GraphViewState · NodeDrag · ConnectDrag · MarqueeDrag

Layer: graph · Path: src/graph/state.rs · Exports: GraphViewState, NodeDrag, ConnectDrag, MarqueeDrag

The view-state: the only thing the library owns across frames. The caller owns the node/edge data; this struct owns the view — where the camera is, what’s selected, and what’s mid-drag. It is stored in egui’s temp memory keyed by the GraphView’s id, so it must be Clone + Default to live in the temp store.

Design

• Purpose. Persist the minimum the graph needs between frames. Loaded at the top of GraphView::show (get_temp(id).unwrap_or_default()), mutated through the frame, written back with insert_temp at the end. The caller almost never touches it directly — it observes effects via GraphResponse instead.
• scene_rect. The [egui::Scene] view window expressed in world coordinates. GraphView::show hands a &mut to it into Scene::show, and Scene mutates it in place on pan/zoom. Controls’ zoom buttons rescale it around its center; fit replaces it with the content bounds expanded by core::SPACE_8; the minimap recenters it.
• Rect::ZERO sentinel. The Default scene_rect is Rect::ZERO, the “uninitialised” marker — Scene interprets it as “no camera yet” and auto-fits the content on the first frame. After the first frame it holds a real world rect.
• Selection model. selection: HashSet<NodeId> plus an Option<(Port, Port)> edge selection (mutually managed: selecting a node clears the edge selection and vice-versa). Delete/Backspace removes the selected edge first, else drains the selected nodes.
• Transient drag state. Three optional sub-structs, each present only while a drag is live: drag (node move), connect (wire), marquee (box-select). connect and edge_selection round-trip through the Scene closure (read in, resolved, written out); drag / marquee / hovered_node are maintained across frames.

GraphViewState fields

#[derive(Clone, Debug)]; Default sets scene_rect = Rect::ZERO, all collections empty, all options None.

Helper structs

NodeDrag — #[derive(Clone, Copy, Debug)]

ConnectDrag — #[derive(Clone, Copy, Debug)]

MarqueeDrag — #[derive(Clone, Copy, Debug)]

API

These are plain data structs — no methods. Construct/inspect their public fields directly. GraphViewState::default() is the canonical constructor; the canvas does this for you. All four derive Clone (state) / Clone + Copy (the three drags) so they round-trip through egui temp storage and the Scene closure cheaply.

Usage

#![allow(unused)]
fn main() {
use ouroboros_ui::graph::GraphViewState;

// The canvas owns this; you rarely touch it. But you *can* read/seed it:
let id = egui::Id::new("my_graph");

// Pre-position the camera (skip the first-frame auto-fit):
ui.data_mut(|d| {
    let mut st: GraphViewState = d.get_temp(id).unwrap_or_default();
    st.scene_rect = egui::Rect::from_min_size(egui::pos2(0.0, 0.0), egui::vec2(800.0, 600.0));
    d.insert_temp(id, st);
});

// Inspect the persisted selection out-of-band (normally use GraphResponse::selection):
let selected: usize = ui.data(|d| {
    d.get_temp::<GraphViewState>(id).map(|s| s.selection.len()).unwrap_or(0)
});
}

Composition / Notes

• Single source of camera truth. There is exactly one GraphViewState per GraphView id; clobbering it (e.g. inserting a fresh default()) resets the camera to the auto-fit sentinel and clears selection.
• scene_rect is world, not screen. A smaller scene_rect means more zoomed in (the window covers less world). This is the opposite mental model from a screen rect.
• Not the same as Viewport. Viewport is a standalone pan+zoom transform helper that the live canvas does not use; the canvas drives scene_rect through egui::Scene. Don’t confuse the two camera representations.
• Identity vocab. NodeId, Port, PortSide — see identity.
• Foundation: architecture · tokens · theming · guards. Layer overview: README.