Glass object artifacts

[gracelorn]

Hi guys!
So I am making these simple kitchen scales. Currently they are made up of two objects – the glass top (a chamfered box) and a white plane underneath (which is placed some 0.5 mm below the chamfered box). When I rendered it with the glass material refraction mode set to “One-sided (solid)” it looked great, with very realistic shadows and nice caustics. But my only problem with it is that it is too noisy compared to the rest of the image and requires more passes before the noise goes away (Image 1).
When I set the refraction mode to “Hybrid”, it appears much less noisy (the absence of the shadows is not a problem for me), but produces these strange dark stripes in the shape of a cross (Image 2). I wonder what the cause of this might be. Any ideas?

[Ludvik Koutny]

Is the bottom face of the glass by any chance coplanar (on the same position) with the top face of the white surface?

[Ondra]

try setting acceleration structure to "BVH" (in the devel/debug tab, activated in the About tab)

[gracelorn]

The white plane is about 0.5 mm below the glass, so they are definitely not intersecting. I tried to further subdivide the geometry of the glass object, and it (almost) did the trick (see attached image). Now those artifacts are less noticeable, but still present.

[gracelorn]

try setting acceleration structure to "BVH" (in the devel/debug tab, activated in the About tab)

Thanks Keymaster, it solved the problem completely. But the render time increased significantly (from 9 to 15 minutes).

[Ludvik Koutny]

I think Keymaster asked about it because he guessed what could be the source of the problem. It still is a bug :) I think this proves that it is somewhere in the Embree kernel, but hopefully it will get fixed soon :)

[gracelorn]

I think Keymaster asked about it because he guessed what could be the source of the problem. It still is a bug :)

I thought this might be a bug, too. That's why I reported it, to help make the already great renderer even better :)
Also, is there an intention to implement in the future such option as fake "transparent shadows" (like in V-Ray) just for such cases? I mean, you don't always need physically accurate shadows from glass objects, and in some situations fake transparent shadows would be a life-saver.

[Ludvik Koutny]

I think Keymaster asked about it because he guessed what could be the source of the problem. It still is a bug :)

Also, is there an intention to implement in the future such option as fake "transparent shadows" (like in V-Ray) just for such cases? I mean, you don't always need physically accurate shadows from glass objects, and in some situations fake transparent shadows would be a life-saver.

That is exactly what hybrid glass does...  it's just very shitty naming. It will be fixed in next Alpha ;)

[gracelorn]

Oh, I thought this mode meant no shadow at all. I think I need to do some more testing then :) Thanks for the help. Looking forward to the next alpha release.

[Ondra]

I think Keymaster asked about it because he guessed what could be the source of the problem. It still is a bug :) I think this proves that it is somewhere in the Embree kernel, but hopefully it will get fixed soon :)

Actually, it is already fixed in current build, and will not happen in A6

[puttipong]

I have the same problem, now waiting for A6. Thank you very much :)