Implementation of connectgaps for the surface trace

[archmoj]

Fixes #2812.

TODO:

• Fix hover codepen

[etpinard]

Looking good @archmoj Some very nice method ♻️ work here!

Bringing in @alexcjohnson here, I remember we had a discussion about surface vs heatmap/contour interpolation with Mikola a few years back (I found https://github.com/plotly/streambed/issues/2268, but maybe it's somewhere else). Does simply reusing the heatmap/ methods for surface feel ok to you?

[alexcjohnson]

Looks good to me. Whether it's fast... that's another question. It's not slower than heatmap/contour anyway, and it only adds this overhead if you opt in, so I'm happy to add it here. If someone's sufficiently interested in improving performance later we can investigate reimplementing this on the GL side.

I'm more bothered though by what happens with connectgaps turned off for this data - the trace disappears entirely, since there are no mesh squares with all corners specified. Compare that to contour for the same data without connectgaps:

There we give even islands or thin strips some nonzero size, and three corners of a square are enough to fill in half of the square.

But that's a more complex issue for another time.

[archmoj]

Glad you liked the quick prototype!
We may still need to find a way to fix the hover.
Please try this codepen and possibly describe what should be the expected behaviour if the user hover over the interpolated points?
As a side note for isosurface traces the interpolated data is not displayed.

[alexcjohnson]

Ah good call on hover, NaN labels squished in the corner aren't too useful 😉
Contour treats the interpolated points no differently from real data. Perhaps at some point it would be nice to indicate which are interpolated, but as a first cut matching contour and labeling exactly what was drawn should be fine.

[etpinard]

Looks good. Now that gl3d jasmine tests are behaving better, let's add one 🔒 ing this down!

[archmoj]

Good call. Done in afe36a6.

[etpinard]

Nicely done @archmoj

💃 💃