From 0f103c99df587ce7472e09b5ef999954c1cf939d Mon Sep 17 00:00:00 2001
From: Andreas Reich <r_andreas2@web.de>
Date: Wed, 29 Nov 2023 19:04:22 +0100
Subject: [PATCH] improve time panel time_ctrl overwrite behavior

---
 crates/re_time_panel/src/lib.rs              | 20 +++++++++++++-------
 crates/re_viewer_context/src/time_control.rs |  6 +++---
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/crates/re_time_panel/src/lib.rs b/crates/re_time_panel/src/lib.rs
index 77ec5263f7ae..d96b8a97b898 100644
--- a/crates/re_time_panel/src/lib.rs
+++ b/crates/re_time_panel/src/lib.rs
@@ -67,8 +67,9 @@ impl TimePanel {
         time_panel_expanded: bool,
     ) {
         // Naturally, many parts of the time panel need the time control.
-        // Copy it once, read/edit, and then write back at the end.
-        let mut time_ctrl = ctx.rec_cfg.time_ctrl.read().clone();
+        // Copy it once, read/edit, and then write back at the end if there was a change.
+        let time_ctrl_before = ctx.rec_cfg.time_ctrl.read().clone();
+        let mut time_ctrl_after = time_ctrl_before.clone();
 
         // this is the size of everything above the central panel (window title bar, top bar on web,
         // etc.)
@@ -115,7 +116,7 @@ impl TimePanel {
                     ui.horizontal(|ui| {
                         ui.spacing_mut().interact_size = Vec2::splat(top_bar_height);
                         ui.visuals_mut().button_frame = true;
-                        self.collapsed_ui(ctx, ui, &mut time_ctrl);
+                        self.collapsed_ui(ctx, ui, &mut time_ctrl_after);
                     });
                 } else {
                     // Expanded:
@@ -129,7 +130,7 @@ impl TimePanel {
                                 ui.horizontal(|ui| {
                                     ui.spacing_mut().interact_size = Vec2::splat(top_bar_height);
                                     ui.visuals_mut().button_frame = true;
-                                    self.top_row_ui(ctx, ui, &mut time_ctrl);
+                                    self.top_row_ui(ctx, ui, &mut time_ctrl_after);
                                 });
                             })
                             .response
@@ -148,15 +149,20 @@ impl TimePanel {
                         let mut streams_frame = egui::Frame::default();
                         streams_frame.inner_margin.left = margin.x;
                         streams_frame.show(ui, |ui| {
-                            self.expanded_ui(ctx, ui, &mut time_ctrl);
+                            self.expanded_ui(ctx, ui, &mut time_ctrl_after);
                         });
                     });
                 }
             },
         );
 
-        // Apply potential changes of the time control:
-        *ctx.rec_cfg.time_ctrl.write() = time_ctrl;
+        // Apply time control if there were any changes.
+        // This means that if anyone else meanwhile changed the time control, these changes are lost now.
+        // At least though we don't overwrite them if we didn't change anything at all.
+        // Since changes on the time control via the time panel are rare, this should be fine.
+        if time_ctrl_before != time_ctrl_after {
+            *ctx.rec_cfg.time_ctrl.write() = time_ctrl_after;
+        }
     }
 
     #[allow(clippy::unused_self)]
diff --git a/crates/re_viewer_context/src/time_control.rs b/crates/re_viewer_context/src/time_control.rs
index 302266dae9e7..1ffa239cd95b 100644
--- a/crates/re_viewer_context/src/time_control.rs
+++ b/crates/re_viewer_context/src/time_control.rs
@@ -6,7 +6,7 @@ use re_log_types::{Duration, TimeInt, TimeRange, TimeRangeF, TimeReal, TimeType,
 use crate::NeedsRepaint;
 
 /// The time range we are currently zoomed in on.
-#[derive(Clone, Copy, Debug, serde::Deserialize, serde::Serialize)]
+#[derive(Clone, Copy, Debug, serde::Deserialize, serde::Serialize, PartialEq)]
 pub struct TimeView {
     /// Where start of the range.
     pub min: TimeReal,
@@ -20,7 +20,7 @@ pub struct TimeView {
 }
 
 /// State per timeline.
-#[derive(Clone, Copy, Debug, serde::Deserialize, serde::Serialize)]
+#[derive(Clone, Copy, Debug, serde::Deserialize, serde::Serialize, PartialEq)]
 struct TimeState {
     /// The current time (play marker).
     time: TimeReal,
@@ -79,7 +79,7 @@ pub enum PlayState {
 }
 
 /// Controls the global view and progress of the time.
-#[derive(serde::Deserialize, serde::Serialize, Clone)]
+#[derive(serde::Deserialize, serde::Serialize, Clone, PartialEq)]
 #[serde(default)]
 pub struct TimeControl {
     /// Name of the timeline (e.g. "log_time").