Vray material wrapper GI problem

[MrDream]

Hi,
I am having issue with material wrapper when enable GI.
I have a domelight with an HDRI image than in my ground plane I have the material wrapper with catch shadow on and -1 on alpha to get the correct alpha. I am projecting the footage onto the ground to get the correct reflection on my object. I plugged my HDRI into the reflection and background overrides.
Everything is fine till the point I switch on the GI in the render settings. After i switch on the GI I can actually see the ground plane in my render it gets darker not transparent as used to be with GI off.

Please HELP!!! This is drawing me crazy
Thanks

[MrDream]

Hello again,
I actually solved the problem I had before. Now I can catch shadow on the ground plane and everything seemed to be working besides the fact that my shadows on the ground plane now are not visible on my object....
I have a chrome ball in the scene placed on the ground is casting shadow on the ground but the shadow is not reflected back on the sphere.
Any idea way???

[tashko.zashev]

Hi,

Can you post a screenshot of the result you get?

I made a simple example file:


scene.zip

[MrDream]

This is what happening


and after I thick the box this is the result

[Svetlozar Draganov]

Thanks for the screen-shots.

When matte-for-all-secondary-rays is OFF all secondary rays like reflection and refractions are not taken into account matte-surface and the returned result is what is in Base Slot of VrayMtlWrapper. In that case it is a VrayMtl with projected texture in self illumination with not shadows (shadows cannot be casted on self-illuminated materials). That's why the reflections from the floor are accurate but the shadow from the matte-surface is missing.

Respectively, when that option is ON secondary rays now take into account matte-surface and they reflect the shadows from the mate-surface accurately but the self-illuminated-projected-texture is now transparent and the background is shown instead.

It is not possible to have both the shadows and the reflection from the plane without additional setup - one option would be to bake the matte-surface and blend it with the self-illuminated texture or use it as a mask for VrayBlendMtl. Another approach would be to plug self-illuminated texture into diffuse slot and match the ground-illumination with the background using Color Gain slider.

[MrDream]

Hi and thanks for answering,
So are you saying that if I have a VRayBlendMTL and I plug the VRayMTL with the self_Ill into the base material of the VRayBlendMTL and a VRayMTL with the diffuse channel as a coat i would be able to get the result I am looking for?
Thanks again

[Svetlozar Draganov]

I actually meant to use plug the projected texture inside diffuse-slot instead of self-illumination one. This is necessary because self-illuminated objects couldn't catch shadows, that's why in your example the shadows are missing in the sphere-reflections.
Here is one simple example.

First thing we need to import the texture twice, one of those instances will be used in the environment the other one will be used for the diffuse slot of VrayMtl. Two instances of the same textures are needed cause we need to tweak Color Gain in one of them while the other shouldn't be affected.
Here is how the things looks inside Maya:


VrayMtl with diffuse-texture is assigned as a base-material of VrayMtlWrapper which is applied to the plane. As you can see we now have correct reflection of the ground plane in sphere and the shadow is also reflected properly. The issue now is that the color of the diffuse-texture won't be the same as the one in the environment and we need to match them somehow.
One way to do that is to use Color Gain option of file-node where the texture is loaded.


SceneFile>wrapper-reflection-03.zip