[vtkusers] Toolkit Implementation

[Doug Henry]

I'm wondering if there are resources (documentation) available that
dicuss the process of implementing a renderer for an unsupported
toolkit?  I found a vtk package for FLTK which looks like what I would
expect, but I'm unsure of some things that are being done.  For
example, vtkOpenGLRenderWindow is subclassed to create
vtkFLTKOpenGLRenderWindow, which seems reasonable.  But there are some
mystery files created through the use of VTK_MAKE_INSTANTIATOR cmake
macro.  Anything that helps to explain the minimal set of things that
need implemented would be extremely helpful.

Thanks,

Doug