add new system to be able to move the camera

examples/ios/src/lib.rs

@@ -32,8 +32,37 @@ fn main() {
         .add_plugin(AudioPlugin)
         .add_startup_system(setup_scene)
         .add_startup_system(setup_music)
+        .add_system(touch_camera)
         .run();
 }
+
+fn touch_camera(
+    windows: ResMut<Windows>,
+    mut touches: EventReader<TouchInput>,
+    mut camera: Query<&mut Transform, With<Camera>>,
+    mut last_position: Local<Option<Vec2>>,
+) {
+    for touch in touches.iter() {
+        match touch.phase {
+            TouchPhase::Started => *last_position = None,
+            _ => (),
+        }
+        if let Some(last_position) = *last_position {
+            let window = windows.get_primary().unwrap();
+            let mut transform = camera.single_mut();
+            *transform = Transform::from_xyz(
+                transform.translation.x
+                    + (touch.position.x - last_position.x) / window.width() * 5.0,
+                transform.translation.y,
+                transform.translation.z
+                    + (touch.position.y - last_position.y) / window.height() * 5.0,
+            )
+            .looking_at(Vec3::ZERO, Vec3::Y);
+        }
+        *last_position = Some(touch.position);
+    }
+}
+
 /// set up a simple 3D scene
 fn setup_scene(
     mut commands: Commands,