On touch screens, press-and-hold equals a secondary click (#4195)

* Closes #3444
* Closes #865

On a touch screen, if you press down on a widget and hold for 0.6
seconds (`MAX_CLICK_DURATION`), it will now trigger a secondary click,
i.e. `Response::secondary_clicked` will be `true`. This means you can
now open context menus on touch screens.

crates/egui/src/context.rs

@@ -2,7 +2,6 @@
 
 use std::{borrow::Cow, cell::RefCell, panic::Location, sync::Arc, time::Duration};
 
-use ahash::HashMap;
 use epaint::{
     emath::TSTransform, mutex::*, stats::*, text::Fonts, util::OrderedFloat, TessellationOptions, *,
 };
@@ -421,36 +420,30 @@ impl ContextImpl {
                 // but the `screen_rect` is the most important part.
             }
         }
-        let pixels_per_point = self.memory.options.zoom_factor
-            * new_raw_input
-                .viewport()
-                .native_pixels_per_point
-                .unwrap_or(1.0);
+        let native_pixels_per_point = new_raw_input
+            .viewport()
+            .native_pixels_per_point
+            .unwrap_or(1.0);
+        let pixels_per_point = self.memory.options.zoom_factor * native_pixels_per_point;
 
         let all_viewport_ids: ViewportIdSet = self.all_viewport_ids();
 
         let viewport = self.viewports.entry(self.viewport_id()).or_default();
 
-        self.memory
-            .begin_frame(&viewport.input, &new_raw_input, &all_viewport_ids);
+        self.memory.begin_frame(&new_raw_input, &all_viewport_ids);
 
         viewport.input = std::mem::take(&mut viewport.input).begin_frame(
             new_raw_input,
             viewport.repaint.requested_immediate_repaint_prev_frame(),
             pixels_per_point,
         );
 
-        viewport.frame_state.begin_frame(&viewport.input);
+        let screen_rect = viewport.input.screen_rect;
+
+        viewport.frame_state.begin_frame(screen_rect);
 
         {
-            let area_order: HashMap<LayerId, usize> = self
-                .memory
-                .areas()
-                .order()
-                .iter()
-                .enumerate()
-                .map(|(i, id)| (*id, i))
-                .collect();
+            let area_order = self.memory.areas().order_map();
 
             let mut layers: Vec<LayerId> = viewport.widgets_prev_frame.layer_ids().collect();
 
@@ -488,7 +481,6 @@ impl ContextImpl {
         }
 
         // Ensure we register the background area so panels and background ui can catch clicks:
-        let screen_rect = viewport.input.screen_rect();
         self.memory.areas_mut().set_state(
             LayerId::background(),
             containers::area::State {
@@ -1106,6 +1098,7 @@ impl Context {
             highlighted,
             clicked: false,
             fake_primary_click: false,
+            long_touched: false,
             drag_started: false,
             dragged: false,
             drag_stopped: false,
@@ -1141,6 +1134,10 @@ impl Context {
                 res.fake_primary_click = true;
             }
 
+            if enabled && sense.click && Some(id) == viewport.interact_widgets.long_touched {
+                res.long_touched = true;
+            }
+
             let interaction = memory.interaction();
 
             res.is_pointer_button_down_on = interaction.potential_click_id == Some(id)
@@ -1168,7 +1165,8 @@ impl Context {
 
             // is_pointer_button_down_on is false when released, but we want interact_pointer_pos
             // to still work.
-            let is_interacted_with = res.is_pointer_button_down_on || clicked || res.drag_stopped;
+            let is_interacted_with =
+                res.is_pointer_button_down_on || res.long_touched || clicked || res.drag_stopped;
             if is_interacted_with {
                 res.interact_pointer_pos = input.pointer.interact_pos();
                 if let (Some(transform), Some(pos)) = (
@@ -1179,7 +1177,7 @@ impl Context {
                 }
             }
 
-            if input.pointer.any_down() && !res.is_pointer_button_down_on {
+            if input.pointer.any_down() && !is_interacted_with {
                 // We don't hover widgets while interacting with *other* widgets:
                 res.hovered = false;
             }
@@ -1847,6 +1845,7 @@ impl Context {
                 let interact_widgets = self.write(|ctx| ctx.viewport().interact_widgets.clone());
                 let InteractionSnapshot {
                     clicked,
+                    long_touched: _,
                     drag_started: _,
                     dragged,
                     drag_stopped: _,
@@ -1956,7 +1955,10 @@ impl ContextImpl {
                         })
                         .collect()
                 };
-                let focus_id = self.memory.focus().map_or(root_id, |id| id.accesskit_id());
+                let focus_id = self
+                    .memory
+                    .focused()
+                    .map_or(root_id, |id| id.accesskit_id());
                 platform_output.accesskit_update = Some(accesskit::TreeUpdate {
                     nodes,
                     tree: Some(accesskit::Tree::new(root_id)),
@@ -2221,7 +2223,7 @@ impl Context {
 
     /// If `true`, egui is currently listening on text input (e.g. typing text in a [`TextEdit`]).
     pub fn wants_keyboard_input(&self) -> bool {
-        self.memory(|m| m.interaction().focus.focused().is_some())
+        self.memory(|m| m.focused().is_some())
     }
 
     /// Highlight this widget, to make it look like it is hovered, even if it isn't.
@@ -2481,7 +2483,7 @@ impl Context {
         .on_hover_text("Is egui currently listening for text input?");
         ui.label(format!(
             "Keyboard focus widget: {}",
-            self.memory(|m| m.interaction().focus.focused())
+            self.memory(|m| m.focused())
                 .as_ref()
                 .map(Id::short_debug_format)
                 .unwrap_or_default()

crates/egui/src/frame_state.rs

@@ -75,7 +75,7 @@ impl Default for FrameState {
 }
 
 impl FrameState {
-    pub(crate) fn begin_frame(&mut self, input: &InputState) {
+    pub(crate) fn begin_frame(&mut self, screen_rect: Rect) {
         crate::profile_function!();
         let Self {
             used_ids,
@@ -94,8 +94,8 @@ impl FrameState {
         } = self;
 
         used_ids.clear();
-        *available_rect = input.screen_rect();
-        *unused_rect = input.screen_rect();
+        *available_rect = screen_rect;
+        *unused_rect = screen_rect;
         *used_by_panels = Rect::NOTHING;
         *tooltip_state = None;
         *scroll_target = [None, None];

crates/egui/src/input_state.rs

@@ -11,8 +11,13 @@ use touch_state::TouchState;
 /// If the pointer moves more than this, it won't become a click (but it is still a drag)
 const MAX_CLICK_DIST: f32 = 6.0; // TODO(emilk): move to settings
 
-/// If the pointer is down for longer than this, it won't become a click (but it is still a drag)
-const MAX_CLICK_DURATION: f64 = 0.6; // TODO(emilk): move to settings
+/// If the pointer is down for longer than this it will no longer register as a click.
+///
+/// If a touch is held for this many seconds while still,
+/// then it will register as a "long-touch" which is equivalent to a secondary click.
+///
+/// This is to support "press and hold for context menu" on touch screens.
+const MAX_CLICK_DURATION: f64 = 0.8; // TODO(emilk): move to settings
 
 /// The new pointer press must come within this many seconds from previous pointer release
 const MAX_DOUBLE_CLICK_DELAY: f64 = 0.3; // TODO(emilk): move to settings
@@ -544,6 +549,14 @@ impl InputState {
             .cloned()
             .collect()
     }
+
+    /// A long press is something we detect on touch screens
+    /// to trigger a secondary click (context menu).
+    ///
+    /// Returns `true` only on one frame.
+    pub(crate) fn is_long_touch(&self) -> bool {
+        self.any_touches() && self.pointer.is_long_press()
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -651,6 +664,8 @@ pub struct PointerState {
     pub(crate) has_moved_too_much_for_a_click: bool,
 
     /// Did [`Self::is_decidedly_dragging`] go from `false` to `true` this frame?
+    ///
+    /// This could also be the trigger point for a long-touch.
     pub(crate) started_decidedly_dragging: bool,
 
     /// When did the pointer get click last?
@@ -751,6 +766,7 @@ impl PointerState {
                             button,
                         });
                     } else {
+                        // Released
                         let clicked = self.could_any_button_be_click();
 
                         let click = if clicked {
@@ -1027,21 +1043,21 @@ impl PointerState {
     ///
     /// See also [`Self::is_decidedly_dragging`].
     pub fn could_any_button_be_click(&self) -> bool {
-        if !self.any_down() {
-            return false;
-        }
-
-        if self.has_moved_too_much_for_a_click {
-            return false;
-        }
-
-        if let Some(press_start_time) = self.press_start_time {
-            if self.time - press_start_time > MAX_CLICK_DURATION {
+        if self.any_down() || self.any_released() {
+            if self.has_moved_too_much_for_a_click {
                 return false;
             }
-        }
 
-        true
+            if let Some(press_start_time) = self.press_start_time {
+                if self.time - press_start_time > MAX_CLICK_DURATION {
+                    return false;
+                }
+            }
+
+            true
+        } else {
+            false
+        }
     }
 
     /// Just because the mouse is down doesn't mean we are dragging.
@@ -1060,6 +1076,19 @@ impl PointerState {
             && !self.any_click()
     }
 
+    /// A long press is something we detect on touch screens
+    /// to trigger a secondary click (context menu).
+    ///
+    /// Returns `true` only on one frame.
+    pub(crate) fn is_long_press(&self) -> bool {
+        self.started_decidedly_dragging
+            && !self.has_moved_too_much_for_a_click
+            && self.button_down(PointerButton::Primary)
+            && self.press_start_time.map_or(false, |press_start_time| {
+                self.time - press_start_time > MAX_CLICK_DURATION
+            })
+    }
+
     /// Is the primary button currently down?
     #[inline(always)]
     pub fn primary_down(&self) -> bool {

crates/egui/src/interaction.rs

@@ -14,6 +14,10 @@ pub struct InteractionSnapshot {
     /// The widget that got clicked this frame.
     pub clicked: Option<Id>,
 
+    /// This widget was long-pressed on a touch screen,
+    /// so trigger a secondary click on it (context menu).
+    pub long_touched: Option<Id>,
+
     /// Drag started on this widget this frame.
     ///
     /// This will also be found in `dragged` this frame.
@@ -56,6 +60,7 @@ impl InteractionSnapshot {
     pub fn ui(&self, ui: &mut crate::Ui) {
         let Self {
             clicked,
+            long_touched,
             drag_started,
             dragged,
             drag_stopped,
@@ -74,6 +79,10 @@ impl InteractionSnapshot {
             id_ui(ui, clicked);
             ui.end_row();
 
+            ui.label("long_touched");
+            id_ui(ui, long_touched);
+            ui.end_row();
+
             ui.label("drag_started");
             id_ui(ui, drag_started);
             ui.end_row();
@@ -123,6 +132,21 @@ pub(crate) fn interact(
 
     let mut clicked = None;
     let mut dragged = prev_snapshot.dragged;
+    let mut long_touched = None;
+
+    if input.is_long_touch() {
+        // We implement "press-and-hold for context menu" on touch screens here
+        if let Some(widget) = interaction
+            .potential_click_id
+            .and_then(|id| widgets.get(id))
+        {
+            dragged = None;
+            clicked = Some(widget.id);
+            long_touched = Some(widget.id);
+            interaction.potential_click_id = None;
+            interaction.potential_drag_id = None;
+        }
+    }
 
     // Note: in the current code a press-release in the same frame is NOT considered a drag.
     for pointer_event in &input.pointer.pointer_events {
@@ -142,7 +166,7 @@ pub(crate) fn interact(
             }
 
             PointerEvent::Released { click, button: _ } => {
-                if click.is_some() {
+                if click.is_some() && !input.pointer.is_decidedly_dragging() {
                     if let Some(widget) = interaction
                         .potential_click_id
                         .and_then(|id| widgets.get(id))
@@ -179,6 +203,15 @@ pub(crate) fn interact(
         }
     }
 
+    if !input.pointer.could_any_button_be_click() {
+        interaction.potential_click_id = None;
+    }
+
+    if !input.pointer.any_down() || input.pointer.latest_pos().is_none() {
+        interaction.potential_click_id = None;
+        interaction.potential_drag_id = None;
+    }
+
     // ------------------------------------------------------------------------
 
     let drag_changed = dragged != prev_snapshot.dragged;
@@ -201,9 +234,14 @@ pub(crate) fn interact(
         .map(|w| w.id)
         .collect();
 
-    let hovered = if clicked.is_some() || dragged.is_some() {
-        // If currently clicking or dragging, nothing else is hovered.
-        clicked.iter().chain(&dragged).copied().collect()
+    let hovered = if clicked.is_some() || dragged.is_some() || long_touched.is_some() {
+        // If currently clicking or dragging, only that and nothing else is hovered.
+        clicked
+            .iter()
+            .chain(&dragged)
+            .chain(&long_touched)
+            .copied()
+            .collect()
     } else if hits.click.is_some() || hits.drag.is_some() {
         // We are hovering over an interactive widget or two.
         hits.click.iter().chain(&hits.drag).map(|w| w.id).collect()
@@ -220,6 +258,7 @@ pub(crate) fn interact(
 
     InteractionSnapshot {
         clicked,
+        long_touched,
         drag_started,
         dragged,
         drag_stopped,

crates/egui/src/introspection.rs

@@ -194,7 +194,6 @@ impl Widget for &memory::InteractionState {
         let memory::InteractionState {
             potential_click_id,
             potential_drag_id,
-            focus: _,
         } = self;
 
         ui.vertical(|ui| {