Why does displacement not work sometimes?

Those Things

Often, when I try to use displacement on an object, it works just fine, but other times it doesn't. No displacement happens at all, and you can tell the render engine isn't even considering the displacement map, or its settings. Is there another setting that keeps displacement from working, that I don't know about? Or is it just a fidgety thing? 

SimonJM

Answers may depend upon whcih render engine you are using.  3Delight has the in-built facility for 'micro-displacement' which enables it to handle such things well, even on a low ploygon count mesh.  Iray, however, is not quite so good with displacment and you need a fairly high polygon count for it to work with; you can selectively increase the sub-division (SubD) level of individual surfaces so that you do not 'explode' the RAM consumption by having SubD apply to the whole figure.

I would, therefore, check which render engine you have selected and then. if Iray, check the mesh density on the surface(s) in question and investigate applying SubD - either (yoiu may need to  conver the object geometry to SubD before youcan do this - Edit> Geometry> from the menu for example) for the whole item or for individual surfaces.  It is also worth checking that theer is a dispalcement map and the strength setting is > 0, etc.!

Richard Haseltine

For Iray the mesh resolution and SubD level are crucial as Iray does not do sub-polygon displacement the way 3Delight does.