View Full Version : clip volumetric object?

06-13-2011, 05:45 PM
I've been searching but haven't come up with anything yet.

is there a way to clip a volumetric object with another object. so say I have a group of hypervoxels. and want to cut out the middle with an object but see the ones behind it. a normal matte object would cut it out fine, but would also cover up what's behind it. Is there a way to have a clip matte type object, like you do with DP boolean, but instead of for surfaces for volumetric stuff, turbulence or hypervoxels? so essentially a ray goes inside the cut out one, but doesn't see anything inside the object and just registers what's on the other side.


06-13-2011, 07:11 PM
Not possible. Volumetric is added at the absolute end of ray-tracing, when regular geometry is well known and shaded. Volumetric evaluation is even receiving RGBA information what ray hit and can then use to blend (so volumetric can f.e. color correct (f.e. brighten) globally whole scene, including reflection).

06-13-2011, 10:32 PM
thanks for the response, at least now I know to stop looking :)

06-14-2011, 01:39 PM
I did an experiment some years ago. Check out this thread (http://www.newtek.com/forums/showthread.php?t=90863) (scroll down for the scenefiles).

Elmar Moelzer
06-14-2011, 01:47 PM
In VoluMedic you can do it the other way round with bounding Objects.
They dont cut things away, but only keep the intersection of the Bounding Object and the volume.
There are 3 types, Box, Sphere and Cylinder. I am thinking about expanding that in the future.

06-17-2011, 03:37 PM
It is trivial to do if you use HDVR(R). Each voxel in volume may be assigned to one of 8 Transfer functions, assign the "empty" group of voxels to transfer function with zero opacity and you have what you have asked. Clearly, such case is very particular, you may assign any TF to this region and play with it interactively at 1080p resolution with virtually no quality compromise as soon as you have dual i7 machine.