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html5之canvas进阶的代码详解(图)

时间:2021-07-01 10:21:17 帮助过:39人阅读

1)用路径绘图:

beginPath()——开始一条新路径;

closePath()——尝试闭合现有路径,方法是绘制一条线,连接最后那条线的终点与初始坐标;

fill()——填充用子路径描述的图形;

isPointInPath(x,y)——如果指定的点在当前路径所描述的图形之内则返回true;

lineTo(x,y)——绘制一条到指定坐标的子路径;

moveTo(x,y)——移动到指定坐标而不绘制子路径;

rect(x,y,w,h)——绘制一个矩形,其左上角位于(x,y),宽度是w,高度是h;

stroke()——给子路径描述的图形绘制轮廓线;

<style type="text/css">
        canvas{
            border:thin solid black;
            margin: 4px;
        }
        body > *{
            float: left;
        }
    </style>
<canvas id="canvas1" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //由直线创建路径
        var ctx=document.getElementById("canvas1").getContext("2d");
        ctx.fillStyle="#136455";
        ctx.strokeStyle="blue";
        ctx.lineWidth=4;

        ctx.beginPath();
        ctx.moveTo(10,10);
        ctx.lineTo(110,10);
        ctx.lineTo(110,120);
        ctx.closePath();
        ctx.fill();

        ctx.beginPath();
        ctx.moveTo(150,10);
        ctx.lineTo(200,10);
        ctx.lineTo(200,120);
        ctx.lineTo(190,120);
        ctx.fill();
        ctx.stroke();

        ctx.beginPath();
        ctx.moveTo(250,10);
        ctx.lineTo(250,120);
        ctx.stroke();
    </script>


lineCap——在绘制线条或闭合图形时设置线条末端的样式;

    <canvas id="canvas2" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //设置lineCap属性
        var ctx2=document.getElementById("canvas2").getContext("2d");
        ctx2.strokeStyle="red";
        ctx2.lineWidth=2;

        ctx2.beginPath();
        ctx2.moveTo(0,50);
        ctx2.lineTo(200,50);
        ctx2.stroke();

        ctx2.strokeStyle="black";
        ctx2.lineWidth=40;

        var xpos=50;
        var styles=["butt","round","square"];
        for(var i=0;i<styles.length;i++){
            ctx2.beginPath();
            ctx2.lineCap=styles[i];
            ctx2.moveTo(xpos,50);
            ctx2.lineTo(xpos,150);
            ctx2.stroke();
            xpos+=50;
        }
    </script>


    <canvas id="canvas3" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //用Rect方法绘制矩形
        var ctx3=document.getElementById("canvas3").getContext("2d");
        ctx3.fillStyle="yellow";
        ctx3.strokeStyle="black";
        ctx3.lineWidth=4;

        ctx3.beginPath();
        ctx3.moveTo(110,10);
        ctx3.lineTo(110,100);
        ctx3.lineTo(10,10);
        ctx3.closePath();

        ctx3.rect(110,10,100,90);
        ctx3.rect(110,100,130,30);
        ctx3.fill();
        ctx3.stroke();
    </script>


2)绘制圆弧:

arc(x,y,rad,startAngle,endAngle,direction)——绘制一段圆弧到(x,y),半径为rad,起始角度为 startAngle,结束角度为endAngle。可选参数direction指定了圆弧的方向;

arcTo(x1,y1,x2,y2,rad)——绘制一段半径为rad,经过(x1,y1),直到(x2,y2)的圆弧;

    <canvas id="canvas4" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //使用arcTo方法
        var ctx4=document.getElementById("canvas4").getContext("2d");
        var point1=[100,10];
        var point2=[200,10];
        var point3=[200,110];

        ctx4.fillStyle="yellow";
        ctx4.strokeStyle="black";
        ctx4.lineWidth=4;

        ctx4.beginPath();
        ctx4.moveTo(point1[0],point1[1]);
        ctx4.arcTo(point2[0],point2[1],point3[0],point3[1],100);
        ctx4.stroke();

        drawPoint(point1[0],point1[1]);
        drawPoint(point2[0],point2[1]);
        drawPoint(point3[0],point3[1]);

        ctx4.beginPath();
        ctx4.moveTo(point1[0],point1[1]);
        ctx4.lineTo(point2[0],point2[1]);
        ctx4.lineTo(point3[0],point3[1]);
        ctx4.stroke();

        function drawPoint(x,y){
            ctx4.lineWidth=1;
            ctx4.strokeStyle="red";
            ctx4.strokeRect(x-2,y-2,4,4);
        }
    </script>


    <canvas id="canvas5" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //响应鼠标移动绘制圆弧
        var canvasElem = document.getElementById("canvas5");
        var ctx5 = canvasElem.getContext("2d");

        var point1 = [100, 10];
        var point2 = [200, 10];
        var point3 = [200, 110];

        draw();

        canvasElem.onmousemove = function (e) {
            if (e.ctrlKey) {
                point1 = [e.clientX, e.clientY];
            } else if(e.shiftKey) {
                point2 = [e.clientX, e.clientY];
            } else {
                point3 = [e.clientX, e.clientY];
            }
            ctx5.clearRect(0, 0, 540, 140);
            draw();
        }

        function draw() {

            ctx5.fillStyle = "yellow";
            ctx5.strokeStyle = "black";
            ctx5.lineWidth = 4;

            ctx5.beginPath();
            ctx5.moveTo(point1[0], point1[1]);
            ctx5.arcTo(point2[0], point2[1], point3[0], point3[1], 50);
            ctx5.stroke();

            drawPoint(point1[0], point1[1]);
            drawPoint(point2[0], point2[1]);
            drawPoint(point3[0], point3[1]);

            ctx5.beginPath();
            ctx5.moveTo(point1[0], point1[1]);
            ctx5.lineTo(point2[0], point2[1]);
            ctx5.lineTo(point3[0], point3[1]);
            ctx5.stroke();
        }

        function drawPoint(x, y) {
            ctx5.lineWidth = 1;
            ctx5.strokeStyle = "red";
            ctx5.strokeRect(x -2, y-2, 4, 4);
        }
    </script>


    <canvas id="canvas6" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //使用arc方法
        var ctx6=document.getElementById("canvas6").getContext("2d");
        ctx6.fillStyle="yellow";
        ctx6.lineWidth=3;

        ctx6.beginPath();
        ctx6.arc(70,70,60,0,Math.PI,true);
        ctx6.stroke();
        ctx6.beginPath();
        ctx6.arc(200,70,60,Math.PI/2,Math.PI/4,false);
        ctx6.fill();
        ctx6.stroke();

        ctx6.beginPath();
        var val=0;
        for(var i=0;i<4;i++){
            ctx6.arc(350,70,60,val,val+Math.PI/4,false);
            val+=Math.PI/2;
        }
        ctx6.closePath();
        ctx6.fill();
        ctx6.stroke();
    </script>


3)绘制贝塞尔曲线

bezierCurveTo(cx1,cy1,cx2,cy2,x,y)——绘制一段贝塞尔曲线到点(x,y),控制点为(cx1,cy1)和(cx2,cy2);

quadraticCurveTo(cx,xy,x,y)——绘制一段二次贝塞尔曲线到点(x,y),控制点为(cx,cy);

<canvas id="canvas" width="500" height="140">
            Your browser doesn't support the <code>canvas</code> element
        </canvas>
        <script>
            var canvasElem = document.getElementById("canvas");
            var ctx = canvasElem.getContext("2d");

            var startPoint = [50, 100];
            var endPoint = [400, 100];
            var cp1 = [250, 50];
            var cp2 = [350, 50];
            
            canvasElem.onmousemove = function(e) {
                if (e.shiftKey) {
                    cp1 = [e.clientX, e.clientY];
                } else if (e.ctrlKey) {
                    cp2 = [e.clientX, e.clientY];
                }
                ctx.clearRect(0, 0, 500, 140);
                draw();
            }
            
            draw();

            function draw() {
                ctx.lineWidth = 3;
                ctx.strokeStyle = "black";                  
                ctx.beginPath();
                ctx.moveTo(startPoint[0], startPoint[1]);
                ctx.bezierCurveTo(cp1[0], cp1[1], cp2[0], cp2[1], 
                    endPoint[0], endPoint[1]);
                ctx.stroke();
    
                ctx.lineWidth = 1;
                ctx.strokeStyle = "red";            
                var points = [startPoint, endPoint, cp1, cp2];
                for (var i = 0; i < points.length; i++) {
                    drawPoint(points[i]);    
                }
                drawLine(startPoint, cp1);
                drawLine(endPoint, cp2);
            }

            function drawPoint(point) {
                ctx.beginPath();

                ctx.strokeRect(point[0] -2, point[1] -2, 4, 4);
            }
            
            function drawLine(from, to) {
                ctx.beginPath();
                ctx.moveTo(from[0], from[1]);
                ctx.lineTo(to[0], to[1]);
                ctx.stroke();
            }
        </script>

        <canvas id="canvas" width="500" height="140">
            Your browser doesn't support the <code>canvas</code> element
        </canvas>
        <script>
          //绘制二次贝塞尔曲线
            var canvasElem = document.getElementById("canvas");
            var ctx = canvasElem.getContext("2d");

            var startPoint = [50, 100];
            var endPoint = [400, 100];
            var cp1 = [250, 50];
            
            canvasElem.onmousemove = function(e) {
                if (e.shiftKey) {
                    cp1 = [e.clientX, e.clientY];
                }
                ctx.clearRect(0, 0, 500, 140);
                draw();
            }
            
            draw();

            function draw() {
                ctx.lineWidth = 3;
                ctx.strokeStyle = "black";                  
                ctx.beginPath();
                ctx.moveTo(startPoint[0], startPoint[1]);
                ctx.quadraticCurveTo(cp1[0], cp1[1], endPoint[0], endPoint[1]);
                ctx.stroke();
    
                ctx.lineWidth = 1;
                ctx.strokeStyle = "red";            
                var points = [startPoint, endPoint, cp1];
                for (var i = 0; i < points.length; i++) {
                    drawPoint(points[i]);    
                }
                drawLine(startPoint, cp1);
                drawLine(endPoint, cp1);
            }

            function drawPoint(point) {
                ctx.beginPath();

                ctx.strokeRect(point[0] -2, point[1] -2, 4, 4);
            }
            
            function drawLine(from, to) {
                ctx.beginPath();
                ctx.moveTo(from[0], from[1]);
                ctx.lineTo(to[0], to[1]);
                ctx.stroke();
            }
        </script>


4)创建剪辑区域

clip()——创建新的裁剪区域;

    <canvas id="canvas7" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        var ctx7=document.getElementById("canvas7").getContext("2d");

        ctx7.fillStyle="yellow";
        ctx7.beginPath();
        ctx7.rect(0,0,500,140);
        ctx7.fill();

        ctx7.beginPath();
        ctx7.rect(100,20,300,100);
        ctx7.clip();

        ctx7.fillStyle="red";
        ctx7.beginPath();
        ctx7.rect(0,0,500,140);
        ctx7.fill();
    </script>


5)绘制文本:

fillText(<text>,x,y,width)——在位置(x,y)上绘制并填充文本。宽度参数可选,用来设置文本宽度的上限;

strokeText(<text>,x,y,width)——在位置(x,y)上绘制并描边文本。宽度参数可选,用来设置文本宽度的上限;

font——设置绘制文本时使用的字体;

textAlign——设置文本的对齐方式:start、end、left、right、center;

textBaseline——设置文本的基线:top、hanging、middle、alphabetic、ideographic、bottom;

6)使用特效和转换:

6.1)使用阴影:

shadowBlur——设置阴影的模糊程度;

shadowColor——设置阴影的颜色;

shadowOffsetX——设置阴影的水平偏移量;

shadowOffsetY——设置阴影的垂直偏移量;

   <canvas id="canvas8" width="500" height="140">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //给图形和文本应用阴影
        var ctx8=document.getElementById("canvas8").getContext("2d");

        ctx8.fillStyle="lightgrey";
        ctx8.strokeStyle="black";
        ctx8.lineWidth=3;

        ctx8.shadowOffsetX=5;
        ctx8.shadowOffsetY=5;
        ctx8.shadowBlur=5;
        ctx8.shadowColor="grey";

        ctx8.beginPath();
        ctx8.arc(420,70,50,0,Math.PI,true);
        ctx8.stroke();

        ctx8.beginPath();
        ctx8.arc(420,80,40,0,Math.PI,false);
        ctx8.fill();

        ctx8.font="100px sans-serif";
        ctx8.fillText("hello",50,100);
        ctx8.strokeText("hello",50,100);
    </script>


6.2)使用透明度:

globalAlpha——给文本和图形设置透明度(从0到1);

    <canvas id="canvas9" width="300" height="120">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //使用globalAlpha属性,设置透明度
        var ctx9=document.getElementById("canvas9").getContext("2d");

        ctx9.fillStyle="lightgrey";
        ctx9.strokeStyle="black";
        ctx9.lineWidth=3;

        ctx9.font="100px sans-serif";
        ctx9.fillText("hello",10,100);
        ctx9.strokeText("hello",10,100);

        ctx9.fillStyle="red";
        ctx9.globalAlpha=0.5;
        ctx9.fillRect(10,10,240,100);
    </script>


6.3)使用合成:

globalCompositeOperation——与透明度属性结合使用,来控制图形和文本在画布上绘制的方式;

globalCompositeOperation允许的值:

=copy——将来源绘制于目标之上,忽略一切透明度设置;

=source-atop——在两个图像都不透明处显示来源图像,

目标图像不透明但来源图像透明处显示目标图像,其它位置显示为透明;

=source-in——来源图像和目标图像都不透明处显示来源图像。其它位置显示为透明;

=source-out——来源图像不透明但目标图像透明处显示来源图像。其它位置显示为透明;

=source-over——来源图像不透明处显示来源图像。其它位置显示目标图像;

=destination-atop——与source-atop相同,但用目标图像替代来源图像,反之亦然;

=destination-in——与source-in相同,但用目标图像替代来源图像,反之亦然;

=destination-over——source-over相同,但用目标图像替代来源图像,反之亦然;

=destination-out——source-out相同,但用目标图像替代来源图像,反之亦然;

=lighter——显示来源图像与目标图像的总和,颜色值限制最高255(100%);

=xor——对来源图像和目标图像执行异或运算;

    <canvas id="canvas10" width="300" height="120">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <label>Comosition Value:</label>
    <select id="list">
        <option>copy</option>
        <option>destination-atop</option>
        <option>destination-in</option>
        <option>destination-over</option>
        <option>destination-out</option>
        <option>lighter</option>
        <option>source-atop</option>
        <option>source-in</option>
        <option>source-out</option>
        <option>source-over</option>
        <option>xor</option>
    </select>
    <script>
        //使用globalCompositeOperation属性
        var ctx10=document.getElementById("canvas10").getContext("2d");

        ctx10.fillStyle="lightgrey";
        ctx10.strokeStyle="black";
        ctx10.lineWidth=3;

        var compVal="copy";

        document.getElementById("list").onchange=function(e){
            compVal= e.target.value;
            draw();
        }

        draw();

        function draw(){
            ctx10.clearRect(0,0,300,120);
            ctx10.globalAlpha=1.0;
            ctx10.font="100px sans-serif";
            ctx10.fillText("hello",10,100);
            ctx10.strokeText("hello",10,100);

            ctx10.globalCompositeOperation=compVal;

            ctx10.fillStyle="red";
            ctx10.globalAlpha=0.5;
            ctx10.fillRect(100,10,150,100);
        }
    </script>


6.4)使用变换:

scale(<xScale>,<yScale>)——沿X轴缩放画布xScale倍,沿Y轴yScale倍;

rotate(<angle>)——使画布围绕点(0,0)顺时针旋转指定的弧度数;

translate(<x>,<y>)——重映射画布坐标为沿X轴x,沿Y轴y;

transform(a,b,c,d,e,f)——合并现有的变换和a-f值所指定的矩阵;

setTansform(a,b,c,d,e,f)——用a-f值所指定的矩阵替换现有的变换;

    <canvas id="canvas11" width="400" height="200">
        您的浏览器不支持<code>canvas</code>!
    </canvas>
    <script>
        //使用变换
        var ctx11=document.getElementById("canvas11").getContext("2d");

        ctx11.fillStyle="lightgrey";
        ctx11.strokeStyle="black";
        ctx11.lineWidth=3;

        ctx11.clearRect(0,0,300,120);
        ctx11.globalAlpha=1.0;
        ctx11.font="100px sans-serif";
        ctx11.fillText("hello",10,100);
        ctx11.strokeText("hello",10,100);

        ctx11.scale(1.3,1.3);
        ctx11.translate(100,-50);
        ctx11.rotate(0.5);

        ctx11.fillStyle="red";
        ctx11.globalAlpha=0.5;
        ctx11.fillRect(100,10,150,100);
        ctx11.strokeRect(0,0,300,200);
    </script>

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