Improve VisualBounds2D behavior in graph view (#8438)

* Closes #8429 

This implements improved handling of `VisualBounds2D`. Specifically, it:

* Always defaults to the data bounds when user has not modified the view
(@nikolausWest's suggestion).
* Zooms in and out of view when resizing the view (@abey79's
suggestion).
* Fixes the `VisualBounds2D` selection panel bug (submitted by @Wumpf)

---------

Co-authored-by: Andreas Reich <[email protected]>

crates/viewer/re_ui/src/zoom_pan_area.rs

@@ -5,7 +5,7 @@
 //! * `view`-space: The space where the pan-and-zoom area is drawn.
 //! * `scene`-space: The space where the actual content is drawn.
 
-use egui::{emath::TSTransform, Area, Rect, Response, Ui, UiKind};
+use egui::{emath::TSTransform, Area, Rect, Response, Ui, UiKind, Vec2};
 
 /// Helper function to handle pan and zoom interactions on a response.
 fn register_pan_and_zoom(ui: &Ui, resp: &Response, ui_from_scene: &mut TSTransform) {
@@ -19,16 +19,22 @@ fn register_pan_and_zoom(ui: &Ui, resp: &Response, ui_from_scene: &mut TSTransfo
             let zoom_delta = ui.ctx().input(|i| i.zoom_delta());
             let pan_delta = ui.ctx().input(|i| i.smooth_scroll_delta);
 
+            // Most of the time we can return early. This is also important to
+            // avoid `ui_from_scene` to change slightly due to floating point errors.
+            if zoom_delta == 1.0 && pan_delta == Vec2::ZERO {
+                return;
+            }
+
             // Zoom in on pointer, but only if we are not zoomed out too far.
             if zoom_delta < 1.0 || ui_from_scene.scaling < 1.0 {
                 *ui_from_scene = *ui_from_scene
                     * TSTransform::from_translation(pointer_in_scene.to_vec2())
                     * TSTransform::from_scaling(zoom_delta)
                     * TSTransform::from_translation(-pointer_in_scene.to_vec2());
-            }
 
-            // We clamp the resulting scaling to avoid zooming out too far.
-            ui_from_scene.scaling = ui_from_scene.scaling.min(1.0);
+                // We clamp the resulting scaling to avoid zooming out too far.
+                ui_from_scene.scaling = ui_from_scene.scaling.min(1.0);
+            }
 
             // Pan:
             *ui_from_scene = TSTransform::from_translation(pan_delta) * *ui_from_scene;

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

@@ -1,4 +1,4 @@
-use egui::{emath::TSTransform, Rect};
+use egui::Rect;
 use re_format::format_f32;
 use re_types::blueprint::components::VisualBounds2D;
 use re_ui::UiExt;
@@ -16,7 +16,6 @@ pub struct GraphViewState {
     pub show_debug: bool,
 
     pub visual_bounds: Option<VisualBounds2D>,
-    pub ui_from_world: Option<TSTransform>,
     pub rect_in_ui: Option<Rect>,
 }
 
@@ -25,7 +24,7 @@ impl GraphViewState {
         let Some(rect) = self.layout_state.bounding_rect() else {
             return;
         };
-        ui.grid_left_hand_label("Layout")
+        ui.grid_left_hand_label("Bounding box")
             .on_hover_text("The bounding box encompassing all entities in the view right now");
         ui.vertical(|ui| {
             ui.style_mut().wrap_mode = Some(egui::TextWrapMode::Extend);

crates/viewer/re_view_graph/src/view.rs

@@ -183,22 +183,14 @@ Display a graph of nodes and edges.
         let layout = state.layout_state.get(request, params);
 
         // Prepare the view and the transformations.
-        let prev_rect_in_ui = state.rect_in_ui;
         let rect_in_ui = *state.rect_in_ui.insert(ui.max_rect());
 
-        let ui_from_world = state
-            .ui_from_world
-            .get_or_insert_with(|| fit_to_rect_in_scene(rect_in_ui, rect_in_scene.into()));
+        let mut ui_from_world = fit_to_rect_in_scene(rect_in_ui, rect_in_scene.into());
 
-        // We ensure that the view's center is kept during resizing.
-        if let Some(prev) = prev_rect_in_ui {
-            if prev != rect_in_ui {
-                let delta = rect_in_ui.center() - prev.center();
-                ui_from_world.translation += delta;
-            }
-        }
+        // We store a copy of the transformation to see if it has changed.
+        let ui_from_world_ref = ui_from_world;
 
-        let resp = zoom_pan_area(ui, rect_in_ui, ui_from_world, |ui| {
+        let resp = zoom_pan_area(ui, rect_in_ui, &mut ui_from_world, |ui| {
             let mut world_bounding_rect = egui::Rect::NOTHING;
 
             for graph in &graphs {
@@ -217,8 +209,7 @@ Display a graph of nodes and edges.
             blueprint::components::VisualBounds2D::from(ui_from_world.inverse() * rect_in_ui);
         if resp.double_clicked() {
             bounds_property.reset_blueprint_component::<blueprint::components::VisualBounds2D>(ctx);
-            state.ui_from_world = None;
-        } else if rect_in_scene != updated_rect_in_scene {
+        } else if ui_from_world != ui_from_world_ref {
             bounds_property.save_blueprint_component(ctx, &updated_rect_in_scene);
         }
         // Update stored bounds on the state, so visualizers see an up-to-date value.