Plot items now have optional id which is returned in the plot's response when hovered (#3920)

This allows users to check which item the user interacts with in the
plot.



https://github.com/emilk/egui/assets/1220815/1a174b38-8414-49be-a802-d187cd93d154

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui_demo_lib/src/demo/plot_demo.rs

@@ -791,8 +791,28 @@ impl InteractionDemo {
         let PlotResponse {
             response,
             inner: (screen_pos, pointer_coordinate, pointer_coordinate_drag_delta, bounds, hovered),
+            hovered_plot_item,
             ..
         } = plot.show(ui, |plot_ui| {
+            plot_ui.line(
+                Line::new(PlotPoints::from_explicit_callback(
+                    move |x| x.sin(),
+                    ..,
+                    100,
+                ))
+                .color(Color32::RED)
+                .id(egui::Id::new("sin")),
+            );
+            plot_ui.line(
+                Line::new(PlotPoints::from_explicit_callback(
+                    move |x| x.cos(),
+                    ..,
+                    100,
+                ))
+                .color(Color32::BLUE)
+                .id(egui::Id::new("cos")),
+            );
+
             (
                 plot_ui.screen_from_plot(PlotPoint::new(0.0, 0.0)),
                 plot_ui.pointer_coordinate(),
@@ -824,6 +844,15 @@ impl InteractionDemo {
         );
         ui.label(format!("pointer coordinate drag delta: {coordinate_text}"));
 
+        let hovered_item = if hovered_plot_item == Some(egui::Id::new("sin")) {
+            "red sin"
+        } else if hovered_plot_item == Some(egui::Id::new("cos")) {
+            "blue cos"
+        } else {
+            "none"
+        };
+        ui.label(format!("hovered plot item: {hovered_item}"));
+
         response
     }
 }

crates/egui_plot/src/items/mod.rs

@@ -49,6 +49,8 @@ pub(super) trait PlotItem {
 
     fn bounds(&self) -> PlotBounds;
 
+    fn id(&self) -> Option<Id>;
+
     fn find_closest(&self, point: Pos2, transform: &PlotTransform) -> Option<ClosestElem> {
         match self.geometry() {
             PlotGeometry::None => None,
@@ -120,6 +122,7 @@ pub struct HLine {
     pub(super) name: String,
     pub(super) highlight: bool,
     pub(super) style: LineStyle,
+    id: Option<Id>,
 }
 
 impl HLine {
@@ -130,6 +133,7 @@ impl HLine {
             name: String::default(),
             highlight: false,
             style: LineStyle::Solid,
+            id: None,
         }
     }
 
@@ -180,6 +184,13 @@ impl HLine {
         self.name = name.to_string();
         self
     }
+
+    /// Set the line's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for HLine {
@@ -232,6 +243,10 @@ impl PlotItem for HLine {
         bounds.max[1] = self.y;
         bounds
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A vertical line in a plot, filling the full width
@@ -242,6 +257,7 @@ pub struct VLine {
     pub(super) name: String,
     pub(super) highlight: bool,
     pub(super) style: LineStyle,
+    id: Option<Id>,
 }
 
 impl VLine {
@@ -252,6 +268,7 @@ impl VLine {
             name: String::default(),
             highlight: false,
             style: LineStyle::Solid,
+            id: None,
         }
     }
 
@@ -302,6 +319,13 @@ impl VLine {
         self.name = name.to_string();
         self
     }
+
+    /// Set the line's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for VLine {
@@ -354,6 +378,10 @@ impl PlotItem for VLine {
         bounds.max[0] = self.x;
         bounds
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A series of values forming a path.
@@ -364,6 +392,7 @@ pub struct Line {
     pub(super) highlight: bool,
     pub(super) fill: Option<f32>,
     pub(super) style: LineStyle,
+    id: Option<Id>,
 }
 
 impl Line {
@@ -375,6 +404,7 @@ impl Line {
             highlight: false,
             fill: None,
             style: LineStyle::Solid,
+            id: None,
         }
     }
 
@@ -432,6 +462,13 @@ impl Line {
         self.name = name.to_string();
         self
     }
+
+    /// Set the line's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 /// Returns the x-coordinate of a possible intersection between a line segment from `p1` to `p2` and
@@ -528,6 +565,10 @@ impl PlotItem for Line {
     fn bounds(&self) -> PlotBounds {
         self.series.bounds()
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A convex polygon.
@@ -538,6 +579,7 @@ pub struct Polygon {
     pub(super) highlight: bool,
     pub(super) fill_color: Option<Color32>,
     pub(super) style: LineStyle,
+    id: Option<Id>,
 }
 
 impl Polygon {
@@ -549,6 +591,7 @@ impl Polygon {
             highlight: false,
             fill_color: None,
             style: LineStyle::Solid,
+            id: None,
         }
     }
 
@@ -600,6 +643,13 @@ impl Polygon {
         self.name = name.to_string();
         self
     }
+
+    /// Set the polygon's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for Polygon {
@@ -654,6 +704,10 @@ impl PlotItem for Polygon {
     fn bounds(&self) -> PlotBounds {
         self.series.bounds()
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// Text inside the plot.
@@ -665,6 +719,7 @@ pub struct Text {
     pub(super) highlight: bool,
     pub(super) color: Color32,
     pub(super) anchor: Align2,
+    id: Option<Id>,
 }
 
 impl Text {
@@ -676,6 +731,7 @@ impl Text {
             highlight: false,
             color: Color32::TRANSPARENT,
             anchor: Align2::CENTER_CENTER,
+            id: None,
         }
     }
 
@@ -712,6 +768,13 @@ impl Text {
         self.name = name.to_string();
         self
     }
+
+    /// Set the text's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for Text {
@@ -768,6 +831,10 @@ impl PlotItem for Text {
         bounds.extend_with(&self.position);
         bounds
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A set of points.
@@ -790,6 +857,7 @@ pub struct Points {
     pub(super) highlight: bool,
 
     pub(super) stems: Option<f32>,
+    id: Option<Id>,
 }
 
 impl Points {
@@ -803,6 +871,7 @@ impl Points {
             name: Default::default(),
             highlight: false,
             stems: None,
+            id: None,
         }
     }
 
@@ -860,6 +929,13 @@ impl Points {
         self.name = name.to_string();
         self
     }
+
+    /// Set the points' id which is used to identify them in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for Points {
@@ -1018,6 +1094,10 @@ impl PlotItem for Points {
     fn bounds(&self) -> PlotBounds {
         self.series.bounds()
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A set of arrows.
@@ -1028,6 +1108,7 @@ pub struct Arrows {
     pub(super) color: Color32,
     pub(super) name: String,
     pub(super) highlight: bool,
+    id: Option<Id>,
 }
 
 impl Arrows {
@@ -1039,6 +1120,7 @@ impl Arrows {
             color: Color32::TRANSPARENT,
             name: Default::default(),
             highlight: false,
+            id: None,
         }
     }
 
@@ -1075,6 +1157,13 @@ impl Arrows {
         self.name = name.to_string();
         self
     }
+
+    /// Set the arrows' id which is used to identify them in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for Arrows {
@@ -1150,6 +1239,10 @@ impl PlotItem for Arrows {
     fn bounds(&self) -> PlotBounds {
         self.origins.bounds()
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// An image in the plot.
@@ -1164,6 +1257,7 @@ pub struct PlotImage {
     pub(super) tint: Color32,
     pub(super) highlight: bool,
     pub(super) name: String,
+    id: Option<Id>,
 }
 
 impl PlotImage {
@@ -1183,6 +1277,7 @@ impl PlotImage {
             rotation: 0.0,
             bg_fill: Default::default(),
             tint: Color32::WHITE,
+            id: None,
         }
     }
 
@@ -1330,6 +1425,10 @@ impl PlotItem for PlotImage {
         bounds.extend_with(&right_bottom);
         bounds
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -1344,6 +1443,7 @@ pub struct BarChart {
     pub(super) element_formatter: Option<Box<dyn Fn(&Bar, &BarChart) -> String>>,
 
     highlight: bool,
+    id: Option<Id>,
 }
 
 impl BarChart {
@@ -1355,6 +1455,7 @@ impl BarChart {
             name: String::new(),
             element_formatter: None,
             highlight: false,
+            id: None,
         }
     }
 
@@ -1454,6 +1555,13 @@ impl BarChart {
         }
         self
     }
+
+    /// Set the bar chart's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for BarChart {
@@ -1512,6 +1620,10 @@ impl PlotItem for BarChart {
         bar.add_shapes(plot.transform, true, shapes);
         bar.add_rulers_and_text(self, plot, shapes, cursors);
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 /// A diagram containing a series of [`BoxElem`] elements.
@@ -1524,6 +1636,7 @@ pub struct BoxPlot {
     pub(super) element_formatter: Option<Box<dyn Fn(&BoxElem, &BoxPlot) -> String>>,
 
     highlight: bool,
+    id: Option<Id>,
 }
 
 impl BoxPlot {
@@ -1535,6 +1648,7 @@ impl BoxPlot {
             name: String::new(),
             element_formatter: None,
             highlight: false,
+            id: None,
         }
     }
 
@@ -1602,6 +1716,13 @@ impl BoxPlot {
         self.element_formatter = Some(formatter);
         self
     }
+
+    /// Set the box plot's id which is used to identify it in the plot's response.
+    #[inline]
+    pub fn id(mut self, id: Id) -> Self {
+        self.id = Some(id);
+        self
+    }
 }
 
 impl PlotItem for BoxPlot {
@@ -1660,6 +1781,10 @@ impl PlotItem for BoxPlot {
         box_plot.add_shapes(plot.transform, true, shapes);
         box_plot.add_rulers_and_text(self, plot, shapes, cursors);
     }
+
+    fn id(&self) -> Option<Id> {
+        self.id
+    }
 }
 
 // ----------------------------------------------------------------------------

crates/egui_plot/src/lib.rs

@@ -117,6 +117,11 @@ pub struct PlotResponse<R> {
 
     /// The transform between screen coordinates and plot coordinates.
     pub transform: PlotTransform,
+
+    /// The id of a currently hovered item if any.
+    ///
+    /// This is `None` if either no item was hovered, or the hovered item didn't provide an id.
+    pub hovered_plot_item: Option<Id>,
 }
 
 // ----------------------------------------------------------------------------
@@ -803,7 +808,7 @@ impl Plot {
         }
         .unwrap_or_else(|| PlotMemory {
             auto_bounds: default_auto_bounds,
-            hovered_item: None,
+            hovered_legend_item: None,
             hidden_items: Default::default(),
             transform: PlotTransform::new(plot_rect, min_auto_bounds, center_axis.x, center_axis.y),
             last_click_pos_for_zoom: None,
@@ -848,14 +853,14 @@ impl Plot {
         let legend = legend_config
             .and_then(|config| LegendWidget::try_new(plot_rect, config, &items, &mem.hidden_items));
         // Don't show hover cursor when hovering over legend.
-        if mem.hovered_item.is_some() {
+        if mem.hovered_legend_item.is_some() {
             show_x = false;
             show_y = false;
         }
         // Remove the deselected items.
         items.retain(|item| !mem.hidden_items.contains(item.name()));
         // Highlight the hovered items.
-        if let Some(hovered_name) = &mem.hovered_item {
+        if let Some(hovered_name) = &mem.hovered_legend_item {
             items
                 .iter_mut()
                 .filter(|entry| entry.name() == hovered_name)
@@ -1137,7 +1142,7 @@ impl Plot {
             clamp_grid,
         };
 
-        let plot_cursors = prepared.ui(ui, &response);
+        let (plot_cursors, hovered_plot_item) = prepared.ui(ui, &response);
 
         if let Some(boxed_zoom_rect) = boxed_zoom_rect {
             ui.painter()
@@ -1151,7 +1156,7 @@ impl Plot {
         if let Some(mut legend) = legend {
             ui.add(&mut legend);
             mem.hidden_items = legend.hidden_items();
-            mem.hovered_item = legend.hovered_item_name();
+            mem.hovered_legend_item = legend.hovered_item_name();
         }
 
         if let Some((id, _)) = linked_cursors.as_ref() {
@@ -1195,6 +1200,7 @@ impl Plot {
             inner,
             response,
             transform,
+            hovered_plot_item,
         }
     }
 }
@@ -1645,7 +1651,7 @@ struct PreparedPlot {
 }
 
 impl PreparedPlot {
-    fn ui(self, ui: &mut Ui, response: &Response) -> Vec<Cursor> {
+    fn ui(self, ui: &mut Ui, response: &Response) -> (Vec<Cursor>, Option<Id>) {
         let mut axes_shapes = Vec::new();
 
         if self.show_grid.x {
@@ -1669,10 +1675,10 @@ impl PreparedPlot {
         }
 
         let hover_pos = response.hover_pos();
-        let cursors = if let Some(pointer) = hover_pos {
+        let (cursors, hovered_item_id) = if let Some(pointer) = hover_pos {
             self.hover(ui, pointer, &mut shapes)
         } else {
-            Vec::new()
+            (Vec::new(), None)
         };
 
         // Draw cursors
@@ -1726,7 +1732,7 @@ impl PreparedPlot {
             }
         }
 
-        cursors
+        (cursors, hovered_item_id)
     }
 
     fn paint_grid(&self, ui: &Ui, shapes: &mut Vec<(Shape, f32)>, axis: Axis, fade_range: Rangef) {
@@ -1826,7 +1832,7 @@ impl PreparedPlot {
         }
     }
 
-    fn hover(&self, ui: &Ui, pointer: Pos2, shapes: &mut Vec<Shape>) -> Vec<Cursor> {
+    fn hover(&self, ui: &Ui, pointer: Pos2, shapes: &mut Vec<Shape>) -> (Vec<Cursor>, Option<Id>) {
         let Self {
             transform,
             show_x,
@@ -1837,7 +1843,7 @@ impl PreparedPlot {
         } = self;
 
         if !show_x && !show_y {
-            return Vec::new();
+            return (Vec::new(), None);
         }
 
         let interact_radius_sq = (16.0_f32).powi(2);
@@ -1853,8 +1859,6 @@ impl PreparedPlot {
             .min_by_key(|(_, elem)| elem.dist_sq.ord())
             .filter(|(_, elem)| elem.dist_sq <= interact_radius_sq);
 
-        let mut cursors = Vec::new();
-
         let plot = items::PlotConfig {
             ui,
             transform,
@@ -1862,8 +1866,11 @@ impl PreparedPlot {
             show_y: *show_y,
         };
 
-        if let Some((item, elem)) = closest {
+        let mut cursors = Vec::new();
+
+        let hovered_plot_item_id = if let Some((item, elem)) = closest {
             item.on_hover(elem, shapes, &mut cursors, &plot, label_formatter);
+            item.id()
         } else {
             let value = transform.value_from_position(pointer);
             items::rulers_at_value(
@@ -1875,9 +1882,10 @@ impl PreparedPlot {
                 &mut cursors,
                 label_formatter,
             );
-        }
+            None
+        };
 
-        cursors
+        (cursors, hovered_plot_item_id)
     }
 }
 

crates/egui_plot/src/memory.rs

@@ -14,8 +14,8 @@ pub struct PlotMemory {
     /// the bounds, for example by moving or zooming.
     pub auto_bounds: Vec2b,
 
-    /// Which item is hovered?
+    /// Display string of the hovered legend item if any.
-    pub hovered_item: Option<String>,
+    pub hovered_legend_item: Option<String>,
 
     /// Which items _not_ to show?
     pub hidden_items: ahash::HashSet<String>,