Is there any way to add gridlines to a gRaphael line chart? - raphael

Question

I have a line chart that I've created with gRaphael. It has axes and tick marks, but I'd like to have grid lines. Is there built-in way to achieve this or an add on library that can help me?

Answer 1

gRaphael does not have a built-in way to add grid lines, but it is pretty easy to draw them, either by editing the source code or manipulating your graph object after you create it.
I had found an extension called RaphAlytics and used its drawGrid() function in cases where I needed a bounding box with a grid.
You can adapt this function for any gRaphael graph as needed to draw gridlines. On a line chart, I needed to draw horizontal gridlines that were aligned with the left axis marks on a line chart, so I used the function as an example like this:
// Draw horizontal gridlines
for (var i = 0; i < g.axis[1].text.items.length; i++) {
r.path(['M', x, g.axis[1].text.items[i].attrs.y, 'H', w + x]).attr({
stroke : '#EEE'
}).toBack();
}
Here's a working fiddle to illustrate that example: http://jsfiddle.net/KM3BB/1/

Answer 2

I tried doing this yesterday. Short answer: gRaphaël can't do this for you with any linechart options nor axis options, you have to do-it-yourself with Raphaël.
Something like:
var r = Raphael("holder"), txtattr = { font: "12px sans-serif" };
r.path('M 15 200.5 L 310 200.5 M 15 180.5 L 310 200.5');
r.linechart(10, 10, 300, 220, x, [y, y2, y3]);
This means under my linechart draw a path which starts from 15,200.5 and draws a straight line to 310,200.5 moves to 15,180.5 and draws a line to 310,180.5. Don't ask me why but the .5 is important for getting the stroke to actually be 1px wide and solid black. Otherwise it seems to get aliased to 2px wide at 50% opacity. You have to calculate the exact placement in regards to your linechart yourself.
You can also play with the path function in the playground by changing r to paper.
You might also consider looking at Google Chart Tools if your looking for things like defining the exact range of the axis (as opposed to just the min and max of the input).