Chart.js - 绘制水平线

I would like to draw a horizontal line in a chart using Chart.js. But I'm not able to do it.

I've read this question - Chart.js — drawing an arbitrary vertical line - but I can't transform the code for drawing horizontal lines not vertical.

I hope you can help me (especially potatopeelings :)).

解决方案

Here is the JavaScript code to draw a horizontal line.

var data = {
    labels: ["JAN", "FEB", "MAR", "APR", "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"],
    datasets: [{
        data: [12, 3, 2, 1, 8, 8, 2, 2, 3, 5, 7, 1]
    }]
};

var ctx = document.getElementById("LineWithLine").getContext("2d");

Chart.types.Line.extend({
    name: "LineWithLine",
    initialize: function () {
        Chart.types.Line.prototype.initialize.apply(this, arguments);
    },
    draw: function () {
        Chart.types.Line.prototype.draw.apply(this, arguments);

        var point = this.datasets[0].points[this.options.lineAtIndex]
        var scale = this.scale
        console.log(this);

        // draw line
        this.chart.ctx.beginPath();
        this.chart.ctx.moveTo(scale.startPoint+12, point.y);
        this.chart.ctx.strokeStyle = '#ff0000';
        this.chart.ctx.lineTo(this.chart.width, point.y);
        this.chart.ctx.stroke();

        // write TODAY
        this.chart.ctx.textAlign = 'center';
        this.chart.ctx.fillText("TODAY", scale.startPoint + 35, point.y+10);
    }
});

new Chart(ctx).LineWithLine(data, {
    datasetFill : false,
    lineAtIndex: 2
});

http://jsfiddle.net/7a4hhzge/455/

This is based off of the code used to draw an arbitrary vertical line, it may not be perfect but you should be able to adjust it to fit your needs.