BiDir darkening surface at glancing angles
Posted: Wed Sep 11, 2019 6:01 pm
Hi,
I have been struggling for a few days to identify if I am doing something wrong or if this is a bug. The only thing I have changed between renders is the integrator from Path to BiDir.
What you can see is that at more extreme angles (on the floor near the back of the room, and on the columns where it meets the wall), the BiDir integrator is darkening the surface. Even in direct light. This does not happen with regular path (either OpenCL or CPU).
Edit: The room is made of solid meshes with flat shading applied. The floor is separate from the walls and the walls are separate from the ceiling. The room is "open" to the sky to the above right. I have checked all the normals with both overlay showing direction and face colour mode in Blender 2.80. I am using BlendLuxCore-v2.2beta4-blender2.80-win64-opencl but originally noticed the issue on beta 3.
Things tested with BiDir all exhibit the same problem:
- Metropolis vs. Sobol sampler
- Glossy vs. matte vs. disney shaders
- Sky envionment vs. flat colour environment vs. mesh emitter vs. sun lamp
- Rendering to insane sample count (< 3/256 noise level took 36 hours at 4K scene and yielded 12,336 samples per pixel)
- Using an image texture on surfaces. With bump vs no bump vs solid colour with bump vs no bump
- Hiding and unhiding different meshes (walls, ceiling)
All these things yielded no fix for BiDir, yet could never reproduce it with Path.
Is this a known issue, or am I doing something silly?
Edit 2: Attached sample .blend file in case it's useful
I have been struggling for a few days to identify if I am doing something wrong or if this is a bug. The only thing I have changed between renders is the integrator from Path to BiDir.
What you can see is that at more extreme angles (on the floor near the back of the room, and on the columns where it meets the wall), the BiDir integrator is darkening the surface. Even in direct light. This does not happen with regular path (either OpenCL or CPU).
Edit: The room is made of solid meshes with flat shading applied. The floor is separate from the walls and the walls are separate from the ceiling. The room is "open" to the sky to the above right. I have checked all the normals with both overlay showing direction and face colour mode in Blender 2.80. I am using BlendLuxCore-v2.2beta4-blender2.80-win64-opencl but originally noticed the issue on beta 3.
Things tested with BiDir all exhibit the same problem:
- Metropolis vs. Sobol sampler
- Glossy vs. matte vs. disney shaders
- Sky envionment vs. flat colour environment vs. mesh emitter vs. sun lamp
- Rendering to insane sample count (< 3/256 noise level took 36 hours at 4K scene and yielded 12,336 samples per pixel)
- Using an image texture on surfaces. With bump vs no bump vs solid colour with bump vs no bump
- Hiding and unhiding different meshes (walls, ceiling)
All these things yielded no fix for BiDir, yet could never reproduce it with Path.
Is this a known issue, or am I doing something silly?
Edit 2: Attached sample .blend file in case it's useful