Fix transform for IBL environment maps

[jjhembd]

Description

This PR flips the X-axis of the transform applied to IBL environment maps.

Prior to this PR, a mirror ball shows the environment map image in its original orientation, rather than in the expected mirrored view.

The environment used in our test Sandcastles is the Kiara 6 Afternoon image from polyhaven.com. Notice how the sun is to the left of the shadowed peak in the distance. A rocky outcrop in the foreground angles from the sun towards the right of the image.

Before this PR, a mirror ball shows the same orientation in the reflection. Again, the sun is to the left of the shadowy peak, with the outcrop angling toward the right.

After this PR, the orientation of the environment is flipped from left to right, as expected for a mirror ball reflection.

This new orientation matches the glTF Sample Viewer.

Issue number and link

Addresses part of #12028.

Testing plan

Load this local Sandcastle and view the "Mirror Ball" model with "Environment Map Lighting".

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @jjhembd!

✅ We can confirm we have a CLA on file for you.

[ggetz]

Thanks @jjhembd, looks good! Can we add a unit test?

[jjhembd]

@ggetz OK, I added a spec checking the value of the IBL transform.

[ggetz]

Thanks @jjhembd. The spec seems to be timing out in CI?

[jjhembd]

The spec seems to be timing out in CI?

@ggetz Yes, and I can't explain why. The spec passes locally, and similar specs (loading the same environment map) run through on CI.

[ggetz]

@jjhembd My guess would be the KTX2 loading. I would make sure the URL is correct in both environments and that the environment supports the needed features with OctahedralProjectedCubeMap.isSupported.

[jjhembd]

@ggetz it's the same URL as the other specs. But the other IBL specs had this check:

        if (!scene.highDynamicRangeSupported) {
          return;
        }

This condition fails on the WebGL stub, so the spec is skipped.

I added the same check to the new spec.

[ggetz]

Great, thanks @jjhembd!