Cross-widget text select (#3870)

* Closes #3816


![cross-widget-text-selection](https://github.com/emilk/egui/assets/1148717/5582b9d2-8b04-47b7-9637-f48e44064a70)

Turn off with `style.interaction.multi_widget_text_select`.

There is an API for this in `LabelSelectionState`, but it's pretty
bare-bones.

This became really hairy implementation-wise, but it works decently
well.

# Limitations
* Drag-select to scroll doesn't work
* A selection disappears if you scroll past one of its end-points
* Only the text of labels and links are selectable
 
## TODO
* [x] An option to turn it off
* [x] An API for querying about the selected text, and to deselect it.
* [x] Scrolling past selection behaves weird
* [x] Shift-click to select a range

crates/egui/src/context.rs

@@ -625,7 +625,7 @@ impl Context {
     /// ```
     pub fn begin_frame(&self, new_input: RawInput) {
         crate::profile_function!();
-
+        crate::text_selection::LabelSelectionState::begin_frame(self);
         self.write(|ctx| ctx.begin_frame_mut(new_input));
     }
 }
@@ -697,13 +697,13 @@ impl Context {
 
     /// Read-write access to [`GraphicLayers`], where painted [`crate::Shape`]s are written to.
     #[inline]
-    pub(crate) fn graphics_mut<R>(&self, writer: impl FnOnce(&mut GraphicLayers) -> R) -> R {
+    pub fn graphics_mut<R>(&self, writer: impl FnOnce(&mut GraphicLayers) -> R) -> R {
         self.write(move |ctx| writer(&mut ctx.viewport().graphics))
     }
 
     /// Read-only access to [`GraphicLayers`], where painted [`crate::Shape`]s are written to.
     #[inline]
-    pub(crate) fn graphics<R>(&self, reader: impl FnOnce(&GraphicLayers) -> R) -> R {
+    pub fn graphics<R>(&self, reader: impl FnOnce(&GraphicLayers) -> R) -> R {
         self.write(move |ctx| reader(&ctx.viewport().graphics))
     }
 
@@ -1616,6 +1616,8 @@ impl Context {
             crate::gui_zoom::zoom_with_keyboard(self);
         }
 
+        crate::text_selection::LabelSelectionState::end_frame(self);
+
         let debug_texts = self.write(|ctx| std::mem::take(&mut ctx.debug_texts));
         if !debug_texts.is_empty() {
             // Show debug-text next to the cursor.
@@ -2041,7 +2043,7 @@ impl Context {
     /// Can be used to implement drag-and-drop (see relevant demo).
     pub fn translate_layer(&self, layer_id: LayerId, delta: Vec2) {
         if delta != Vec2::ZERO {
-            self.graphics_mut(|g| g.list(layer_id).translate(delta));
+            self.graphics_mut(|g| g.entry(layer_id).translate(delta));
         }
     }
 
@@ -2352,6 +2354,15 @@ impl Context {
                 let font_image_size = self.fonts(|f| f.font_image_size());
                 crate::introspection::font_texture_ui(ui, font_image_size);
             });
+
+        CollapsingHeader::new("Label text selection state")
+            .default_open(false)
+            .show(ui, |ui| {
+                ui.label(format!(
+                    "{:#?}",
+                    crate::text_selection::LabelSelectionState::load(ui.ctx())
+                ));
+            });
     }
 
     /// Show stats about the allocated textures.

crates/egui/src/input_state.rs

@@ -840,6 +840,7 @@ impl PointerState {
     }
 
     /// Was any pointer button pressed (`!down -> down`) this frame?
+    ///
     /// This can sometimes return `true` even if `any_down() == false`
     /// because a press can be shorted than one frame.
     pub fn any_pressed(&self) -> bool {

crates/egui/src/layers.rs

@@ -110,7 +110,8 @@ impl LayerId {
 }
 
 /// A unique identifier of a specific [`Shape`] in a [`PaintList`].
-#[derive(Clone, Copy, PartialEq, Eq)]
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct ShapeIdx(pub usize);
 
 /// A list of [`Shape`]s paired with a clip rectangle.
@@ -151,6 +152,12 @@ impl PaintList {
         self.0[idx.0] = ClippedShape { clip_rect, shape };
     }
 
+    /// Set the given shape to be empty (a `Shape::Noop`).
+    #[inline(always)]
+    pub fn reset_shape(&mut self, idx: ShapeIdx) {
+        self.0[idx.0].shape = Shape::Noop;
+    }
+
     /// Translate each [`Shape`] and clip rectangle by this much, in-place
     pub fn translate(&mut self, delta: Vec2) {
         for ClippedShape { clip_rect, shape } in &mut self.0 {
@@ -165,20 +172,28 @@ impl PaintList {
     }
 }
 
+/// This is where painted [`Shape`]s end up during a frame.
 #[derive(Clone, Default)]
-pub(crate) struct GraphicLayers([IdMap<PaintList>; Order::COUNT]);
+pub struct GraphicLayers([IdMap<PaintList>; Order::COUNT]);
 
 impl GraphicLayers {
-    pub fn list(&mut self, layer_id: LayerId) -> &mut PaintList {
+    /// Get or insert the [`PaintList`] for the given [`LayerId`].
+    pub fn entry(&mut self, layer_id: LayerId) -> &mut PaintList {
         self.0[layer_id.order as usize]
             .entry(layer_id.id)
             .or_default()
     }
 
+    /// Get the [`PaintList`] for the given [`LayerId`].
     pub fn get(&self, layer_id: LayerId) -> Option<&PaintList> {
         self.0[layer_id.order as usize].get(&layer_id.id)
     }
 
+    /// Get the [`PaintList`] for the given [`LayerId`].
+    pub fn get_mut(&mut self, layer_id: LayerId) -> Option<&mut PaintList> {
+        self.0[layer_id.order as usize].get_mut(&layer_id.id)
+    }
+
     pub fn drain(&mut self, area_order: &[LayerId]) -> Vec<ClippedShape> {
         crate::profile_function!();
 

crates/egui/src/painter.rs

@@ -144,7 +144,7 @@ impl Painter {
 impl Painter {
     #[inline]
     fn paint_list<R>(&self, writer: impl FnOnce(&mut PaintList) -> R) -> R {
-        self.ctx.graphics_mut(|g| writer(g.list(self.layer_id)))
+        self.ctx.graphics_mut(|g| writer(g.entry(self.layer_id)))
     }
 
     fn transform_shape(&self, shape: &mut Shape) {
@@ -257,21 +257,21 @@ impl Painter {
 /// # Paint different primitives
 impl Painter {
     /// Paints a line from the first point to the second.
-    pub fn line_segment(&self, points: [Pos2; 2], stroke: impl Into<Stroke>) {
+    pub fn line_segment(&self, points: [Pos2; 2], stroke: impl Into<Stroke>) -> ShapeIdx {
         self.add(Shape::LineSegment {
             points,
             stroke: stroke.into(),
-        });
+        })
     }
 
     /// Paints a horizontal line.
-    pub fn hline(&self, x: impl Into<Rangef>, y: f32, stroke: impl Into<Stroke>) {
-        self.add(Shape::hline(x, y, stroke));
+    pub fn hline(&self, x: impl Into<Rangef>, y: f32, stroke: impl Into<Stroke>) -> ShapeIdx {
+        self.add(Shape::hline(x, y, stroke))
     }
 
     /// Paints a vertical line.
-    pub fn vline(&self, x: f32, y: impl Into<Rangef>, stroke: impl Into<Stroke>) {
-        self.add(Shape::vline(x, y, stroke));
+    pub fn vline(&self, x: f32, y: impl Into<Rangef>, stroke: impl Into<Stroke>) -> ShapeIdx {
+        self.add(Shape::vline(x, y, stroke))
     }
 
     pub fn circle(
@@ -280,31 +280,36 @@ impl Painter {
         radius: f32,
         fill_color: impl Into<Color32>,
         stroke: impl Into<Stroke>,
-    ) {
+    ) -> ShapeIdx {
         self.add(CircleShape {
             center,
             radius,
             fill: fill_color.into(),
             stroke: stroke.into(),
-        });
+        })
     }
 
-    pub fn circle_filled(&self, center: Pos2, radius: f32, fill_color: impl Into<Color32>) {
+    pub fn circle_filled(
+        &self,
+        center: Pos2,
+        radius: f32,
+        fill_color: impl Into<Color32>,
+    ) -> ShapeIdx {
         self.add(CircleShape {
             center,
             radius,
             fill: fill_color.into(),
             stroke: Default::default(),
-        });
+        })
     }
 
-    pub fn circle_stroke(&self, center: Pos2, radius: f32, stroke: impl Into<Stroke>) {
+    pub fn circle_stroke(&self, center: Pos2, radius: f32, stroke: impl Into<Stroke>) -> ShapeIdx {
         self.add(CircleShape {
             center,
             radius,
             fill: Default::default(),
             stroke: stroke.into(),
-        });
+        })
     }
 
     pub fn rect(
@@ -313,26 +318,26 @@ impl Painter {
         rounding: impl Into<Rounding>,
         fill_color: impl Into<Color32>,
         stroke: impl Into<Stroke>,
-    ) {
-        self.add(RectShape::new(rect, rounding, fill_color, stroke));
+    ) -> ShapeIdx {
+        self.add(RectShape::new(rect, rounding, fill_color, stroke))
     }
 
     pub fn rect_filled(
         &self,
         rect: Rect,
         rounding: impl Into<Rounding>,
         fill_color: impl Into<Color32>,
-    ) {
-        self.add(RectShape::filled(rect, rounding, fill_color));
+    ) -> ShapeIdx {
+        self.add(RectShape::filled(rect, rounding, fill_color))
     }
 
     pub fn rect_stroke(
         &self,
         rect: Rect,
         rounding: impl Into<Rounding>,
         stroke: impl Into<Stroke>,
-    ) {
-        self.add(RectShape::stroke(rect, rounding, stroke));
+    ) -> ShapeIdx {
+        self.add(RectShape::stroke(rect, rounding, stroke))
     }
 
     /// Show an arrow starting at `origin` and going in the direction of `vec`, with the length `vec.length()`.
@@ -366,8 +371,14 @@ impl Painter {
     ///     .paint_at(ui, rect);
     /// # });
     /// ```
-    pub fn image(&self, texture_id: epaint::TextureId, rect: Rect, uv: Rect, tint: Color32) {
-        self.add(Shape::image(texture_id, rect, uv, tint));
+    pub fn image(
+        &self,
+        texture_id: epaint::TextureId,
+        rect: Rect,
+        uv: Rect,
+        tint: Color32,
+    ) -> ShapeIdx {
+        self.add(Shape::image(texture_id, rect, uv, tint))
     }
 }
 

crates/egui/src/style.rs

@@ -720,6 +720,12 @@ pub struct Interaction {
 
     /// Can you select the text on a [`crate::Label`] by default?
     pub selectable_labels: bool,
+
+    /// Can the user select text that span multiple labels?
+    ///
+    /// The default is `true`, but text seelction can be slightly glitchy,
+    /// so you may want to disable it.
+    pub multi_widget_text_select: bool,
 }
 
 /// Controls the visual style (colors etc) of egui.
@@ -1120,6 +1126,7 @@ impl Default for Interaction {
             show_tooltips_only_when_still: true,
             tooltip_delay: 0.0,
             selectable_labels: true,
+            multi_widget_text_select: true,
         }
     }
 }
@@ -1580,6 +1587,7 @@ impl Interaction {
             show_tooltips_only_when_still,
             tooltip_delay,
             selectable_labels,
+            multi_widget_text_select,
         } = self;
         ui.add(Slider::new(resize_grab_radius_side, 0.0..=20.0).text("resize_grab_radius_side"));
         ui.add(
@@ -1590,7 +1598,13 @@ impl Interaction {
             "Only show tooltips if mouse is still",
         );
         ui.add(Slider::new(tooltip_delay, 0.0..=1.0).text("tooltip_delay"));
-        ui.checkbox(selectable_labels, "Selectable text in labels");
+
+        ui.horizontal(|ui| {
+            ui.checkbox(selectable_labels, "Selectable text in labels");
+            if *selectable_labels {
+                ui.checkbox(multi_widget_text_select, "Across multiple labels");
+            }
+        });
 
         ui.vertical_centered(|ui| reset_button(ui, self));
     }

crates/egui/src/text_selection/cursor_range.rs

@@ -234,10 +234,10 @@ impl CCursorRange {
     }
 
     #[inline]
-    pub fn two(min: CCursor, max: CCursor) -> Self {
+    pub fn two(min: impl Into<CCursor>, max: impl Into<CCursor>) -> Self {
         Self {
-            primary: max,
-            secondary: min,
+            primary: max.into(),
+            secondary: min.into(),
         }
     }