width——对应于canvas元素的width属性;
getContext(
2)绘制矩形:
fillRect(x,y,w,h)——绘制一个实心矩形;
strokeRect(x,y,w,h)——绘制一个空心矩形;
clearRect(x,y,w,h)——清除指定的矩形;
canvas{ border:medium double black; margin: 4px; } body > *{ float: left; }
<canvas id="canvas1" width="500" height="200"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //绘制矩形 var ctx=document.getElementById("canvas1").getContext("2d"); //ctx.fillRect(10,10,50,50); var offset=10; var size=50; var count=5; for(var i=0;i<count;i++){ ctx.fillRect(i*(offset+size)+offset,offset,size,size); ctx.strokeRect(i*(offset+size)+offset,(2*offset)+size,size,size); ctx.clearRect(i*(offset+size)+offset,offset+5,size,size-10); } </script>
3)设置画布绘制状态:
lineWidth——获取或设置线条的宽度(默认值为1.0);
lineJoin——获取或设置线条与图形连接时的样式(默认值为miter);
fillStyle——获取或设置用于实心图形的样式(默认值为black);
strokeStyle——获取或设置用于线条的样式(默认值为black);
<canvas id="canvas2" width="500" height="70"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //在执行操作前绘制设置状态 var ctx=document.getElementById("canvas2").getContext("2d"); ctx.lineWidth=2; ctx.strokeRect(10,10,50,50); ctx.lineWidth=4; ctx.strokeRect(70,10,50,50); ctx.lineWidth=6; ctx.strokeRect(130,10,50,50); ctx.lineWidth=8; ctx.strokeRect(200,10,50,50); </script>
<canvas id="canvas3" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //设置lineJoin属性 var ctx=document.getElementById("canvas3").getContext("2d"); ctx.lineWidth=20; ctx.lineJoin="round"; ctx.strokeRect(20,20,100,100); ctx.lineJoin="bevel"; ctx.strokeRect(160,20,100,100); ctx.lineJoin="miter"; ctx.strokeRect(300,20,100,100); </script>
<canvas id="canvas4" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //设置填充和笔触样式 var ctx=document.getElementById("canvas4").getContext("2d"); var offset=10; var size=50; var count=5; var lineWidth=3; var fillColors=["black","grey","lightgrey","red","blue"]; var strokeColors=["rgb(0,0,0)","rgb(100,100,100)","rgb(200,200,200)","rgb(255,0,0)","rgb(0,0,255)"]; for(var i=0;i<count;i++){ ctx.fillStyle=fillColors[i]; ctx.strokeStyle=strokeColors[i]; ctx.fillRect(i*(offset+size)+offset,offset,size,size); ctx.strokeRect(i*(offset+size)+offset,(2*offset)+size,size,size); } </script>
4)使用渐变
createLinearGradient(x0,y0,x1,y1)——创建线性渐变,返回CanvasGradient对象;
createRadialGradient(x0,y0,r0,x1,y1,r1)——创建径向渐变,返回CanvasGradient对象;
CanvasGradient对象的方法:
addColorStop(<position>,
<canvas id="canvas5" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用线性渐变 var ctx=document.getElementById("canvas5").getContext("2d"); //var grad=ctx.createLinearGradient(0,0,500,140); var grad=ctx.createLinearGradient(10,10,60,60); grad.addColorStop(0,"red"); grad.addColorStop(0.5,"white"); grad.addColorStop(1,"black"); ctx.fillStyle=grad; //ctx.fillRect(0,0,500,140); ctx.fillRect(10,10,50,50); </script>
<canvas id="canvas6" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用径向渐变 var ctx=document.getElementById("canvas6").getContext("2d"); var grad=ctx.createRadialGradient(250,70,20,200,60,100); grad.addColorStop(0,"red"); grad.addColorStop(0.5,"white"); grad.addColorStop(1,"black"); ctx.fillStyle=grad; ctx.fillRect(0,0,500,140); </script>
<canvas id="canvas7" width="500" height="140"> 您的浏览器不支持<code>canvas</code>! </canvas>
<script> //使用较小的图形和径向渐变 var ctx=document.getElementById("canvas7").getContext("2d"); var grad=ctx.createRadialGradient(250,70,20,200,60,100); grad.addColorStop(0,"red"); grad.addColorStop(0.5,"white"); grad.addColorStop(1,"black"); ctx.fillStyle=grad; ctx.fillRect(150,20,75,50); ctx.lineWidth=8; ctx.strokeStyle=grad; ctx.strokeRect(250,20,75,50); </script>
5)使用图案
createPattern(
int2的值是指定重复样式:分别有repeat、repeat-x、repeat-y、no-repeat;
<canvas id="canvas8" width="500" height="150"> 您的浏览器不支持<code>canvas</code>! </canvas> <img id="banana" hidden src="images/banana-small.png"/>
<script> //使用图像类的图案 var ctx=document.getElementById("canvas8").getContext("2d"); var imageElem=document.getElementById("banana"); var pattern=ctx.createPattern(imageElem,"repeat"); ctx.fillStyle=pattern; ctx.fillRect(0,0,500,148); </script>
6)保存和恢复状态
save()——保存绘制状态属性的值,并把它们推入状态栈;
restore()——取出状态栈的第一组值,用它们来设置绘制状态;
<canvas id="canvas9" width="500" height="150" preload="auto"> 您的浏览器不支持<code>canvas</code>! </canvas> <p> <button>Save</button> <button>Restore</button> </p>
<script> //保存和恢复状态 var ctx=document.getElementById("canvas9").getContext("2d"); var grad=ctx.createLinearGradient(500,0,500,140); grad.addColorStop(0,"red"); grad.addColorStop(0.5,"white"); grad.addColorStop(1,"black"); var colors=["black",grad,"red","green","yellow","black","grey"]; var cIndex=0; ctx.fillStyle=colors[cIndex]; draw(); var buttons=document.getElementsByTagName("button"); for(var i=0;i<buttons.length;i++){ buttons[i].onclick=handleButtonPress; } function handleButtonPress(e){ switch(e.target.innerHTML){ case 'Save': ctx.save(); cIndex=(cIndex+1)%colors.length; ctx.fillStyle=colors[cIndex]; draw(); break; case 'Restore': cIndex=Math.max(0,cIndex-1); ctx.restore(); draw(); break; } } function draw(){ ctx.fillRect(0,0,500,140); } </script>
7)绘制图像
drawImage方法——在画布上绘制图像,指定一个img、canvas或video元素作为来源;
<canvas id="canvas10" width="500" height="150" preload="auto"> 您的浏览器不支持<code>canvas</code>! </canvas> <img id="banana2" hidden src="images/banana-small.png"/>
<script> //使用drawImage方法 var ctx2=document.getElementById("canvas10").getContext("2d"); var imageElement=document.getElementById("banana2"); ctx2.drawImage(imageElement,10,10); ctx2.drawImage(imageElement,120,10,100,120); ctx2.drawImage(imageElement,20,20,100,50,250,10,100,120); </script>
<video id="vid" src="raw/timessquare.webm" controls preload="auto" width="360" height="240"> 您的浏览器不支持; </video> <canvas id="canvas11" width="360" height="240"> 您的浏览器不支持; </canvas> <p> <button id="pressme">Snapshot</button> <button id="pressme2">PressMe</button> </p> <canvas id="canvas12" width="360" height="240"> 您的浏览器不支持; </canvas>
<script> //使用视频作为drawImage方法的来源 var ctx3=document.getElementById("canvas11").getContext("2d"); var imageElement3=document.getElementById("vid"); document.getElementById("pressme").onclick=function(e){ ctx3.drawImage(imageElement3,0,0,360,240); } var width=100; var height=10; ctx3.lineWidth=5; ctx3.strokeStyle="red"; setInterval(function(){ ctx3.drawImage(imageElement3,0,0,360,240); ctx3.strokeRect(180-(width/2),120-(height/2),width,height); },25); setInterval(function(){ width=(width-1)%200; height=(height+3)%200; },100); </script> <script> //将画布作为drawImage方法的来源 var srcCanvasElement=document.getElementById("canvas11"); var ctx4=srcCanvasElement.getContext("2d"); var ctx5=document.getElementById("canvas12").getContext("2d"); var imageElement4=document.getElementById("vid"); document.getElementById("pressme2").onclick=takeSnapshot; var width=100; var height=10; ctx4.lineWidth=5; ctx4.strokeStyle="red"; ctx5.lineWidth=30; ctx5.strokeStyle="black"; setInterval(function(){ ctx4.drawImage(imageElement4,0,0,360,240); ctx4.strokeRect(180-(width/2),120-(height/2),width,height); },25); setInterval(function(){ width=(width+1)%200; height=(height+3)%200; },100); function takeSnapshot(){ ctx5.drawImage(srcCanvasElement,0,0,360,240); ctx5.strokeRect(0,0,360,240); } </script>
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