Add a method to set the interact distance on the Plot

Closes emilk#4519

crates/egui_demo_lib/src/demo/plot_demo.rs

@@ -133,6 +133,7 @@ struct LineDemo {
     show_axes: bool,
     show_grid: bool,
     line_style: LineStyle,
+    interact_distance: f32,
 }
 
 impl Default for LineDemo {
@@ -148,6 +149,7 @@ impl Default for LineDemo {
             show_axes: true,
             show_grid: true,
             line_style: LineStyle::Solid,
+            interact_distance: 16.0,
         }
     }
 }
@@ -165,6 +167,7 @@ impl LineDemo {
             show_axes,
             show_grid,
             line_style,
+            interact_distance,
         } = self;
 
         ui.horizontal(|ui| {
@@ -197,6 +200,10 @@ impl LineDemo {
                 ui.checkbox(show_grid, "Show grid");
                 ui.checkbox(coordinates, "Show coordinates on hover")
                     .on_hover_text("Can take a custom formatting function.");
+                ui.horizontal(|ui| {
+                    ui.add(egui::DragValue::new(interact_distance).clamp_range(0.0..=100.0));
+                    ui.label("Interact distance");
+                });
             });
 
             ui.vertical(|ui| {
@@ -278,6 +285,7 @@ impl LineDemo {
         let mut plot = Plot::new("lines_demo")
             .legend(Legend::default())
             .y_axis_width(4)
+            .interact_distance(self.interact_distance)
             .show_axes(self.show_axes)
             .show_grid(self.show_grid);
         if self.square {

crates/egui_plot/src/lib.rs

@@ -170,6 +170,7 @@ pub struct Plot<'a> {
 
     show_x: bool,
     show_y: bool,
+    interact_distance: f32,
     label_formatter: LabelFormatter<'a>,
     coordinates_formatter: Option<(Corner, CoordinatesFormatter<'a>)>,
     x_axes: Vec<AxisHints<'a>>, // default x axes
@@ -217,6 +218,7 @@ impl<'a> Plot<'a> {
 
             show_x: true,
             show_y: true,
+            interact_distance: 16.0,
             label_formatter: None,
             coordinates_formatter: None,
             x_axes: vec![AxisHints::new(Axis::X)],
@@ -382,6 +384,17 @@ impl<'a> Plot<'a> {
         self
     }
 
+    /// The snapping distance for hovering an item or plot point
+    ///
+    /// The cursor will snap to the closest item to the pointer if it is closer than this value.
+    ///
+    /// Default: `16.0`
+    #[inline]
+    pub fn interact_distance(mut self, distance: f32) -> Self {
+        self.interact_distance = distance;
+        self
+    }
+
     /// Provide a function to customize the on-hover label for the x and y axis
     ///
     /// ```
@@ -751,6 +764,7 @@ impl<'a> Plot<'a> {
             view_aspect,
             mut show_x,
             mut show_y,
+            interact_distance,
             label_formatter,
             coordinates_formatter,
             x_axes,
@@ -1173,6 +1187,7 @@ impl<'a> Plot<'a> {
             items,
             show_x,
             show_y,
+            interact_distance,
             label_formatter,
             coordinates_formatter,
             show_grid,
@@ -1455,6 +1470,7 @@ struct PreparedPlot<'a> {
     items: Vec<Box<dyn PlotItem>>,
     show_x: bool,
     show_y: bool,
+    interact_distance: f32,
     label_formatter: LabelFormatter<'a>,
     coordinates_formatter: Option<(Corner, CoordinatesFormatter<'a>)>,
     // axis_formatters: [AxisFormatter; 2],
@@ -1666,7 +1682,7 @@ impl<'a> PreparedPlot<'a> {
             return (Vec::new(), None);
         }
 
-        let interact_radius_sq = (16.0_f32).powi(2);
+        let interact_radius_sq = self.interact_distance.powi(2);
 
         let candidates = items
             .iter()