From 388c8aae45f024a00d473fd90ba92043c7fd6e1c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jochen=20G=C3=B6rtler?= <grtlr@users.noreply.github.com>
Date: Wed, 11 Dec 2024 15:32:24 +0100
Subject: [PATCH] Partial revert #8390: removal of `Area` in `zoom_pan_area`
 (#8416)

### Related

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* Closes #1234
* Part of #1337
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* #8390 (partial revert)

### What

We encountered some problems with this implementation.

Discussion:
https://rerunio.slack.com/archives/C04MTSM2U91/p1733921898485069

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---
 crates/viewer/re_ui/src/zoom_pan_area.rs | 67 +++++++++++++-----------
 1 file changed, 35 insertions(+), 32 deletions(-)

diff --git a/crates/viewer/re_ui/src/zoom_pan_area.rs b/crates/viewer/re_ui/src/zoom_pan_area.rs
index 9dac80ce4130..46020aa15c34 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, Rect, Response, Ui, UiBuilder};
+use egui::{emath::TSTransform, Area, Rect, Response, Ui, UiKind};
 
 /// 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) {
@@ -58,42 +58,45 @@ 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.
 pub fn zoom_pan_area(
-    ui: &mut Ui,
+    ui: &Ui,
     view_bounds_in_ui: Rect,
     ui_from_scene: &mut TSTransform,
     draw_contents: impl FnOnce(&mut Ui),
 ) -> Response {
-    let zoom_pan_layer_id = egui::LayerId::new(ui.layer_id().order, ui.id().with("zoom_pan_area"));
-
-    // Put the layer directly on-top of the main layer of the ui:
-    ui.ctx().set_sublayer(ui.layer_id(), zoom_pan_layer_id);
-
-    let mut ui = ui.new_child(
-        UiBuilder::new()
-            .layer_id(zoom_pan_layer_id)
-            .max_rect(view_bounds_in_ui)
-            .sense(egui::Sense::click_and_drag()),
-    );
-
-    // 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);
-
-    let pan_response = 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(&mut ui);
+    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(zoom_pan_layer_id, *ui_from_scene);
+        .set_transform_layer(area_resp.response.layer_id, *ui_from_scene);
 
-    pan_response
+    area_resp.inner
 }