公司项目要用js画柱状图，本来想用个插件吧 chart.js 忽然一想 我们也用不了那么大的插件。自己写个吧，也能看看自己那点数学水平能够不！
有几个小亮点吧
1.函数x 和 函数y 对坐标进行了转化 假设以画布的左上角为原点 那算起来真是太坑爹了
2.画矩形用画粗线 ，哎呀 那个画矩形那四个点真是要命啊 ，还是画线实在！
抛砖引玉一下。大神勿喷！
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>报告结果</title>
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<style>
body{text-align:center;}
#canvas{width:300px;margin:0 auto;}
</style>
<canvas id="canvas" width="300" height="300"></canvas>
<script type="text/javascript">
var canvas = document.getElementById('canvas');
var cx = canvas.getContext('2d');
/*
var x_width = 300;
var y_width = 300;
var x_left = 50;
var x_right = 230;
var y_up_top = 50;
var y_up_bottom = 150;
var y_down = 80;
*/
draw();
function draw() {
//轴
drawLine(-50,0,250,0,0.5,'#999999');
drawLine(0,200,0,-80,0.5,'#999999');
//刻度
for(var i=2;i<=10;i=i+2){
cx.fillText(i,x(-15),y(g(i))+10);
drawLine(-50,g(i),250,g(i),0.5,'#f0f0f0');
}
//第一个线
var color = ['#ffbfab','#fee17b','#effe87','#c2f3a1','#effe87'];
var grades = [7,8,6,10,8];
for(var i=20,j=0;j<5;j++,i=i+8){
drawLine(i,0,i,g(grades[j]),8,color[j]);
}
var grades = [6,7,6,9,8];
for(var i=80,j=0;j<5;j++,i=i+8){
drawLine(i,0,i,g(grades[j]),8,color[j]);
}
var grades = [5,7,5,1,8];
for(var i=140,j=0;j<5;j++,i=i+8){
drawLine(i,0,i,g(grades[j]),8,color[j]);
}
var grades = [5,7,5,7,8];
for(var i=200,j=0;j<5;j++,i=i+8){
drawLine(i,0,i,g(grades[j]),8,color[j]);
} }
function x(x){
return x+50;
}
function y(y){
return 200-y;
}
function g(grade){
return 15*grade;
} //画线
function drawLine(b_x,b_y,e_x,e_y,width,color){
cx.strokeStyle = color;
cx.lineWidth = width;
cx.beginPath();
cx.moveTo(x(b_x),y(b_y));
cx.lineTo(x(e_x),y(e_y));
cx.closePath();
cx.stroke();
} </script>
</body>
</html>