Widget events correspond to touches on the screen. However, the concept of touch in Kivy is broader than might be intuitively assumed. It includes mouse events, finger touches, and magic pen touches. For the sake of simplicity, we will often assume in this chapter that we are using a mouse but it doesn't matter if we were using a touch screen (and the finger or magic pen instead). The following are the three basic
on_touch_down: When a new touch starts. For example, the action of pressing a button of the mouse or touching the screen.
on_touch_move: When the touch is moved. For example, dragging the mouse or slide the finger over the screen.
on_touch_up: When the touch ends. For example, ...