It would be also nice to have a slider to shift the entire transfer function left or right.

I'm not sure GPU Memory shall be in the "simple interface":
It seems to me like an advanced feature where the default value should be "good enough". No ?

What do you mean by good enough? Its there at all because I was told that there is no way to determine the available memory automatically. An alternative would be to just display what is set and a tooltip that this can be changed under advanced/rendering/techniques

There is no way of guessing the right amount of memory, true. But we can still use the smallest amount by default. That will then work for everyone.
Advanced users can then increase that number in the advanced panel.
This information is useful only the first time the Volume Rendering panel is used, then it's useless (because it's supposed to remember what the default is).
It could even go to the Settings panel.

ok. Lets do it your way.

On second thought, the minimum grpahics memory is probably is 256MB. The use case scenario for VR is viewing of a CT data set, 512^3 which is 134 mega voxels. This will not result in a good user experience.

btw: gpu memory does not remember from last time. I have to set it manually every time I start a new nightly build. Very annoying

V2: color in the shift preset slider is accidental. It should be like a regular slider.

correction: gpu memory gets reset to 256 every time I start slicer. mac 8-15 nightly build

Fixed in r18501