Hello,
I have a question concerning the shading of models. I don't know if this is possible with shaders or if this is possible at all. Well, first of all here's a picture:

In picture no. 1 you can see three spheres belonging to one model with gouraud shading (the red cross is the model origin).
But what i want to achieve is an effect as it is shown in the second picture.
Well, it's similar to the shading of clouds: Light will be reduced permenantly as long as it shines through a cloud.
Sorry, i don't know a better way to explain it in english .

Is this possible with a shader? Does anybody wrote such a shader already?
Thanks!