That’s what I noticed too. That seems to have been the root of the issue. Thank you so much for your patience and helping my finally realize the error of my process!
The original file I was using looks like:
which is standard cubemap format, which mislead me to believe that it was encoded correctly as a cubemap and not as a single image.
This is what went wrong:
At first I converted the 6 jpgs into a cubemap jpg and then compressed that cubemap jpg into ktx.
Now, I just created a cubemap natively in PVRTexTool and then compressed it with DirectX11 BC1 (-dxt.ktx) and got this:
https://swivel-api-dev.s3.amazonaws.com/skybox_textures/combinedTest/skybox-dxt.ktx
which (thankfully!!!) shows up here:
https://playground.babylonjs.com/#UHQ4FB#7
The only issue with that version is that the sides are flipped. I compressed it in PVRTexTool with the vertical flipped flag turned on (as suggested in the documentation).
When I compressed it instead with vertical flipped flag turned off, it shows up correctly!:
https://playground.babylonjs.com/#UHQ4FB#8
Lastly:
In this version of skybox creation (using CubeTexture.createFromPrefilteredData), seams can be seen where the images are stitched together. I noticed that, when using the new CubeTexture() constructor, the image seams are not really noticeable (back when I was testing which function to use with the separate, uncompressed jpgs). Is there a way to mitigate this? Or is this a byproduct of having to use CubeTexture.createFromPrefilteredData?
Thanks!