Issues with Sun and Distant light

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CodeHD
Posts: 98
Joined: Tue Dec 11, 2018 12:38 pm

Issues with Sun and Distant light

Post by CodeHD » Tue Feb 26, 2019 10:59 pm

I was just playing around with glass and caustics and noticed the following two things with Sun and Distant light:

Setup (.blend attached):
- Diffuse Plane
- Glass Cylinder vertically above
- Sun source shining down vertically.
- BiDir of course for the caustics, any sampler
- v2.2alpha0 and a late 2.1 daily build

Issue #1:
The cylinder shouldn't cause much attenuation of light as the Sunlight is passing throgh 2 perpendicular surfaces. A bit darker underneath maybe due to Fresnel reflections sending some light back.

With the default Sun this looks as expected:
Sun_size1_BiDir.png
With the relative size set to 0.1, the circle underneath becomes brighter than the plane
Sun_size0p1_BiDir.png
With the distant source, this behaviour seems a bit worse, being visible at a size (half angle) of 0.25 degree, like the Sun.
Distant_size0p25_BiDir.png
Issue #2:
In the image with the distant source, notice how the plane gets darker away from the camera. This shouldn't be the case for a matte surface illuminated homogeneously.

Observations:
- Only happens with BiDir, not Path
- Independent of sampler and its settings.
- Only happens with distant, not Sun
Attachments
DistantSource.blend
(537.98 KiB) Downloaded 6 times

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