View Full Version : Fast skin render artefacts with instanced objects

03-09-2013, 10:25 AM
Hi folks,

I have noticed that the Fast Skin shader node generates render artefacts in the surfaces of instanced objects (in both LW11.03 and LW11.5). This leads to random flickering dark patches crossing over the surfaces of instanced objects (with Fast Skin) as they move around a scene.

To investigate the problem further I've produced a test scene and rendered out some images illustrating the issues (see below). In the test scene, two of the three toroids are mesh objects with Fast Skin applied to them, whilst the third is an instance of one of these meshes. In the three images I've swapped the position of the instanced toroid with one of the mesh versions. If there are just mesh objects in the scene (see reference image), they all render okay and without artefacts. However, when one of the toroids is an instance it renders with artefacts and, in some cases, it also induces artefacts in the nearest mesh object (if it is the mesh that the instance is sourced from).

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BTW, changing render settings such as ray recursion and shading/light samples has no influence on the outcome. Ticking the "Exclude from VStack" option suppresses the artefacts slightly but does not totally eliminate them.

Has anyone else seen/reported this bug?


03-09-2013, 12:08 PM
Fast skin is a pre-processed shader, and as such doesnt work well for animation without flickering anyway. I would suspect that the instance issue (even on stills) has to do with the pre-process too.

03-09-2013, 02:28 PM
These pre-process materials/nodes never should existed, they are just way too limiting in lot of cases :).

03-10-2013, 05:35 AM
Okay, thanks guys for the explanation.

In that case, what do to reckon is the best alternative to Fast Skin for instanced objects that also doesn't have a huge render-time hit? I'm trying to get something like a bone-china or alabaster type of surface with some deep back-scatter.