Caustics appear cut off / with artifacts!


This guide concerns cases similar to the example below:


We are rendering a simple pool with water casting caustics. 



When seen from above, the caustics are "cut off" close to where they are exceeding the camera view, and various artifacts (unwanted triangle-shaped patterns) are visible. 



This can happen if all of the following conditions are met:

  • Autobump is disabled.
  • The object which is generating caustics uses displacement.
  • The object is partly outside of the current camera view.


This is because displacement is not calculated for objects, which are outside of the current camera view, so some visible portion of caustics will be generated from a flat (non-displaced) part of the geometry. When autobump is enabled, it will automatically apply bump to those areas, which will solve this issue, but if autobump is disabled, the place where displacement is "cut off" will be clearly visible. 

Note: autobump is enabled by default for all new scenes. If it's disabled, it means that either you disabled it (possibly by accident), or that you are editing a scene where someone else disabled this option.



Solutions: 

1. Make sure that autobump is enabled. It can be found in the Development / Experimental Stuff rollout. This is the best and most reliable solution.



Enabling autobump immediately fixes the issue. 


OR



2. If you wish to keep autobump disabled and have caustics generated purely by displacement (generally there is no reason to do this):
Use the following string option:

float geometry.displace.maxSizeScreenOutFrustumMultiplier = 1

See: How to use string options? 
Warning: enabling displacement for areas outside of camera view can often result in a dramatic increase of RAM usage!






If you cannot solve this issue using the above methods, or if you are having some other problem with rendering caustics, please contact us.