HTML5游戏框架cnGameJS开发实录-外部输入模块篇

1.为什么我们需要外部输入模块？

　　在游戏中我们常常用到类似这样的操作：鼠标点击某位置，玩家对象移动到该位置，或者按鼠标方向键，玩家向不同方向移动，等等。这些操作无一不用与外部输入设备打交道。作为游戏的设计者，我们很需要在任何时候知道鼠标目前的位置，键盘的点击状况等，从而方便我们对游戏元素加以控制。因此作为一个游戏框架，外部输入模块也是必不可少的。

2.提供哪些功能，怎样使用？

　　外部输入模块主要实现的功能就是动态记录鼠标相对于canvas的位置，以及记录键盘上哪些键是按下的，哪些键刚刚松开，并触发相应的回调函数。

　　我们可以通过框架保存的两个字段获取鼠标当前在canvas的位置：

var x=cnGame.input.mouseX;
var y=cnGame.input.mouseY;

　　由于canvas下的游戏编程模式是通过一个游戏循环来实现的帧动画（关于游戏循环请看：HTML5游戏框架cnGameJS开发实录（游戏循环篇）），因此单纯对键盘keyup与keydown的绑定，往往并不能达到期望效果，举个例子，我们如果想在键盘按下左键时使元素一直向左移动：

cnGame.input.onKeyDown("left",(){
    player.move(-10);
 })

　　我们会发现这种方法并不能很好的运用在帧动画的编程模型。由于当我们按着键盘左方向键时，其回调函数会不断触发，因此触发频率并不能和你的帧动画的频率一致（要么太快要么太慢，取决于你的帧频率），所以更好的选择是每次帧更新时，判断左键是否按下，如果是按下游戏元素就向左移动一定位置，这样游戏元素就成为帧动画的一部分，随着每次帧的更新而更新：

/*每次帧更新调用的函数*/
var update=function(){
   cnGame.input.isPressed("left",function(){player.move(-10);})
}

3.代码实现

　　首先看如何保持鼠标在canvas的位置。鼠标相对于canvas的位置，其实就是鼠标相对于页面的位置和canvas的位置之差。在之前的HTML5游戏框架cnGameJS开发实录（核心函数模块篇）里已经介绍过，在框架的初始化函数里，我们已经通过getCanvasPos获取到canvas在页面的位置，因此鼠标相对于canvas的位置可以如此计算：　

/**
     *记录鼠标在canvas内的位置
    **/    
    var recordMouseMove=function(eve){
        var pageX,pageY,x,y;
        eve=cg.core.getEventObj(eve);
        pageX = eve.pageX || eve.clientX + document.documentElement.scrollLeft - document.documentElement.clientLeft;
        pageY = eve.pageY || eve.clientY + document.documentElement.scrollTop - document.documentElement.clientTop;
        cg.input.mouseX=pageX-cg.x;
        cg.input.mouseY=pageY-cg.y;
            
    }

　　之后再看看键盘输入的记录如何实现，我们需要一个数组，保存每个键的名值对（键名和键编码），以及一些对象，保存每个键对应的按下和松开的回调函数，还有最后一个对象，保存那些需要禁止默认行为的键名。（禁止键盘默认行为在游戏开发中很必要，可以防止玩家在操控时游戏对象时触发不必要的浏览器默认行为，例如滚动条滚动等）。

　首先是建立键名和键编码的字典：

/**
     *键盘按键编码和键名
    **/    
    var k=[];
    k[8] = "backspace"
    k[9] = "tab"
    k[13] = "enter"
    k[16] = "shift"
    k[17] = "ctrl"
    k[18] = "alt"
    k[19] = "pause"
    k[20] = "capslock"
    k[27] = "esc"
    k[32] = "space"
    k[33] = "pageup"
    k[34] = "pagedown"
    k[35] = "end"
    k[36] = "home"
    k[37] = "left"
    k[38] = "up"
    k[39] = "right"
    k[40] = "down" 
    k[45] = "insert"
    k[46] = "delete"
    
    k[91] = "leftwindowkey"
    k[92] = "rightwindowkey"
    k[93] = "selectkey"
    k[106] = "multiply"
    k[107] = "add"
    k[109] = "subtract"
    k[110] = "decimalpoint"
    k[111] = "divide"
    
    k[144] = "numlock"
    k[145] = "scrollock"
    k[186] = "semicolon"
    k[187] = "equalsign"
    k[188] = "comma"
    k[189] = "dash"
    k[190] = "period"
    k[191] = "forwardslash"
    k[192] = "graveaccent"
    k[219] = "openbracket"
    k[220] = "backslash"
    k[221] = "closebracket"
    k[222] = "singlequote"
    
    var numpadkeys = ["numpad1","numpad2","numpad3","numpad4","numpad5","numpad6","numpad7","numpad8","numpad9"]
    var fkeys = ["f1","f2","f3","f4","f5","f6","f7","f8","f9"]
    var numbers = ["0","1","2","3","4","5","6","7","8","9"]
    var letters = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
    for(var i = 0; numbers[i]; i++)     { k[48+i] = numbers[i] }
    for(var i = 0; letters[i]; i++)     { k[65+i] = letters[i] }
    for(var i = 0; numpadkeys[i]; i++)  { k[96+i] = numpadkeys[i] }
    for(var i = 0; fkeys[i]; i++)       { k[112+i] = fkeys[i] }

　　有点长，不过其实没啥技术含量，就是方便我们以后知道某个编码的键名是什么。例如我们按下左键，那么流程就是：获取到左键的键盘编码->在字典中得到键名->在对象中通过键名获取到之前同样通过键名保存的处理程序，并执行。

　　为键盘绑定处理程序的代码如下：

/**
     *记录键盘按下的键
    **/    
    var recordPress=function(eve){
        eve=cg.core.getEventObj(eve);
        var keyName=k[eve.keyCode];
        pressed_keys[keyName]=true;    
        if(keydown_callbacks[keyName]){
            for(var i=0,len=keydown_callbacks[keyName].length;i<len;i++){
                keydown_callbacks[keyName][i]();
                
            }
        
        }
        if(keydown_callbacks["allKeys"]){
            for(var i=0,len=keydown_callbacks["allKeys"].length;i<len;i++){
                keydown_callbacks["allKeys"][i]();
                
            }
        }
        if(preventDefault_keys[keyName]){
            cg.core.preventDefault(eve);
        }
    }

　　每个键的处理程序可以有多个，所以这里保存处理程序的对象保存的是一个数组。另外需要注意通过pressed_keys数组保存了按下的键（pressed_keys[keyName]=true;），就是为了方便实现之前说过的在帧更新中进行一致的参数更新（可以在每次update时通过isPressed（keyName）判断某个键是否按下）。

　　最后附上该输入模块所有源代码：

/**
 *
 *输入记录模块
 *
**/
cnGame.register("cnGame.input",function(cg){
                                            
    this.mouseX=0;
    this.mouseY=0;
    /**
     *记录鼠标在canvas内的位置
    **/    
    var recordMouseMove=function(eve){
        var pageX,pageY,x,y;
        eve=cg.core.getEventObj(eve);
        pageX = eve.pageX || eve.clientX + document.documentElement.scrollLeft - document.documentElement.clientLeft;
        pageY = eve.pageY || eve.clientY + document.documentElement.scrollTop - document.documentElement.clientTop;
        cg.input.mouseX=pageX-cg.x;
        cg.input.mouseY=pageY-cg.y;
            
    }        
    
    cg.core.bindHandler(window,"mousemove",recordMouseMove);
    
    /**
     *被按下的键的集合
    **/    
    var pressed_keys={};
    /**
     *要求禁止默认行为的键的集合
    **/    
    var preventDefault_keys={};
    /**
     *键盘按下触发的处理函数
    **/    
    var keydown_callbacks={};
    /**
     *键盘弹起触发的处理函数
    **/    
    var keyup_callbacks={};

    
    /**
     *键盘按键编码和键名
    **/    
    var k=[];
    k[8] = "backspace"
    k[9] = "tab"
    k[13] = "enter"
    k[16] = "shift"
    k[17] = "ctrl"
    k[18] = "alt"
    k[19] = "pause"
    k[20] = "capslock"
    k[27] = "esc"
    k[32] = "space"
    k[33] = "pageup"
    k[34] = "pagedown"
    k[35] = "end"
    k[36] = "home"
    k[37] = "left"
    k[38] = "up"
    k[39] = "right"
    k[40] = "down" 
    k[45] = "insert"
    k[46] = "delete"
    
    k[91] = "leftwindowkey"
    k[92] = "rightwindowkey"
    k[93] = "selectkey"
    k[106] = "multiply"
    k[107] = "add"
    k[109] = "subtract"
    k[110] = "decimalpoint"
    k[111] = "divide"
    
    k[144] = "numlock"
    k[145] = "scrollock"
    k[186] = "semicolon"
    k[187] = "equalsign"
    k[188] = "comma"
    k[189] = "dash"
    k[190] = "period"
    k[191] = "forwardslash"
    k[192] = "graveaccent"
    k[219] = "openbracket"
    k[220] = "backslash"
    k[221] = "closebracket"
    k[222] = "singlequote"
    
    var numpadkeys = ["numpad1","numpad2","numpad3","numpad4","numpad5","numpad6","numpad7","numpad8","numpad9"]
    var fkeys = ["f1","f2","f3","f4","f5","f6","f7","f8","f9"]
    var numbers = ["0","1","2","3","4","5","6","7","8","9"]
    var letters = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
    for(var i = 0; numbers[i]; i++)     { k[48+i] = numbers[i] }
    for(var i = 0; letters[i]; i++)     { k[65+i] = letters[i] }
    for(var i = 0; numpadkeys[i]; i++)  { k[96+i] = numpadkeys[i] }
    for(var i = 0; fkeys[i]; i++)       { k[112+i] = fkeys[i] }
    
    /**
     *记录键盘按下的键
    **/    
    var recordPress=function(eve){
        eve=cg.core.getEventObj(eve);
        var keyName=k[eve.keyCode];
        pressed_keys[keyName]=true;    
        if(keydown_callbacks[keyName]){
            for(var i=0,len=keydown_callbacks[keyName].length;i<len;i++){
                keydown_callbacks[keyName][i]();
                
            }
        
        }
        if(keydown_callbacks["allKeys"]){
            for(var i=0,len=keydown_callbacks["allKeys"].length;i<len;i++){
                keydown_callbacks["allKeys"][i]();
                
            }
        }
        if(preventDefault_keys[keyName]){
            cg.core.preventDefault(eve);
        }
    }
    /**
     *记录键盘松开的键
    **/    
    var recordUp=function(eve){
        eve=cg.core.getEventObj(eve);
        var keyName=k[eve.keyCode];
        pressed_keys[keyName]=false;
        if(keyup_callbacks[keyName]){
            for(var i=0,len=keyup_callbacks[keyName].length;i
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