Module toolbar_hover_tracker 

ToolbarHoverTracker — host-side state holder that converts MouseMoved events into hovered_id: Option<WidgetId> for the Toolbar primitive.

The toolbar rasterisers accept a hovered_id so they can tint the matching button’s background, but the host has to track which button the mouse is over across mouse-move events — the rasteriser itself is stateless. Doing that by hand means converting from screen-space coordinates back through a ToolbarLayout per move event, plus remembering to clear the hover when the cursor leaves the bar. Easy to forget; easy to get wrong.

This helper owns that bookkeeping: feed it mouse-move events together with the current layout, ask it for the active hovered_id at render time, and pass that straight to Backend::draw_toolbar.

Usage

struct App {
    hover: ToolbarHoverTracker,
    // ...
}

impl AppLogic for App {
    fn handle(&mut self, ev: UiEvent, backend: &mut dyn Backend) -> Reaction {
        if let UiEvent::MouseMoved { position, .. } = ev {
            let layout = backend.toolbar_layout(self.bar_rect(backend), &self.bar());
            if self.hover.update(&layout, position.x, position.y) {
                return Reaction::Redraw;
            }
        }
        // ...
    }

    fn render(&self, backend: &mut dyn Backend, _area: ()) {
        backend.draw_toolbar_interactive(
            self.bar_rect(backend),
            &self.bar(),
            &InteractionState::from_parts(self.hover.hovered_id().cloned(), None),
        );
    }
}

Structs

ToolbarHoverTracker

Tracks the toolbar button currently under the mouse. Cheap to keep per toolbar (or per panel, if a panel hosts multiple) — one Option<WidgetId> plus a single hit_test call per mouse-move.