glFog or depth cueing

I couldn’t figure out how in vtk to get a rendering effect like ‘fog’ where things fade as they get farther away from the camera. This is sometimes called ‘depth cueing’ such as in this product…

or this one

Could someone point me to the api steps that would be used to reproduce this effect or access the glFog opengl extension that creates this via vtk?

It may be an overkill, but you can actually render volumetric fog by adding a volume rendered actor to the renderer.