1、合成--新建合成
3、添加一个纯色图层背景
5、选择两层，右键--预合成
7、快捷键p，添加位置动画从上往下落
9、添加表达式，在时间轴上到表达式输入框复制下面代码e = .7;g = 5000;nMax = 9;n = 0;if (numKeys > 0){ n = nearestKey(time像粜杵泳).index; if (key(n).time > time) n--;}if (n > 0){ t = time - key(n).time; v = -velocityAtTime(key(n).time - .001)*e; vl = length(v); if (value instanceof Array){ vu = (vl > 0) ? normalize(v) : [0,0,0]; }else{ vu = (v < 0) ? -1 : 1;}tCur = 0;segDur = 2*vl/g; tNext = segDur;nb = 1; // number of bounceswhile (tNext < t && nb <= nMax){ vl *= e; segDur *= e; tCur = tNext; tNext += segDur; nb++ }if(nb <= nMax){ delta = t - tCur; value + vu*delta*(vl - g*delta/2); }else{ value}}else value
