Exporting c3.js line charts to png images does not work

Question

I am using SVG.toDataURL() to export c3js charts to png images. Exporting the charts to png works properly.

In case of the line charts, they are not rendered properly. e.g.

1. The x and y axis width is increased.
2. Lines are not proper, instead of the lines it shows dark black regions.

jsfiddle

Below is the code to export png

 function exportImageAsPNG(){
        var svgElements = $("#chart").find('svg');
        var svg ;
        svgElements.each(function() {
            svg = this;
        });
        var img = document.getElementById("fromcanvas");
        svg.toDataURL("image/png", {
            callback: function(data) {
                img.setAttribute("src", data)
            }
        })
    }

Same thing happens when I use the canvag library.

var $container = $('#chart'),
content = $container.html().trim(),
canvas = document.getElementById('svg-canvas');

// Draw svg on canvas
canvg(canvas, content);

// Change img be SVG representation
var theImage = canvas.toDataURL('image/png');

$("#hiddenPng").attr('href', theImage);
$("#hiddenPng span").trigger("click");

Answer 1

Maybe a little bit late, but I hope this solution helps future devs:

• the validated solution above didn't work for me with Barchart and others
• so, base on the same principle, here's what I did to make the export work with every chart type. Here are some example:

Assume we have this in html, and the chart is already generated with c3:

<div id="chartID" class="chart-content"></div>

Then, in our JS, this is export function :

function exportChartToPng(chartID){
//fix weird back fill
d3.select('#'+chartID).selectAll("path").attr("fill", "none");
//fix no axes
d3.select('#'+chartID).selectAll("path.domain").attr("stroke", "black");
//fix no tick
d3.select('#'+chartID).selectAll(".tick line").attr("stroke", "black");
var svgElement = $('#'+chartID).find('svg')[0];
saveSvgAsPng(svgElement, chartID+'.png');
}

Note : the saveSvgAsPng tools is from https://github.com/exupero/saveSvgAsPng

Answer 2

The issue is that the exporter function only considers inline CSS styles when performing the export. In other words, the exporter is losing track of C3's css settings, thus your graph will look like this fellow's right before it exports

https://github.com/c3js/c3/issues/356

Most importantly, the black triangles are caused by the fill property of some specific .c3 elements. c3.css sets these to none by default, but your exporter doesn't know that.

See:

And, if you manually turn off the fill property from c3.min.css...

You'll want to somehow set the fill CSS property of those specific elements as inline CSS (as in ) before exporting

Here's a quick, plainJS fix for this, add these lines between genChart(); and exportImageAsPNG(); as shown to fix your problem.

    genChart();
    var nodeList = document.getElementById('chart').querySelector('svg').querySelectorAll('.c3-chart path');
    var nodeList2 = document.getElementById('chart').querySelector('svg').querySelectorAll('.c3-axis path');
    var nodeList3 = document.getElementById('chart').querySelector('svg').querySelectorAll('.c3 line');
    var line_graph = Array.from(nodeList);
    var x_and_y = Array.from(nodeList2).concat(Array.from(nodeList3));
    line_graph.forEach(function(element){
        element.style.fill = "none";
    })
    x_and_y.forEach(function(element){
        element.style.fill = "none";
        element.style.stroke = "black";
    })
    exportImageAsPNG();

JSFiddle: https://jsfiddle.net/vtange/vajs3cmf/