Cycles: transparent object has black line where it intersect with other objects #85840
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Reference: blender/blender#85840
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System Information
Operating system: Windows-10-10.0.18363 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 461.40
Blender Version
Broken: 2.91.2
Short description of error
When rendering transparent objects that intersect with other objects, black lines will appear on the intersecting area.
Exact steps for others to reproduce the error
Cycles_Black_Line_Transparency.blend
Added subscriber: @Netseeker
#92017 was marked as duplicate of this issue
Added subscriber: @APEC
Added subscriber: @adreacooper
Added subscriber: @DylanLobbregt
Added subscriber: @PratikPB2123
Changed status from 'Needs Triage' to: 'Confirmed'
Can confirm with current master (
7223a0348f)Unsure but little similar to #87868 (Plane with transparent scattered as particle generates artifact in the intersection with the emitter object)
I think it is the same thing due to how Cycles treats transparent shader. Also there are 2 things I need to stress. First one is that the black lines or artifacts appear less obvious when 2 intersected faces are more perpendicular. I think LuxCore render has some slider to tweak it but it probably has something blender's unit system. Second one is that to my surprise, this issue has been there since 2.8 at least and it seems no one talks about it...
Renderman for Blender released yesterday and I checked transparent shader with renderman and the problem is still there but it is way less obvious than cycles render result.
I also think this could be caused by Blender's internal unit is meter which is not accurate as cm or mm. Or maybe it is about single precision value floating point value?
Added subscriber: @Francesco-Della-Torre
Same issue in this video: https://youtu.be/NKEelAytWGg?t=123
Changed status from 'Confirmed' to: 'Needs Developer To Reproduce'
@Francesco-Della-Torre
it was Confirmed, why you change the status?
Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'
Added subscribers: @Evan-Allred, @mano-wii
Added subscriber: @Andruxa696
Added subscriber: @antoniov
I have found a similar issue when render with transparent materials in Cycles (Eeevee works).
Here a simple array of cubes. Tested in Windows 11 with 2.93, 3.0 and 3.1 using NVIDIA RTX2080TI CUDA or OPTIX.
In viewport you get this.
When you render you get this.
I've seen the artifacts in the viewport when you move the view and sometimes everything is transparent, sometimes it isn't.
TransparentBug.blend
In your case @antoniov, it seems that the problem can be worked around by increasing the number of Max Bounces of transparency.
It's possible that it's a limitation.
Added subscriber: @juang3d
What is weird is to have a different behavior between Viewport and Render since there are not different bounces settings for viewport
@mano-wii Thanks, bounces fix the problem, but I agree with @juang3d It's weird to get different results.
Added subscriber: @ParallelMayhem
Added subscriber: @ThomasDinges
Changed status from 'Confirmed' to: 'Resolved'
No black line for me anymore with Blender 3.5 Alpha.
Man, as I checked, in 3.4 and 3.5, the problem is still there but looks a little better.
Please check out my file below, you can definitely see the line there.
What Cycles need is a slider or a value to control the precision like other render engine, as I checked, Octane render has a value to make this line less obvious.
This problem is not about light bounce, it is just about the unit and the precision.
Also, it is not obvious when camera is not that close, but if you have a character with skin tight suit like superman or spiderman, your suit will eventually overlap with body mesh and when you use long focal length camera like 150mm then the problem will be more obvious. I use mask map to hide body parts but at this point the only workaround is to use mask modifier to hide mesh part but due to the topology, some part will still have problems.
Also, it is not obvious when camera is not that close, but if you have a character with skin tight suit like superman or spiderman, your suit will eventually overlap with body mesh and when you use long focal length camera like 150mm then the problem will be more obvious. I use mask map to hide body parts but at this point the only workaround is to use mask modifier to hide mesh part but due to the topology, some part will still have problems.
My dude, it is barely visible at maximum contrast.
Ray Epsilon has its own pros and cons.
Sounds like a co-planar face issue, which has already been talked about. Also, that's not how you should handle clothes.
It is not "barely visible". It depends on many things. First, if you render 4k or even higher res, the problem will be more visible.
Second, if your character's size is correct like 1.6-1.8m tall, then skin tight clothes will be a problem.
Imagine you make a swimming competition scene and your character's waist constant moves and swimming suit will overlap with your character's body. Also, my character has a bunch of corrective morph and the suit has corrective morphs as well, it is impossible to avoid overlapping and if you use mask modifier to hide body part, some parts like armpit, chest have different topology with the suit, some faces will still be problematic and I currently use both mask modifier and mask map and an extra shapekey to correct the overlapping issue.