Add an indictor when queries are pending to vgplot mosaic clients

[domoritz]

As discussed in #506 (comment).

We probably don't want to show an indicator when the request is only a few ms (so the UI doesn't flash).

[Danish-Dsouza]

I will take this one. Should I just use setTimeout() to delay the indicator when it would show for less than a few ms?

[domoritz]

We will have to review the whole implementation but setTimeout is probably a component of it.

[Danish-Dsouza]

Got it. I'm not going to mess with the MosaicClient itself but simply add queryPending() implementations in each input type and plot if that's okay.

[domoritz]

Hmm, I think that's maybe not enough since you would need to constantly pull to get updates. Maybe we should implement it as a signal.

[Danish-Dsouza]

Any suggestions on how I could go about doing that? The signal would have to be global across the mosaic instance right? Presumably it would originate from the co-ordinator?

[domoritz]

I was imagining a signal per client.

[jheer]

I would recommend using queryPending (in conjunction with queryResult / queryError) to start. I don’t see why you’d need to constantly pull?

MosaicClient is too general for a full solution so I agree that subclasses should be responsible for this. Might make sense to provide an intermediate abstract class that “knows” more about the rendering for better reuse.

[Danish-Dsouza]

@jheer Neat, that's the implementation I had in progress. I'll make the PR soon. Could I be assigned?

[domoritz]

We don't need to assign issues. Just go ahead with a pull request.