add web scroll event

Cargo.toml

@@ -29,7 +29,26 @@ redox_syscall = { version = "0.2.1" }
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 wasm-bindgen = "0.2.69"
 # js-sys = "0.3"
-web-sys = { version = "0.3", features = ["Node", "Element", "console", "CanvasRenderingContext2d", "Document",  "Element", "ImageData", "HtmlCanvasElement", "HtmlElement", "Window", "CssStyleDeclaration", "MouseEvent", "KeyboardEvent", "DomRect"] }
+
+[target.'cfg(target_arch = "wasm32")'.dependencies.web-sys]
+version = "0.3"
+features = [
+    "Node", 
+    "Element", 
+    "console", 
+    "CanvasRenderingContext2d", 
+    "Document",  
+    "Element", 
+    "ImageData", 
+    "HtmlCanvasElement", 
+    "HtmlElement", 
+    "Window", 
+    "CssStyleDeclaration", 
+    "MouseEvent", 
+    "KeyboardEvent", 
+    "WheelEvent",
+    "DomRect"
+]
 
 [features]
 default = ["bundled"]

src/sys/web.rs

@@ -273,6 +273,26 @@ impl Window {
                 closure.forget();
             }
 
+            // wheel (scroll)
+            {
+                let events = events.clone();
+
+                let closure = Closure::wrap(Box::new(move |e: web_sys::WheelEvent| {
+                    events.borrow_mut().push(
+                        ScrollEvent {
+                            x: e.delta_x() as i32,
+                            y: e.delta_y() as i32,
+                        }
+                        .to_event(),
+                    )
+                }) as Box<dyn FnMut(_)>);
+                document()
+                    .unwrap()
+                    .add_event_listener_with_callback("wheel", closure.as_ref().unchecked_ref())
+                    .unwrap();
+                closure.forget();
+            }
+
             if let Ok(context) = context_2d(&canvas) {
                 return Some(Window {
                     x,