Add maxLines option for gridLines [v2 enhancement]

[morleyzhi]

One of the projects I'm working on doesn't have any axis labels, so I wound up in a situation where there were a lot of gridLines, to the point where it made the chart illegible. I think being able to add a max number to the gridLines config could be useful:

                xAxes: [{
                    gridLines: {
                        display: true
                        drawTicks: false
                        maxLines: 100
                    }
                    ticks: {
                        display: false
                    }
                }]

In fact, I've already done this on an illegitimate fork:

https://github.com/morleyzhi/OkChart.js/commit/5d42d12ffe3168ba28def36135fcc3dfa6725061

If you think this is worth folding into Chart.js proper, I can make a pull request for it.

[etimberg]

@morleyzhi there's a similar option here https://github.com/nnnick/Chart.js/blob/v2.0-dev/src/scales/scale.linear.js#L162

If yours produces different results, I'd be more than happy to look over a PR.

[morleyzhi]

I don't think the maxTicksLimit does what I'm intending. It limits ticks but not gridlines.

This is with maxTicksLimit set to 100. There's definitely more than 100 gridLines:

In contrast, this is with my maxLines prop:

I'll make a PR that uses maxTicksLimit to also limit the number of gridlines.

[morleyzhi]

...Actually, I just imported the latest version of Chart.js, and it looks like it works. So we're good. Thanks!

[morleyzhi]

Sorry about this -- I was mistaken. I had added back in the ticks display for testing, and I mistook the label-spacing for maxTicksLimit usage.

[etimberg]

Merged #1863