D3 force layout: making pan on drag (zoom) smoother

Question

I've got a d3.js static force layout graph that can get rather big (sometimes parts of it are clipped), so I'd like to let the user pan the whole graph by dragging. I don't think I need dragging of individual nodes, I've got a feeling that's just going to be confusing, but would like to make it possible to show the parts of the graph that are clipped by the svg boundaries.

I've got a minimal example at http://bl.ocks.org/3811811 which uses

visF.append("rect")
 .attr("class", "background")
 .attr("width", width)
 .attr("height", height)
 .call(d3.behavior.zoom().on("zoom", redrawVisF));
function redrawVisF () {
  visF.attr("transform","translate(" + d3.event.translate + ")" + " scale(" + d3.event.scale + ")");
}

to implement the panning, but I find it really "skittery" and not very smooth at all, to the point where I'm guessing it will stop people from trying the drag function at all. Has anyone got a clue why this happens and/or an idea for how to fix it?

Prynne

Answer 1

The problem is that d3.behavior.zoom retrieves the current mouse position relative to the clicked item's container element, and you are moving the container element! So the relative position is constantly changing, hence the jittering effect you're seeing.

You probably want to move the background <rect> so that it's a direct child of the <svg> element. This achieves two things:

1. The position will now be relative to the <svg> container, which isn't moving.
2. Currently, you are moving the <rect> when you zoom or pan, so the zoomable area changes and some parts of the viewport are no longer zoomable. Having the background <rect> in the same place fixes this problem too.

Jorry

Aha, I was moving rect as well; making them "independent" seems to work :-) Thank you so much for solving this. – Prynne