canvas自由拼图

自由拼图?

自由拼图是美图秀秀中的一个功能，它可以让用户在背景图片上插入自己的图片，并可以对插入图片旋转，拖拽，缩放。当然，如果用户对插入的图片不满意，可以用另一张图片替换选中的图片，或者删除选中图片。

效果

本屌之前用actionscript实现过，参见仿美图秀秀的自由拼图（注意里面基本上没代码说明）.
这里用html5的canvas实现。

这个是本屌博客园去年一篇文章的效果，内容也是说的这个，不过很无耻的只贴了代码，没有任何说明。
下面的是录制的效果视频
http://v.youku.com/v_show/id_XMTM3MTgzMzIyOA==.html

布局

<div id='html5_puzzle' ms-controller='html5_puzzle' class='ms-controller'>
    <div id='puzzle_model'>
        <ul>
            <li>
                <img src='imgs/small_img/1.jpg'>
                ...
            </li>
        </ul>
    </div
    ><div id='puzzle_canvas'>
        <div id='canvas_inner'>
            <canvas id="main_canvas"></canvas>
            <img class='middleware_img'>
            <img class='middleware_img'>
            ...
            <div id='canvas_menu'>
                <a href='javascript:void(0)' id='puzzle_delete'>删除</a>
                <a href='javascript:void(0)' id='puzzle_update'>更改图片</a>
            </div>
            <img id="puzzle_bg" src="imgs/1.jpg" width='548' height='411'/>
            <canvas id='canvas_middleware'></canvas>
        </div>
    </div>
    <div id='puzzle_control'>
        <a href="javascript:;" id="puzzle_add">
            <span>添加</span>
            <input type="file" multiple="" id='puzzle_add_input'>
        </a
        ><a id='puzzle_upload'>上传</a>
    </div>
</div>

• #main_canvas是主要的工作区域

• .middleware_img是若干<img>,<input>读取从外面选中的若干图片数据，将数据以Base64编码，依次写入<img>的src属性。这些<img>后面将会被当作参数，传给canvas

• #canvas_middleware是代理。<input>读取的数据由#canvas_middleware调用toDataURL()方法编码成Base64形式

• #puzzle_bg和.middleware_img作用差不多，只不过这里是将背景图片的src传给它。它会将背景图片数据传给canvas

读取选中图片

    var img_upload_instance=new img_upload({
        add_btn:'puzzle_add',
        onSelect:onSelect//读取图片回调
    });

define("html5_imgupload",["avalon-min"], function(avalon){
    var html5_img_upload=function(options){
        this.init(options);
    }
    html5_img_upload.prototype = {
        init : function(options) {
            //如果有自定义属性，覆盖默认属性
            avalon.mix(html5_img_upload.prototype,options);
            this.init_events();
        },
        init_events : function() {
            var _this=this;
            avalon.bind($(this.add_btn),'change',function(e) {
                _this.get_files(e);
            });
        },
        file_filter:[],
        ori_images:[],
        add_btn:null,
        upload_btn:null,
        max_upload_num:9,
        onSelect:function(file_filter){},
        _start:0,//已经读取图片数量
        filter:function(files) {
            var arrFiles=[];
            for (var i=0,file;file=files[i];i++){
                if(this._start+i<this.max_upload_num){
                    if(file.type.indexOf("image")==0||(!file.type&&/\.(?:jpg|png|gif)$/.
                    test(file.name)))
                        arrFiles.push(file);
                    else {
                        alert('文件'+file.name+'不是图片');
                    }
                }else{
                    alert('一次最多能上传'+this.max_upload_num+'张图片');
                    break;
                }
            }
            return arrFiles;
        },
        get_files:function(e) {
            var files=e.target.files||e.dataTransfer.files;
            this.file_filter=this.file_filter.concat(this.filter(files));
            this.onSelect(this.file_filter);
        },
        destroy_hook:function(){},
        _destroy:function(){
            this.file_filter=[];
            $(this.add_btn).value='';
            this.ori_images=[];
            this._start=0;
            this.destroy_hook();
        },
        upload:function(i,file_filter){}
    };
    return html5_img_upload;
});

自定义图片选取回调

<div id='puzzle_canvas'>
    <div id='canvas_inner'>
        <canvas id="main_canvas"></canvas>
        <img ms-repeat='middleware_list' ms-attr-src='el' class='middleware_img'>
        ...
    </div>
</div>

    function onSelect(file_filter){
        for(var i=this._start,len=file_filter.length;i<len;i++) {//遍历选中图片
            var reader=new FileReader();
            reader.onload=(function(i){//图片读取的回调
                return function(e){
                    var dataURL=e.target.result,canvas_middleware=$('canvas_middleware'),
                    ctx=canvas_middleware.getContext('2d'),img=new Image();
                    img.onload = function() {//图片加载的回调
                        if(img.width>200||img.height>200){//等比例缩放
                            var prop=Math.min(200/img.width,200/img.height);
                            img.width=img.width*prop;
                            img.height=img.height*prop;
                        }
                        //设置中转canvas尺寸
                        canvas_middleware.width=img.width;
                        canvas_middleware.height=img.height;
                        ctx.drawImage(img, 0, 0, img.width, img.height);
                        //将读取图片转换成base64,写入.middleware_list的src
                        html5_puzzle.middleware_list.push(canvas_middleware.
                        toDataURL("image/jpeg"));
                        if(!file_filter[i+1]){
                            //图片延迟加载到canvas,因为canvas有个读取过程，但是没有回调
                            var t = window.setTimeout(function() {
                                canvas_puzzle.init();
                                clearTimeout(t);
                            }, 1000);
                        }
                    };
                    img.src = dataURL;
                };
                delete reader;
            })(i);
            reader.readAsDataURL(file_filter[i]);//开始读取图片
        }
        this._start=0;
        img_upload_instance._destroy();
    }

canvas初始化

    var canvas = new canvasElement.Element();
    canvas.init('main_canvas', {
        width : canvas_w,
        height : canvas_h
    });

    Canvas.Element.prototype.init = function(el, oConfig) {
        if (el == '') {
            return;
        }
        this._initElement(el);
        this._initConfig(oConfig);
        this._createCanvasBackground();
        this._createContainer();
        this._initEvents();
        this._initCustomEvents();
    };
    Canvas.Element.prototype._initElement = function(el) {
        this._oElement = document.getElementById(el);
        this._oContextTop = this._oElement.getContext('2d');
    };
    Canvas.Element.prototype._initCustomEvents = function() {//设置自定义事件
        this.onRotateStart = new Canvas.CustomEvent('onRotateStart');
        this.onRotateMove = new Canvas.CustomEvent('onRotateMove');        
        this.onRotateComplete = new Canvas.CustomEvent('onRotateComplete');
        this.onDragStart = new Canvas.CustomEvent('onDragStart');    
        this.onDragMove = new Canvas.CustomEvent('onDragMove');
        this.onDragComplete = new Canvas.CustomEvent('onDragComplete');
    };
    Canvas.Element.prototype._initConfig = function(oConfig) {
        this._oConfig = oConfig;
        this._oElement.width = this._oConfig.width;
        this._oElement.height = this._oConfig.height;
        this._oElement.style.width = this._oConfig.width + 'px';
        this._oElement.style.height = this._oConfig.height + 'px';
    };
    Canvas.Element.prototype._initEvents = function() {
        var _this=this;
        avalon.bind(this._oElement,'mousedown',function(e){
             _this.onMouseDown(e);
        });
        avalon.bind(this._oElement,'mouseup',function(e){
             _this.onMouseUp(e);
        });
        avalon.bind(this._oElement,'mousemove',function(e){
            _this.onMouseMove(e);
        });
    };
    Canvas.Element.prototype._createContainer = function() {
        var canvasEl = document.createElement('canvas');
        canvasEl.id = this._oElement.id + '-canvas-container';
        ...
        this._oContextContainer = oContainer.getContext('2d'); 
    };
    Canvas.Element.prototype._createCanvasBackground = function() {
        var canvasEl = document.createElement('canvas');
        canvasEl.id = this._oElement.id + '-canvas-background';
        ...
        this._oContextBackground = oBackground.getContext('2d'); 
    };

可以看到初始化过程中多次创建<canvas>

• main_canvas-background-canvas绘制背景图片

• main_canvas-container-canvas绘制除当前操作的图片外的其余图片

• main_canvas绘制当前操作的图片

从上到下：main_canvas->main_canvas-container-canvas->main_canvas-background-canvas

canvas context:

• main_canvas->_oContextTop

• main_canvas-container-canvas->_oContextContainer

• main_canvas-background-canvas->_oContextBackground

这下就看到canvas自由拼图的原理了，原来是3个canvas上下重叠起来，操作的时候对不同的canvas进行不同目标的绘制。

canvas绘制图片

接着图片选取完成后canvas_puzzle.init()

    var canvas_img=[];
    ...
    var canvas_puzzle= function() {
        return {
            init : function() {
                var img_list=document.querySelectorAll('.middleware_img');
                //第一张作为背景图片
                canvas_img[0]=new canvasImg.Img($('puzzle_bg'), {});
                avalon.each(img_list,function(i,el){
                    canvas_img.push(new canvasImg.Img(el, {}));
                    canvas.addImage(canvas_img[i+1]);
                });
                canvas.setCanvasBackground(canvas_img[0]);
                ...
            }
        };
    }();

• canvasImg.Img是canvas对图片的封装.第一个参数是<img>,前面提到的#puzzle_bg和.middleware_img就是作为第一个参数传入canvasImg.Img.第二个参数用来自定义图片的一些属性，比如边框宽度，4个角的大小等，如果定义的话会覆盖默认值。

• canvasImg.Img封装图片后的效果
  

• canvas.addImage(canvas_img[i+1])将canvas对除背景图片外的图片的封装绘制到canvas上

    Canvas.Element.prototype.addImage = function(oImg) {
        if(isEmptyObject(this._aImages))
            this._aImages = [];
        this._aImages.push(oImg);
        this.renderAll(false,true);
    };

_aImages是保存canvas图片封装的数组，renderAll()方法很重要，后面会说到。

• canvas.setCanvasBackground(canvas_img[0])将背景图片绘制到canvas

    Canvas.Element.prototype.setCanvasBackground = function(oImg) {
        this._backgroundImg = oImg;
        var originalImgSize = oImg.getOriginalSize();
        this._oContextBackground.drawImage(oImg._oElement, 0, 0, originalImgSize.width, 
        originalImgSize.height);
    };
    Canvas.Img.prototype.getOriginalSize = function() {//获得canvas尺寸
        return { width: this._oElement.width, height: this._oElement.height }
    };

canvas事件操作

mousedown

    Canvas.Element.prototype.onMouseDown = function(e) {
        $('canvas_menu').style.display="none";
        var mp = this.findMousePosition(e);//鼠标相对位置
        if (this._currentTransform != null || this._aImages == null) {
            return;
        }
        var oImg = this.findTargetImage(mp, false);//获取目标图片
        //事件触发位置是不是在4个角上
        var action = (!this.findTargetCorner(mp, oImg)) ? 'drag' : 'rotate';
        if (action == "rotate") {
            this.onRotateMove.fire(e);//触发自定义事件
        } else if (action == "drag") {
            this.onDragMove.fire(e);
        }
        this._prevTransform=this._currentTransform = { 
            target: oImg,
            action: action,
            scalex: oImg.scalex,
            offsetX: mp.ex - oImg.left,
            offsetY: mp.ey - oImg.top,
            ex: mp.ex, ey: mp.ey,
            left: oImg.left, top: oImg.top,
            theta: oImg.theta 
        };
        //设置菜单位置
        $('canvas_menu').style.transform='rotate('+oImg.theta*180/3.14+'deg)';
        $('canvas_menu').style.left=oImg.left+"px";
        $('canvas_menu').style.top=oImg.top+"px";
        this.renderAll(false,false);
    };

• this._prevTransform保存当前目标图片状态，替换图片时会用到这个变量

• renderAll()方法是整个绘制的核心方法

Canvas.Element.prototype.renderAll=function(allOnTop,allowCorners) {
    var containerCanvas=allOnTop?this._oContextTop:this._oContextContainer;
    this._oContextTop.clearRect(0,0,parseInt(this._oConfig.width),parseInt(this._oConfig.height));
    containerCanvas.clearRect(0,0,parseInt(this._oConfig.width),parseInt(this._oConfig.height));
    if(allOnTop){//所有图片都要在最上面
        var originalImgSize=this._backgroundImg.getOriginalSize();
        //在最上层canvas绘制背景图片
        this._oContextTop.drawImage(this._backgroundImg._oElement, 0, 0,
        originalImgSize.width,originalImgSize.height);
    }
    for(var i=0,l=this._aImages.length-1;i<l;i+=1){
        this.drawImageElement(containerCanvas,this._aImages[i],allowCorners);            
    }
    var last_aImages=this._aImages[this._aImages.length-1];
    this.drawImageElement(this._oContextTop,last_aImages ,allowCorners);
};

可以看到，如果allOnTop=false,从_aImages封装图片的数组的第一个元素到倒数第二个元素，会绘制到中间一层container-canvas,而_aImages数组的最后一个元素，即当前操作的图片，会绘制到最上面一层top-canvas，当然如果改变操作对象，_aImages数组也会相应的变化，保证当前操作的图片在_aImages数组的最后一个位置。
如果allOnTop=true,_aImages数组中的所有图片还有背景图片都会被绘制到最上面一层top-canvas.
设置allOnTop参数的目的在于上传时只有所有图片都在一个canvas context上，调用toDataURL()方法，就能获得整个拼图的base64字符串。
第二个参数allowCorners表示绘制时是否添加边框，边角。

前面将选中图片及背景图片绘制到canvas，最后this.renderAll(false,true)让边框，边角可见，是为了让用户知道图片可以进行操作。

    Canvas.Element.prototype.addImage = function(oImg) {
        ...
        this.renderAll(false,true);
    };

另外，无论怎么设置，renderAll()方法最终都会调用drawImageElement()方法进行实际意义上的绘制

Canvas.Element.prototype.drawImageElement = function(context,oImg,allowCorners) {
    if(oImg){
        oImg.cornervisibility=allowCorners;
        var offsetY = oImg.height / 2;
        var offsetX = oImg.width / 2;
        context.save();
        context.translate(oImg.left, oImg.top);
        context.rotate(oImg.theta);
        context.scale(oImg.scalex, oImg.scaley);
        this.drawBorder(context, oImg, offsetX, offsetY);
        var originalImgSize = oImg.getOriginalSize();
        var polaroidHeight =((oImg.height-originalImgSize.height)-(oImg.width-originalImgSize.width))/2;
        context.drawImage(oImg._oElement,-originalImgSize.width/2,(-originalImgSize.height)/2-polaroidHeight, 
        originalImgSize.width,originalImgSize.height);
        if (allowCorners)
            this.drawCorners(context, oImg, offsetX, offsetY);
        context.restore();
    }
};

mousemove

Canvas.Element.prototype.onMouseMove = function(e) {
    var mp = this.findMousePosition(e);
    if(this._aImages == null)
        return;
    if(this._currentTransform==null){
        var targetImg = this.findTargetImage(mp, true);
        this.setCursor(mp, targetImg);
    }
    else {
        if (this._currentTransform.action == 'rotate') {
            this.rotateImage(mp);
            this.scaleImage(mp);
            this.onRotateMove.fire(e);
        }        
        else {
            this.translateImage(mp);
            this.onDragMove.fire(e);
        }
        this.renderTop();
    }        
};

里面的renderTop()方法只在最上层canvas绘制当前操作的图片

Canvas.Element.prototype.renderTop = function() {
    this._oContextTop.clearRect(0,0,parseInt(this._oConfig.width), parseInt(this._oConfig.height));
    this.drawImageElement(this._oContextTop, this._aImages[this._aImages.length-1],true);
};

mouseup

    Canvas.Element.prototype.onMouseUp = function(e) {
        if (this._aImages == null) {
            return;
        }
        var target=this._currentTransform.target;
        if (target)
            target.setImageCoords();//重置图片canvas封装
        if(this._currentTransform!= null&&this._currentTransform.action=="rotate") {
            this.onRotateComplete.fire(e);
        } else if (this._currentTransform!=null&&this._currentTransform.action == "drag"){
            this.onDragComplete.fire(e);
        }
        this._currentTransform = null;
        this.renderTop();
        if(this._aImages.length>0)//没有选中的图片
            $('canvas_menu').style.display="block";
    };

替换图片

    <div id='canvas_menu'>
        ...
        <a href='javascript:void(0)' id='puzzle_update'>更改图片</a>
    </div>

    avalon.bind($('puzzle_update'),'click',function(){
        update_puzzle=true;
        $('puzzle_add_input').click();
    });

可以看到，这里依然使用了<input>点击选中图片，不过设置了update_puzzle=true,表示当前处在替换图片的情况下

    function onSelect(file_filter){
        for(var i=this._start,len=file_filter.length;i<len;i++) {
            var reader=new FileReader();
            reader.onload=(function(i){//图片读取的回调
                return function(e){
                    ...
                    img.onload = function() {
                        ...
                        var t = window.setTimeout(function() {
                        if(!update_puzzle)
                            canvas_puzzle.init();
                        else{
                            //当前操作图片
                            var target=canvas._prevTransform.target;
                            //传入替换的图片和被替换图片的位置，状态信息
                            canvas._aImages[getCurImg()]=new canvasImg.Img(document.
                            querySelectorAll('.middleware_img')[0],{
                                top:target.top,
                                left:target.left,
                                scalex:target.scalex,
                                scaley:target.scaley,
                                angle:canvas.curAngle
                            });
                            //重新绘制最上层
                            canvas.renderTop();
                            html5_puzzle.middleware_list.clear();
                            update_puzzle=false;
                        }
                        clearTimeout(t);
                      }, 1000);
                    };
                };
                delete reader;
            })(i);
            reader.readAsDataURL(file_filter[i]);
        }
        ...
    }
    function getCurImg(){//获取读取操作图片在_aImages中的位置
        var oImg=canvas._prevTransform.target;
        for(var i=0;i<canvas._aImages.length;i++){
            if(canvas._aImages[i]._oElement.src==oImg._oElement.src){
                return i;
            }
        }
    }

删除图片

    <div id='canvas_menu'>
        <a href='javascript:void(0)' id='puzzle_delete'>删除</a>
        ...
    </div>

    avalon.bind($('puzzle_delete'),'click',function(){
        canvas._aImages.splice(getCurImg(),1);//从_aImages数组中删除
        canvas.renderAll(false,false);//重新绘制
        $('canvas_menu').style.display="none";
        ...
    });

拼图转换成base64字符串

    Canvas.Element.prototype.canvasTo = function(format) {//canvas=>dataurl
        this.renderAll(true,false);//所有图片都绘制到最上层，并且不绘制边框，边角
        if (format == 'jpeg' || format == 'png') {
            return this._oElement.toDataURL('image/'+format);
        }
    };

上传

        avalon.post('...',{
            imgData:canvas.canvasTo('jpeg').substr(22)
        },function(data){
            ...
        },'json');

后台用Base64解析imgData字符串就可以了

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