How can I draw an vertical line at a particular point on the x-axis using Chart.js?
In particular, I want to draw a line to indicate the current day on a LineChart. Here's a mockup of the chart:
http://i.stack.imgur.com/VQDWR.png
Update - this answer is for Chart.js 1.x, if you are looking for a 2.x answer check the comments and other answers.
You extend the line chart and include logic for drawing the line in the draw function.
Preview
HTML
<div>
<canvas id=LineWithLine width=600 height=400></canvas>
</div>
Script
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,
draw: function () {
Chart.types.Line.prototype.draw.apply(this, arguments);
var point = this.datasets[0].points[this.options.lineAtIndex]
var scale = this.scale
// draw line
this.chart.ctx.beginPath();
this.chart.ctx.moveTo(point.x, scale.startPoint + 24);
this.chart.ctx.strokeStyle = '#ff0000';
this.chart.ctx.lineTo(point.x, scale.endPoint);
this.chart.ctx.stroke();
// write TODAY
this.chart.ctx.textAlign = 'center';
this.chart.ctx.fillText(TODAY, point.x, scale.startPoint + 12);
}
});
new Chart(ctx).LineWithLine(data, {
datasetFill : false,
lineAtIndex: 2
});
The option property lineAtIndex controls which point to draw the line at.
Fiddle - http://jsfiddle.net/dbyze2ga/14/
