크기가 0인 입자입니다. 고유한 이름이 있고 인자 4개가 있습니다:
- position: The X/Y position of the particle, relative to the center of the world.
- velocity: the velocity of the particle. Unit: meters/second.
- force: the force with which the particle is moving around.
- mass: the mass of the particle. This influences forces with which the particle interacts with other items.