Add an ItemId newtype to identify plot items

Cargo.lock

@@ -1278,7 +1278,7 @@ dependencies = [
  "ahash",
  "egui",
  "enum-map",
- "itertools",
+ "itertools 0.15.0",
  "log",
  "profiling",
 ]
@@ -1331,6 +1331,7 @@ dependencies = [
  "emath",
  "env_logger",
  "log",
+ "nohash-hasher",
  "performance_lines",
  "serde",
 ]

Cargo.toml

@@ -64,6 +64,7 @@ env_logger = { version = "0.11.8", default-features = false, features = [
 ] }
 image = { version = "0.25", default-features = false }
 log = "0.4"
+nohash-hasher = "0.2.0"
 serde = { version = "1", features = ["derive"] }
 wasm-bindgen-futures = "0.4"
 web-sys = "0.3.83"

egui_plot/Cargo.toml

@@ -39,6 +39,7 @@ egui = { workspace = true, default-features = false }
 emath = { workspace = true, default-features = false }
 
 ahash.workspace = true
+nohash-hasher.workspace = true
 
 #! ### Optional dependencies
 ## Enable this when generating docs.

egui_plot/src/item_id.rs

@@ -0,0 +1,64 @@
+//! Identifiers for the items within a plot.
+
+use core::hash::Hash;
+use core::num::NonZeroU64;
+
+/// The seeds used when hashing an [`ItemId`] source.
+///
+/// Fixed so that the same source always produces the same [`ItemId`],
+/// which is what lets [`crate::PlotMemory`] be persisted between runs.
+const HASH_SEEDS: (u64, u64, u64, u64) = (9, 10, 11, 12);
+
+/// An `ItemIdSet` is a `HashSet<ItemId>` that skips hashing,
+/// since an [`ItemId`] already is a high-entropy hash.
+pub type ItemIdSet = nohash_hasher::IntSet<ItemId>;
+
+/// An `ItemIdMap<V>` is a `HashMap<ItemId, V>` that skips hashing,
+/// since an [`ItemId`] already is a high-entropy hash.
+pub type ItemIdMap<V> = nohash_hasher::IntMap<ItemId, V>;
+
+/// Identifies a [`crate::PlotItem`] within a plot.
+///
+/// An `ItemId` only has to be unique within the plot it is used in.
+///
+/// By default each item derives its `ItemId` from the name it was created with,
+/// but you can set one explicitly, e.g. with [`crate::Line::id`]. Do that when
+/// the name changes between frames, or when several items share a name.
+///
+/// This is niche-optimized, so that `Option<ItemId>` is the same size as `ItemId`.
+#[derive(Clone, Copy, Eq, Hash, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub struct ItemId(NonZeroU64);
+
+impl nohash_hasher::IsEnabled for ItemId {}
+
+impl ItemId {
+    /// Hash any source (e.g. a string, an integer, or a tuple of those) into an [`ItemId`].
+    ///
+    /// Prefer a tuple over formatting a string:
+    ///
+    /// ```
+    /// # use egui_plot::ItemId;
+    /// # let (row, column) = (0, 0);
+    /// let good = ItemId::new(("my_cell", row, column)); // No allocation
+    /// let bad = ItemId::new(format!("my_cell {row} {column}")); // Allocates
+    /// # let _ = (good, bad);
+    /// ```
+    pub fn new(source: impl Hash) -> Self {
+        let (a, b, c, d) = HASH_SEEDS;
+        let hash = ahash::RandomState::with_seeds(a, b, c, d).hash_one(source);
+        Self(NonZeroU64::new(hash).unwrap_or(NonZeroU64::MIN)) // The hash was exactly zero (very bad luck)
+    }
+
+    /// The inner value, which is a high-entropy hash.
+    #[inline(always)]
+    pub fn value(self) -> u64 {
+        self.0.get()
+    }
+}
+
+impl core::fmt::Debug for ItemId {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "ItemId({:04X})", self.value() as u16)
+    }
+}

egui_plot/src/items/arrows.rs

@@ -1,7 +1,7 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 
 use egui::Color32;
-use egui::Id;
 use egui::Shape;
 use egui::Stroke;
 use egui::Ui;
@@ -10,6 +10,7 @@ use emath::Rot2;
 use crate::axis::PlotTransform;
 use crate::bounds::PlotBounds;
 use crate::data::PlotPoints;
+use crate::item_id::ItemId;
 use crate::items::PlotGeometry;
 use crate::items::PlotItem;
 use crate::items::PlotItemBase;
@@ -71,13 +72,15 @@ impl<'a> Arrows<'a> {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// The id only has to be unique within the plot.
+    ///
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }

egui_plot/src/items/bar_chart.rs

@@ -1,8 +1,8 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 
 use egui::Color32;
 use egui::CornerRadius;
-use egui::Id;
 use egui::Shape;
 use egui::Stroke;
 use egui::Ui;
@@ -17,6 +17,7 @@ use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
 use crate::colors::highlighted_color;
 use crate::cursor::Cursor;
+use crate::item_id::ItemId;
 use crate::items::ClosestElem;
 use crate::items::PlotConfig;
 use crate::items::PlotGeometry;
@@ -161,13 +162,15 @@ impl BarChart {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// The id only has to be unique within the plot.
+    ///
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }

egui_plot/src/items/box_plot.rs

@@ -1,8 +1,8 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 
 use egui::Color32;
 use egui::CornerRadius;
-use egui::Id;
 use egui::Shape;
 use egui::Stroke;
 use egui::Ui;
@@ -16,6 +16,7 @@ use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
 use crate::colors::highlighted_color;
 use crate::cursor::Cursor;
+use crate::item_id::ItemId;
 use crate::items::ClosestElem;
 use crate::items::PlotConfig;
 use crate::items::PlotGeometry;
@@ -127,13 +128,15 @@ impl BoxPlot {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// The id only has to be unique within the plot.
+    ///
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }

egui_plot/src/items/filled_area.rs

@@ -1,8 +1,8 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 use std::sync::Arc;
 
 use egui::Color32;
-use egui::Id;
 use egui::Mesh;
 use egui::Pos2;
 use egui::Shape;
@@ -14,6 +14,7 @@ use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
 use crate::colors::DEFAULT_FILL_ALPHA;
 use crate::data::PlotPoints;
+use crate::item_id::ItemId;
 use crate::items::PlotGeometry;
 use crate::items::PlotItem;
 use crate::items::PlotItemBase;
@@ -115,10 +116,12 @@ impl FilledArea {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
+    ///
+    /// The id only has to be unique within the plot.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }

egui_plot/src/items/line.rs

@@ -1,7 +1,7 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 
 use egui::Color32;
-use egui::Id;
 use egui::Shape;
 use egui::Stroke;
 use egui::Ui;
@@ -13,6 +13,7 @@ use crate::aesthetics::LineStyle;
 use crate::axis::PlotTransform;
 use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
+use crate::item_id::ItemId;
 use crate::items::PlotGeometry;
 use crate::items::PlotItem;
 use crate::items::PlotItemBase;
@@ -97,13 +98,15 @@ impl HLine {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// The id only has to be unique within the plot.
+    ///
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }
@@ -232,13 +235,15 @@ impl VLine {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
+    ///
+    /// The id only has to be unique within the plot.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }

egui_plot/src/items/mod.rs

@@ -8,7 +8,6 @@ use std::ops::RangeInclusive;
 
 use egui::Align2;
 use egui::Color32;
-use egui::Id;
 use egui::PopupAnchor;
 use egui::Pos2;
 use egui::Shape;
@@ -22,6 +21,7 @@ use crate::axis::PlotTransform;
 use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
 use crate::cursor::Cursor;
+use crate::item_id::ItemId;
 pub use crate::items::arrows::Arrows;
 pub use crate::items::bar_chart::Bar;
 pub use crate::items::bar_chart::BarChart;
@@ -61,15 +61,15 @@ mod text;
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct PlotItemBase {
     name: String,
-    id: Id,
+    id: ItemId,
     highlight: bool,
     allow_hover: bool,
 }
 
 impl PlotItemBase {
     /// Create a new plot item base with the given name.
     pub fn new(name: String) -> Self {
-        let id = Id::new(&name);
+        let id = ItemId::new(&name);
         Self {
             name,
             id,
@@ -141,8 +141,10 @@ pub trait PlotItem {
     /// Returns a mutable reference to the base data of the plot item.
     fn base_mut(&mut self) -> &mut PlotItemBase;
 
-    /// Returns the ID of the plot item.
-    fn id(&self) -> Id {
+    /// Returns the [`ItemId`] of the plot item.
+    ///
+    /// This only identifies the item within its plot.
+    fn id(&self) -> ItemId {
         self.base().id
     }
 

egui_plot/src/items/plot_image.rs

@@ -1,8 +1,8 @@
+use core::hash::Hash;
 use std::ops::RangeInclusive;
 
 use egui::Color32;
 use egui::CornerRadius;
-use egui::Id;
 use egui::ImageOptions;
 use egui::Shape;
 use egui::Stroke;
@@ -16,6 +16,7 @@ use emath::pos2;
 use crate::axis::PlotTransform;
 use crate::bounds::PlotBounds;
 use crate::bounds::PlotPoint;
+use crate::item_id::ItemId;
 use crate::items::PlotGeometry;
 use crate::items::PlotItem;
 use crate::items::PlotItemBase;
@@ -114,13 +115,15 @@ impl PlotImage {
         self
     }
 
-    /// Sets the id of this plot item.
+    /// Sets the [`ItemId`] of this plot item.
     ///
-    /// By default the id is determined from the name passed to [`Self::new`],
+    /// The id only has to be unique within the plot.
+    ///
+    /// By default the id is derived from the name passed to [`Self::new`],
     /// but it can be explicitly set to a different value.
     #[inline]
-    pub fn id(mut self, id: impl Into<Id>) -> Self {
-        self.base_mut().id = id.into();
+    pub fn id(mut self, id: impl Hash) -> Self {
+        self.base_mut().id = ItemId::new(id);
         self
     }
 }