Question about Matte objects

[JulianT_CD]

Hi!

Basic question I guess: If I make a bunch of objects that are close to each other Matte objects with these settings:



...do the Matte objects internally receive a full calculation of all the light paths and just don't display them visibly? So in other words, are the Matte objects internally correctly shadowed and do they contain the reflections, refractions and GI from other Matte and non-Matte objects? So do they see each other in their fully lit and shadowed glory even if I can't see it in the Framebuffer?

I just want to make sure that all interreflections between Matte objects are calculated correctly and that my non-Matte objects also get the full and correct contribution from the Matte objects surrounding them. Basically what I am trying to imitate is the "Render Mask" feature, in that the masked objects render strictly on a black background, but still receive all the light/shadows they would normally receive if there weren't any objects set as Mattes.

Thanks!

[Svetlozar Draganov]

No GI is the option that specifies whether other matte-objects will be taken into account or not, here is its description:

No GI on other mattes – this will cause the object to appear as a matte object in reflections, refractions, GI etc for other matte objects. Note that if this is ON, refractions for the matte object might not be calculated (the object will appear a matte object to itself and will not be able to "see" the refractions on the other side).

If you would like all the matte objects to interact with each other as other geometry in the scene this option should be disabled otherwise it should be ON.

[JulianT_CD]

Thanks Svetlozar! Glad to read I employed Matte objects correctly.

One more thing though concerning Matte->Non-Matte interactions: If you don't check "Shadows" on Matte objects, do all secondary rays of non-Matte objects still see the Matte object shadowed even though the shadows are not visible to primary rays? From my experience, enabling "Shadows" clearly leads to secondary rays from non-Matte objects returning darker values, suggesting that the "Shadows" parameter not only controls what primary rays see, but also what secondary rays see. Is that correct?

Well actually, now that I think about it, the same question should be asked for Matte-->Matte interactions as well: Do their secondary rays see each other shadowed only when "Shadows" is ON?

[Svetlozar Draganov]

The Shadows option in Matte Properties affects only the Primary Rays, the shadow will be visible for the secondary rays, here is an example:
(The shadow is not visible for the primary rays but it is certainly visible in the reflections of the sphere)

[JulianT_CD]

Ok, thanks. I did that check, too, but I wasn't sure if this holds also true for diffuse reflection rays (i.e. GI)?

I asked, because I observed that objects which have a matte object placed underneath them (most commonly a floor) turn brighter on their underside when compared to using the floor as a non-matte object with a diffuse texture project via "Camera Map Per Pixel" onto it. I assumed this had to do with the secondary rays not seeing the floor shadowed. Since this doesn't seem to be the case, I wonder where the brightening of the underside is coming from? I think I read somewhere, that a matte object is internally treated as a surface with a 100% white albedo or something like that. Can you elaborate on whats happening with the albedo of a matte object?

I don't have a sample scene at hand right now. But I hope you still understand what I mean...?

Thanks again!

[Svetlozar Draganov]

I will need a scene for that since according to my tests the illumination of the object above the ground plane is the same regardless its matte-status:

scene:http://ftp.chaosgroup.com/support/scenes/matte_test.max

[JulianT_CD]

The Shadows option in Matte Properties affects only the Primary Rays, the shadow will be visible for the secondary rays, here is an example:
[ATTACH=CONFIG]30185[/ATTACH](The shadow is not visible for the primary rays but it is certainly visible in the reflections of the sphere)

Hi Svetlozar,

I just revisited your simple test scene. Please make the red sphere very reflective, check "Matte for refl/ref" and uncheck "Shadows" in the VRayMtlWrapper for the Floor. Keep all other settings as they are in your screenshot. The shadow disappears. Why?

So with "Matte for refl/ref" active I need to enable "Shadows" for them to be visible for secondary rays. Is that how it's supposed to work? You said the "Shadows" option is only for primary rays.

[Svetlozar Draganov]

This is how it works, the Shadows option allows Matte object to capture the shadows of other objects, deactivating that option will remove the shadows from everywhere not only from the primary rays.