Cycles: rays miss triangles #46110
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Reference: blender/blender#46110
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System Information
OS: windows 7 64bit, CPU: i5-3550 GPU: ATI HD7850
Blender Version
2.75a
c27589e
Short description of error
I found these reoprts connected to this problem: #34094 D819
f770bc4757
(9489205c5c
)I found that it seems to be a particular range of angle between faces in wich the rays are able to miss the triangles.
Fireflies or worse are the consequences.
Exact steps for others to reproduce the error
1.put the camera inside a cylinder (32 vertices)
2.rotate the cam so it is looking at the round part of the cylinder
3. set the background shader strength to 5000
4.render it on 200 samples
It should show some fireflies all over the image.
File: triangle_miss.blend
This problem occured to me on an extreme case as I built a sealing for a room.
I'll attach a simplified file of it: sealing_light.blend
btw. the "a" version of blender 2.75 has some problem with my GPU so I renderd with CPU.
Changed status to: 'Open'
Added subscriber: @BOBtheROSS
Added subscriber: @Foaly
Tried it on GPU. I also get the fireflies.
And I noticed: the bigger the cylinder, the more fireflies.
Changed status from 'Open' to: 'Archived'
There are two sources of issue:
Original watertight paper suggests fallback to double precision arithmetic when it's detected system determinant is zero. This gives some extra stability (of watertight-ness if you want) in cases when ray hits exact edge of a triangle.
BVH nodes intersection was never implemented to be watertight, which might cause missing ray-triangle checks all together if ray hits exact boundary of the node.
Here's a quick patch which might be considered a proof of concept solution of the issue
P261: Patch for #46110
However, it has two issues still:
a. Consumer GPUs are really slow for double precision arithmetic
b. Extending BVH node boundary might cause some slowdown
But since this never really worked 100% robust it's still considered a TODO. So thanks for the report, but will look into this as a part of general improvement after 2.76 release.