phy_position_x;
返回： Real（实数）
This variable can be used to get (or to set) the x position of
the instance within the game room physics world. Please note that
the physics world may present errors when instances are moved by
directly setting this variable as it will interrupt the continuous
simulation.
xx = phy_position_x;
yy = phy_position_y;
The above code stores the instance x and y position in two variables.