making things move as3 ---缓动和弹性公式

简单缓动，长形：

var dx:Number = targetX - sprite.x;

var dy:Number = targetY - sprite.y;

vx = dx * easing;

vy = dy * easing;

sprite.x += vx;

sprite.y += vy;

简单缓动，中形：

vx = (targetX - sprite.x) * easing;

vy = (targetY - sprite.y) * easing;

sprite.x += vx;

sprite.y += vy;

简单缓动，短形：

sprite.x += (targetX - sprite.x) * easing;

sprite.y += (targetY - sprite.y) * easing;

简单弹性，长形：

var ax:Number = (targetX - sprite.x) * spring;

var ay:Number = (targetY - sprite.y) * spring;

vx += ax;

vy += ay;

vx *= friction;

vy *= friction;

sprite.x += vx;

sprite.y += vy;


简单弹性，中形：

vx += (targetX - sprite.x) * spring;

vy += (targetY - sprite.y) * spring;

vx *= friction;

vy *= friction;

sprite.x += vx;

sprite.y += vy;

简单弹性，短形：

vx += (targetX - sprite.x) * spring;

vy += (targetY - sprite.y) * spring;

sprite.x += (vx *= friction);

sprite.y += (vy *= friction);

偏移弹性运动：

var dx:Number = sprite.x - fixedX;

var dy:Number = sprite.y - fixedY;

var angle:Number = Math.atan2(dy, dx);

var targetX:Number = fixedX + Math.cos(angle) * springLength;

var targetY:Number = fixedX + Math.sin(angle) * springLength;