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",function(){
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<len;i++){
keyup_callbacks[keyName][i]();
}
}
if(keyup_callbacks["allKeys"]){
for(var i=0,len=keyup_callbacks["allKeys"].length;i<len;i++){
keyup_callbacks["allKeys"][i]();
}
}
if(preventDefault_keys[keyName]){
cg.core.preventDefault(eve);
}
}
cg.core.bindHandler(window,"keydown",recordPress);
cg.core.bindHandler(window,"keyup",recordUp);
/**
*判断某个键是否按下
**/
this.isPressed=function(keyName){
return !!pressed_keys[keyName];
};
/**
*禁止某个键按下的默认行为
**/
this.preventDefault=function(keyName){
if(cg.core.isArray(keyName)){
for(var i=0,len=keyName.length;i<len;i++){
arguments.callee.call(this,keyName[i]);
}
}
else{
preventDefault_keys[keyName]=true;
}
}
/**
*绑定键盘按下事件
**/
this.onKeyDown=function(keyName,handler){
keyName=keyName||"allKeys";
if(cg.core.isUndefined(keydown_callbacks[keyName])){
keydown_callbacks[keyName]=[];
}
keydown_callbacks[keyName].push(handler);
}
/**
*绑定键盘弹起事件
**/
this.onKeyUp=function(keyName,handler){
keyName=keyName||"allKeys";
if(cg.core.isUndefined(keyup_callbacks[keyName])){
keyup_callbacks[keyName]=[];
}
keyup_callbacks[keyName].push(handler);
}
/**
*清除键盘按下事件处理程序
**/
this.clearDownCallbacks=function(keyName){
if(keyName){
keydown_callbacks[keyName]=[];
}
else{
keydown_callbacks={};
}
}
/**
*清除键盘弹起事件处理程序
**/
this.clearUpCallbacks=function(keyName){
if(keyName){
keyup_callbacks[keyName]=[];
}
else{
keyup_callbacks={};
}
}
});