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[网页设计]用canvas绘制折线图

 1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4   <meta charset="UTF-8"> 5   <title>用canvas绘制折线图</title> 6 </head> 7 <body> 8   <canvas id="cv"></canvas> 9 </body>10 </html>11 <script>12   var cv = document.getElementById("cv");13   cv.width = 600;14   cv.height = 400;15   cv.style.border = "1px solid red";16   var ctx = cv.getContext("2d");17   var data2 = [.3, .1, .2, .4, .2, .7, .3, .9];18   var data3 = [3, 12, 14, 17, 29, 33, 40, 52];19 20   getBrokenLine(data2, "#f00");21   getBrokenLine(data3, "#0f0");22 23   //封装一个折线图的函数24   function getBrokenLine(data, color) {25     var maxNum = Math.max.apply(null, data);  //求数组中的最大值26     var padding = 20, //边距27         x0 = padding, //原点x轴坐标28         y0 = cv.height - padding, //原点y轴坐标29         xArrow_x = padding, //x轴箭头处坐标x30         xArrow_y = padding, //x轴箭头处坐标y31         yArrow_x = cv.width - padding, //y轴箭头处坐标x32         yArrow_y = cv.height - padding, //y轴箭头处坐标y33         arrowWidth = 10,  //箭头的宽度34         xLength = cv.width - 2*padding - arrowWidth,  //x轴的长度35         yLength = cv.height - 2*padding - arrowWidth, //y轴的长度36         pointsWidth = xLength/(data.length + 1);  //折线上每个点之间的距离37 38     ctx.beginPath();//控制绘制的折线不受坐标轴样式属性的影响39     //绘制x轴40     ctx.moveTo(x0, y0);41     ctx.lineTo(xArrow_x, xArrow_y);42     ctx.moveTo(xArrow_x, xArrow_y);43     ctx.lineTo(xArrow_x - arrowWidth, xArrow_y + arrowWidth);44     ctx.moveTo(xArrow_x, xArrow_y);45     ctx.lineTo(xArrow_x + arrowWidth, xArrow_y + arrowWidth);46 47     //绘制y轴48     ctx.moveTo(x0, y0);49     ctx.lineTo(yArrow_x, yArrow_y);50     ctx.moveTo(yArrow_x, yArrow_y);51     ctx.lineTo(yArrow_x - arrowWidth, yArrow_y - arrowWidth);52     ctx.moveTo(yArrow_x, yArrow_y);53     ctx.lineTo(yArrow_x - arrowWidth, yArrow_y + arrowWidth);54     ctx.strokeStyle = "#000";55 56     //中断(坐标轴和折线的)连接57     ctx.stroke();58     ctx.beginPath();59 60     //绘制折线61     for (var i = 0; i < data.length; i++) {62       var pointX = padding + (i + 1) * pointsWidth;63       var pointY = padding + arrowWidth + (1 - data[i]/maxNum) * yLength;64       ctx.lineTo(pointX, pointY);65     }66     ctx.strokeStyle = color;67     ctx.stroke();68   }69 </script>

效果图如下: