html5游戏-追踪算法

追踪算法的原理：目标位置 - 当前位置 / 速度，即： dx = targetX - currentX / speed, dy = targetY - currentY / speed

var getStep = function(iTarget, iNow) {
        var iStep = (iTarget - iNow) / this.speed;
        if (iStep == 0){ return 0; }
        if (Math.abs(iStep) < 1){ return (iStep > 0 ? 1 : -1); }
        return iStep;
 };

var dx = getStep(this.ctx.owner.owner.player.x,this.ctx.owner.x),
      dy = getStep(this.ctx.owner.owner.player.y,this.ctx.owner.y);