I have come across this issue when adding a people MS pass to a base render.
The people are having shadows from all lights, even behind walls, cast.
I’m not sure if I’m being clear so have made some example images to show what I mean!!
Ignoring that fact that the expected image has the wrong gamma! if you add the expected result to the base, you would get something close to the desired. The ball ms has too much shadow, the area where the wall should be blocking it out, so when combined that area has double the shadow?
Hopefully someone has understood this, and has a good solution to this!!
There is an option in the V-Ray Object settings, “No GI on other mattes” which also affects the way matte objects cast shadows on other matte objects. Play with it and see if it does what you need.
I’m having the same issue here.
I don’t recall this being the case with Vray Mattes (either material or vray properties based mattes) prior to sp3a. Is anyone else noticing this for the first time? Objects that are matted (with matte, receive shadows, affect alpha all checked at a -1 alpha) are not casting shadows on un-matted objects. The matted objects receive the proper shadowing from the un-matted ones . . . but don’t cast the proper shadows on the un-matted objects unless I uncheck the ‘matte’ option . . . and then, of course, the matte doesn’t get any shadows at all.
Playing with the ‘No GI on other mattes’ only causes matted objects to shadow themselves, which, in most cases I would guess, is not what we need.
Anyone?
After looking at this more carefully, I don’t think it can be done in one pass; you will have to render some passes separately and composite them to get the result that you need.
What you need is the ratio of the lighting of the scene with the sphere and the scene without the sphere (but with all other objects).
What the matte/shadow material calculates is the ratio of lighting with all objects and the scene without any objects. The matte/shadow material is not specifically aware that you are interested in the sphere only.
You can however calculate the required ratio by rendering the necessary passes directly and compositing them together.
