html5 canvas简单画板

canvas简单画板，花了几个小时搞定的简单玩意，目前只是初步demo，有时间在完善一下。

<!doctype html>
<html>
<head>
<title>canvas简单画板</title>
<style type="text/css">
#can{ 600px; height:500px; border:1px solid #ccc; margin-top:0px; margin-left:20px;}
</style>
</head>
<body>
<h2 style="padding-left:20px">canvas简单画板</h2>
<canvas id="can" width="600" height="500"></canvas>
  <script type="text/javascript">
                function getBodyOffsetTop(el){
                    var top = 0;
                    do{
                        top = top + el.offsetTop;
                    }while(el = el.offsetParent);
                    return top;
                }
                function getBodyOffsetLeft(el){
                    var left = 0;
                    do{
                        left = left + el.offsetLeft;
                    }while(el = el.offsetParent);
                    return left;
                }
                function Drawing(canvas,options){
                    typeof canvas == 'string' && (canvas = document.getElementById(canvas));
                    if(!canvas || !canvas.getContext){
                        throw new Error(100,'do not support canvas!');
                    }
                    this.option = {
                        colors:['#000000','#ff0000','#00ff00','#0000ff','#00ffff','#7fef02','#4488bb']
                    };
                    this.setOption(options);
                    this.init(canvas);
                }
                Drawing.prototype = {
                    setOption:function(options){
                        typeof options == 'object' || (options = {});
                        for(var i in options){
                            switch(i){
                                case 'colors':
                                    this.option[i] = options[i];
                                    break;
                            }
                        }
                    },
                    init:function(canvas){
                        this.canvas = canvas;
                        this.context = canvas.getContext('2d');
                        this.context.lineWidth = 1;
                        this.context.lineJons = 'round';
                        this.context.lineCep = 'round';
                        this.isButtonDown = false;
                        this.historyStroker = [];
                        this.curStroker = {color:'#000000',path:[]};
                        this.lastX = 0;
                        this.lastY = 0;
                        this.curColor = '#000000';
                        this.toolbarspos ={};
                        this.bindEvent();
                        this.ResetDrawToolbar();
                    },
                    bindEvent:function(){
                        var self = this;
                        this.canvas.addEventListener('mousemove',function(event){
                            var x = event.pageX-getBodyOffsetLeft(this),
                                y = event.pageY-getBodyOffsetTop(this);
                            self.onMouseMove({x:x,y:y});
                        },false);
                        this.canvas.addEventListener('mousedown',function(event){
                            var x = event.pageX-getBodyOffsetLeft(this),
                                y = event.pageY-getBodyOffsetTop(this);
                            self.onMouseDown(event,{x:x,y:y});
                        },false);
                        this.canvas.addEventListener('mouseup',function(event){
                            var x = event.pageX-getBodyOffsetLeft(this),
                                y = event.pageY-getBodyOffsetTop(this);
                            self.onMouseUp(event,{x:x,y:y});
                        },false);
                        this.canvas.addEventListener('click',function(event){
                            var x = event.pageX-getBodyOffsetLeft(this),
                                y = event.pageY-getBodyOffsetTop(this);
                            self.onClick({x:x,y:y});
                        },false);
                    },
                    onMouseMove:function(pos){
                        if(this.isButtonDown){
                            var p = this.toolbarspos;
                            for(var i in p){
                                if(pos.x >= p[i].x
                                && pos.x <= p[i].x+p[i].w 
                                && pos.y >= p[i].y
                                && pos.y <= p[i].y+p[i].h){
                                    return;
                                }
                            }
                            this.context.lineTo(pos.x,pos.y);
                            this.context.stroke();
                            this.lastX = pos.x;
                            this.lastY = pos.y;
                            this.curStroker.path.push(pos);
                        }
                    },
                    onMouseDown:function(event,pos){
                        if(event.button == 0){
                            var p = this.toolbarspos;
                            for(var i in p){
                                if(pos.x >= p[i].x
                                && pos.x <= p[i].x+p[i].w 
                                && pos.y >= p[i].y
                                && pos.y <= p[i].y+p[i].h){
                                    return;
                                }
                            }
                            this.isButtonDown = true;
                            this.lastX = pos.x;
                            this.lastY = pos.y;
                            this.context.beginPath();
                            this.context.moveTo(this.lastX,this.lastY);
                            this.curStroker.color = this.curColor;
                            this.curStroker.path.push(pos);
                        }
                    },
                    onMouseUp:function(event,pos){
                        if(event.button == 0){
                            var p = this.toolbarspos;
                            for(var i in p){
                                if(pos.x >= p[i].x
                                && pos.x <= p[i].x+p[i].w 
                                && pos.y >= p[i].y
                                && pos.y <= p[i].y+p[i].h){
                                    return;
                                }
                            }
                            this.isButtonDown = false;
                            this.historyStroker.push(this.curStroker);
                            this.curStroker = {color:this.curColor,path:[]};
                        }
                    },
                    ResetDrawAll:function(){
                        this.context.clearRect(0,0,500,500);
                        this.ResetDrawCentre();
                        this.ResetDrawToolbar();
                    },
                    ResetDrawCentre:function(){ 
                        var p = this.historyStroker,p2,
                        curColor = this.context.strokeStyle;
                        for(var i=0; i< p.length;i++){ 
                            this.context.strokeStyle = p[i].color;
                            this.context.beginPath();
                            for(var t=0; t<p[i].path.length;t++){
                                p2 = p[i].path[t];
                                if(t==0) this.context.moveTo(p2.x,p2.y);
                                this.context.lineTo(p2.x,p2.y);
                                this.context.stroke();
                            }
                            this.context.beginPath();
                        }
                        this.context.strokeStyle = curColor;
                    },
                    ResetDrawToolbar:function(){
                        var curcolor = this.context.fillStyle;
                        for(var i=0; i<this.option.colors.length;i++){
                            this.context.fillStyle = this.option.colors[i];
                            if(this.curColor == this.context.fillStyle){
                                this.context.fillRect(i*35+5,2,30,20);
                                this.toolbarspos[i] ={x:i*35+5,y:2,w:30,h:20};
                            }else{
                                this.context.fillRect(i*35+5,5,30,20);
                                this.toolbarspos[i] = {x:i*35+5,y:5,w:30,h:20};
                            }
                            this.context.stroke();
                        }
                        this.context.fillStyle = curcolor;
                    },
                    onClick:function(pos){
                        var p = this.toolbarspos;
                        for(var i in p){
                            if(pos.x >= p[i].x
                            && pos.x <= p[i].x+p[i].w 
                            && pos.y >= p[i].y
                            && pos.y <= p[i].y+p[i].h){
                                this.curColor = this.option.colors[i];
                                this.context.strokeStyle = this.curColor;
                                this.ResetDrawAll();
                            }
                        }
                    }
                };
                new Drawing('can');
            </script></body>
</html>

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原文地址：https://www.cnblogs.com/xingzhi/p/2276277.html