entities::UnderlayType::Pdf)
-                        && self.tabs[i].xref_unloaded.is_unloaded(underlay.definition_handle.value()) =>
+                    if self.tabs[i].xref_unloaded.is_unloaded(underlay.definition_handle.value()) =>
                 {
                     Some(entity.common().handle)
                 }
@@ -1021,8 +1020,8 @@ pub(super) fn on_ribbon_tool_click(&mut self, tool_id: String, event: ModuleEven
                             "XREF: cannot reload nested reference '{}'. Reload it in its host drawing.",
                             name
                         ).as_ref());
-                    } else if *kind == crate::io::xref_model::RefKind::Pdf {
-                        // A PDF reloads by clearing its definition's unloaded state.
+                    } else if *kind == crate::io::xref_model::RefKind::Underlay {
+                        // An underlay reloads by clearing its definition's unloaded state.
                         for (key, row_name, row_kind, _) in &picked {
                             if row_kind != kind || row_name != name {
                                 continue;

src/app/update/mod.rs

@@ -1426,6 +1426,7 @@ impl OpenCADStudio {
                 Task::none()
             }
             message @ (Message::AttachPick
+            | Message::UnderlayAttachPick(_)
             | Message::AttachPickResult(_)
             | Message::XrefAttach(_)
             | Message::XrefAttachBrowseResult(_)) => self.update_xref_attach(message),