optimize away alpha channels on some GLTF upload paths

[Dan-Linden]

Describe how this enhancement should work

optimize away alpha channels on some GLTF upload paths

Test Plan

https://github.com/secondlife/viewer/blob/release/2024.06-atlasaurus/doc/testplans/optimize_away_alpha.md

[Dan-Linden]

#606 failed QA because the original bug does not repro.

Question 1) What might be the negative consequence of this being merged into GLTF Maint 2?
Question 2) What needs to be changed in the test plan?

The test from viewer#606 that failed:

1. Download and unzip this GLTF + textures file: https://drive.google.com/file/d/1dKPDAVCINbtTuKA8ffLm3DzezKZu7EaW/view?usp=drive_link
2. Upload the Material in the test viewer and the current Release 7.1.2.7215179142 viewer.
3. Drag the 4 textures that were uploaded to your Textures folder onto different boxes.
4. Uncheck Advanced->Render Types->Alpha
5. Verify the 4 textures remain visible.
6. Observed: This bug passes on the Release 7.1.2.7215179142 viewer which is suppose to contain the bug. This test may not be set up correctly.

[Dan-Linden]

New test: (now with a set of textures with modified alpha)

1. Download and unzip this GLTF + textures file: https://drive.google.com/file/d/1iePvjqmCGq7azKuskNjVCxJ4jJnPyCQy/view?usp=drive_link
2. Upload the "opaque alpha test.gltf" material to Second Life (the 4 textures have an opaque alpha channel)
3. Download the 4 textures as TGA or PNG and verify they do not have an alpha channel.
4. Upload the "modified alpha test.gltf" material to Second Life (the 4 textures have a non-opaque alpha channel)
5. Download the 4 textures as TGA or PNG and verify they do have an alpha channel.

Observed:
RELEASE 7.0.1.6894459864 - GLTF Material Import
opaque alpha test - The alphas are stripped.
modified alpha test - The Base Color alpha remains, all others were stripped.

RC 7.1.4.8149792635 - GLTF PBR Maint 2
opaque alpha test - The alphas are stripped.
modified alpha test - The Base Color alpha remains, all others were stripped.

Observations:

• The opaque alphas were being stripped out in the GLTF Material Import viewer.
• It appears this checkin Fix failure to optimize away alpha channel on some GLTF upload paths #606 didn't change any behavior.
• The non-opaque alphas are being stripped from the normal, orm, and emissive maps. Although they are not used, perhaps we want to keep them.

[brad-linden]

does this need to be tested on atlasaurus or develop? is this still relevant?

[Dan-Linden]

This needs to be tested on Atlasaurus.

[DmitrySProductengine]

Deferred QA.
Verified on the Second Life Release 7.1.9.10326512121 (64bit) on Win11/OSX in the scope of IQA #306.

Unfortunately, the link provided in the test plan leads to a 404 page.
https://github.com/secondlife/viewer/blob/release/gltf-maint2/doc/testplans/optimize_away_alpha.md

According to the comment on a similar issue in the ticket #906, the current link should be to the Atlasaurus branch:
https://github.com/secondlife/viewer/blob/release/2024.06-atlasaurus/doc/testplans/optimize_away_alpha.md

Also, the PE team does not have access to test files with non-opaque alpha channel (https://drive.google.com/file/d/1iePvjqmCGq7azKuskNjVCxJ4jJnPyCQy/view?usp=drive_link).

The PE team has access to previous test files with an opaque alpha channel.
According to the test plan and the test example with opaque alpha: the test passed - all alphas are stripped.

But, as I understand it, the issue remains in the non-opaque alpha channel. Unfortunately, I was unable to find or create such a test GLTF file - so I ask for access to the existing test example for the PE team.