本文實例講述了JS+HTML5 Canvas實現簡單的寫字板功能。分享給大家供大家參考，具體如下：
先來看運行效果：
具體代碼如下：
<!DOCTYPE html><html><head> <meta charset="utf-8"> <title>www.survivalescaperooms.com JS寫字板</title> <script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script> <style type="text/css"> body,html { padding: 0; margin: 0; } a,div,span { font-family: "Arial","Microsoft YaHei","黑體","宋體",sans-serif; } .canvas-box { display: block; margin: 40px auto; background: #f5f5f5; } .color-box { width: 1080px; display: block; margin: 20px auto; text-align: center; } .color-item { display: inline-block; vertical-align: middle; width: 48px; height: 24px; margin: 10px; background: #989898; cursor: pointer; } .red { background: #e01d5b; } .blue { background: #1d6ae0; } .green { background: #1de087; } .yellow { background: #f3e41d; } .orange { background: #f9850b; } .black { background: #333; } .color-item.active { border: solid 3px #565656; } .btn { display: block; width: 120px; height: 40px; line-height: 40px; margin: 10px auto; text-align: center; font-size: 18px; border: solid 1px #999; border-radius: 5px; cursor: pointer; } </style></head><body> <canvas class="canvas-box" id="canvas"></canvas> <div class="color-box"> <span class="color-item red"></span> <span class="color-item blue"></span> <span class="color-item green"></span> <span class="color-item yellow"></span> <span class="color-item orange"></span> <span class="color-item black active"></span> </div> <div class="btn" onclick="clearDraw()">清除</div><script type="text/javascript">var canvas = document.getElementById('canvas');var context = canvas.getContext("2d");var isDraw = false; //定義變量控制畫筆是否可用var movePos; //定義變量存放初始畫筆開始位置var linWidth = 10;var linColor = '#333';window.onload = function(){ draw();}function draw(){ canvas.width = 500; canvas.height = 500; context.strokeStyle = "red"; context.lineWidth = 10; context.beginPath(); context.strokeRect(0,0,500,500); //設置畫筆顏色，寬度 context.strokeStyle = "red"; context.lineWidth = 1; //使線段連續，圓滑 context.lineCap = "round"; context.lineJoin = "round"; drawDashedLine(context,0,0,500,500); drawDashedLine(context,0,500,500,0); drawLine(context,0,250,500,250); drawLine(context,250,0,250,500);}//畫虛線（參照網上大神）function drawDashedLine(context, x1, y1, x2, y2, dashLength) { dashLength = dashLength === undefined ? 5 : dashLength; var deltaX = x2 - x1; var deltaY = y2 - y1; var numDashes = Math.floor( Math.sqrt(deltaX * deltaX + deltaY * deltaY) / dashLength); for (var i=0; i < numDashes; ++i) { context[ i % 2 === 0 ? 'moveTo' : 'lineTo' ] (x1 + (deltaX / numDashes) * i, y1 + (deltaY / numDashes) * i); } context.stroke();};//畫直線function drawLine(context,x1,y1,x2,y2){ context.moveTo(x1,y1); context.lineTo(x2,y2); context.stroke();};//獲取鼠標相對與canvas位置function getPos(x,y){ var box = canvas.getBoundingClientRect(); return {x: x-box.left,y: y-box.top};};//畫筆function drawing(e){ if(isDraw){ var position = getPos(e.clientX,e.clientY); context.strokeStyle = linColor; context.lineWidth = linWidth; context.save(); context.beginPath(); context.moveTo(movePos.x,movePos.y); context.lineTo(position.x,position.y); context.stroke(); movePos = position; context.restore(); }}//鼠標點下canvas.onmousedown = function(e){ isDraw = true; movePos = getPos(e.clientX,e.clientY); drawing(e);}//鼠標移動canvas.onmousemove = function(e){ drawing(e);}//鼠標松開canvas.onmouseup = function(e){ isDraw = false;}//鼠標離開canvas.onmouseout =function(e){ isDraw = false;}//選擇畫筆顏色$('.color-item').on('click',function(){ $(this).addClass('active').siblings().removeClass('active'); linColor = $(this).css('background-color');});//清除function clearDraw(){ context.clearRect(0,0,500,500); draw();}</script></body></html>感興趣的朋友還可以使用在線HTML/CSS/JavaScript代碼運行工具：http://tools.VeVB.COm/code/HtmlJsRun測試上述代碼，親身體驗一下運行效果。
更多關于JavaScript相關內容還可查看本站專題：《JavaScript+HTML5特效與技巧匯總》、《JavaScript圖形繪制技巧總結》、《JavaScript錯誤與調試技巧總結》、《JavaScript數據結構與算法技巧總結》、《JavaScript遍歷算法與技巧總結》及《JavaScript數學運算用法總結》
希望本文所述對大家JavaScript程序設計有所幫助。
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