用Flash制作一个类似弹弓的小游戏教程

核心提示： 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，用Flash制作一个类似弹弓的小游戏教程(4)，var ball:MovieClip = _root.attachMovie("ball", "ball", 2, {_x:250, _y:

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。

var ball:MovieClip = _root.attachMovie("ball", "ball", 2, {_x:250, _y:100});
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 based on the stretching of
　　　　the sling, in the direction of the displacement, scaled by a coefficient that also encapsulates 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;
　　}
};

测试最终效果。