html5之canvas起步的代码示例详解(图)

2019年8月23日03:10:37
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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(<context>)——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>

html5之canvas起步的代码示例详解(图)
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>

html5之canvas起步的代码示例详解(图)

<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>

html5之canvas起步的代码示例详解(图)

    <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>

html5之canvas起步的代码示例详解(图)
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>

html5之canvas起步的代码示例详解(图)

    <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>

html5之canvas起步的代码示例详解(图)

    <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>

html5之canvas起步的代码示例详解(图)
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>

html5之canvas起步的代码示例详解(图)

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>

html5之canvas起步的代码示例详解(图)
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>

html5之canvas起步的代码示例详解(图)

    <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>

html5之canvas起步的代码示例详解(图)

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