Glass Object Ray Tracing Problem

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Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Glass Object Ray Tracing Problem

Post by Jan »

Hi, I am having problems rendering both Transmission and Reflection simultaneously in Glass materials. It is either only one or the other.

Here is the setup:

Green Area Lights pointing perpendicularly to the Glass Object from some distance and so was the viewing direction and expect maximum reflection.
Red Laser Lights above and entering at a angle toward the Glass Object with Homogeneous Volume Inside and expect Transmission to any viewing direction.
solid preview.jpg

However these are what I got:

Only Reflected Green Area Lights from Glass Object is visible while a segment of Red Laser Lights inside the Glass Object cannot be seen when Visible to Camera is enabled.
glass visible to camera checked.jpg
Only Transmitted Red Laser Lights is visible while reflected Green Area Lights cannot be seen when Visible to Camera is disabled.
glass visible to camera unchecked.jpg

Are there other settings or fine tuning to make to allow for both to show up please???
Attachments
Glass Ray Tracing.blend
(1.14 MiB) Downloaded 122 times
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Glass Object Ray Tracing Problem

Post by Jan »

p.s.

Here is another better illustration with global illumination.

Glass Cube Object - Visible to Camera Unchecked
glass object raytracing test_ visible to camera unchecked.jpg

Glass Cube Object - Visible to Camera Unchecked
glass object raytracing test_visible to camera checked.jpg
Volumetric lights are lost and maybe as well Torus Object bounce light reflections from Matte Plane Object underneath.

Snap16.jpg
Attachments
Glass Ray Tracing 2.blend
(1.29 MiB) Downloaded 116 times
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Glass Object Ray Tracing Problem

Post by Jan »

P.S.

Animated GIF (please click on the image)
animated.gif
CodeHD
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Posts: 437
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Location: Germany

Re: Glass Object Ray Tracing Problem

Post by CodeHD »

What you are seeing is a classic case of "SDS" caustics (spcular-diffuse-specular), which are inherently difficult to render. With a laser light, even impossible.

The homogeneous volume scattering is diffuse. Glass is specular, and both entering and exiting the cube are counted as spearate events. Hence Entering -> scattering -> exiting = SDS

When you set invisible to camera, it seems that the glass surface (towards the camera) is set to a null surface, which removes the specular component there - making the laser visible. At the same time, this is true for the green reflection, which disappears when the reflecting surface is invisible.

The only setting I can think of that might(!) help is the caustics cache.
Jan
Posts: 37
Joined: Sun Jan 10, 2021 2:37 pm

Re: Glass Object Ray Tracing Problem

Post by Jan »

CodeHD wrote: Mon Apr 05, 2021 6:25 pm What you are seeing is a classic case of "SDS" caustics (spcular-diffuse-specular), which are inherently difficult to render. With a laser light, even impossible.

The homogeneous volume scattering is diffuse. Glass is specular, and both entering and exiting the cube are counted as spearate events. Hence Entering -> scattering -> exiting = SDS

When you set invisible to camera, it seems that the glass surface (towards the camera) is set to a null surface, which removes the specular component there - making the laser visible. At the same time, this is true for the green reflection, which disappears when the reflecting surface is invisible.

The only setting I can think of that might(!) help is the caustics cache.

Thanks :!: :idea: Recalled BRDF function and light rays integration. Caustic illuminated diffused surfaces (refracted and internally reflected light rays from glass material upon the diffused microscopic particles :?: ) and then bouncing its bright lit rays but only from small surface area to another specular surface (glass cube front face). The very finite sampling points due to limited computing power plus the former so no wonder they turned up invisible on the camera despite knowing it should be there :lol: I even initially thought BlendLuxCore erroneously make the Glass Object opaque to Volumetric Lights so they cannot be seen by the Camera. :twisted:

I tested it with another specular Material that is Mirror and fortunately the results are still the same to prove the SDS issue. :D

Also removed the Glass Cube Object Front Face so the Laser will be visible now and then try to reflect it from a Mirror Object.
solid 2.jpg
solid 1.jpg

Front View
rendered front.jpg
cannot even understand why the volumetric lights suddenly turned so red and overshadowed the blue color of the Sky :?

Mirrored View
rendered mirrored.jpg
mirrored image degraded while Volumetric Lights are still invisible ;)


p.s. they were all rendered using Bidir
Attachments
Glass Ray Tracing 3 SDS.blend
(1.33 MiB) Downloaded 105 times
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