Martin has answered some of your questions, but I'll try to elaborate.
Current officially supported image formats are as Martin specified, with the addition of TGA. PNG's can also be loaded, but support is minimal. It will be improved in the future.
Alpha channels are always rendered out as separate images at this point and saved automatically in the temp folder as Martin mentioned. Layered images with alpha, z-buffer, and other passes all in one file will be implemented in the future. Z-buffer support will come along with that.
We have no immediate plans to support GPU-accelerated rendering. In general this is a specialized area that very few applications are supporting for generalized rendering. Support on the GPU-side is improving, but it will be some time before it's practical to support this.
For speed questions you will have to test this yourself for your particular needs. Given its rendering approach that is focused in displacement, TG2 is capable of doing things that most other renderers are not, and in this sense it is fast by comparison to other renderers not optimized for these types of scenes. TG2 can render quite fast in other scenes as well (space and planetary shots for example) where other renderers, including Vue, would produce both inferior results and longer render time. I would say however that our focus is competing on quality first while optimization efforts are ongoing.
Finally, to speak generally regarding working with other applications, this is something we will be improving significantly in the future. We don't intend TG2 to become much more general purpose, so while object rendering will be improved within TG2, we will be focusing most on an effective import/export system to handle more complex object rendering tasks. Integrating with other applications in a non-proprietary way is a significant goal for continued development.
For now there are a number of options discussed throughout the forums here, which you should be able to find with a few forum searches. If you need help finding the info you need let me know and I'll link you to a few of the most helpful threads.
- Oshyan
