particle.py 文件源码

def radial(cls, r, theta):
        """Provide a radial acceleration.

         Arguments:
             r (float): speed in pixels per second (per second)
             theta (float): angle in degrees (0 = +X axis, 90 = +Y axis)
         """
        radians = math.radians(theta)
        ax = r * math.cos(radians)
        ay = r * math.sin(radians)
        return cls(ax=ax, ay=ay)