Improve choice of number of decimals to show when hovering in plot

CHANGELOG.md

@@ -14,6 +14,7 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 
 ### Changed 🔧
 * Improved plot grid appearance ([#2412](https://github.com/emilk/egui/pull/2412)).
+* Improved the algorithm for picking the number of decimals to show when hovering values in the `Plot`.
 
 ### Fixed 🐛
 * Expose `TextEdit`'s multiline flag to AccessKit ([#2448](https://github.com/emilk/egui/pull/2448)).

crates/egui/src/widgets/plot/items/bar.rs

@@ -185,7 +185,11 @@ impl RectElement for Bar {
 
     fn default_values_format(&self, transform: &ScreenTransform) -> String {
         let scale = transform.dvalue_dpos();
-        let y_decimals = ((-scale[1].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+        let scale = match self.orientation {
-        format!("\n{:.*}", y_decimals, self.value)
+            Orientation::Horizontal => scale[0],
+            Orientation::Vertical => scale[1],
+        };
+        let decimals = ((-scale.abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+        crate::plot::format_number(self.value, decimals)
     }
 }

crates/egui/src/widgets/plot/items/box_elem.rs

@@ -269,9 +269,15 @@ impl RectElement for BoxElem {
 
     fn default_values_format(&self, transform: &ScreenTransform) -> String {
         let scale = transform.dvalue_dpos();
-        let y_decimals = ((-scale[1].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+        let scale = match self.orientation {
+            Orientation::Horizontal => scale[0],
+            Orientation::Vertical => scale[1],
+        };
+        let y_decimals = ((-scale.abs().log10()).ceil().at_least(0.0) as usize)
+            .at_most(6)
+            .at_least(1);
         format!(
-            "\nMax = {max:.decimals$}\
+            "Max = {max:.decimals$}\
              \nQuartile 3 = {q3:.decimals$}\
              \nMedian = {med:.decimals$}\
              \nQuartile 1 = {q1:.decimals$}\

crates/egui/src/widgets/plot/items/mod.rs

@@ -1648,6 +1648,7 @@ fn add_rulers_and_text(
         let mut text = elem.name().to_owned(); // could be empty
 
         if show_values {
+            text.push('\n');
             text.push_str(&elem.default_values_format(plot.transform));
         }
 
@@ -1694,8 +1695,8 @@ pub(super) fn rulers_at_value(
 
     let text = {
         let scale = plot.transform.dvalue_dpos();
-        let x_decimals = ((-scale[0].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+        let x_decimals = ((-scale[0].abs().log10()).ceil().at_least(0.0) as usize).clamp(1, 6);
-        let y_decimals = ((-scale[1].abs().log10()).ceil().at_least(0.0) as usize).at_most(6);
+        let y_decimals = ((-scale[1].abs().log10()).ceil().at_least(0.0) as usize).clamp(1, 6);
         if let Some(custom_label) = label_formatter {
             custom_label(name, &value)
         } else if plot.show_x && plot.show_y {

crates/egui/src/widgets/plot/mod.rs

@@ -1647,3 +1647,16 @@ fn fill_marks_between(out: &mut Vec<GridMark>, step_size: f64, (min, max): (f64,
     });
     out.extend(marks_iter);
 }
+
+/// Helper for formatting a number so that we always show at least a few decimals,
+/// unless it is an integer, in which case we never show any decimals.
+pub fn format_number(number: f64, num_decimals: usize) -> String {
+    let is_integral = number as i64 as f64 == number;
+    if is_integral {
+        // perfect integer - show it as such:
+        format!("{:.0}", number)
+    } else {
+        // make sure we tell the user it is not an integer by always showing a decimal or two:
+        format!("{:.*}", num_decimals.at_least(1), number)
+    }
+}

crates/egui_demo_lib/src/demo/plot_demo.rs

@@ -11,6 +11,124 @@ use plot::{
 
 // ----------------------------------------------------------------------------
 
+#[derive(PartialEq, Eq)]
+enum Panel {
+    Lines,
+    Markers,
+    Legend,
+    Charts,
+    Items,
+    Interaction,
+    CustomAxes,
+    LinkedAxes,
+}
+
+impl Default for Panel {
+    fn default() -> Self {
+        Self::Lines
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+#[derive(PartialEq, Default)]
+pub struct PlotDemo {
+    line_demo: LineDemo,
+    marker_demo: MarkerDemo,
+    legend_demo: LegendDemo,
+    charts_demo: ChartsDemo,
+    items_demo: ItemsDemo,
+    interaction_demo: InteractionDemo,
+    custom_axes_demo: CustomAxisDemo,
+    linked_axes_demo: LinkedAxisDemo,
+    open_panel: Panel,
+}
+
+impl super::Demo for PlotDemo {
+    fn name(&self) -> &'static str {
+        "🗠 Plot"
+    }
+
+    fn show(&mut self, ctx: &Context, open: &mut bool) {
+        use super::View as _;
+        Window::new(self.name())
+            .open(open)
+            .default_size(vec2(400.0, 400.0))
+            .vscroll(false)
+            .show(ctx, |ui| self.ui(ui));
+    }
+}
+
+impl super::View for PlotDemo {
+    fn ui(&mut self, ui: &mut Ui) {
+        ui.horizontal(|ui| {
+            egui::reset_button(ui, self);
+            ui.collapsing("Instructions", |ui| {
+                ui.label("Pan by dragging, or scroll (+ shift = horizontal).");
+                ui.label("Box zooming: Right click to zoom in and zoom out using a selection.");
+                if cfg!(target_arch = "wasm32") {
+                    ui.label("Zoom with ctrl / ⌘ + pointer wheel, or with pinch gesture.");
+                } else if cfg!(target_os = "macos") {
+                    ui.label("Zoom with ctrl / ⌘ + scroll.");
+                } else {
+                    ui.label("Zoom with ctrl + scroll.");
+                }
+                ui.label("Reset view with double-click.");
+                ui.add(crate::egui_github_link_file!());
+            });
+        });
+        ui.separator();
+        ui.horizontal(|ui| {
+            ui.selectable_value(&mut self.open_panel, Panel::Lines, "Lines");
+            ui.selectable_value(&mut self.open_panel, Panel::Markers, "Markers");
+            ui.selectable_value(&mut self.open_panel, Panel::Legend, "Legend");
+            ui.selectable_value(&mut self.open_panel, Panel::Charts, "Charts");
+            ui.selectable_value(&mut self.open_panel, Panel::Items, "Items");
+            ui.selectable_value(&mut self.open_panel, Panel::Interaction, "Interaction");
+            ui.selectable_value(&mut self.open_panel, Panel::CustomAxes, "Custom Axes");
+            ui.selectable_value(&mut self.open_panel, Panel::LinkedAxes, "Linked Axes");
+        });
+        ui.separator();
+
+        match self.open_panel {
+            Panel::Lines => {
+                self.line_demo.ui(ui);
+            }
+            Panel::Markers => {
+                self.marker_demo.ui(ui);
+            }
+            Panel::Legend => {
+                self.legend_demo.ui(ui);
+            }
+            Panel::Charts => {
+                self.charts_demo.ui(ui);
+            }
+            Panel::Items => {
+                self.items_demo.ui(ui);
+            }
+            Panel::Interaction => {
+                self.interaction_demo.ui(ui);
+            }
+            Panel::CustomAxes => {
+                self.custom_axes_demo.ui(ui);
+            }
+            Panel::LinkedAxes => {
+                self.linked_axes_demo.ui(ui);
+            }
+        }
+    }
+}
+
+fn is_approx_zero(val: f64) -> bool {
+    val.abs() < 1e-6
+}
+
+fn is_approx_integer(val: f64) -> bool {
+    val.fract().abs() < 1e-6
+}
+
+// ----------------------------------------------------------------------------
+
 #[derive(PartialEq)]
 struct LineDemo {
     animate: bool,
@@ -754,7 +872,6 @@ impl ChartsDemo {
 
         Plot::new("Normal Distribution Demo")
             .legend(Legend::default())
-            .data_aspect(1.0)
             .clamp_grid(true)
             .show(ui, |plot_ui| plot_ui.bar_chart(chart))
             .response
@@ -865,121 +982,3 @@ impl ChartsDemo {
             .response
     }
 }
-
-// ----------------------------------------------------------------------------
-
-#[derive(PartialEq, Eq)]
-enum Panel {
-    Lines,
-    Markers,
-    Legend,
-    Charts,
-    Items,
-    Interaction,
-    CustomAxes,
-    LinkedAxes,
-}
-
-impl Default for Panel {
-    fn default() -> Self {
-        Self::Lines
-    }
-}
-
-// ----------------------------------------------------------------------------
-
-#[derive(PartialEq, Default)]
-pub struct PlotDemo {
-    line_demo: LineDemo,
-    marker_demo: MarkerDemo,
-    legend_demo: LegendDemo,
-    charts_demo: ChartsDemo,
-    items_demo: ItemsDemo,
-    interaction_demo: InteractionDemo,
-    custom_axes_demo: CustomAxisDemo,
-    linked_axes_demo: LinkedAxisDemo,
-    open_panel: Panel,
-}
-
-impl super::Demo for PlotDemo {
-    fn name(&self) -> &'static str {
-        "🗠 Plot"
-    }
-
-    fn show(&mut self, ctx: &Context, open: &mut bool) {
-        use super::View as _;
-        Window::new(self.name())
-            .open(open)
-            .default_size(vec2(400.0, 400.0))
-            .vscroll(false)
-            .show(ctx, |ui| self.ui(ui));
-    }
-}
-
-impl super::View for PlotDemo {
-    fn ui(&mut self, ui: &mut Ui) {
-        ui.horizontal(|ui| {
-            egui::reset_button(ui, self);
-            ui.collapsing("Instructions", |ui| {
-                ui.label("Pan by dragging, or scroll (+ shift = horizontal).");
-                ui.label("Box zooming: Right click to zoom in and zoom out using a selection.");
-                if cfg!(target_arch = "wasm32") {
-                    ui.label("Zoom with ctrl / ⌘ + pointer wheel, or with pinch gesture.");
-                } else if cfg!(target_os = "macos") {
-                    ui.label("Zoom with ctrl / ⌘ + scroll.");
-                } else {
-                    ui.label("Zoom with ctrl + scroll.");
-                }
-                ui.label("Reset view with double-click.");
-                ui.add(crate::egui_github_link_file!());
-            });
-        });
-        ui.separator();
-        ui.horizontal(|ui| {
-            ui.selectable_value(&mut self.open_panel, Panel::Lines, "Lines");
-            ui.selectable_value(&mut self.open_panel, Panel::Markers, "Markers");
-            ui.selectable_value(&mut self.open_panel, Panel::Legend, "Legend");
-            ui.selectable_value(&mut self.open_panel, Panel::Charts, "Charts");
-            ui.selectable_value(&mut self.open_panel, Panel::Items, "Items");
-            ui.selectable_value(&mut self.open_panel, Panel::Interaction, "Interaction");
-            ui.selectable_value(&mut self.open_panel, Panel::CustomAxes, "Custom Axes");
-            ui.selectable_value(&mut self.open_panel, Panel::LinkedAxes, "Linked Axes");
-        });
-        ui.separator();
-
-        match self.open_panel {
-            Panel::Lines => {
-                self.line_demo.ui(ui);
-            }
-            Panel::Markers => {
-                self.marker_demo.ui(ui);
-            }
-            Panel::Legend => {
-                self.legend_demo.ui(ui);
-            }
-            Panel::Charts => {
-                self.charts_demo.ui(ui);
-            }
-            Panel::Items => {
-                self.items_demo.ui(ui);
-            }
-            Panel::Interaction => {
-                self.interaction_demo.ui(ui);
-            }
-            Panel::CustomAxes => {
-                self.custom_axes_demo.ui(ui);
-            }
-            Panel::LinkedAxes => {
-                self.linked_axes_demo.ui(ui);
-            }
-        }
-    }
-}
-
-fn is_approx_zero(val: f64) -> bool {
-    val.abs() < 1e-6
-}
-
-fn is_approx_integer(val: f64) -> bool {
-    val.fract().abs() < 1e-6
-}