Unify the time formatting between the time panel and the plot (#1369)

* Unify the time formatting between the time panel and the plot

* typo

* Add a link explaining how leap-seconds work in UTC

crates/re_log_types/src/time.rs

@@ -44,6 +44,32 @@ impl Time {
         20 <= years_since_epoch && years_since_epoch <= 150
     }
 
+    /// Returns the absolute datetime, if this is a valid, unambiguous, absolute time.
+    pub fn to_chrono(&self) -> Option<chrono::DateTime<chrono::Utc>> {
+        let ns_since_epoch = self.nanos_since_epoch();
+        if self.is_abolute_date() {
+            use chrono::TimeZone as _;
+            if let chrono::LocalResult::Single(datetime) = chrono::Utc.timestamp_opt(
+                ns_since_epoch / 1_000_000_000,
+                (ns_since_epoch % 1_000_000_000) as _,
+            ) {
+                Some(datetime)
+            } else {
+                None
+            }
+        } else {
+            None
+        }
+    }
+
+    pub fn is_exactly_midnight(&self) -> bool {
+        // This is correct despite leap seconds because
+        // during positive leap seconds, UTC actually has a discontinuity
+        // (the same integer is reused for two different times).
+        // See https://en.wikipedia.org/wiki/Unix_time#Leap_seconds
+        self.nanos_since_epoch() % (24 * 60 * 60 * 1_000_000_000) == 0
+    }
+
     /// Human-readable formatting
     pub fn format(&self) -> String {
         let nanos_since_epoch = self.nanos_since_epoch();

crates/re_viewer/src/misc/format_time.rs

@@ -0,0 +1,72 @@
+/// Useful when showing dates/times on a timeline
+/// and you want it compact.
+///
+/// Shows dates when zoomed out, shows times when zoomed in,
+/// shows relative millisecond when really zoomed in.
+pub fn format_time_compact(time: re_log_types::Time) -> String {
+    let ns = time.nanos_since_epoch();
+    let relative_ns = ns % 1_000_000_000;
+    let is_whole_second = relative_ns == 0;
+    if is_whole_second {
+        if let Some(datetime) = time.to_chrono() {
+            return if time.is_exactly_midnight() {
+                // Show just the date:
+                datetime.format("%Y-%m-%dZ").to_string()
+            } else {
+                // Show just the time:
+                let is_whole_minute = ns % 60_000_000_000 == 0;
+                let is_whole_second = ns % 1_000_000_000 == 0;
+                if is_whole_minute {
+                    datetime.time().format("%H:%MZ").to_string()
+                } else if is_whole_second {
+                    datetime.time().format("%H:%M:%SZ").to_string()
+                } else {
+                    datetime.time().format("%H:%M:%S%.3fZ").to_string()
+                }
+            };
+        }
+
+        re_log_types::Duration::from_nanos(ns).to_string()
+    } else {
+        // We are in the sub-second resolution.
+        // Showing the full time (HH:MM:SS.XXX or 3h 2m 6s …) becomes too long,
+        // so instead we switch to showing the time as milliseconds since the last whole second:
+        let ms = relative_ns as f64 * 1e-6;
+        if relative_ns % 1_000_000 == 0 {
+            format!("{ms:+.0} ms")
+        } else if relative_ns % 100_000 == 0 {
+            format!("{ms:+.1} ms")
+        } else if relative_ns % 10_000 == 0 {
+            format!("{ms:+.2} ms")
+        } else if relative_ns % 1_000 == 0 {
+            format!("{ms:+.3} ms")
+        } else if relative_ns % 100 == 0 {
+            format!("{ms:+.4} ms")
+        } else if relative_ns % 10 == 0 {
+            format!("{ms:+.5} ms")
+        } else {
+            format!("{ms:+.6} ms")
+        }
+    }
+}
+
+/// When showing grid-lines representing time.
+///
+/// Given some spacing (e.g. 10s), return the next spacing (60s).
+pub fn next_grid_tick_magnitude_ns(spacing_ns: i64) -> i64 {
+    if spacing_ns <= 1_000_000_000 {
+        spacing_ns * 10 // up to 10 second ticks
+    } else if spacing_ns == 10_000_000_000 {
+        spacing_ns * 6 // to the whole minute
+    } else if spacing_ns == 60_000_000_000 {
+        spacing_ns * 10 // to ten minutes
+    } else if spacing_ns == 600_000_000_000 {
+        spacing_ns * 6 // to an hour
+    } else if spacing_ns == 60 * 60 * 1_000_000_000 {
+        spacing_ns * 12 // to 12 h
+    } else if spacing_ns == 12 * 60 * 60 * 1_000_000_000 {
+        spacing_ns * 2 // to a day
+    } else {
+        spacing_ns.checked_mul(10).unwrap_or(spacing_ns) // multiple of ten days
+    }
+}

crates/re_viewer/src/misc/mod.rs

@@ -1,6 +1,7 @@
 mod app_options;
 pub mod caches;
 pub mod color_map;
+pub mod format_time;
 mod item;
 pub(crate) mod mesh_loader;
 mod selection_state;

crates/re_viewer/src/ui/time_panel/paint_ticks.rs

@@ -4,6 +4,8 @@ use egui::{lerp, pos2, remap_clamp, Align2, Color32, Rect, Rgba, Shape, Stroke};
 
 use re_log_types::{Time, TimeRangeF, TimeReal, TimeType};
 
+use crate::misc::format_time::next_grid_tick_magnitude_ns;
+
 use super::time_ranges_ui::TimeRangesUi;
 
 pub fn paint_time_ranges_and_ticks(
@@ -59,56 +61,6 @@ fn paint_time_range_ticks(
 
     match time_type {
         TimeType::Time => {
-            fn next_grid_tick_magnitude_ns(spacing_ns: i64) -> i64 {
-                if spacing_ns <= 1_000_000_000 {
-                    spacing_ns * 10 // up to 10 second ticks
-                } else if spacing_ns == 10_000_000_000 {
-                    spacing_ns * 6 // to the whole minute
-                } else if spacing_ns == 60_000_000_000 {
-                    spacing_ns * 10 // to ten minutes
-                } else if spacing_ns == 600_000_000_000 {
-                    spacing_ns * 6 // to an hour
-                } else if spacing_ns == 60 * 60 * 1_000_000_000 {
-                    spacing_ns * 12 // to 12 h
-                } else if spacing_ns == 12 * 60 * 60 * 1_000_000_000 {
-                    spacing_ns * 2 // to a day
-                } else {
-                    spacing_ns.checked_mul(10).unwrap_or(spacing_ns) // multiple of ten days
-                }
-            }
-
-            fn grid_text_from_ns(ns: i64) -> String {
-                let relative_ns = ns % 1_000_000_000;
-                if relative_ns == 0 {
-                    let time = Time::from_ns_since_epoch(ns);
-                    if time.is_abolute_date() {
-                        time.format_time("%H:%M:%S")
-                    } else {
-                        re_log_types::Duration::from_nanos(ns).to_string()
-                    }
-                } else {
-                    // We are in the sub-second resolution.
-                    // Showing the full time (HH:MM:SS.XXX or 3h 2m 6s …) becomes too long,
-                    // so instead we switch to showing the time as milliseconds since the last whole second:
-                    let ms = relative_ns as f64 * 1e-6;
-                    if relative_ns % 1_000_000 == 0 {
-                        format!("{ms:+.0} ms")
-                    } else if relative_ns % 100_000 == 0 {
-                        format!("{ms:+.1} ms")
-                    } else if relative_ns % 10_000 == 0 {
-                        format!("{ms:+.2} ms")
-                    } else if relative_ns % 1_000 == 0 {
-                        format!("{ms:+.3} ms")
-                    } else if relative_ns % 100 == 0 {
-                        format!("{ms:+.4} ms")
-                    } else if relative_ns % 10 == 0 {
-                        format!("{ms:+.5} ms")
-                    } else {
-                        format!("{ms:+.6} ms")
-                    }
-                }
-            }
-
             paint_ticks(
                 ui.ctx(),
                 ui.visuals().dark_mode,
@@ -117,7 +69,7 @@ fn paint_time_range_ticks(
                 &ui.clip_rect(),
                 time_range, // ns
                 next_grid_tick_magnitude_ns,
-                grid_text_from_ns,
+                |ns| crate::misc::format_time::format_time_compact(Time::from_ns_since_epoch(ns)),
             )
         }
         TimeType::Sequence => {

crates/re_viewer/src/ui/view_time_series/ui.rs

@@ -5,7 +5,10 @@ use egui::{
 
 use re_arrow_store::TimeType;
 
-use crate::{ui::view_time_series::scene::PlotSeriesKind, ViewerContext};
+use crate::{
+    misc::format_time::next_grid_tick_magnitude_ns, ui::view_time_series::scene::PlotSeriesKind,
+    ViewerContext,
+};
 
 use super::SceneTimeSeries;
 
@@ -140,72 +143,29 @@ pub(crate) fn view_time_series(
 
 fn format_time(time_type: TimeType, time_int: i64) -> String {
     if time_type == TimeType::Time {
-        let ns_since_epoch = time_int;
-        let time = re_log_types::Time::from_ns_since_epoch(ns_since_epoch);
-        if time.is_abolute_date() {
-            use chrono::TimeZone as _;
-            if let chrono::LocalResult::Single(datetime) = chrono::Utc.timestamp_opt(
-                ns_since_epoch / 1_000_000_000,
-                (ns_since_epoch % 1_000_000_000) as _,
-            ) {
-                let is_start_of_new_day =
-                    datetime.time() == chrono::NaiveTime::from_hms_opt(0, 0, 0).unwrap();
-                if is_start_of_new_day {
-                    // Show just the date:
-                    return datetime.format("%Y-%m-%dZ").to_string();
-                } else {
-                    // Show just the time:
-                    let is_whole_minute = ns_since_epoch % 60_000_000_000 == 0;
-                    let is_whole_second = ns_since_epoch % 1_000_000_000 == 0;
-                    if is_whole_minute {
-                        return datetime.time().format("%H:%MZ").to_string();
-                    } else if is_whole_second {
-                        return datetime.time().format("%H:%M:%SZ").to_string();
-                    } else {
-                        return datetime.time().format("%H:%M:%S%.3fZ").to_string();
-                    }
-                }
-            }
-        }
+        let time = re_log_types::Time::from_ns_since_epoch(time_int);
+        crate::misc::format_time::format_time_compact(time)
+    } else {
+        time_type.format(re_log_types::TimeInt::from(time_int))
     }
-
-    time_type.format(re_log_types::TimeInt::from(time_int))
 }
 
 fn ns_grid_spacer(
     canvas_size: egui::Vec2,
     input: &egui::plot::GridInput,
 ) -> Vec<egui::plot::GridMark> {
-    fn next_time_step(spacing_ns: i64) -> i64 {
-        if spacing_ns <= 1_000_000_000 {
-            spacing_ns * 10 // up to 10 second ticks
-        } else if spacing_ns == 10_000_000_000 {
-            spacing_ns * 6 // to the whole minute
-        } else if spacing_ns == 60_000_000_000 {
-            spacing_ns * 10 // to ten minutes
-        } else if spacing_ns == 600_000_000_000 {
-            spacing_ns * 6 // to an hour
-        } else if spacing_ns == 60 * 60 * 1_000_000_000 {
-            spacing_ns * 12 // to 12 h
-        } else if spacing_ns == 12 * 60 * 60 * 1_000_000_000 {
-            spacing_ns * 2 // to a day
-        } else {
-            spacing_ns.checked_mul(10).unwrap_or(spacing_ns) // multiple of ten days
-        }
-    }
-
     let minimum_medium_line_spacing = 150.0; // ≈min size of a label
     let max_medium_lines = canvas_size.x as f64 / minimum_medium_line_spacing;
 
     let (min_ns, max_ns) = input.bounds;
     let width_ns = max_ns - min_ns;
 
     let mut small_spacing_ns = 1;
-    while width_ns / (next_time_step(small_spacing_ns) as f64) > max_medium_lines {
-        small_spacing_ns = next_time_step(small_spacing_ns);
+    while width_ns / (next_grid_tick_magnitude_ns(small_spacing_ns) as f64) > max_medium_lines {
+        small_spacing_ns = next_grid_tick_magnitude_ns(small_spacing_ns);
     }
-    let medium_spacing_ns = next_time_step(small_spacing_ns);
-    let big_spacing_ns = next_time_step(medium_spacing_ns);
+    let medium_spacing_ns = next_grid_tick_magnitude_ns(small_spacing_ns);
+    let big_spacing_ns = next_grid_tick_magnitude_ns(medium_spacing_ns);
 
     let mut current_ns = (min_ns.floor() as i64) / small_spacing_ns * small_spacing_ns;
     let mut marks = vec![];