SDF strategy for 'fancy' scattergl traces

[etpinard]

fixes #566

See details in gl-vis/gl-scatter2d-fancy#5

@dfcreative is the man!

[dy]

@etpinard looking at baselines I've tuned up rendering a bit in gl-scatter2d-sdf@1.3.1, border size should be more consistent. But still rendering in Ubuntu seems to be a bit off

[etpinard]

@dfcreative done in 18fae27

[etpinard]

Waiting on more thorough feedback from #566 authors; dropping from the 1.24.0 milestone.

[etpinard]

I noticed something. Looks like something is up with the zoom box:

Current master:

Off this branch:

the shaded area used to be transparent, and now it appears to be opaque. I'll investigate next week.

[dy]

@etpinard fixed with gl-vis/gl-scatter2d-sdf@6ebe332

[etpinard]

@dfcreative thanks for the fix!

The new patch affect the gl2d_17 baseline:

Can you comment on that?

[dy]

@etpinard thanks, fixed with gl-vis/gl-scatter2d-sdf@1c9ec60
Not the best solution, but persistent across @gl-vis.
That is because for scatter-sdf we have to use special alpha mode (actually natural one), and across other gl-vis components we use another alpha mode, therefore we have to switch context back and forth between alpha modes.

[etpinard]

@dfcreative much better!

Ok. Well, this PR is ready to be merged once the latest gl-scatter2d-sdf patch is published 🎉

This PR should be part of the next minor release v1.25.0 set for early next week.

[dy]

@etpinard published!

[etpinard]

Amazing job @dfcreative ... merging 🎉