Implement incremental graph layouts (#8308)

### Related

* Closes #8282

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* Closes #1234
* Part of #1337
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### What

We made the decision to carry over layout information between timestamps
as it leads to a much nicer user experience. This PR implements that
feature.

@abey79 Some of the logic in `provider.rs` has to change again for
blueprint support. I plan to do a cleanup pass in #8299.



https://github.com/user-attachments/assets/ae5b8c8e-9482-452c-bcf0-feb73fc165f0

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---------

Co-authored-by: Antoine Beyeler <49431240+abey79@users.noreply.github.com>
Co-authored-by: Andreas Reich <andreas@rerun.io>
Co-authored-by: Jan Procházka <honza.spacir@gmail.com>

crates/viewer/re_space_view_graph/src/layout/provider.rs

@@ -33,11 +33,26 @@ pub struct ForceLayoutProvider {
 
 impl ForceLayoutProvider {
     pub fn new(request: LayoutRequest) -> Self {
+        Self::new_impl(request, None)
+    }
+
+    pub fn new_with_previous(request: LayoutRequest, layout: &Layout) -> Self {
+        Self::new_impl(request, Some(layout))
+    }
+
+    // TODO(grtlr): Consider consuming the old layout to avoid re-allocating the extents.
+    // That logic has to be revised when adding the blueprints anyways.
+    fn new_impl(request: LayoutRequest, layout: Option<&Layout>) -> Self {
         let nodes = request.graphs.iter().flat_map(|(_, graph_template)| {
-            graph_template
-                .nodes
-                .iter()
-                .map(|n| (n.0, fj::Node::from(n.1)))
+            graph_template.nodes.iter().map(|n| {
+                let mut fj_node = fj::Node::from(n.1);
+                if let Some(rect) = layout.and_then(|l| l.get_node(n.0)) {
+                    let pos = rect.center();
+                    fj_node = fj_node.position(pos.x as f64, pos.y as f64);
+                }
+
+                (n.0, fj_node)
+            })
         });
 
         let mut node_index = ahash::HashMap::default();

crates/viewer/re_space_view_graph/src/ui/state.rs

@@ -104,15 +104,25 @@ impl LayoutState {
                 self // no op
             }
             // We need to recompute the layout.
-            Self::None | Self::Finished { .. } => {
+            Self::None => {
                 let provider = ForceLayoutProvider::new(new_request);
                 let layout = provider.init();
 
                 Self::InProgress { layout, provider }
             }
-            Self::InProgress { provider, .. } if provider.request != new_request => {
-                let provider = ForceLayoutProvider::new(new_request);
-                let layout = provider.init();
+            Self::Finished { layout, .. } => {
+                let mut provider = ForceLayoutProvider::new_with_previous(new_request, &layout);
+                let mut layout = provider.init();
+                provider.tick(&mut layout);
+
+                Self::InProgress { layout, provider }
+            }
+            Self::InProgress {
+                layout, provider, ..
+            } if provider.request != new_request => {
+                let mut provider = ForceLayoutProvider::new_with_previous(new_request, &layout);
+                let mut layout = provider.init();
+                provider.tick(&mut layout);
 
                 Self::InProgress { layout, provider }
             }

tests/python/release_checklist/check_graph_time_layout.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import os
+import random
+from argparse import Namespace
+from uuid import uuid4
+
+import rerun as rr
+import rerun.blueprint as rrb
+
+README = """\
+# Time-varying graph view
+
+Please watch out for any twitching, jumping, or other wise unexpected changes to
+the layout when navigating the timeline.
+
+Please check the following:
+* Scrub the timeline to see how the graph layout changes over time.
+"""
+
+
+def log_readme() -> None:
+    rr.log("readme", rr.TextDocument(README, media_type=rr.MediaType.MARKDOWN), static=True)
+
+
+def log_graphs() -> None:
+    nodes = ["root"]
+    edges = []
+
+    # Randomly add nodes and edges to the graph
+    for i in range(50):
+        existing = random.choice(nodes)
+        new_node = str(i)
+        nodes.append(new_node)
+        edges.append((existing, new_node))
+
+        rr.set_time_sequence("frame", i)
+        rr.log("graph", rr.GraphNodes(nodes, labels=nodes), rr.GraphEdges(edges, graph_type=rr.GraphType.Directed))
+
+    rr.send_blueprint(
+        rrb.Blueprint(
+            rrb.Grid(
+                rrb.GraphView(origin="graph", name="Graph"),
+                rrb.TextDocumentView(origin="readme", name="Instructions"),
+            )
+        )
+    )
+
+
+def run(args: Namespace) -> None:
+    rr.script_setup(args, f"{os.path.basename(__file__)}", recording_id=uuid4())
+
+    log_readme()
+    log_graphs()
+
+
+if __name__ == "__main__":
+    import argparse
+
+    parser = argparse.ArgumentParser(description="Interactive release checklist")
+    rr.script_add_args(parser)
+    args = parser.parse_args()
+    run(args)