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I'm trying to render a cityscape, but I get some weird dark patches on the buildings all the time. The scene is just conceptional, so it's all without textures or fancy reflections/ transparacy. The buildings are also really simple (most of the time just cubes)

It kind of looks like the effects you get when you have two faces at the same position, or your normals are screwed up. (It's neither of those, I already checked that.) On the buildings close to the camera it's just a little dark lining along some of the edges here and there, but the further the faces get away, the worse it gets and somtimes a complete face is completely dark.

Meddeling with the light sources or shadow functions doesn't seem to do anything (except disabeling either the "cast" or "receive" shadow option for the material, which stops the effect)

Oh, one more thing, it all really started, once I increased the maximal clipping distance (the city is qite large), even though I don't know if that is the source.

Does anyone have an idea how to fix this?

Pic here

Blend file here

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    $\begingroup$ It's a lot easier to help you if you provide an image of what's going wrong. Even better if you post your blend file. Use pasteall.org/blend $\endgroup$ – cegaton Jan 2 '15 at 22:30
  • $\begingroup$ As I already mentioned, I suspected and checked Z-fighting prior to posting this. As far as I found there are neither hidden objects, nor hidden faces in the afected areas, that could cause this. But thanks anyway. Ps: Pic and blend file added. $\endgroup$ – Guest_23456 Jan 3 '15 at 9:04
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If you change the start clip distance on the camera to a higher number the black edges disappear.

enter image description here

enter image description here

The reason for this has to do with how blender approximates the calculations for the Z-Depth within the clipping distance.

It's very well explained here: http://blendermama.com/black-faces-error-from-camera-clipping.html

In this other link: https://discoverylinux.wordpress.com/2011/10/08/guida-eliminare-il-flickering-in-blender-2-5/ the author recommends keeping the start and end clip distances to contain only the geometry in the scene for better precision.

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