Events#onDragStart

This signal is dispatched if the Game Object has been inputEnabled and enableDrag has been set.
It is sent when a Phaser.Pointer starts to drag the Game Object, taking into consideration the various
drag limitations that may be set.
It is sent four arguments:
{any} The Game Object that received the event.
{Phaser.Pointer} The Phaser.Pointer object that caused the event.
{number} The x coordinate that the drag started from.
{number} The y coordinate that the drag started from.