JS+html5 canvas實現的簡單繪制折線圖效果示例

2019-11-19 17:10:42

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本文實例講述了JS+html5 canvas實現的簡單繪制折線圖效果。分享給大家供大家參考，具體如下：

1、實例代碼：

<!DOCTYPE html><html>  <head>    <meta charset='utf-8'>    <title>畫圖</title>    <style>      #divContainer{        margin-top: 20px;        text-align: center;      }      #cv{        width: 300px;        height: 200px;        border-bottom: 2px solid #000;        border-left: 2px solid #000;      }    </style>  </head>  <body>    <div id="divContainer">      鋁錠價走勢圖<br/>      <canvas id="cv">你的設備不支持圖表數據顯示</canvas>    </div>    <script>      (function(){        window.onload = function(){          //數據源          var dict = [            {x: "2015-04-24", y: 13400},            {x: "2015-04-25", y: 13380},            {x: "2015-04-26", y: 13370},            {x: "2015-04-27", y: 13370},            {x: "2015-04-28", y: 13380}          ]          //數據源提取          var len = dict.length;          var xArr = [], yArr = [], tmp_yArr = [];          for(var i=0; i<len; i++){            xArr.push(i * 60);            tmp_yArr.push(dict[i].y);          }          var tmp_minY = Math.min.apply(Math, tmp_yArr);//最小值          var tmp_maxY = Math.max.apply(Math, tmp_yArr);//最大值          if(tmp_maxY - tmp_minY <= 100){            for(var i=0; i<len; i++){              yArr.push(tmp_yArr[i] - tmp_minY + 50);//與最小的做比較            }          }          else{//如果相差太大會導致圖表不美觀            for(var i=0; i<len; i++){              yArr.push(tmp_yArr[i] / 500);            }          }          var minY = Math.min.apply(Math, yArr);          var maxY = Math.max.apply(Math, yArr);          //canvas 準備          var canvas = document.getElementById("cv");//獲取canvas畫布          var ctx = canvas.getContext("2d");          //畫折線          for(var i=0 ;i<len; i++){            var x = xArr[i];            var y = maxY - yArr[i] + minY;            if(i === 0){              ctx .moveTo(x, y);            }            else{              ctx .lineTo(x, y);            }          }          ctx .stroke();          //畫點          for(var i=0; i<len; i++){            var x = xArr[i];            var y = maxY - yArr[i] + minY;            var xMemo = dict[i].x;            var yMemo = "¥" + dict[i].y;            ctx.beginPath();            ctx.fillStyle = "#000";            ctx.arc(x, y, 2, 0, 2*Math.PI);//畫點            ctx.fill();            ctx.fillText(yMemo, x + 3, y - 10);            ctx.fillText(xMemo, x + 3, canvas.height - 10, 40);//畫文字          }        }      })();    </script>  </body></html>

2、運行效果圖如下：