Real-time BC6H compressor, which runs entirelly on GPU (implemented using DX11 and pixel shaders). Features two presets. "Fast" presets compresses a standard 256x256x6 envmap with a full mipmap in ~0.07ms on NVIDIA GTX 660 or AMD R9 270 (both are mid-range GPUs). "Quality" preset compresses a standard 256x256x6 envmap with a full mipmap in ~6.84ms and compression quality is comparable to fast/normal presets of offline compressors.
This source code is public domain. You can do anything you want with it. It would be cool if you add attribution or just let me know that you used it for some project, but it's not required.