light blockers associated with specified lights possible?

[jasonhuang1115]

Hi,

I am trying to figure this out but get stuck and wondering if it's impossible at the moment in VRay.

I want to set a piece/group of objects to block specified light(s) diffuse and specular contribution while the light blocker is not showing up in the reflection of other scene objects.

ex. If there is a light blocker between a shiny character and a rect light, I want the light blocker to occlude the lighting for the character but not show up in the character's reflection. Is it possible? I have been testing with turning on/off Primary visibility and reflection visibility, and setting up VrayObjectProperties, but still cannot achieve this level of control.

[Svetlozar Draganov]

Here is one example with Primary Visibility OFF , and with "Matte-Reflections".
By Matte-Reflection I mean - that Light-Blocker has Vray-Override-Mtl - and in Reflection slot of it is plugged Vray-Mtl-Wrapper with activated Matte-Surface.
With this setup if a reflection ray hits Light-Blocker it will give information for the background.

One more example - with Primary Visibility OFF and Visible in Reflections OFF - in this situation Light Blocker will be invisible in reflection - objects behind should be visible instead of it.

and one more - same setup like the above one - with Affect Reflections OFF on the VrayLight.

Light_Blocker.zip

[jasonhuang1115]

Thanks a bunch, Svetlozar, for the breakdown and sample files. Really appreciate it!

[jasonhuang1115]

Hi Svetlozar,

I checked the sample scene and realized that the REAL ISSUE I am facing is that the light blocker is not blocking the reflection of the light. First of all, I wouldn't want to have the black reflection of the light blocker as in example 1. With the 3rd example, though the light's reflection is gone by turning "Affect Reflections" OFF, but that means if the sphere is animated to move in and out of the shadowing of the light blocker, the 3rd example won't work as I don't really want to animated "Affect Reflections, if this attribute is animate-able.

Basically, with the "Affect Reflection" turn off, the light blocker lose its ability to block a light's specular contribution as in real world when a character walking pass a pillar that is between the character and the light. And if we use the Material override trick as in example 1, then we get a undesired black reflection on the character. Hope it makes sense.

[Svetlozar Draganov]

Hello there,

Thank you very much for the explanation.
Unfortunately I am afraid that the effect you want to achieve is not possible to be rendered out on a single pass.
If the Light Blocker is invisible for reflections the reflection of the object behind will be seen in the "character-object"- in our case this is the light.
If you don't want to see Lights Reflection - Affect Reflections should be OFF from Light Parameters - and in this case you are loosing reflection of the light even when the character-object is not behind Light Blocker.

When a Reflection Ray is fired from "character-object" there are three versions in our scene.
1-reflection ray hit Light-Blocker.
2-reflection ray hit Light (if Light Blocker is invisible for reflections)
3-reflection ray hit Background (if Light Blocker and Light are invisible for reflections)

[jasonhuang1115]

Thank you, Svetlozar. Though it's not possible to achieve this effect in single pass, it's great that I understand clearly what's going on. If we can figure out a way so that, in the scenario Light-Blocker is visible for reflections, when the reflection ray hit the Light-Blocker, it will look up to the LightDome or Environment for reflections, then it can be a workaround.

[Svetlozar Draganov]

Hello Jason,

Yes I think that a workaround with Matte-Reflections and Backed Background for Environment Reflection should work.
The first thing is to bake spherical background - which later will be used as a Reflection Override.
You can do this by using Vray Spherical Camera with FOV 360 - and arrange this camera to your "character" location - in my scene I placed the character-sphere and spherical camera at 0,0,0
It is very important to render with Aspect Ration = 2 when you are rendering Spherical Cam with FOV=360 > for example image resolution should be 1024x512 or 2048x1024 and etc. otherwise you will get distorted result.
The result should be something like this.
Then this image should be placed into Vray Environment Tab > Reflection Override and with the Matte-Reflection setup which I sent you before you can reflect this image into your character.
This is example of how the final result will look like with Backed Background
and how it will look like without Backed BG

You can download all files from the link bellow - there are two Maya files , one for Environment Backing, and the Second one with Matte-Reflection Setup.
https://dl-web.dropbox.com/get/Publi...zip?w=8dc72fa1

[jasonhuang1115]

Hi, Svetlozar ,

I couldn't download the sample files from dropbox. I do have a dropbox account. But even after I logged in I still couldn't access the download page.

[Svetlozar Draganov]

Hello Jason,

Could you please send me an email - svetlozar.draganov@chaosgroup.com and I'll return an answer with attached files.
Please add "Light Blocker" into the subject of the email.

Thank you in advance.

[jasonhuang1115]

Hi Svetlozar,

I juast sent you the email. Thank YOU!

[jasonhuang1115]

reflection lookup to LightDome for this setup possible?

Hi Svetlozar,

I ran into an issue with the current workaround. The baked environment background does provide an environment look-up for reflections when the reflection ray hits the LIGHT BLOCKER, but it doesn't work if the desired reflection is coming from a LightDome. I suppose we can sync the rotation of the lat-long environment map between a LightDome and the Environment Reflection texture override, but I am wondering if it is possible to not use the Override Environment at all (in Render Settings > VRay > Environment) and make the reflection ray to look up what's in the LightDome?

Let me explain the effect I am looking for in an example:
I feed the LightDome with animated HDR (lat-long) to serve as the fill light for an interior scene where a character moves in and out of shadows caused by localized key lights and LIGHT BLOCKERS at different positions. In this scenario, I need the LIGHT BLOCKERS to block key lights' diffuse, specular and reflection contribution to the character (as we already achieved in these sample scenes), and when reflection rays hit LIGHT BLOCKERS, they will look up to what's in the animated HDR fed to the LightDome. Is it possible to do it in one pass at the moment?

[Svetlozar Draganov]

Hello again,

Once reflection ray pass through matte object (lightblocker) it always hits Background Texture.
You can use the same texture in both places- DomeLight and Environment Override to achieve the effect you want , but it is not possible to do it without Environment Texture.

[jasonhuang1115]

I see. I've learned quite a bit from this discussion. Thanks a bunch, Svetlozar.

- Jason