Not expected shadow behavior with Matte Shadow Receiver

[estraulino]

There is this behavior that I think it is not life-like:
When rays of a light are completely obstructed, they cast shadows that should not be casted. I found out this behavior when using a rectangle light with directionality value of 1 and an infinte plane with Matte_shadow_receiver, but after making some tests, activating shadow render elements, using other materials and changing the directionality values, I think it is inherent in how shadows are calculated. This creates out of this world images and is specially problematic when creating PNG with shadows using Matte_shadow_receiver and in postproduction.

The behavior is highly noticeable when using a matte shadow receiver material and using high directionality values for rectangular lights or spotlights (as far as i know), but the issue is visible when looking at render elements. It is as if the shadows are calculated as a projection, instead of as a lack of projection of light (It is the best way i can think of it)

https://drive.google.com/drive/folde...L6?usp=sharing

[konstantin_chaos]

Hi estraulino,

This looks like a V-Ray Core bug.
I was able to reproduce the same in V-Ray for Maya:


I'll investigate further and create an issue for it.
Thank you for reporting it!
Konstantin

[estraulino]

Hi Konstantin,

Yeah, I found that issue in Rhino too, but I didn't know where should I post it. Where should I post if I find issues in multiple versios of vray?

Kind of related to this issue. I found another weird behavior related to light directionality. If there is a rectangular light (It does NOT happen with disc lights) with a Directionality value higher that 0.75 behind a glass material, the light behind the glass dims substancially. At a directionality of 0.8 it is almost completley dimmed, and when the value hits 1, there is no light. Even if the intensity value is incredibly high.

This happens in both Rhino and SketchUp.
The dimming also seems to depend on the distance between the light source and the glass material.

[konstantin_chaos]

Hi,

Yeah, I found that issue in Rhino too, but I didn't know where should I post it. Where should I post if I find issues in multiple versios of vray?

I reported this issue in our bug tracking system.
There is no need for you to do anything additional.

I found another weird behavior related to light directionality. If there is a rectangular light (It does NOT happen with disc lights) with a Directionality value higher that 0.75 behind a glass material, the light behind the glass dims substancially. At a directionality of 0.8 it is almost completley dimmed, and when the value hits 1, there is no light. Even if the intensity value is incredibly high.

This looks like a bug.
It used to be that even without refraction, the dimming would happen. This was fixed at one point.
What you've described is a left over issue.
I'll report it as a bug.

Regards,
SketchUp