Add smart magnify gesture support for macOS (#2554)

* Add smart magnification gesture

* Deliver position of smart magnification event

* Document smart magnification event

* Revert "Deliver position of smart magnification event"

This reverts commit ac0e61a9a4e67bf54fc80230660051d366846bd4.

* Remove mention of touchpad from smart magnification event

* Update change log

* Mention minimum macOS version supporting smart magnification

* Improve doc

CHANGELOG.md

@@ -40,7 +40,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - **Breaking:** Split the `platform::unix` module into `platform::x11` and `platform::wayland`. The extension types are similarly renamed.
 - **Breaking:**: Removed deprecated method `platform::unix::WindowExtUnix::is_ready`.
 - Removed `parking_lot` dependency.
-- **Breaking:** On macOS, add support for two-finger touchpad magnification and rotation gestures with new events `WindowEvent::TouchpadMagnify` and `WindowEvent::TouchpadRotate`.
+- **Breaking:** On macOS, add support for two-finger touchpad magnification and rotation gestures with new events `WindowEvent::TouchpadMagnify` and `WindowEvent::TouchpadRotate`. Also add support for touchpad smart-magnification gesture with a new event `WindowEvent::SmartMagnify`.
 - **Breaking:** On web, the `WindowBuilderExtWebSys::with_prevent_default` setting (enabled by default), now additionally prevents scrolling of the webpage in mobile browsers, previously it only disabled scrolling on desktop.
 - On Wayland, `wayland-csd-adwaita` now uses `ab_glyph` instead of `crossfont` to render the title for decorations.
 - On Wayland, a new `wayland-csd-adwaita-crossfont` feature was added to use `crossfont` instead of `ab_glyph` for decorations.

examples/touchpad_gestures.rs

@@ -29,6 +29,9 @@ fn main() {
                         println!("Zoomed out {}", delta);
                     }
                 }
+                WindowEvent::SmartMagnify { .. } => {
+                    println!("Smart zoom");
+                }
                 WindowEvent::TouchpadRotate { delta, .. } => {
                     if delta > 0.0 {
                         println!("Rotated counterclockwise {}", delta);

src/event.rs

@@ -444,6 +444,25 @@ pub enum WindowEvent<'a> {
         phase: TouchPhase,
     },
 
+    /// Smart magnification event.
+    ///
+    /// On a Mac, smart magnification is triggered by a double tap with two fingers
+    /// on the trackpad and is commonly used to zoom on a certain object
+    /// (e.g. a paragraph of a PDF) or (sort of like a toggle) to reset any zoom.
+    /// The gesture is also supported in Safari, Pages, etc.
+    ///
+    /// The event is general enough that its generating gesture is allowed to vary
+    /// across platforms. It could also be generated by another device.
+    ///
+    /// Unfortunatly, neither [Windows](https://support.microsoft.com/en-us/windows/touch-gestures-for-windows-a9d28305-4818-a5df-4e2b-e5590f850741)
+    /// nor [Wayland](https://wayland.freedesktop.org/libinput/doc/latest/gestures.html)
+    /// support this gesture or any other gesture with the same effect.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - Only available on **macOS 10.8** and later.
+    SmartMagnify { device_id: DeviceId },
+
     /// Touchpad rotation event with two-finger rotation gesture.
     ///
     /// Positive delta values indicate rotation counterclockwise and
@@ -594,6 +613,9 @@ impl Clone for WindowEvent<'static> {
                 delta: *delta,
                 phase: *phase,
             },
+            SmartMagnify { device_id } => SmartMagnify {
+                device_id: *device_id,
+            },
             TouchpadRotate {
                 device_id,
                 delta,
@@ -700,6 +722,7 @@ impl<'a> WindowEvent<'a> {
                 delta,
                 phase,
             }),
+            SmartMagnify { device_id } => Some(SmartMagnify { device_id }),
             TouchpadRotate {
                 device_id,
                 delta,

src/platform_impl/macos/view.rs

@@ -858,6 +858,20 @@ declare_class!(
             AppState::queue_event(EventWrapper::StaticEvent(window_event));
         }
 
+        #[sel(smartMagnifyWithEvent:)]
+        fn smart_magnify_with_event(&self, _event: &NSEvent) {
+            trace_scope!("smartMagnifyWithEvent:");
+
+            let window_event = Event::WindowEvent {
+                window_id: self.window_id(),
+                event: WindowEvent::SmartMagnify {
+                    device_id: DEVICE_ID,
+                },
+            };
+
+            AppState::queue_event(EventWrapper::StaticEvent(window_event));
+        }
+
         #[sel(rotateWithEvent:)]
         fn rotate_with_event(&self, event: &NSEvent) {
             trace_scope!("rotateWithEvent:");