Add topic & node dependency graph

[nshro]

Overview

This introduces a new feature to visualize ROS2 entity dependencies as an interactive tree structure. It adds a dependency graph model, a dedicated UI panel, and integrates this into the entity inspection workflow.

Highlights

Dependency Graph Model

Implemented RosDependencyGraph and RosDependencyNode classes to recursively model hierarchical relationships between ROS entities.

Supports:

• Node → Subscribed Topics
• Topic → Publishing Nodes

Skips system topics (e.g., /parameter_events) to maintain clarity.

Graph UI Panel

Added a new widget: RosEntityGraphPanel that renders the dependency tree.

Features:

• Lazy subtree expansion
• Error handling (invalid/missing entity info)
• Styling for nodes/topics (color & underline)
• "Space" key to collapse/expand all items at the same level

Notes

Tree nodes are color-coded:

• 🟩 Green for Nodes
• ⚪ White for Topics
• 🔶 Yellow for “No Publisher”
• 🔴 Red for errors

[Tiryoh]

Good patch! The dependency graph feature looks solid. I have a few suggestions for improvements.

Also, could you replace the demo movie in top-level README.md with the following URL?

https://github.com/user-attachments/assets/576b9ecd-81cd-4b26-948c-65cea6ce49af

[Tiryoh]

The visited parameter is unused here. Since max_depth already prevents infinite recursion, we can remove this parameter to clean up the interface.

[nshro]

Thanks! I forgot to remove them. bcc0547

[Tiryoh]

The node expansion logic is duplicated between on_tree_node_selected() and update_graph(). Both methods follow the same pattern:

1. Create RosDependencyGraph
2. Call _populate_tree()
3. Expand the node

How about creating a helper method like _rebuild_node() to reduce duplication?

Suggested change

	def update_graph(self) -> None:
	if self._tree:
	self._tree.remove()
	if self._entity is None:
	return
	self._tree = Tree(TreeLabel.label(self._entity), data=self._entity)
	self.mount(self._tree)
	graph = RosDependencyGraph(self._entity, self._ros, max_depth=EXPANSION_DEPTH)
	self._populate_tree(self._tree.root, graph.root)
	self._tree.root.expand()
	def update_graph(self) -> None:
	if self._tree:
	self._tree.remove()
	if self._entity is None:
	return
	self._tree = Tree(TreeLabel.label(self._entity), data=self._entity)
	self.mount(self._tree)
	self._rebuild_node(self._tree.root, self._entity)

[nshro]

I have consolidate the node expansion logic in _populate_tree() 340d4ab

[Tiryoh]

The conditional logic in on_tree_node_selected() could be extracted into _should_expand_node() for better readability.

Suggested change

	def on_tree_node_selected(self, event: Tree.NodeSelected) -> None:
	node = event.node
	entity = node.data # type: RosEntity | None
	if not isinstance(entity, RosEntity):
	return
	if entity.type != RosEntityType.Node:
	return
	if node.children and all(child.is_expanded for child in node.children):
	return
	if self._subtree_depth(node) > EXPANSION_DEPTH:
	return
	try:
	node._children.clear()
	node._expanded = False
	graph = RosDependencyGraph(entity, self._ros, max_depth=EXPANSION_DEPTH)
	self._populate_tree(node, graph.root)
	node.expand()
	except Exception as e:
	node.add_leaf(TreeLabel.ERROR(str(e)))
	def on_tree_node_selected(self, event: Tree.NodeSelected) -> None:
	node = event.node
	entity = node.data
	if not self._should_expand_node(node, entity):
	return
	self._rebuild_node(node, entity)
	def _should_expand_node(self, node: TreeNode, entity: RosEntity | None) -> bool:
	if not isinstance(entity, RosEntity):
	return False
	if entity.type != RosEntityType.Node:
	return False
	if node.children and all(child.is_expanded for child in node.children):
	return False
	if self._subtree_depth(node) > EXPANSION_DEPTH:
	return False
	return True
	def _rebuild_node(self, node: TreeNode, entity: RosEntity) -> None:
	try:
	node._children.clear()
	node._expanded = False
	graph = RosDependencyGraph(entity, self._ros, max_depth=EXPANSION_DEPTH)
	self._populate_tree(node, graph.root)
	node.expand()
	except Exception as e:
	node.add_leaf(TreeLabel.error(str(e)))

[nshro]

I refactored on_tree_node_selected as you pointed out. Thanks! 226414d

[nshro]

@Tiryoh I have attached the screencast to README.md. bf42255

[Tiryoh]

LGTM!

[Tiryoh]

I accidentally pushed the documentation update to this branch. Please ignore it.