1）htmlcanvaselement对象的成员：
height——对应于canvas元素的height属性；
width——对应于canvas元素的width属性；
getcontext(af16c4db277e0498b5fa9e30613367f1)——为画布返回绘图上下文；
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>,<color>)——给渐变的梯度线添加一种纯色；
<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(<imgelement>,int2)——创建图案，指定图案文件的来源和重复方式；
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>
以上就是html5之canvas起步的代码示例详解（图）的详细内容。