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Viewport shows artifacts in rendered mode (for certain geometry)
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--- Operating System, Graphics card ---
OS: Windows 7 Professional 64-bit
PC: Intel Xeon 5670/12GB
Graphics: ATI RadeonHD 5800

--- Blender version with error, and version that worked ---
Tested and confirmed the problem with two workstations (same config as mine) on the following versions:
2.62, 2.63, 2.64, 2.65, 2.66, 2.66a (official 64bit releases)
2.67 rc (r56271) 64bit

--- Short description of error ---
For certain geometry I get artifacts in the 3D-viewport in rendered mode. They are apparent in perspective view, but seem to get much worse when switching to orthogonal. When doing a full f12-render they do not show up in the result.

It is possible that this part of the geometry is just screwed up. Still I would like to know what exactly goes wrong. I couldn't find any problem with these particular meshes.

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---
Just switch viewmode of both of the top 3D-views in the testscene to rendered and enjoy the view.



Event Timeline

Ctrl +A (rotation & scale) will fix it.

Confirmed, these objects have a scale of 0 along the Z axis. In addition the vertices inside the object are at an extreme distance along this axis.

The reason there is a difference between the viewport and render is that in the viewport all objects are instanced for quick updates. I don't think we can fix this, I suggest to either scale the mesh down along the Y axis in edit mode, or apply the transformation. We can handle such degenerate meshes up to a point but in this case floating point precision is not enough to do it.

Thank you for the tip!

Still, what I find funny is that parts of the symmetrical mesh (some of them even further away from the y-axis) don't produce the glitch while some others do (I have only cut out the erraneous parts of course). Scaling affects the whole mesh, so I can't see how this problem could only affect parts of a mesh.

Anyhow, this is a purely academic question, as ctrl+a will indeed fix the problem for the entire mesh.