JavaScript canvas绘制折线图
网络编程 2021-07-04 15:02www.168986.cn编程入门
这篇文章主要为大家详细介绍了JavaScript canvas绘制折线图，文中示例代码介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们可以参考一下
本文实例为大家分享了canvas绘制折线图的具体代码，供大家参考，具体内容如下
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
<style>
canvas {
border: 1px solid #c;
}
</style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
/1.构造函数/
var LineChart = function (ctx) {
/获取绘图工具/
this.ctx = ctx || document.querySelector('canvas').getContext('2d');
/画布的大小/
this.canvasWidth = this.ctx.canvas.width;
this.canvasHeight = this.ctx.canvas.height;
/网格的大小/
this.gridSize = 10;
/坐标系的间距/
this.space = 20;
/坐标原点/
this.x0 = this.space;
this.y0 = this.canvasHeight - this.space;
/箭头的大小/
this.arrowSize = 10;
/绘制点/
this.dottedSize = 6;
/点的坐标 和数据有关系 数据可视化/
}
/2.行为方法/
LineChart.prototype.init = function (data) {
this.drawGrid();
this.drawAxis();
this.drawDotted(data);
};
/绘制网格/
LineChart.prototype.drawGrid = function () {
/x方向的线/
var xLineTotal = Math.floor(this.canvasHeight / this.gridSize);
this.ctx.strokeStyle = '#eee';
for (var i = 0; i <= xLineTotal; i++) {
this.ctx.beginPath();
this.ctx.moveTo(0, i this.gridSize - 0.5);
this.ctx.lineTo(this.canvasWidth, i this.gridSize - 0.5);
this.ctx.stroke();
}
/y方向的线/
var yLineTotal = Math.floor(this.canvasWidth / this.gridSize);
for (var i = 0; i <= yLineTotal; i++) {
this.ctx.beginPath();
this.ctx.moveTo(i this.gridSize - 0.5, 0);
this.ctx.lineTo(i this.gridSize - 0.5, this.canvasHeight);
this.ctx.stroke();
}
};
/绘制坐标系/
LineChart.prototype.drawAxis = function () {
/X轴/
this.ctx.beginPath();
this.ctx.strokeStyle = '#000';
this.ctx.moveTo(this.x0, this.y0);
this.ctx.lineTo(this.canvasWidth - this.space, this.y0);
this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 + this.arrowSize / 2);
this.ctx.lineTo(this.canvasWidth - this.space - this.arrowSize, this.y0 - this.arrowSize / 2);
this.ctx.lineTo(this.canvasWidth - this.space, this.y0);
this.ctx.stroke();
this.ctx.fill();
/Y轴/
this.ctx.beginPath();
this.ctx.strokeStyle = '#000';
this.ctx.moveTo(this.x0, this.y0);
this.ctx.lineTo(this.space, this.space);
this.ctx.lineTo(this.space + this.arrowSize / 2, this.space + this.arrowSize);
this.ctx.lineTo(this.space - this.arrowSize / 2, this.space + this.arrowSize);
this.ctx.lineTo(this.space, this.space);
this.ctx.stroke();
this.ctx.fill();
};
/绘制所有点/
LineChart.prototype.drawDotted = function (data) {
/1.数据的坐标 需要转换 canvas坐标/
/2.再进行点的绘制/
/3.把线连起来/
var that = this;
/记录当前坐标/
var prevCanvasX = 0;
var prevCanvasY = 0;
data.forEach(function (item, i) {
/ x = 原点的坐标 + 数据的坐标 /
/ y = 原点的坐标 - 数据的坐标 /
var canvasX = that.x0 + item.x;
var canvasY = that.y0 - item.y;
/绘制点/
that.ctx.beginPath();
that.ctx.moveTo(canvasX - that.dottedSize / 2, canvasY - that.dottedSize / 2);
that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY - that.dottedSize / 2);
that.ctx.lineTo(canvasX + that.dottedSize / 2, canvasY + that.dottedSize / 2);
that.ctx.lineTo(canvasX - that.dottedSize / 2, canvasY + that.dottedSize / 2);
that.ctx.closePath();
that.ctx.fill();
/点的连线/
/当时第一个点的时候 起点是 x0 y0/
/当时不是第一个点的时候 起点是 上一个点/
if(i == 0){
that.ctx.beginPath();
that.ctx.moveTo(that.x0,that.y0);
that.ctx.lineTo(canvasX,canvasY);
that.ctx.stroke();
}else{
/上一个点/
that.ctx.beginPath();
that.ctx.moveTo(prevCanvasX,prevCanvasY);
that.ctx.lineTo(canvasX,canvasY);
that.ctx.stroke();
}
/记录当前的坐标，下一次要用/
prevCanvasX = canvasX;
prevCanvasY = canvasY;
});
};
/3.初始化/
var data = [
{
x: 100,
y: 120
},
{
x: 200,
y: 160
},
{
x: 300,
y: 240
},
{
x: 400,
y: 120
},
{
x: 500,
y: 80
}
];
var lineChart = new LineChart();
lineChart.init(data);
</script>
</body>
</html>
运行结果如下
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