OK - I've taken the suggestions, and did some experiments, and here's what I've found:
- Simply changing the texture file format to PNG: still opaque
- Using the 6/2/2006 code base (last one before refactoring): still opaque
- Exporting using the "Generate Release" option in old code base: object not visible
- Exporting using the "Generate Release" option in new code base: object is transparent, but is drawn first so that no other object appears on the other side
- Add a second object that uses the texture, then export using "Generate Release" option in old code base: TRANSPARENCY!
- Add a second object that uses the texture, then export using "Generate Release" option in new code base: TRANSPARENCY!
So, the transparency works only if you have more than one object using the texture AND you select Generate Release. Without generate release, the texture is in the DirectX A8R8G8B8 DDS format, while although it does contain the alpha values (I've verified this in PRP Explorer), the Plasma engine only makes it transparent if it is in DXT5 DDS format.
Oh - and I forgot to mention: you need to delete the
_TexCache when you change to Generate Release; otherwise, the cached texture is in the wrong DDS format.