attachMovie("sling", "sling_1", _root.getNextHighestDepth(), {_x:20, _y:200});
attachMovie("sling", "sling_2", _root.getNextHighestDepth(), {_x:480, _y:200});
attachMovie("ball", "ball", _root.getNextHighestDepth(), {_x:250, _y:100});
_root.createEmptyMovieClip("elastic", _root.getNextHighestDepth());
ball.onPress = function() {
startDrag(this);
};
ball.onRelease = function() {
stopDrag();
};
elastic.onEnterFrame = function() {
this.clear();
this.lineStyle(2, 0x009900);
this.moveTo(sling_1._x, sling_1._y);
if (ball._y>182) {
dist_x = ball._x-sling_1._x;
dist_y = ball._y-sling_1._y;
distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);
elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);
angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling);
this.lineTo(sling_1._x+elastic_length*Math.cos(angle), sling_1._y+elastic_length*Math.sin(angle));
} else {
this.lineTo(sling_2._x, sling_2._y);
}
this.moveTo(sling_2._x, sling_2._y);
if (ball._y>182) {
dist_x = ball._x-sling_2._x;
dist_y = ball._y-sling_2._y;
distance_from_sling = Math.sqrt(dist_x*dist_x+dist_y*dist_y);
elastic_length = Math.sqrt(distance_from_sling*distance_from_sling-18*18);
angle = Math.atan2(dist_y, dist_x)+Math.asin(18/distance_from_sling)*-1;
this.lineTo(sling_2._x+elastic_length*Math.cos(angle), sling_2._y+elastic_length*Math.sin(angle));
} else {
this.lineTo(sling_2._x, sling_2._y);
}
};
测试效果:
在这里我们可以很轻松的计算出小球在线上的角度来。

稍微做一下改动。
来源:网页教学网 作者:闪电儿