技术教程 编程教程 用canvas绘制折线图 正文

用canvas绘制折线图

2023-04-23,,

 <!DOCTYPE html>

 <html lang="en">

 <head>

     <meta charset="UTF-8">

     <title>用canvas绘制折线图</title>

 </head>

 <body>

     <canvas id="cv"></canvas>

 </body>

 </html>

 <script>

     var cv = document.getElementById("cv");

     cv.width = 600;

     cv.height = 400;

     cv.style.border = "1px solid red";

     var ctx = cv.getContext("2d");

     var data2 = [.3, .1, .2, .4, .2, .7, .3, .9];

     var data3 = [3, 12, 14, 17, 29, 33, 40, 52];

     getBrokenLine(data2, "#f00");

     getBrokenLine(data3, "#0f0");

     //封装一个折线图的函数

     function getBrokenLine(data, color) {

         var maxNum = Math.max.apply(null, data);    //求数组中的最大值

         var padding = 20,  //边距

                 x0 = padding,  //原点x轴坐标

                 y0 = cv.height - padding,  //原点y轴坐标

                 xArrow_x = padding, //x轴箭头处坐标x

                 xArrow_y = padding, //x轴箭头处坐标y

                 yArrow_x = cv.width - padding,  //y轴箭头处坐标x

                 yArrow_y = cv.height - padding, //y轴箭头处坐标y

                 arrowWidth = 10,    //箭头的宽度

                 xLength = cv.width - 2*padding - arrowWidth,    //x轴的长度

                 yLength = cv.height - 2*padding - arrowWidth,  //y轴的长度

                 pointsWidth = xLength/(data.length + 1);    //折线上每个点之间的距离

         ctx.beginPath();//控制绘制的折线不受坐标轴样式属性的影响

         //绘制x轴

         ctx.moveTo(x0, y0);

         ctx.lineTo(xArrow_x, xArrow_y);

         ctx.moveTo(xArrow_x, xArrow_y);

         ctx.lineTo(xArrow_x - arrowWidth, xArrow_y + arrowWidth);

         ctx.moveTo(xArrow_x, xArrow_y);

         ctx.lineTo(xArrow_x + arrowWidth, xArrow_y + arrowWidth);

         //绘制y轴

         ctx.moveTo(x0, y0);

         ctx.lineTo(yArrow_x, yArrow_y);

         ctx.moveTo(yArrow_x, yArrow_y);

         ctx.lineTo(yArrow_x - arrowWidth, yArrow_y - arrowWidth);

         ctx.moveTo(yArrow_x, yArrow_y);

         ctx.lineTo(yArrow_x - arrowWidth, yArrow_y + arrowWidth);

         ctx.strokeStyle = "#000";

         //中断（坐标轴和折线的）连接

         ctx.stroke();

         ctx.beginPath();

         //绘制折线

         for (var i = 0; i < data.length; i++) {

             var pointX = padding + (i + 1) * pointsWidth;

             var pointY = padding + arrowWidth + (1 - data[i]/maxNum) * yLength;

             ctx.lineTo(pointX, pointY);

         }

         ctx.strokeStyle = color;

         ctx.stroke();

     }

 </script>

效果图如下：

用canvas绘制折线图的相关教程结束。

《用canvas绘制折线图.doc》

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