Sometime when Displacement is active (under the Global Switch tab) the rendering process is really really slow due to a pass called “Unloading Geometry” together with the “Build Light Cache” pass and the IrradianceMap passes.
I don’t understand the reason why this “Unloading Geometry” pass happens and what it depends from, most of the time it is present after I import in the scene external models, and the only way to avoid it is to disable “Displacement” under the Global Switch tab.
This message appears when the V-Ray geometry cache overflows. The size of this cache is controlled from the “Dynamic memory limit” option in the Raycaster settings in the System rollout. If this value is too low, the cache will overflow very often leading to performance issues. Increasing this value usually helps.
If you are rendering large-resolution images, it will also help to increase the “Edge length” parameter for the displacement.
Default is 4.0 By what amount can I increase this? Never messed with this setting. I’ve got 6GB Ram and setting my Dynamic limit to 4000MB. Can I set edge lenght to 8? or 16? Or should it be a small increase like maybe set it to 4.1?
Each time you increase the resolution twice, you can increase this by 2.0 This should probably be a setting somewhere so that it is adjusted automatically, will make a note to look into it.
When you say increase resolution twice what does this mean in terms of a base resolution. If my main resolution is 1920x1080 what should this figure be set to ? How would I determine the optimal setting for this specific res ?
Well you have to watch out for artifacts in the displacement; as the value gets larger, V-Ray will subdivide less and will produce larger triangles. What is an acceptable value depends also on the displacement map that is used (e.g. smooth maps can do with larger values, noisy maps will need smaller values to capture the detail).