From 8e2cf5f9a03bad498e41eb391e03200223e29af6 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
Date: Mon, 16 Dec 2024 10:35:41 +0100
Subject: [PATCH] Fix broken interaction outside of graph views (#8457)
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## Related

* Closes #8454

UI interaction was sometimes broken outside of graph views. This PR is
the cure.

* Reverts https://github.com/rerun-io/rerun/pull/8416

---------

Co-authored-by: Jochen Görtler <me@jgoertler.com>
---
 crates/viewer/re_ui/src/zoom_pan_area.rs | 86 +++++++++++++-----------
 crates/viewer/re_view_graph/src/view.rs  |  2 +-
 2 files changed, 47 insertions(+), 41 deletions(-)

diff --git a/crates/viewer/re_ui/src/zoom_pan_area.rs b/crates/viewer/re_ui/src/zoom_pan_area.rs
index bfb97c1ef597..f3f2530ba571 100644
--- a/crates/viewer/re_ui/src/zoom_pan_area.rs
+++ b/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, Vec2};
+use egui::{emath::TSTransform, Rect, Response, Ui, UiBuilder, 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) {
@@ -63,46 +63,52 @@ pub fn fit_to_rect_in_scene(rect_in_ui: Rect, rect_in_scene: Rect) -> TSTransfor
 }
 
 /// Provides a zoom-pan area for a given view.
+///
+/// Will fill the entire `max_rect` of the `parent_ui`.
 pub fn zoom_pan_area(
-    ui: &Ui,
-    view_bounds_in_ui: Rect,
-    ui_from_scene: &mut TSTransform,
+    parent_ui: &mut Ui,
+    to_global: &mut TSTransform,
     draw_contents: impl FnOnce(&mut Ui),
 ) -> Response {
-    let area_resp = Area::new(ui.id().with("zoom_pan_area"))
-        .constrain_to(view_bounds_in_ui)
-        .order(ui.layer_id().order)
-        .kind(UiKind::GenericArea)
-        .show(ui.ctx(), |ui| {
-            // Transform to the scene space:
-            let visible_rect_in_scene = ui_from_scene.inverse() * view_bounds_in_ui;
-
-            // set proper clip-rect so we can interact with the background.
-            ui.set_clip_rect(visible_rect_in_scene);
-
-            // A Ui for sensing drag-to-pan, scroll-to-zoom, etc
-            let mut drag_sense_ui = ui.new_child(
-                egui::UiBuilder::new()
-                    .sense(egui::Sense::click_and_drag())
-                    .max_rect(visible_rect_in_scene),
-            );
-
-            drag_sense_ui.set_min_size(visible_rect_in_scene.size());
-            let pan_response = drag_sense_ui.response();
-
-            // Update the transform based on the interactions:
-            register_pan_and_zoom(ui, &pan_response, ui_from_scene);
-
-            // Update the clip-rect with the new transform, to avoid frame-delays
-            ui.set_clip_rect(ui_from_scene.inverse() * view_bounds_in_ui);
-
-            // Add the actual contents to the area:
-            draw_contents(ui);
-            pan_response
-        });
-
-    ui.ctx()
-        .set_transform_layer(area_resp.response.layer_id, *ui_from_scene);
-
-    area_resp.inner
+    // Create a new egui paint layer, where we can draw our contents:
+    let zoom_pan_layer_id = egui::LayerId::new(
+        parent_ui.layer_id().order,
+        parent_ui.id().with("zoom_pan_area"),
+    );
+
+    // Put the layer directly on-top of the main layer of the ui:
+    parent_ui
+        .ctx()
+        .set_sublayer(parent_ui.layer_id(), zoom_pan_layer_id);
+
+    let global_view_bounds = parent_ui.max_rect();
+
+    let mut local_ui = parent_ui.new_child(
+        UiBuilder::new()
+            .layer_id(zoom_pan_layer_id)
+            .max_rect(to_global.inverse() * global_view_bounds)
+            .sense(egui::Sense::click_and_drag()),
+    );
+    local_ui.set_min_size(local_ui.max_rect().size()); // Allocate all available space
+
+    // Set proper clip-rect so we can interact with the background:
+    local_ui.set_clip_rect(local_ui.max_rect());
+
+    let pan_response = local_ui.response();
+
+    // Update the `to_global` transform based on use interaction:
+    register_pan_and_zoom(&local_ui, &pan_response, to_global);
+
+    // Update the clip-rect with the new transform, to avoid frame-delays
+    local_ui.set_clip_rect(to_global.inverse() * global_view_bounds);
+
+    // Add the actual contents to the area:
+    draw_contents(&mut local_ui);
+
+    // Tell egui to apply the transform on the layer:
+    local_ui
+        .ctx()
+        .set_transform_layer(zoom_pan_layer_id, *to_global);
+
+    pan_response
 }
diff --git a/crates/viewer/re_view_graph/src/view.rs b/crates/viewer/re_view_graph/src/view.rs
index 581dd8bdcec9..edb59eceb27d 100644
--- a/crates/viewer/re_view_graph/src/view.rs
+++ b/crates/viewer/re_view_graph/src/view.rs
@@ -190,7 +190,7 @@ Display a graph of nodes and edges.
         // 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, &mut ui_from_world, |ui| {
+        let resp = zoom_pan_area(ui, &mut ui_from_world, |ui| {
             let mut world_bounding_rect = egui::Rect::NOTHING;
 
             for graph in &graphs {