generative modeling for Rhino
Is there a possibility to write own custom shaders for Grasshopper Preview?
what do you mean by a 'shader' exactly?
"Shader" -> little programs that terminate how things are rendered in the Rhino Viewport, (part of the render pipeline).
I have no idea what the possibilities are with regards to writing custom shaders. I fear you may end up having to implement your own display pipeline (in addition to Rhino's OpenGL and GDI pipelines). Maybe not, maybe it is possible. You'll need to ask Jeff Lasor on the Rhino developer forum that.
If you just want to play with custom materials (colours, transparencies, highlights) then it's fairly easy, the [Create Material] and [Custom Preview] components do this. I think it's also possible to create materials with textures, but I don't know how exactly. Also, in Rhino5 you should be able to leverage the RDK, but again, I know too little about this to give any useful feedback.
I'm just missing the environment map on my grasshopper objects.
Is that on a wishlist somewhere?