Implement WheelEvent Interface

Note: The WheelEvent interface supports rotation in all 3 spatial
dimensions. This implementation only supports two due to limitations
in the Glutin compositor.

The wheelevent interface is a dom interface that triggers for any
attached device that can rotate in one or more spatial dimensions.
Traditionally this is the mouse wheel though other devices could be
used as well. E.g. the trackball on a trackball mouse.

components/script/dom/wheelevent.rs

@@ -0,0 +1,163 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use crate::dom::bindings::codegen::Bindings::MouseEventBinding::MouseEventMethods;
+use crate::dom::bindings::codegen::Bindings::WheelEventBinding;
+use crate::dom::bindings::codegen::Bindings::WheelEventBinding::WheelEventMethods;
+use crate::dom::bindings::error::Fallible;
+use crate::dom::bindings::inheritance::Castable;
+use crate::dom::bindings::num::Finite;
+use crate::dom::bindings::reflector::reflect_dom_object;
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::bindings::str::DOMString;
+use crate::dom::event::{Event, EventBubbles, EventCancelable};
+use crate::dom::mouseevent::MouseEvent;
+use crate::dom::window::Window;
+use dom_struct::dom_struct;
+use std::cell::Cell;
+
+#[dom_struct]
+pub struct WheelEvent {
+    mouseevent: MouseEvent,
+    delta_x: Cell<Finite<f64>>,
+    delta_y: Cell<Finite<f64>>,
+    delta_z: Cell<Finite<f64>>,
+    delta_mode: Cell<u32>,
+}
+
+impl WheelEvent {
+    fn new_inherited() -> WheelEvent {
+        WheelEvent {
+            mouseevent: MouseEvent::new_inherited(),
+            delta_x: Cell::new(Finite::wrap(0.0)),
+            delta_y: Cell::new(Finite::wrap(0.0)),
+            delta_z: Cell::new(Finite::wrap(0.0)),
+            delta_mode: Cell::new(0),
+        }
+    }
+
+    pub fn new_unintialized(window: &Window) -> DomRoot<WheelEvent> {
+        reflect_dom_object(
+            Box::new(WheelEvent::new_inherited()),
+            window,
+            WheelEventBinding::Wrap,
+        )
+    }
+
+    pub fn new(
+        window: &Window,
+        type_: DOMString,
+        can_bubble: EventBubbles,
+        cancelable: EventCancelable,
+        view: Option<&Window>,
+        detail: i32,
+        delta_x: Finite<f64>,
+        delta_y: Finite<f64>,
+        delta_z: Finite<f64>,
+        delta_mode: u32,
+    ) -> DomRoot<WheelEvent> {
+        let ev = WheelEvent::new_unintialized(window);
+        ev.InitWheelEvent(
+            type_,
+            bool::from(can_bubble),
+            bool::from(cancelable),
+            view,
+            detail,
+            delta_x,
+            delta_y,
+            delta_z,
+            delta_mode,
+        );
+
+        ev
+    }
+
+    pub fn Constructor(
+        window: &Window,
+        type_: DOMString,
+        init: &WheelEventBinding::WheelEventInit,
+    ) -> Fallible<DomRoot<WheelEvent>> {
+        let event = WheelEvent::new(
+            window,
+            type_,
+            EventBubbles::from(init.parent.parent.parent.parent.bubbles),
+            EventCancelable::from(init.parent.parent.parent.parent.cancelable),
+            init.parent.parent.parent.view.deref(),
+            init.parent.parent.parent.detail,
+            init.deltaX,
+            init.deltaY,
+            init.deltaZ,
+            init.deltaMode,
+        );
+
+        Ok(event)
+    }
+}
+
+impl WheelEventMethods for WheelEvent {
+    // https://w3c.github.io/uievents/#widl-WheelEvent-deltaX
+    fn DeltaX(&self) -> Finite<f64> {
+        self.delta_x.get()
+    }
+
+    // https://w3c.github.io/uievents/#widl-WheelEvent-deltaY
+    fn DeltaY(&self) -> Finite<f64> {
+        self.delta_y.get()
+    }
+
+    // https://w3c.github.io/uievents/#widl-WheelEvent-deltaZ
+    fn DeltaZ(&self) -> Finite<f64> {
+        self.delta_z.get()
+    }
+
+    // https://w3c.github.io/uievents/#widl-WheelEvent-deltaMode
+    fn DeltaMode(&self) -> u32 {
+        self.delta_mode.get()
+    }
+
+    // https://w3c.github.io/uievents/#widl-WheelEvent-initWheelEvent
+    fn InitWheelEvent(
+        &self,
+        type_arg: DOMString,
+        can_bubble_arg: bool,
+        cancelable_arg: bool,
+        view_arg: Option<&Window>,
+        detail_arg: i32,
+        delta_x_arg: Finite<f64>,
+        delta_y_arg: Finite<f64>,
+        delta_z_arg: Finite<f64>,
+        delta_mode_arg: u32,
+    ) {
+        if self.upcast::<Event>().dispatching() {
+            return;
+        }
+
+        self.upcast::<MouseEvent>().InitMouseEvent(
+            type_arg,
+            can_bubble_arg,
+            cancelable_arg,
+            view_arg,
+            detail_arg,
+            self.mouseevent.ScreenX(),
+            self.mouseevent.ScreenY(),
+            self.mouseevent.ClientX(),
+            self.mouseevent.ClientY(),
+            self.mouseevent.CtrlKey(),
+            self.mouseevent.AltKey(),
+            self.mouseevent.ShiftKey(),
+            self.mouseevent.MetaKey(),
+            self.mouseevent.Button(),
+            self.mouseevent.GetRelatedTarget().deref(),
+        );
+        self.delta_x.set(delta_x_arg);
+        self.delta_y.set(delta_y_arg);
+        self.delta_z.set(delta_z_arg);
+        self.delta_mode.set(delta_mode_arg);
+    }
+
+    // https://dom.spec.whatwg.org/#dom-event-istrusted
+    fn IsTrusted(&self) -> bool {
+        self.mouseevent.IsTrusted()
+    }
+}