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Line thickness drawing issue with discontinuities

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  • May 1, 2014 at 4:07 am #6244

    adlerhn

    I have noticed that the line chart doesn’t draw the lines with consistent thickness when there are discontinuities in the graph. It looks like some part are re-drawn, or drawn thicker than requested.

    A simple way of reproducing the issue, with the realtime example:

    https://canvasjs.com/editor/?id=https://canvasjs.com/example/gallery/dynamic/realtime_line/

    Change the y value assigned so that there are discontinuities once in a while:

    y: ((xVal%100)<5) ? “” :yVal

    And set a very narrow line thickness, so that the issue is more noticeable. I actually noticed it with lineThickness = 1, but for the sake of reproducing the error, let’s assign something really small, like 0.01.

    lineThickness: 0.01,

    The graph should be barely visible, but it is more visible (thicker line) in some parts than in others.

    The full html (copy-pasted from the modified example) would be:

    <!DOCTYPE HTML>
<html>

<head>
	<script type="text/javascript">
	window.onload = function () {

		var dps = []; // dataPoints

		var chart = new CanvasJS.Chart("chartContainer",{
			title :{
				text: "Live Random Data"
			},			
			data: [{
				type: "line",
                lineThickness: 0.01,
				dataPoints: dps 
			}]
		});

		var xVal = 0;
		var yVal = 100;	
		var updateInterval = 20;
		var dataLength = 500; // number of dataPoints visible at any point

		var updateChart = function (count) {
			count = count || 1;
			// count is number of times loop runs to generate random dataPoints.
			
			for (var j = 0; j < count; j++) {	
				yVal = yVal +  Math.round(5 + Math.random() *(-5-5));
				dps.push({
					x: xVal,
					y: ((xVal%100)<5) ? "" :yVal
				});
				xVal++;
			};
			if (dps.length > dataLength)
			{
				dps.shift();				
			}
			
			chart.render();		

		};

		// generates first set of dataPoints
		updateChart(dataLength); 

		// update chart after specified time. 
		setInterval(function(){updateChart()}, updateInterval); 

	}
	</script>
	<script type="text/javascript" src="/assets/script/canvasjs.min.js"></script>
</head>
<body>
	<div id="chartContainer" style="height: 300px; width:100%;">
	</div>
</body>
</html>

    PS. Congratulations on the library. It is very simple, lightweight, and powerful at the same time.

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