本文实例讲述了JS+html5canvas实现的简单绘制折线图效果。分享给大家供大家参考，具体如下
本文实例讲述了JS+html5 canvas实现的简单绘制折线图效果。分享给大家供大家参考，具体如下：
1、实例代码：
<!DOCTYPE html>
<html>
<head>
<meta charset='utf-8'>
<title>画图</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">
铝锭价走势图<br/>
<canvas id="cv">你的设备不支持图表数据显示</canvas>
</div>
<script>
(function(){
window.onload = function(){
//数据源
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}
]
//数据源提取
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);//与最小的做比较
}
}
else{//如果相差太大会导致图表不美观
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 准备
var canvas = document.getElementById("cv");//获取canvas画布
var ctx = canvas.getContext("2d");
//画折线
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();
//画点
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);//画点
ctx.fill();
ctx.fillText(yMemo, x + 3, y - 10);
ctx.fillText(xMemo, x + 3, canvas.height - 10, 40);//画文字
}
}
})();
</script>
</body>
</html>
2、运行效果图如下：
