AE跟从线条拖尾MG动绘教程 After Effects Vector Shape Layer Trails Tutorial
经由过程表达式去掌握天生拖尾线条结果，MG动绘非常有效的小本领
In this tutorial, Mikey Borup walks us through the process of creating cool looking vector shape layer trails inside of Adobe After Effects.
用到的表达式：
D=Math.sqrt(value[0]*value[0]+value[1]*value[1]);
rot=radiansToDegrees(Math.atan2(value[1],value[0]))
XS=transform.scale[0]/100;
YS=transform.scale[1]/100;
TC=Math.cos(degreesToRadians(rotation+rot));
TS=Math.sin(degreesToRadians(rotation+rot))*.9;
[D*TC*XS,D*TS*YS]+position
