Don't hover things in 2D/3D views if we are dragging something (#1643)

Closes #1185

…and unlike previous attempts, click-to-select still works

crates/re_ui/src/egui_helpers.rs

@@ -0,0 +1,19 @@
+/// Is anything in egui being dragged?
+pub fn is_anything_being_dragged(egui_ctx: &egui::Context) -> bool {
+    // As soon as a button is down, egui considers it a drag.
+    // That is, even a click is considered a drag until it is over.
+    // So we need some special treatment here.
+    // TODO(emilk): make it easier to distinguish between clicks and drags in egui.
+
+    // copied from egui
+    /// If the pointer is down for longer than this, it won't become a click (but it is still a drag)
+    const MAX_CLICK_DURATION: f64 = 0.6;
+    egui_ctx.input(|i| {
+        if let Some(press_start_time) = i.pointer.press_start_time() {
+            let held_time = i.time - press_start_time;
+            held_time > MAX_CLICK_DURATION || i.pointer.is_moving()
+        } else {
+            false
+        }
+    })
+}

crates/re_ui/src/lib.rs

@@ -3,6 +3,7 @@
 mod command;
 mod command_palette;
 mod design_tokens;
+pub mod egui_helpers;
 pub mod icons;
 mod static_image_cache;
 pub mod toasts;

crates/re_viewer/src/ui/view_spatial/ui_2d.rs

@@ -314,9 +314,11 @@ fn view_2d_scrollable(
         highlights,
     );
 
+    let should_do_hovering = !re_ui::egui_helpers::is_anything_being_dragged(parent_ui.ctx());
+
     // Check if we're hovering any hover primitive.
     let mut depth_at_pointer = None;
-    if let Some(pointer_pos_ui) = response.hover_pos() {
+    if let (true, Some(pointer_pos_ui)) = (should_do_hovering, response.hover_pos()) {
         let pointer_pos_space = space_from_ui.transform_pos(pointer_pos_ui);
         let hover_radius = space_from_ui.scale().y * 5.0; // TODO(emilk): from egui?
         let picking_result = scene.picking(

crates/re_viewer/src/ui/view_spatial/ui_3d.rs

@@ -312,9 +312,11 @@ pub fn view_3d(
         highlights,
     );
 
+    let should_do_hovering = !re_ui::egui_helpers::is_anything_being_dragged(ui.ctx());
+
     // TODO(andreas): We're very close making the hover reaction of ui2d and ui3d the same. Finish the job!
     // Check if we're hovering any hover primitive.
-    if let Some(pointer_pos) = response.hover_pos() {
+    if let (true, Some(pointer_pos)) = (should_do_hovering, response.hover_pos()) {
         let picking_result =
             scene.picking(glam::vec2(pointer_pos.x, pointer_pos.y), &rect, &eye, 5.0);