Errors compiling with nvDXT

[NeilJed]

nvDXT is a legacy library compiled with an older version of Visual Studio. Due to "breaking changes" introduced in Visual Studio 2015 there are a large number of errors that occur when trying to link it.

These needs to be fixed or, more practically, the legacy nvDXT library needs to be replaced.

[NeilJed]

Currently working on updating to the newer nVidia DXT library some progress made but haven't committed the changes into the dev branch just yet. There are a lot of changes to data structures that need figuring out.

[sheybey]

There is a port of VTFLib to linux that uses libtxc_dxtn to replace the S3TC utilities that were provided by nvidia DXT. https://github.com/panzi/VTFLib/blob/d90a8a549a8b07d47ae987be497f061fcde0b5c0/src/VTFFile.cpp#L3463

The remaining nvidia-provided features aren't supported, but it seems like it might be a good starting point if you are still considering ditching nvidia DXT.

[NeilJed]

@sheybey Yeah I was looking at several alternative DXT libraries including that one. The reason I'm leaning more towards using the newer nVidia library is mostly because it has a lot of feature parity with the one we are currently using. Filters, sub-formats and also GPU acceleration, plus it's open source and cross platform.

I have a sort of working implementation already in a branch I need to commit, I just need to work out getting the MipMaps sorted out. There's a lot of features in the DXT library that sort of replace stuff in VTFlib so I'm sort of pondering what to deprecate in our codebase and use from theirs.

[thegrb93]

This is blocking other issues since newcomers can't compile it.