Keep viewport layer colour overrides through DXF save and reopen (#99) (#197)

crates/io/src/dxf_ext.rs

@@ -365,6 +365,25 @@ pub(crate) fn read_frozen(tags: &[Tag]) -> Vec<String> {
     list.iter().take(MAX_XDATA_ITEMS).filter(|t| t.code == 1000).map(Tag::str).collect()
 }
 
+/// A viewport's layer colour overrides as CADCraft xdata: `1000 VPCOLORS`, `1002 {`, then per override
+/// `1000 layer` and `1000 colour` (the [`Color::name`] text, which keeps true colours), `1002 }`.
+pub(crate) fn layer_colors_xdata(colors: &[(String, Color)]) -> Vec<Tag> {
+    let mut v = vec![Tag::s(1000, "VPCOLORS"), Tag::s(1002, "{")];
+    for (layer, color) in colors {
+        v.push(Tag::s(1000, layer.clone()));
+        v.push(Tag::s(1000, color.name()));
+    }
+    v.push(Tag::s(1002, "}"));
+    v
+}
+
+/// The overrides written by [`layer_colors_xdata`]; empty for files from other writers, bad pairs are skipped.
+pub(crate) fn read_layer_colors(tags: &[Tag]) -> Vec<(String, Color)> {
+    let list = xdata_list(xdata(tags, APP), "VPCOLORS");
+    let names: Vec<String> = list.iter().take(MAX_XDATA_ITEMS * 2).filter(|t| t.code == 1000).map(Tag::str).collect();
+    names.chunks_exact(2).filter_map(|p| Some((p.first()?.clone(), Color::parse(p.get(1)?)?))).collect()
+}
+
 const POINT_NAMES: [&str; 5] = ["defpt", "p13", "p14", "p15", "p16"];
 
 /// Associativity links from CADCraft xdata; malformed links are skipped.

crates/io/src/dxf_read.rs

@@ -307,7 +307,7 @@ fn entity(kind: &str, tags: &[Tag]) -> Option<(Common, EntityKind)> {
             id: t.i(69).unwrap_or(0) as u32,
             locked: t.i(90).unwrap_or(0) & 16384 != 0,
             frozen_layers: crate::dxf_ext::read_frozen(tags),
-            layer_colors: Vec::new(),
+            layer_colors: crate::dxf_ext::read_layer_colors(tags),
         }),
         "WIPEOUT" => {
             let o = t.p(10);

crates/io/src/dxf_write.rs

@@ -792,9 +792,15 @@ 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() {
+            // One CADCraft xdata group holds both lists: readers stop at the first group of an app.
+            if !v.frozen_layers.is_empty() || !v.layer_colors.is_empty() {
                 w.s(1001, dxf_ext::APP);
-                w.xdata(dxf_ext::frozen_xdata(&v.frozen_layers));
+                if !v.frozen_layers.is_empty() {
+                    w.xdata(dxf_ext::frozen_xdata(&v.frozen_layers));
+                }
+                if !v.layer_colors.is_empty() {
+                    w.xdata(dxf_ext::layer_colors_xdata(&v.layer_colors));
+                }
             }
         }
         EntityKind::Wipeout(wo) => {

crates/io/src/tests.rs

@@ -571,6 +571,43 @@ fn viewport_frozen_layers_roundtrip() {
     assert!(frozen.contains(&(3, Vec::new())), "{frozen:?}");
 }
 
+#[test]
+fn viewport_layer_colors_roundtrip() {
+    let mut d = sample();
+    let paper = Space::Paper("Layout1".into());
+    let vp = |id: u32, frozen: Vec<String>, colors: Vec<(String, Color)>| {
+        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: false,
+            frozen_layers: frozen,
+            layer_colors: colors,
+        })
+    };
+    let colors = vec![("Walls".to_string(), Color::Index(5)), ("A B".to_string(), Color::True(cadcraft_color::Rgb(255, 128, 0)))];
+    d.add(&paper, Common::default(), vp(2, Vec::new(), colors.clone())).unwrap();
+    d.add(&paper, Common::default(), vp(3, Vec::new(), Vec::new())).unwrap();
+    // Frozen layers and colour overrides share one CADCraft xdata group.
+    d.add(&paper, Common::default(), vp(4, vec!["Walls".into()], colors.clone())).unwrap();
+    let back = roundtrip(&d);
+    let found: Vec<(u32, Vec<String>, Vec<(String, Color)>)> = 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(), v.layer_colors.clone())),
+            _ => None,
+        })
+        .collect();
+    assert!(found.contains(&(2, Vec::new(), colors.clone())), "{found:?}");
+    assert!(found.contains(&(3, Vec::new(), Vec::new())), "{found:?}");
+    assert!(found.contains(&(4, vec!["Walls".to_string()], colors)), "{found:?}");
+}
+
 fn full_dim_style() -> DimStyle {
     DimStyle {
         name: "Mech".into(),