VraySpherefade loadable background as empty instead of simple color ?

[Subburb]

Hello !
Playing around, trying to find a robust, simple and still efficient method to render moving objects against massive static geometry.

here's results so far :
- using method of precomputing IM (with no rendering) and adding moving objects with material option "use irrmap" off is quite good, but need some tweaks, adding an AO pass with exclusions, etc..
- rendering first static in flythrough, then setting all static as matte and rendering moving objects always leads to important shadows problems, hard to solve.
- Using Vrayspheregizmo "as is" and trying to composite give hard matting issues. sometimes we can deal with it, sometimes not.
(note : i'm teatching vray, and the official multipass (black, pure, etc..) is too complicated for my students.)

So, i'm trying a variation to simplify this process, keeping advantages in rendering only needed areas:
for each spheregizmo, i simply need to generate an "white disc" alpha corresponding to spheregizmo, wich is MUCH more simplier to composite softly.
so i create a simple sphere over the gizmo, deactivate all object options except "renderable" and "visible to camera", apply a material with 100% refraction with IOR = 1.0 (totally invisible sphere, but wich creates a white disc in alpha)
Of course the counterpart is that now all the disc will be rendered, even parts wich are very far to the objet, or close to camera.

This method is scriptable, wich is quite interesting !

Here's my question :
In VraysphereFade options, if, instead of simple color, we can "load" here the frame with static geometry, probably the blending will be far better than matting with black color ? in this case it will have all advantages : fast rendering, and immediate compositing.....

Maybe i'm wrong ? there's perhaps no solution this way ?

or maybe there's a solution i don't know to "fill" the background with the static frames ?

thanks in advance,
Cheers.

[tashko.zashev]

Hi,

Is it going to work if we just add an option to use the background image instead of a solid color?

[Subburb]

i think, yes. the goal is to render moving objects as overlay on static in background. sound interesting, not sure it'll handle all situations.

i've found another way wich can also be intersting :
i prepare my Vrayspheres, then i link on them a sphere mapped with a material having full refraction with IRO = 1.0 (invisible material). i remove this sphere from all stuff (GI, shadows, etc..).
The second sphere is here ONLY for creating an alpha (white circle) ich is very easy to composite. My tries gave good results so far. Even think to include this method in solidrocks.

i can describe more prcisely if you need.
Thank for your answer.

[tashko.zashev]

Thank you for adding more details on this request.

I think we have an option for this already added to the V-Ray 3 Sphere fade >

It will create the alpha channel you need.

I don't know if this will be also useful, but you can assign Object IDs to your meshes and add an additional multimatte element.