worldPosition.z -= speed; 请问这段代码 -=是什么意思呀，是什么缩写嘛，可以补全一下嘛谢谢
spicyduckhead worldPosition.z -= speed; worldPosition.z = worldPosition.z - speed; 沿着z坐标以speed速度运动
worldPosition.z -= speed; worldPosition.z = worldPosition.z - speed;
