Added wheel support (#321)

* Added wheel support

* Updated docs

ipycanvas/canvas.py

@@ -582,6 +582,7 @@ class Canvas(_CanvasBase):
 
     _client_ready_callbacks = Instance(CallbackDispatcher, ())
 
+    _mouse_wheel_callbacks = Instance(CallbackDispatcher, ())
     _mouse_move_callbacks = Instance(CallbackDispatcher, ())
     _mouse_down_callbacks = Instance(CallbackDispatcher, ())
     _mouse_up_callbacks = Instance(CallbackDispatcher, ())
@@ -1507,6 +1508,10 @@ def on_mouse_out(self, callback, remove=False):
         """Register a callback that will be called on mouse out of the canvas."""
         self._mouse_out_callbacks.register_callback(callback, remove=remove)
 
+    def on_mouse_wheel(self, callback, remove=False):
+        """Register a callback that will be called on mouse wheel movement."""
+        self._mouse_wheel_callbacks.register_callback(callback, remove=remove)
+
     def on_touch_start(self, callback, remove=False):
         """Register a callback that will be called on touch start (new finger on the screen)."""
         self._touch_start_callbacks.register_callback(callback, remove=remove)
@@ -1551,6 +1556,8 @@ def _handle_frontend_event(self, _, content, buffers):
             self._mouse_up_callbacks(content["x"], content["y"])
         if content.get("event", "") == "mouse_out":
             self._mouse_out_callbacks(content["x"], content["y"])
+        if content.get("event", "") == "mouse_wheel":
+            self._mouse_wheel_callbacks(content["x"], content["y"])
 
         if content.get("event", "") == "touch_start":
             self._touch_start_callbacks(
@@ -1749,6 +1756,10 @@ def on_mouse_out(self, callback, remove=False):
         """Register a callback that will be called on mouse out of the canvas."""
         self._canvases[-1].on_mouse_out(callback, remove=remove)
 
+    def on_mouse_wheel(self, callback, remove=False):
+        """Register a callback that will be called on mouse wheel movement."""
+        self._canvases[-1].on_mouse_wheel(callback, remove=remove)
+
     def on_touch_start(self, callback, remove=False):
         """Register a callback that will be called on touch start (new finger on the screen)."""
         self._canvases[-1].on_touch_start(callback, remove=remove)

src/widget.ts

@@ -1338,6 +1338,9 @@ export class CanvasView extends DOMWidgetView {
     this.el.addEventListener('mouseout', {
       handleEvent: this.onMouseOut.bind(this)
     });
+    this.el.addEventListener('wheel', {
+      handleEvent: this.onMouseWheel.bind(this)
+    });
     this.el.addEventListener('touchstart', {
       handleEvent: this.onTouchStart.bind(this)
     });
@@ -1392,6 +1395,14 @@ export class CanvasView extends DOMWidgetView {
     this.model.send({ event: 'mouse_out', ...this.getCoordinates(event) }, {});
   }
 
+  private onMouseWheel(event: WheelEvent) {
+    this.model.send(
+      { event: 'mouse_wheel', x: event.deltaX, y: event.deltaY },
+      {}
+    );
+    event.preventDefault();
+  }
+
   private onTouchStart(event: TouchEvent) {
     const touches: Touch[] = Array.from(event.touches);
     this.model.send(