• 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x
    30                 xArrow_y = padding, //x轴箭头处坐标y
    31                 yArrow_x = cv.width - padding,  //y轴箭头处坐标x
    32                 yArrow_y = cv.height - padding, //y轴箭头处坐标y
    33                 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:

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  • 原文地址:https://www.cnblogs.com/2010master/p/5936950.html
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