plot-axis: Expose more conveniece functions to public API. Add axis labels to demo app

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

@@ -43,7 +43,7 @@ pub(super) type YAxisWidget = AxisWidget<Y_AXIS>;
 pub struct AxisHints<const AXIS: usize> {
     pub(super) label: WidgetText,
     pub(super) formatter: AxisFormatterFn,
-    digits: usize,
+    pub(super) digits: usize,
     pub(super) placement: Placement,
 }
 
@@ -104,8 +104,7 @@ impl<const AXIS: usize> AxisHints<AXIS> {
 
     /// Specify maximum number of digits for ticks.
     ///
-    /// This is considered by the default tick formatter
-    /// and affects the width of the internal y-axis widget
+    /// This is considered by the default tick formatter and affects the width of the y-axis
     pub fn max_digits(mut self, digits: usize) -> Self {
         self.digits = digits;
         self

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

@@ -565,22 +565,32 @@ impl Plot {
         self
     }
 
-    /// Set the x axis label of the bottom x-axis
+    /// Set the x axis label of the main x-axis
+    ///
+    /// If no x-axis has been specified so far a new one will be created.
     pub fn x_axis_label(mut self, label: impl Into<WidgetText>) -> Self {
-        if !self.x_axes.is_empty() {
+        if self.x_axes.is_empty() {
+            self.x_axes.push(XAxisHints::default().label(label))
+        } else {
             self.x_axes[0].label = label.into();
         }
         self
     }
-    /// Set the y axis label of the left y-axis
+    /// Set the y axis label of the main y-axis
+    ///
+    /// If no y-axis has been specified so far a new one will be created.
     pub fn y_axis_label(mut self, label: impl Into<WidgetText>) -> Self {
-        if !self.y_axes.is_empty() {
+        if self.y_axes.is_empty() {
+            self.y_axes.push(YAxisHints::default().label(label))
+        } else {
             self.y_axes[0].label = label.into();
         }
         self
     }
 
-    /// Set the x-axis position
+    /// Set the position of the main x-axis
+    ///
+    /// > Note: This requires an x-axis to exist, either by [`Self::custom_x_axes`] or [`Self::x_axis_label`]
     pub fn x_axis_position(mut self, placement: axis::Placement) -> Self {
         if !self.x_axes.is_empty() {
             self.x_axes[0].placement = placement;
@@ -588,7 +598,9 @@ impl Plot {
         self
     }
 
-    /// Set the y-axis position
+    /// Set the position of the main y-axis
+    ///
+    /// > Note: This requires a y-axis to exist, either by [`Self::custom_y_axes`] or [`Self::y_axis_label`]
     pub fn y_axis_position(mut self, placement: axis::Placement) -> Self {
         if !self.y_axes.is_empty() {
             self.y_axes[0].placement = placement;
@@ -596,7 +608,9 @@ impl Plot {
         self
     }
 
-    /// Specify custom formatter for ticks on x-axis
+    /// Specify custom formatter for ticks on the main x-axis
+    ///
+    /// > Note: This requires an x-axis to exist, either by [`Self::custom_x_axes`] or [`Self::x_axis_label`]
     ///
     /// The first parameter of `fmt` is the raw tick value as `f64`.
     /// The second paramter is the maximum requested number of characters per tick label.
@@ -608,7 +622,9 @@ impl Plot {
         self
     }
 
-    /// Specify custom formatter for ticks on y-axis
+    /// Specify custom formatter for ticks on the main y-axis
+    ///
+    /// > Note: This requires a y-axis to exist, either by [`Self::custom_y_axes`] or [`Self::y_axis_label`]
     ///
     /// The first parameter of `formatter` is the raw tick value as `f64`.
     /// The second paramter is the maximum requested number of characters per tick label.
@@ -620,9 +636,23 @@ impl Plot {
         self
     }
 
+    /// Set the main y-axis-width by number of digits
+    ///
+    /// The default is 5 digits.
+    ///
+    /// > Note: This requires a y-axis to exist, either by [`Self::custom_y_axes`] or [`Self::y_axis_label`]
+    ///
+    /// > Todo: This is experimental. Changing the font size might break this.
+    pub fn y_axis_width(mut self, digits: usize) -> Self {
+        if !self.y_axes.is_empty() {
+            self.y_axes[0].digits = digits;
+        }
+        self
+    }
+
     /// Set custom configuration for bottom x-axis
     ///
-    /// More than one axis may be specified.
+    /// More than one axis may be specified. The first specified axis is considered the main axis.
     pub fn custom_x_axes(mut self, hints: Vec<XAxisHints>) -> Self {
         self.x_axes = hints;
         self
@@ -630,7 +660,7 @@ impl Plot {
 
     /// Set custom configuration for left y-axis
     ///
-    /// More than one axis may be specified.
+    /// More than one axis may be specified. The first specified axis is considered the main axis.
     pub fn custom_y_axes(mut self, hints: Vec<YAxisHints>) -> Self {
         self.y_axes = hints;
         self

crates/egui_demo_lib/src/demo/plot_demo.rs

@@ -264,7 +264,11 @@ impl LineDemo {
             ui.ctx().request_repaint();
             self.time += ui.input(|i| i.unstable_dt).at_most(1.0 / 30.0) as f64;
         };
-        let mut plot = Plot::new("lines_demo").legend(Legend::default());
+        let mut plot = Plot::new("lines_demo")
+            .legend(Legend::default())
+            .x_axis_label("")
+            .y_axis_label("")
+            .y_axis_width(4);
         if self.square {
             plot = plot.view_aspect(1.0);
         }
@@ -421,8 +425,10 @@ impl LegendDemo {
             );
             ui.end_row();
         });
-
         let legend_plot = Plot::new("legend_demo")
+            .x_axis_label("")
+            .y_axis_label("")
+            .y_axis_width(2)
             .legend(config.clone())
             .data_aspect(1.0);
         legend_plot
@@ -550,18 +556,16 @@ impl CustomAxisDemo {
         ui.label("Zoom in on the X-axis to see hours and minutes");
 
         let x_axes = vec![
-            XAxisHints::default()
-                .label("Time".to_owned())
-                .formatter(x_fmt),
-            XAxisHints::default().label("Value".to_owned()),
+            XAxisHints::default().label("Time").formatter(x_fmt),
+            XAxisHints::default().label("Value"),
         ];
         let y_axes = vec![
             YAxisHints::default()
-                .label("Percent".to_owned())
+                .label("Percent")
                 .formatter(y_fmt)
                 .max_digits(4),
             YAxisHints::default()
-                .label("Absolute".to_owned())
+                .label("Absolute")
                 .placement(Placement::Opposite),
         ];
         Plot::new("custom_axes")
@@ -660,6 +664,9 @@ impl LinkedAxisDemo {
                 .data_aspect(2.0)
                 .width(150.0)
                 .height(250.0)
+                .y_axis_label("y")
+                .y_axis_position(Placement::Opposite)
+                .y_axis_width(3)
                 .link_axis(link_group_id, self.link_x, self.link_y)
                 .link_cursor(link_group_id, self.link_cursor_x, self.link_cursor_y)
                 .show(ui, LinkedAxisDemo::configure_plot);
@@ -668,6 +675,7 @@ impl LinkedAxisDemo {
             .data_aspect(0.5)
             .width(250.0)
             .height(150.0)
+            .x_axis_label("x")
             .link_axis(link_group_id, self.link_x, self.link_y)
             .link_cursor(link_group_id, self.link_cursor_x, self.link_cursor_y)
             .show(ui, LinkedAxisDemo::configure_plot)
@@ -899,6 +907,9 @@ impl ChartsDemo {
         Plot::new("Normal Distribution Demo")
             .legend(Legend::default())
             .clamp_grid(true)
+            .x_axis_label("")
+            .y_axis_label("")
+            .y_axis_width(3)
             .allow_zoom(self.allow_zoom)
             .allow_drag(self.allow_drag)
             .show(ui, |plot_ui| plot_ui.bar_chart(chart))