测试效果如下：
然后我们通过修改上面的代码，在两个小球之间绘制一条线，可以随中间小球任意移动。 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。 测试效果如下：
最后我们让小球自动运动或者你可以用鼠标拖动小球。 测试最终效果：
以上演示动画的所有Fla源文件提供下载：
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();
};
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_l
ength*Math.sin(angle));
} else {
this.lineTo(sling_2._x, sling_2._y);
}
};
attachMovie("sling", "sling_2", _root.getNextHighestDepth(), {_x:480, _y:200});
attachMovie("ball", "ball", _root.getNextHighestDepth(), {_x:250, _y:100});
_root.createEmptyMovieClip("elastic", _root.getNextHighestDepth());
xspeed = 0;
yspeed = 0;
fire = false;
ball.onPress = function() {
fire = false;
startDrag(this);
};
ball.onRelease = function() {
stopDrag();
fire = true;
};
ball.onEnterFrame = function() {
if (fire) {
this._x += (xspeed*0.001);
this._y += (yspeed*0.001);
}
};
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);
saved_angle = angle;
this.lineTo(sling_1._x+elastic_length*Math.cos(angle), sling_1._y+elastic_
length*Math.sin(angle));
this.lineTo(ball._x,ball._y);
} 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));
this.lineTo(ball._x,ball._y);
} else {
this.lineTo(sling_2._x, sling_2._y);
}
};
var elastic:MovieClip = _root.createEmptyMovieClip("elastic", 1);
var point1:MovieClip = _root.attachMovie("sling", "point1", 3, {_x:50, _y:200});
var point2:MovieClip = _root.attachMovie("sling", "point2", 4, {_x:450, _y:200});
var gravity = 0.1;
var angle1:Number = 0;
var angle2:Number = 0;
var radius:Number = 13.0;
// Or whatever half the width of your ball is.
var elasticCoefficient:Number = 0.001;
// This number will affect the stretchiness of the sling. The greater the number
// the tighter the elastic will be.
var released:Boolean = true;
var forced:Boolean = false;
var acc:Object = {x:0, y:0};
var vel:Object = {x:0, y:0};
_root.onMouseDown = function() {
ball._x = _root._xmouse;
ball._y = _root._ymouse;
ball.startDrag();
_root.released = false;
vel.x = 0;
vel.y = 0;
};
_root.onMouseUp = function() {
ball.stopDrag();
_root.released = true;
};
ball.onPress = function() {
ball.startDrag();
_root.released = false;
vel.x = 0;
vel.y = 0;
};
ball.onRelease = function() {
ball.stopDrag();
_root.released = true;
};
_root.onEnterFrame = function() {
elastic.clear();
elastic.lineStyle(3, 0xFF0000);
if (released) {
ball._x += vel.x;
ball._y += vel.y;
}
if (ball._y>=187) {
/* This area differs from the code in the tutorial.
The reason for that is I didn’t read the code, I just looked at the examples.
I try to gain experience with problem-solving by doing things as close to by
myself as possible. */
forced = true;
var x1:Number = ball._x-point1._x;
var y1:Number = ball._y-point1._y;
var x2:Number = point2._x-ball._x;
var y2:Number = point2._y-ball._y;
var distance1:Number = Math.sqrt(x1*x1+y1*y1);
var distance2:Number = Math.sqrt(x2*x2+y2*y2);
_root.angle1 = Math.atan2(y1, x1);
_root.angle2 = Math.atan2(y2, x2);
var xOffset:Number = Math.cos(angle1+Math.PI/2)*radius;
var yOffset:Number = Math.sin(angle1+Math.PI/2)*radius;
var xOffset2:Number = Math.cos(angle2+Math.PI/2)*radius;
var yOffset2:Number = Math.sin(angle2+Math.PI/2)*radius;
angle1 += Math.sin(radius/distance1);
angle2 += Math.sin(radius/distance2)*-1;
elastic.moveTo(point1._x, point1._y);
elastic.lineTo(ball._x+xOffset, ball._y+yOffset);
elastic.moveTo(point2._x, point2._y);
elastic.lineTo(ball._x+xOffset2, ball._y+yOffset2);
} else {
forced = false;
elastic.moveTo(point1._x, point1._y);
elastic.lineTo(point2._x, point2._y);
}
acc.x = 0;
acc.y = 0;
acc.y = gravity;
if (released && forced) {
/* This section applies the force of the sling to the ball in terms of acceleration bas
ed on the stretching of
the sling, in the direction of the displacement, scaled by a coefficient that also encap
sulates the mass of
the ball. */
acc.x += distance1*Math.sin(angle2)*elasticCoefficient;
acc.y += -distance1*Math.cos(angle1)*elasticCoefficient;
acc.x += distance2*Math.sin(angle1)*elasticCoefficient;
acc.y += -distance2*Math.cos(angle2)*elasticCoefficient;
}
if (released) {
vel.x += acc.x;
vel.y += acc.y;
}
};
类似弹弓的小游戏.rar
