I wonder what's causing this kind of problems and how to get rid of it. I tried to remove doubles and recalculate normals but these don't work. Any ideas? enter image description here

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    $\begingroup$ They look like internal faces. $\endgroup$
    – sambler
    May 9 '15 at 7:30
  • $\begingroup$ I've checked the mesh using the Mesh Lint addon and there are no internal faces there. $\endgroup$
    – Paul Gonet
    May 10 '15 at 12:45
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    $\begingroup$ This is caused by the obsolete blender viewport engine. The alpha faces should be depth-sorted which does not happen and it's a known limitation. $\endgroup$ Jan 5 '16 at 12:58
  • $\begingroup$ I think this is just a viewport display bug as Jerryno said. $\endgroup$
    – PGmath
    Jan 5 '16 at 14:33

Realtime renderer alpha artifacts

I think is related to the way polygons are drawn from the viewport engine.

To make the viewport render faster, the algorithm doesn't take into account whether a face is in front of another, leading to such artifacts. It happens quite the same in other realtime engine like Sketchfab viewer (see Why order matters section). This is pefectly understandable: the software should perform much more calculations if it should not takes into account only the face visibility but also the alpha depth.

See in the image sequence below how till I'm stacking the quads one above the other in order (latest on top) all works well, while switching their position leds to wrong results:

enter image description here

At the end, it seems more important the order in wich faces are "stored" in the file than the alpha&camera-distance factor. The artifacts in the picture comes from a that. Some faces are drawn in front of other even if they are behind.

There are some freshly implemented viewport alpha options for cycles, like BGE's ones, but despite their promising names, they don't work (yet).

Here's a reel of the options in BGE:

enter image description here

While in Cycles you can only see a difference when "Add" is enabled

enter image description here

I personally think developers are "working on it".

  • $\begingroup$ Thanks for the technical explanation Carlo. Hope this kind of display malfunction'll be fixed in the future Blender releases, cause it looks very ugly. BTW I'm impressed by your large blender knowledge. $\endgroup$
    – Paul Gonet
    Jan 6 '16 at 23:31
  • $\begingroup$ Thanks @PaulGonet, for your kindness but it's not much "technical". At the end it's just what I understood so far, I wasn't able to find further references. I wouldn't call it malfunction, nor a bug. It's just "high perfomance mode", and the "beauty/quality mode" is not currently available. $\endgroup$
    – Carlo
    Jan 7 '16 at 0:01

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