Hi,
Is this occasional pull request, or you intended to do that?

intended

Thank you for contribution, and sorry - I'm not going to merge this. There are many reasons for that, the main are:

1. I'm not going to include fbx sdk into umodel's source code, it's huge (especially if including platforms other than Windows), entirely proprietary.
2. Your code is copy-paste from Unreal engine 4. It is great that it can be compiled in UModel's environment with minimal changes, but I can't use that code.
3. I do not like fbx format and sdk, it is terrible,

Other comments to this PR:

• You broke my build system, I'm not going to migrate to Visual Studio build - this won't work with Linux, and it is not so user-friendly (for me) as my system.
• There's a lot of place where you changed my coding style with no reason.

Personally I'd like to say the following. I worked a lot with Fbx sdk in past 2 years, so it would not be hard for me to write StaticMesh exporter by myself, from scratch (without use of UE4 sources). It is much much harder to work with SkeletalMesh and animation. Also, it is not possible to support just statics here - it is pointless (there are many better formats which supports static meshes), and users will demand more. In the future I'm going to support glTF format, I like it much more than fbx. It's probably a few hours of work to implement export of static meshes into glTF.

I see, thanks for your reply.

And how can I get exported content move to my UE4 project?

Two ways.

1. Use UModel's gltf export. You may import static meshes with built-in plugin (it imports only static meshes). Also, there's a third-party plugin which imports all kinds of gltf available.
2. As other people do, use 3ds Max or Blender as intermediate product, which imports psk/psa files and converts them to fbx.

Thanks!
Another question is why does umodel often miss the needed textures and replace them with the null-ones so to speak?

Two ways.

1. Use UModel's gltf export. You may import static meshes with built-in plugin (it imports only static meshes). Also, there's a third-party plugin which imports all kinds of gltf available.
2. As other people do, use 3ds Max or Blender as intermediate product, which imports psk/psa files and converts them to fbx.

there are some bugs of gltf plugin for UE4, so I think gltf is not ready for use in production pipeline now.

Another question is why does umodel often miss the needed textures and replace them with the null-ones so to speak?

This is a FAQ question, not a "github issue".