Touch points on a touch device. It usually refers to the operation of a finger or stylus on a touchscreen device or touchpad.
# number identifier
The unique identifier of a Touch object, and it is read-only. The identifier does not change during the entire movement of a touch action (finger touch) on the plane. It can be used to judge whether the touch process tracked is the same one.
# number screenX
The X-coordinate of the touch point relative to the left edge of the screen.
# number screenY
The Y-coordinate of the touch point relative to the top edge of the screen.