From b7f83a66871d6f0c2e7b1fc0fa23572a8afbadfe Mon Sep 17 00:00:00 2001
From: MarekSpodBiedry <73122968+MarekSpodBiedry@users.noreply.github.com>
Date: Sat, 10 Oct 2026 18:14:21 +0200
Subject: [PATCH] Keep viewport frozen-layer lists through DXF save and reopen
 (#98) (#150)

---
 crates/io/src/dxf_ext.rs   | 14 ++++++++++++++
 crates/io/src/dxf_read.rs  |  2 +-
 crates/io/src/dxf_write.rs |  4 ++++
 crates/io/src/tests.rs     | 33 +++++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/crates/io/src/dxf_ext.rs b/crates/io/src/dxf_ext.rs
index 88328de4..e1641954 100644
--- a/crates/io/src/dxf_ext.rs
+++ b/crates/io/src/dxf_ext.rs
@@ -306,6 +306,20 @@ pub(crate) fn assoc_xdata(assoc: &[DimAssoc]) -> Vec<Tag> {
     v
 }
 
+/// A viewport's frozen layer names as CADCraft xdata: `1000 VPFROZEN`, `1002 {`, one `1000` per layer, `1002 }`.
+pub(crate) fn frozen_xdata(layers: &[String]) -> Vec<Tag> {
+    let mut v = vec![Tag::s(1000, "VPFROZEN"), Tag::s(1002, "{")];
+    v.extend(layers.iter().map(|l| Tag::s(1000, l.clone())));
+    v.push(Tag::s(1002, "}"));
+    v
+}
+
+/// The frozen layer names written by [`frozen_xdata`]; empty for files from other writers.
+pub(crate) fn read_frozen(tags: &[Tag]) -> Vec<String> {
+    let list = xdata_list(xdata(tags, APP), "VPFROZEN");
+    list.iter().take(MAX_XDATA_ITEMS).filter(|t| t.code == 1000).map(Tag::str).collect()
+}
+
 const POINT_NAMES: [&str; 5] = ["defpt", "p13", "p14", "p15", "p16"];
 
 /// Associativity links from CADCraft xdata; malformed links are skipped.
diff --git a/crates/io/src/dxf_read.rs b/crates/io/src/dxf_read.rs
index 68e58e60..54c7f238 100644
--- a/crates/io/src/dxf_read.rs
+++ b/crates/io/src/dxf_read.rs
@@ -288,7 +288,7 @@ fn entity(kind: &str, tags: &[Tag]) -> Option<(Common, EntityKind)> {
             view_height: t.fd(45, 1.0),
             id: t.i(69).unwrap_or(0) as u32,
             locked: t.i(90).unwrap_or(0) & 16384 != 0,
-            frozen_layers: Vec::new(),
+            frozen_layers: crate::dxf_ext::read_frozen(tags),
             layer_colors: Vec::new(),
         }),
         "WIPEOUT" => {
diff --git a/crates/io/src/dxf_write.rs b/crates/io/src/dxf_write.rs
index dd24bf2f..98edc6c7 100644
--- a/crates/io/src/dxf_write.rs
+++ b/crates/io/src/dxf_write.rs
@@ -765,6 +765,10 @@ fn entity(w: &mut W, d: &Drawing, e: &Entity, owner: &str, paper: bool, cx: &Ctx
             w.f(45, v.view_height);
             // Status flags: 16384 = display locked.
             w.i(90, if v.locked { 16384 } else { 0 });
+            if !v.frozen_layers.is_empty() {
+                w.s(1001, dxf_ext::APP);
+                w.xdata(dxf_ext::frozen_xdata(&v.frozen_layers));
+            }
         }
         // Not yet written: images, wipeouts, tables, multileaders, unknown objects.
         _ => {}
diff --git a/crates/io/src/tests.rs b/crates/io/src/tests.rs
index de7dd2d0..e9699c41 100644
--- a/crates/io/src/tests.rs
+++ b/crates/io/src/tests.rs
@@ -419,6 +419,39 @@ fn roundtrip(d: &Drawing) -> Drawing {
     read_dxf(write_dxf(d).as_bytes()).unwrap()
 }
 
+#[test]
+fn viewport_frozen_layers_roundtrip() {
+    let mut d = sample();
+    let paper = Space::Paper("Layout1".into());
+    let vp = |id: u32, frozen: Vec<String>| {
+        EntityKind::Viewport(Viewport {
+            center: Vec3::new(5.0, 4.0, 0.0),
+            width: 8.0,
+            height: 6.0,
+            view_center: Vec2::new(5.0, 2.5),
+            view_height: 12.0,
+            id,
+            locked: true,
+            frozen_layers: frozen,
+            layer_colors: Vec::new(),
+        })
+    };
+    d.add(&paper, Common::default(), vp(2, vec!["Walls".into(), "A B".into()])).unwrap();
+    d.add(&paper, Common::default(), vp(3, Vec::new())).unwrap();
+    let back = roundtrip(&d);
+    let frozen: Vec<(u32, Vec<String>)> = back
+        .layouts
+        .iter()
+        .flat_map(|l| l.entities.iter())
+        .filter_map(|e| match &e.kind {
+            EntityKind::Viewport(v) => Some((v.id, v.frozen_layers.clone())),
+            _ => None,
+        })
+        .collect();
+    assert!(frozen.contains(&(2, vec!["Walls".to_string(), "A B".to_string()])), "{frozen:?}");
+    assert!(frozen.contains(&(3, Vec::new())), "{frozen:?}");
+}
+
 fn full_dim_style() -> DimStyle {
     DimStyle {
         name: "Mech".into(),