Rendering of legends inside _chart.redraw breaks code for legend positioning

[rahulstomar]

I have implemented code to change legend positions (on "postRender" event) and it was working fine with dc 1.7.4 version but now I am wondering why in dc 2.0.0-beta.30, there is a render call for legends in _chart.redraw function which causes for me to call my legend position code each time even on applying filters. Code specifically in

    _chart.redraw = function () {
        sizeSvg();
        _listeners.preRedraw(_chart);

        var result = _chart._doRedraw();

        if (_legend) {
            _legend.render();
        }

        _chart._activateRenderlets('postRedraw');

        return result;
    };

I believe during redrawing of charts or applying filters, legend rendering won't be needed, only in rendering of charts would we need this legend rendering. So my question is do we still need this rendering?

if (_legend) { _legend.render(); }

Or I might be missing something so may I know why we are using this above condition in redrawing?

[gordonwoodhull]

I think the reasoning here was that the domain of the chart, and hence the legend items, can change during a redraw. This is a big change to the functionality of dc.js and it has had a lot of repercussions; I'd even call this the biggest feature of dc.js 2.0, and it's still not complete.

(For example, notice that the original crossfilter demo which inspired dc.js does not include domain changes, and crossfilter to this day does not remove groups.)

Here's the commit that introduced the change: 824b139.

BUT enough history. You want a diagnosis and a solution.

The diagnosis is that the legend does not support redrawing, therefore render is called here instead of redraw.

But that doesn't help you.

Here are two things which might help:

• you can use the new 'renderlet' event to trigger your code after a render or a redraw. This replaces the deprecated renderlet method.
• usually better, you can use the 'pretransition' event to trigger your code after a render or a redraw but before any transitions, so that there isn't any annoying "jump" where things start to get drawn one way and then get redrawn a different way.

If neither of these help, please respond with more details about the kind of transformation you are doing to the legend. It's a very basic component so perhaps there is a feature which should be added here.

[rahulstomar]

Thanks for the explanation and now I can understand why it was needed. Also, as per your suggestion I used pretransition event to trigger my code and it solved my problem.

The transformation that I am doing is, drawing the legends at the top of the chart from left to right. Also, I needed to draw boxes over the legends after legend rendering. So my boxes over legends are being drawn in renderlet and my legend positioning code is called in, as per your suggestion, pretransition. See the screenshot

Again thanks for the help.