Improve stackgl rendering pipeline for transparent traces

[archmoj]

Thanks to fixes made in #4566 and #4480, this PR could fix#3243 as well as #1267.

@alexcjohnson
Commit 27ba6c1 added various failing tests.
Commit efa3cb7 old work done in gl-plot3d rebased and and applied to update the baselines.

[archmoj]

Applied #4725 to update conflicting baseline with extremesopacityscale in 3373d8c.

[jackparmer]

Stumbled upon some nice work that our old colleague Ricky published recently in this area:
https://observablehq.com/@rreusser/faking-transparency-for-3d-surfaces

[alexcjohnson]

ooh Ricky's demo has some nice features for single-surface presentation - I really like his "cartoon edges" and an option to let the wireframe show through an otherwise opaque surface could be cool. But I don't think this helps us with multiple traces - or a single trace that makes multiple surfaces.

I like the dual depth peeling demo he pointed out - not sure quite what's going on there but it looks promising.

[jackparmer]

This issue has been tagged with NEEDS SPON$OR

A community PR for this feature would certainly be welcome, but our experience is deeper features like this are difficult to complete without the Plotly maintainers leading the effort.

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[stevendbrown]

Hi @jackparmer & @archmoj, I'm trying to understand the content of this PR and will be grateful for your help in clarifying what's happening in this PR. It looks like the changes in the PR update or add unit test outputs, but the PR does not include any code to generate those plots, is that right? How were these updated unit test outputs generated if there is no code to generate them?

[archmoj]

Hi @jackparmer & @archmoj, I'm trying to understand the content of this PR and will be grateful for your help in clarifying what's happening in this PR. It looks like the changes in the PR update or add unit test outputs, but the PR does not include any code to generate those plots, is that right? How were these updated unit test outputs generated if there is no code to generate them?

The proposed changes were in gl-plot3d module.
https://github.com/gl-vis/gl-plot3d/compare/gl3d-blend-rebase

[elaude]

Hi, what would be needed to push this over the finish line? My usecase would benefit greatly from correct transparency rendering, so I'd be very happy if this could be fixed. I'm willing to contribute the changes needed myself if there's anything blocking this.

[archmoj]

Hi, what would be needed to push this over the finish line? My usecase would benefit greatly from correct transparency rendering, so I'd be very happy if this could be fixed. I'm willing to contribute the changes needed myself if there's anything blocking this.

@Coding-with-Adam Let's keep track of this for our discussion.
Thanks!

[archmoj]

Hi, what would be needed to push this over the finish line? My usecase would benefit greatly from correct transparency rendering, so I'd be very happy if this could be fixed. I'm willing to contribute the changes needed myself if there's anything blocking this.

As discussed with @gvwilson I'll try to give this another push (after resolving the merge conflicts) and possibly expose this option via a new attribute.