Support pinch, double tap and rotation gestures on iOS (#3130)

This is off by default on iOS. Note that pinch delta may be NaN.

Co-authored-by: Mads Marquart <mads@marquart.dk>

examples/touch_gestures.rs

@@ -0,0 +1,62 @@
+use simple_logger::SimpleLogger;
+use winit::{
+    event::{Event, WindowEvent},
+    event_loop::EventLoop,
+    window::WindowBuilder,
+};
+
+#[path = "util/fill.rs"]
+mod fill;
+
+fn main() -> Result<(), impl std::error::Error> {
+    SimpleLogger::new().init().unwrap();
+    let event_loop = EventLoop::new().unwrap();
+
+    let window = WindowBuilder::new()
+        .with_title("Touchpad gestures")
+        .build(&event_loop)
+        .unwrap();
+    #[cfg(target_os = "ios")]
+    {
+        use winit::platform::ios::WindowExtIOS;
+        window.recognize_doubletap_gesture(true);
+        window.recognize_pinch_gesture(true);
+        window.recognize_rotation_gesture(true);
+    }
+
+    println!("Only supported on macOS/iOS at the moment.");
+
+    let mut zoom = 0.0;
+    let mut rotated = 0.0;
+
+    event_loop.run(move |event, elwt| {
+        if let Event::WindowEvent { event, .. } = event {
+            match event {
+                WindowEvent::CloseRequested => elwt.exit(),
+                WindowEvent::PinchGesture { delta, .. } => {
+                    zoom += delta;
+                    if delta > 0.0 {
+                        println!("Zoomed in {delta:.5} (now: {zoom:.5})");
+                    } else {
+                        println!("Zoomed out {delta:.5} (now: {zoom:.5})");
+                    }
+                }
+                WindowEvent::DoubleTapGesture { .. } => {
+                    println!("Smart zoom");
+                }
+                WindowEvent::RotationGesture { delta, .. } => {
+                    rotated += delta;
+                    if delta > 0.0 {
+                        println!("Rotated counterclockwise {delta:.5} (now: {rotated:.5})");
+                    } else {
+                        println!("Rotated clockwise {delta:.5} (now: {rotated:.5})");
+                    }
+                }
+                WindowEvent::RedrawRequested => {
+                    fill::fill_window(&window);
+                }
+                _ => (),
+            }
+        }
+    })
+}