IRAY Displacement Bug

nakamuram002

It looks like the building got hit by an earthquake!!

In this scene, I used Nobiax's "102 - Small Clay Brick" Shader to texture the Service Station Bldg. Note that this shader uses a displacement map. I had to increase both the Horizontal and Vertical Tiles to 12 in order to make the bricks the size show in the render. It appears to me that the distortion is due to the tiling not being applied to the displacement map. My scene looks OK if I turn displacement off and use bump instead.

Jimbow

That looks like a classic discontinuity problem seen in many renderers when displacement is on, where the distortions could be caused by the UVs not having enough polygonal resolution to work out the triangulation properly, which can also mess up corner discontinuity when displaced and you get corners separating. You probably need to subdivide the object either at the object's polygon level, or using the displacement subdivisions in the shader's editor (beware going above 3 in iray - better to sudbivide the polys and then fine tune with the shader's displacement subdivsion). I expect iray works much like Mental Ray, so the polygons are being triangulated when you hit the render button and distortions can occur.

Added: In fact, lack of poly resolution would explain most of the texture distortion. Imagine the texture being downsized to a few pixels wide and tall, which is what's effectively happening when a face is just one single quad when displaced with a texture.

jestmart

It is because early Poser models used a modeling shortcut to get sharp edges, they split the model along those edges meant to be sharp. Subdivision will just explode the model further.

DAZ_Spooky

jestmart said:

It is because early Poser models used a modeling shortcut to get sharp edges, they split the model along those edges meant to be sharp. Subdivision will just explode the model further.

Subdivision, yes, displacement tesselation, on the Iray shader, will not.

nakamuram002

Thanks for the insight, everyone.

"Displacement Tessalation" -- Is that the same as "SubD Displacement Level"? Increasing the "SubD Displacement Level" by 1 increases rendering time unacceptably, but does not fix the problem. Decreasing it does not fix the problem either. I guess I just have to settle for turning off displacement and using a bump map. Looks like I will have to re -UVMap the brick columns, so the bricks line up.

mjc1016

If the bricks don't line up already, all bets are off as to what is causing the blown corners...

All of the above assumes that the UV mapping is consistent. When two UV regions have alignment problems, visible seams are the least troublesome problem. Adding displacement into the mix makes any visible seams worse, by actually 'moving' them...and if one side is moving 'high' and the other side is moving 'low', without the physical seam being welded, the mesh WILL separate.

Also welding the edges and using loop cuts, bevels or other techniques to preserve the 'hard' edges is the way to go, instead of relying on separate pieces trying to stay 'together'.

Bump maps don't move the actual geometry, so some of the problems won't show up. But they also won't 'self occlude' or cast shadows. So while they'll give the impression of 'depth' and texture to a surface, they won't cause the self-shadowing/visual cues that true 'depth'/texture have...like displacement maps will.