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/io/xref.rs

@@ -1121,7 +1121,6 @@ pub fn collect_entries_with_prev(
     unloaded: &std::collections::HashSet<crate::io::xref_model::UnloadKey>,
     prev: &std::collections::HashMap<u64, std::time::SystemTime>,
 ) -> Vec<crate::io::xref_model::ReferenceEntry> {
-    use codec::entities::UnderlayType;
     use codec::objects::ObjectType;
     use crate::io::xref_model::{
         child_key, decide_status, normalize_lexical, RefKind, RefStatus, RefType,
@@ -1252,16 +1251,13 @@ pub fn collect_entries_with_prev(
         let ObjectType::UnderlayDefinition(def) = obj else {
             continue;
         };
-        if def.underlay_type != UnderlayType::Pdf {
-            continue;
-        }
         let key = handle.value();
         let name = if def.name.trim().is_empty() {
             file_name_only(&def.file_path).to_owned()
         } else {
             def.name.clone()
         };
-        let mut entry = ReferenceEntry::new(key, name, RefKind::Pdf);
+        let mut entry = ReferenceEntry::new(key, name, RefKind::Underlay);
         entry.saved_path = def.file_path.clone();
         if def.unloaded || unloaded.contains(&UnloadKey::Direct(key)) {
             entry.status = RefStatus::Unloaded;

src/io/xref_model.rs

@@ -303,7 +303,8 @@ pub fn wildcard_match(name: &str, pattern: &str) -> bool {
 pub enum RefKind {
     DwgXref,
     Image,
-    Pdf,
+    /// A PDF, DWF or DGN underlay.
+    Underlay,
 }
 
 /// Lifecycle state of a [`ReferenceEntry`].