Make branch lines take their parent's color

A node's color now flows down the lines to its children, mind-map style:
Watering's teal colors the lines to Rain barrel and Drip line. It used to
color the line from the root down to Watering itself, which also left the
shared bus of a parent's branches in whichever child's color was drawn
last. Branches follow their parent by default, and stay dim when the
parent has no color.

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

DESIGN.md

@@ -77,7 +77,9 @@ lines.
 - Connections can set arrowheads (off, end, start, both), a line (solid,
   dashed, dotted, thick, double), a color (a palette color or the node's own)
   and a label, or use a named style. Branches start solid without arrowheads,
-  cross-links as dashed arrows.
+  in their parent's color, so a node's color flows down the lines to its
+  children (dim when the parent has no color). Cross-links start as dim
+  dashed arrows.
 
 **Keys**
 - Medium vim: counts, operators with node targets, registers (with `"+` for the

examples/garden.cum

@@ -43,9 +43,6 @@
             title: "Watering",
             pos: (22, 12),
             color: "teal",
-            branch: (
-                color: "node",
-            ),
         ),
         (
             id: 7,

src/model/look.rs

@@ -49,8 +49,9 @@ pub enum Arrows {
 pub enum LineColor {
     /// A color from the theme's palette.
     Named(ColorName),
-    /// The color of the node the line comes from (for a branch: the child),
-    /// so each branch takes its node's color, mind-map style.
+    /// The color of the node the line comes from: a branch takes its
+    /// parent's (so a node's color flows down the lines to its children,
+    /// mind-map style), a cross-link its start's.
     FollowNode,
 }
 

src/ui/theme.rs

@@ -87,7 +87,14 @@ impl Default for Theme {
             palette,
             node: NodeLook { border: Some(Border::Square), ..NodeLook::default() },
             root: NodeLook { border: Some(Border::Rounded), ..NodeLook::default() },
-            branch: LineLook { line: Some(Stroke::Solid), arrows: Some(Arrows::Off), ..LineLook::default() },
+            // Branches take their parent's color: a node's color flows down
+            // the lines to its children (dim when the parent has no color).
+            branch: LineLook {
+                line: Some(Stroke::Solid),
+                arrows: Some(Arrows::Off),
+                color: Some(LineColor::FollowNode),
+                style: None,
+            },
             link: LineLook { line: Some(Stroke::Dashed), arrows: Some(Arrows::End), ..LineLook::default() },
             node_styles: BTreeMap::new(),
             line_styles: BTreeMap::new(),
@@ -128,9 +135,9 @@ impl Theme {
     }
 
     /// How to draw a branch line, given the look it has and the color of
-    /// its child (for lines that follow their node's color).
-    pub fn branch_style(&self, look: &LineLook, child_color: Color) -> LineStyle {
-        self.line_style(&self.branch, look, child_color)
+    /// its parent (for lines that follow their node's color).
+    pub fn branch_style(&self, look: &LineLook, parent_color: Color) -> LineStyle {
+        self.line_style(&self.branch, look, parent_color)
     }
 
     /// How to draw a cross-link, given the look it has and the color of the
@@ -211,12 +218,21 @@ mod tests {
     }
 
     #[test]
-    fn lines_can_follow_their_node() {
+    fn branches_take_their_parents_color() {
         let theme = Theme::default();
-        let follow = LineLook { color: Some(LineColor::FollowNode), ..LineLook::default() };
-        assert_eq!(theme.branch_style(&follow, Color::Indexed(71)).color, Color::Indexed(71));
-        assert_eq!(theme.branch_style(&follow, Color::Reset).color, theme.muted);
-        let link = theme.link_style(&LineLook::default(), Color::Reset);
-        assert_eq!((link.stroke, link.arrows), (Stroke::Dashed, Arrows::End));
+        let teal = Color::Indexed(37);
+        assert_eq!(theme.branch_style(&LineLook::default(), teal).color, teal, "by default");
+        assert_eq!(
+            theme.branch_style(&LineLook::default(), Color::Reset).color,
+            theme.muted,
+            "no color: dim"
+        );
+        let red = LineLook {
+            color: Some(LineColor::Named(ColorName::parse("red").unwrap())),
+            ..LineLook::default()
+        };
+        assert_eq!(theme.branch_style(&red, teal).color, theme.color(&ColorName::parse("red").unwrap()));
+        let link = theme.link_style(&LineLook::default(), teal);
+        assert_eq!((link.stroke, link.arrows, link.color), (Stroke::Dashed, Arrows::End, theme.muted));
     }
 }

src/view/canvas/render.rs

@@ -244,6 +244,22 @@ mod tests {
         assert_eq!(scene.node_at(crate::view::canvas::ScreenPos::new(30, 5)), Some(g.beds));
     }
 
+    #[test]
+    fn branch_lines_take_their_parents_color() {
+        let (mut doc, g) = garden();
+        let orange = crate::model::ColorName::parse("orange").unwrap();
+        doc.edit(|e| e.update(g.beds, |node| node.look.color = Some(orange.clone()))).unwrap();
+        let theme = Theme::default();
+        let scene =
+            Scene::build(&doc, g.soil, Camera::default(), Size::new(52, 8), &theme, SceneOptions::default());
+        let area = Rect::new(0, 0, 52, 8);
+        let mut buf = Buffer::empty(area);
+        scene.render(area, &mut buf);
+        let color = |col: u16, row: u16| buf[(col, row)].fg;
+        assert_eq!(color(38, 5), theme.color(&orange), "Raised beds → Cedar: orange, the parent's");
+        assert_eq!(color(17, 5), theme.muted, "Garden plans → Raised beds: dim, the root has no color");
+    }
+
     #[test]
     fn folded_branches_links_and_far_zoom() {
         let (mut doc, g) = garden();

src/view/canvas/scene.rs

@@ -190,7 +190,7 @@ impl Scene {
             let child = &self.nodes[child_index];
             let Some(Place::Child { parent, branch }) = doc.place(child.id) else { continue };
             let Some(&parent_index) = self.index.get(parent) else { continue };
-            let style = theme.branch_style(branch, child.color);
+            let style = theme.branch_style(branch, self.nodes[parent_index].color);
             let owner = LineOwner::Branch(child.id);
             self.connect(parent_index, child_index, Bend::NearStart, style, owner, None);
         }