The appropriate place for these would be AbstractTexture, once it is
finished.

This also removes an extra copy of the image for custom textures.

We (the Microsoft C++ team) use the dolphin project as part of our "Real world code" tests.
I noticed a few issues in windows specific code when building dolphin with the MSVC compiler
in its conformance mode (/permissive-).  For more information on /permissive- see our blog
https://blogs.msdn.microsoft.com/vcblog/2016/11/16/permissive-switch/.

These changes are to address 3 different types of issues:

1) Use of qualified names in member declarations

    struct A {
        void A::f() { } // error C4596: illegal qualified name in member declaration
                        // remove redundant 'A::' to fix
    };

2) Binding a non-const reference to a temporary

    struct S{};
  
    // If arg is in 'in' parameter, then it should be made const.
    void func(S& arg){}
  
    int main() {
      //error C2664: 'void func(S &)': cannot convert argument 1 from 'S' to 'S &'
      //note: A non-const reference may only be bound to an lvalue
      func( S() );
   
      //Work around this by creating a local, and using it to call the function
      S s;
      func( s );
    }

3) Add missing #include <intrin.h>

Because of the workaround you are using in the code you will need to include
this.  This is because of changes in the libraries and not /permissive-