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Visual glitches occur on certain models, in Game Engine and possibly the viewport
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Description

System Information
Linux openSUSE 13.2 x64, KDE 4.14.4. AMD Radeon 6870, Mesa 10.3.7.

Blender Version
Broken: 2.73a
Worked: I don't think I noticed this in <= 2.72, but cannot say with certainty due to the bug's probabilistic nature and rare occurrence.

Short description of error
Artefacts are visible on certain meshes, typically lighting errors causing dark or bright spots over the faces of some objects. The problem appears to affect the Game Engine primarily, although I think I noticed a similar issue in the 3D viewport once.

It is pretty random, and might depend on the angle you look from or only happen after you start and stop the game engine several times. It only happens to certain meshes as well, and I couldn't find the exact trigger. In one of my cases, this only seems to happen when the mesh contains shape keys as well as an armature deforming it... and if I add a modifier after the armature (such as a bogus Subsurf), the problem goes away.

I generated a small test blend containing an air vent tube which is subject to this issue. Also two screenshots... one of the issue and one of how it should look like.

Blend file: http://www.pasteall.org/blend/34266
Good screenshot: http://www.pasteall.org/pic/83533
Bad screenshot: http://www.pasteall.org/pic/83532

Exact steps for others to reproduce the error
The effect is pretty random and likely caused by precise circumstances, so apart from my test blend I don't know the exact cause.

Details

Type
Bug

Event Timeline

Mircea Kitsune (mirceakitsune) raised the priority of this task from to Needs Triage by Developer.
Sybren A. Stüvel (sybren) triaged this task as Confirmed, Medium priority.

I can confirm this issue, on Kubuntu Linux 14.10, NVidia Geforce 970 GTS, closed-source drivers 346.16, and self-compiled Blender 2.73 (0d766aa5327098b2b0fa1eb9af88533025a3153d).

It seems to have something to do with the armature modifier - when I remove that, the object displays just fine. Just disabling the armature modifier is not enough, it really needs to be removed for the rendering issue to disappear.

When I disable the shape keys (but keep the armature modifier), the rendering is still wrong, but in a different way. It seems to be a conflict between armature and shape keys.

The bug also manifests itself with a single sun lamp.

Slightly more minimal Blend file:

I've tested on 2.69 and 2.70, and the bug also manifests in those versions.

A third person confirmed the issue on the #gameblender IRC. They didn't mention as much as @Sybren A. Stüvel (sybren)... just that they remember noticing the issue in 2.68, which means it might be older than I initially thought.

Is this a GE only bug? (Just important for tracker policy)

I'm not completely certain if it's GE only, or affects the viewport as well. In the example blend I posted, it only happens in GE. But in different cases, smooth shading doesn't work on certain meshes in the viewport, and flickers if you look from certain angles. The issues look quite similar, and I can't tell if they have the same root cause.

Setting as GameEngine, if you can reproduce in the 3d-viewport,
please report another bug with steps to redo (and reference this one).

I had a look and it worked fine in Blender's viewport.

Jorge Bernal (lordloki) lowered the priority of this task from Confirmed, Medium to Normal.