纯JS制作的窗户雨滴效果

function demo() {
var engine = new RainyDay('canvas','demo1', window.innerWidth, window.innerHeight);
engine.gravity = engine.GRAVITY_NON_LINEAR;
engine.trail = engine.TRAIL_DROPS;
engine.rain([
engine.preset(0, 2, 500)
]);
engine.rain([
engine.preset(3, 3, 0.88),
engine.preset(5, 5, 0.9),
engine.preset(6, 2, 1),
], 100);
}