2020.06.03：
修改了view.js，
原1233~1235：
addListener(document, EVENT_POINTER_MOVE, this.onPointerMove = this.pointermove.bind(this));
addListener(document, EVENT_POINTER_UP, this.onPointerUp = this.pointerup.bind(this));
addListener(document, EVENT_KEY_DOWN, this.onKeyDown = this.keydown.bind(this));
改：
addListener(canvas, EVENT_POINTER_MOVE, this.onPointerMove = this.pointermove.bind(this));
addListener(canvas, EVENT_POINTER_UP, this.onPointerUp = this.pointerup.bind(this));
addListener(canvas, EVENT_KEY_DOWN, this.onKeyDown = this.keydown.bind(this));
原1257~1259：
removeListener(document, EVENT_POINTER_MOVE, this.onPointerMove);
removeListener(document, EVENT_POINTER_UP, this.onPointerUp);
removeListener(document, EVENT_KEY_DOWN, this.onKeyDown);
改：
removeListener(canvas, EVENT_POINTER_MOVE, this.onPointerMove);
removeListener(canvas, EVENT_POINTER_UP, this.onPointerUp);
removeListener(canvas, EVENT_KEY_DOWN, this.onKeyDown);