效果图：
注：下面的代码运行效果，请在支持html5浏览下执行，才能看到效果。
<!doctype html> <html> <head> <title>canvas简单画板</title> <style type="text/css"> #can{ width:600px; height:500px; border:1px solid #ccc; margin-top:0px; margin-left:20px;} </style> </head> <body> <h2>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>
提示：您可以先修改部分代码再运行