大神们，想问一下碰撞/平台的这个例子中为什么要加这句 （selfPreAabb.xMax > otherPreAabb.xMax）判断

Creator 2.x
#1

onCollisionEnter: function (other, self) {
this.node.color = cc.Color.RED;

    this.touchingNumber ++;
    
    // 1st step 
    // get pre aabb, go back before collision
    var otherAabb = other.world.aabb;
    var otherPreAabb = other.world.preAabb.clone();

    var selfAabb = self.world.aabb;
    var selfPreAabb = self.world.preAabb.clone();


    // 2nd step
    // forward x-axis, check whether collision on x-axis
    selfPreAabb.x = selfAabb.x;
    otherPreAabb.x = otherAabb.x;

    if (cc.Intersection.rectRect(selfPreAabb, otherPreAabb)) {
        if (this.speed.x < 0   && (selfPreAabb.xMax > otherPreAabb.xMax)) {         
            this.node.x = otherPreAabb.xMax - this.node.parent.x;
            this.collisionX = -1;
        }
        else if (this.speed.x > 0 && (selfPreAabb.xMin < otherPreAabb.xMin) ) {            
            this.node.x = otherPreAabb.xMin - selfPreAabb.width - this.node.parent.x;
            this.collisionX = 1;
        }

        this.speed.x = 0;
        other.touchingX = true;
        return;
    }

    // 3rd step
    // forward y-axis, check whether collision on y-axis
    selfPreAabb.y = selfAabb.y;
    otherPreAabb.y = otherAabb.y;

    if (cc.Intersection.rectRect(selfPreAabb, otherPreAabb)) {
        if (this.speed.y < 0 && (selfPreAabb.yMax > otherPreAabb.yMax)) {          
            this.node.y = otherPreAabb.yMax - this.node.parent.y;
            this.jumping = false;
            this.collisionY = -1;
        }
        else if (this.speed.y > 0  && (selfPreAabb.yMin < otherPreAabb.yMin)) {               
            this.node.y = otherPreAabb.yMin - selfPreAabb.height - this.node.parent.y;
            this.collisionY = 1;
        }
        
        this.speed.y = 0;
        other.touchingY = true;
    }    
    
},