Table of Contents
基本原理
手指按下处理
手指滑移处理
手指离开处理
优化方案
切换为GPU模式
在滑移时降低显示质量
减少渲染区域
尽可能使用位图而非矢量
减少事件侦听
示例
Home Database Mysql Tutorial 浅谈Adobe Air滑移及其优化

浅谈Adobe Air滑移及其优化

Jun 07, 2016 pm 04:30 PM
adobe ai air optimization

Adobe Air是Adobe公司用来争夺移动设备应用开发的一个重要武器。移动设备的一个重要体验是手指滑移,但Adobe并没有为Air推出官方滑移的SDK。 所以,若打算用Air来开发移动应用,则会碰到滑移这个问题。以下是对基于Air滑移的一些基本原理及其优化方案的讨论

Adobe Air是Adobe公司用来争夺移动设备应用开发的一个重要武器。移动设备的一个重要体验是手指滑移,但Adobe并没有为Air推出官方滑移的SDK。

所以,若打算用Air来开发移动应用,则会碰到滑移这个问题。以下是对基于Air滑移的一些基本原理及其优化方案的讨论,本文最后会给出一个示例。

基本原理

scroll view

上图说明了滑移的显示列表。

ScrollBg是整个滑移的背景,手指在此进行操作,它是侦听手指滑移事件的目标

ScrollTarget是需要进行滑移的对象,其父为ScrollBg。p1,p2和p3为内部的显示对象。

ScrollMask是滑移对象的mask,用于对滑移对象形成遮罩,其父为ScrollBg。

综上,我们需要在ScrollBg上侦听用户手指事件,对ScrollTarget进行滑移,在滑移时我们只能看到被ScrollMask遮罩的那部分。

    在Adobe Air里,MouseEvent等同于手指触摸的TouchEvent,而只有在需要多点触控时,TouchEvent才有其特有的优势。所以我们侦听MouseEvent即可以侦听用户的手指操作。

  • 手指按下处理

  • 通常情况下,手指按下是整个滑移过程的开始。我们可以侦听MouseDown事件来模拟手指按下。

    在MouseDown侦听器里我们还要添加一系列事件侦听器,来构成整个滑移过程的侦听。

    我们需要知道用户的手指移动,于是需要侦听MouseMove事件。我们还需要知道用户手指的释放,于是需要侦听RollOut和MouseUp事件。此外,我们还可能需要侦听EnterFrame事件,来做一些内部的更新逻辑。

    综上,我们在MouseDown侦听器里处理滑移的开始,并为手指移动,手指释放及每帧更新等事件添加侦听器

  • 手指滑移处理

  • 在MouseMove事件侦听器里,我们需要让滑移对象跟随玩家的手指进行移动。

    所以在添加MouseMove侦听器之前,我们需要事先记录滑移对象当前的位置信息(诸如mouseX,mouseY),并在MouseMove侦听器对滑移对象的位置进行记录,通过两个位置的差异,我们可以计算出滑移对象需要移动的距离。

    若需要移动的距离在合理的范围之内(如:不超过边界值的一半大小),我们将对滑移对象的位置进行改变,并进行更新。

    有时候,我们可能会对滑移对象内的对象添加点击事件,但是我们不希望在滑移释放手指的时候触发这些点击事件。这时候我们可以在MouseMove侦听器里通过计算滑移对象的移动距离,来判断是否应该触发点击事件。

    比如若用户的手指只移动了1-2个像素,用户很可能只是希望点击,而非滑移,所以此时我们不进行处理;但是用户的手指移动了10个以上像素,则我们可以认为用户是在进行滑移操作,此时我们将滑移对象的mouseChildren和mouseEnabled属性禁用,则点击事件则不会在滑移时触发了。

    综上,我们在MouseMove侦听器里记录手指的位置,更新滑移对象的位置以跟随手指移动,做一些特殊处理以避免滑移时让用户触发点击事件

  • 手指离开处理

  • 我们可以将RollOut事件和MouseUp事件视为用户手指离开了滑移触发区域,从而为这两个事件添加一个共同的侦听器MouseLeaveHandler。

    在ios和android的原生滑移里,当用户滑移时手指离开屏幕,系统会对滑移对象进行自动滑移,这类似于物理中的惯性。

    所以我们需要对滑移对象进行一个类似“惯性”的缓动,并在缓动结束的时候,做一些滑移结束的处理。

    同时释放MouseMove和MouseLeaveHandler的侦听,并重新添加MouseDown事件的侦听,来侦听新的滑移。

    综上,我们在MouseLeaveHandler里移除MouseMove和手指移开的事件侦听,并对滑移对象做一个”惯性”的缓动,在缓动结束时,做滑移结束的处理。

优化方案

相对于其他移动开发的引擎,Flash的渲染效率较低,在弱CPU的移动设备上体现尤其明显。

滑移需要移动大块显示区域,可能会造成卡顿和跳帧,所以优化是必须要进行的一项工作。

以下是一些我在实践总结出来的优化方案。

  • 切换为GPU模式

  • 经试验,将大面积滑移从cpu模式切换到gpu模式后,滑移的效率显著的提升了,基本可以达到原生滑移的效果。 只需要修改-app.xml里面的

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gpu

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GPU模式的优点是处理大块渲染区域移动的效率会显著提升。 缺点是不能使用滤镜,不能使用混合模式,在某些android机型(基本是低端机)上可能会跑不起来。 其中滤镜可以用位图替代,但是可能会带来内存上升的问题。
  • 在滑移时降低显示质量

  • 相对于PC屏幕,移动设备屏幕的ppi值要高很多。这就意味着,当我们在移动设备上降低显示质量时,实际感觉画质效果并没有PC上丢失的那么多。 所以在滑移开始时,我们可以先降低舞台显示质量。

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    stage.quality = StageQuality.LOW;

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    等滑移结束时,再恢复舞台显示质量。

    此方案带来的效率提升也是显著的。

    但是会显著的降低显示质量,所以需要在效率和效果方面做取舍。

  • 减少渲染区域

  • 减少渲染区域可以从根本上解决渲染压力的问题。

    实际上,在滑移时,有许多区域都在遮罩区域之外,但这些人眼不可见的区域的位置仍然会被CPU计算,从而浪费CPU周期,降低了效率。

    所以,我们可以在EnterFrame事件里,将在遮罩区域之外的滑移对象的visible设为false。从而避免了它们占用CPU周期。

    以下代码片段说明以上的方法。

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    var i:int;

    var numChildren:int = _target.numChildren;

    var child:DisplayObject;

    for(i = 0; i  _bounds.bottom + MAX_VISIBLE_DIST )

            {

                child.visible = false;

            }

            else

            {

                child.visible = true;

            }

        }

        else if( _direct == ScrollDirection.HORIZONTAL || _direct == ScrollDirection.BOTH )

        {

            if( child.x + child.width + _target.x  _bounds.right + MAX_VISIBLE_DIST )

            {

                child.visible = false;

            }

            else

            {

                child.visible = true;

            }

        }

    }

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  • 尽可能使用位图而非矢量

  • 矢量需要CPU实时进行计算,所以尽可能避免在移动设备上使用矢量,尽可能用位图来替代。
  • 减少事件侦听

  • 事件侦听会消耗帧时间,而且不能恰当的销毁事件侦听会带来恐怖的内存泄露。 所以尽可能减少不必要的事件侦听。 比如在滑移时,将目标的mouse相关属性禁用,等待滑移结束时再启用。

    示例

    示例:http://wuzhiwei.net/opensrc/ScrollAs3/ScrollAs3.html
    源码:https://github.com/iWoz/AirScroll
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