I’m working on a model that is a tangle of tubes, and with the curve tube nap brush, i’m able to get very close to my goal with moving a tube once it is drawn out. Problem is that I’m getting areas where the tube overlaps itself, which isn’t realistic. Q: Is there a way to activate some sort of collide feature that will recognize this and bend the tube around itself rather than overlapping?
Hi @Crhsculpt,
Not if you’re drawing out the stroke all at once with a single action. The curve is looking at the depth information for the surface it is snapping to. If you apply the stroke to the curve all at once it is only acting on the surface information at the time the stroke is made.
Subsequent strokes will see the updated surface information, and then overlap the previous stroke rather than intersect through it.
You can create a stroke in multiple stages. Each new stage will be able to see the updated surface information for the previous stage. In this way you can get a single unbroken stroke to overlap itself. Please see the following image:
This may be useful for you if you’re willing to manually draw out the stroke rather than trying to create it all at once.
Adjusting the stroke settings (Stroke> Curve> Curve Step) to produce lower poly geometry with fewer sections will create “stiffer” geometry that will overlap but won’t curve around the previous stroke so closely. A lower res stroke will be easier to adjust without distorting it. I recommend using the mighty Move Topological brush with a wide radius to gently adjust only the section of the curve that you make contact with and not any of the curve underneath. Remember that you can hold ALT after starting a stroke with a move brush to move the geometry in and out along surface normals rather than screen plane movement. That geometry can then be subdivided to smooth it.
Otherwise if you’d care to elaborate on your process and what you want to achieve, we may be able to offer alternate suggestions.
Good luck 
I revisited this subject recently and had best results by using zspheres to control the trajectory of tubes so that it wouldn’t self-overlap. This is feasible for small tangles, but gets more challenging the longer the tubes get. in this case i also needed to interweave it with a second tube.