matte material/ shadow catcher for Blender

[andybot_cg]

Hey everyone! I've made some efforts to get the shadow catcher matte material working in Vray for Blender. Here's what I've been able to put together. Some notes:

1. The matte material seems to have several inputs duplicated, I think they should be combined in the node. (For example, there are 3 places to put the alpha contribution! And they're not all connected)

2. With the background image, I can't find a way for the shadow not to pick up the image in the background. I have to disconnect the background image (in the "world" node) for the shadow to be clean and not show the grass through.

blend file attached.

Andy

[designo]

Andy, that's awesome.

[JuhaW]

This is using object Wrapper, no material nodes needed to create shadow catcher.
Select your shadow catcher objects and run this script, it will change those 5 green values and set "Matte "-text beginning of your object names. Run script again and it toggles selected objects Wrapper off/on and changes object names back.

import bpy

matte = 'Matte '
objs =[o for o in bpy.context.selected_objects if o.type in ('MESH', 'CURVE','SURFACE','META','FONT')]
for o in objs:
    if o.vray.MtlWrapper.use:
        o.vray.MtlWrapper.use = False
        o.name = o.name[6:] if o.name[:6] == matte else o.name

    else:    
        o.vray.MtlWrapper.use = True
        o.vray.MtlWrapper.matte_surface = True
        o.vray.MtlWrapper.affect_alpha = True
        o.vray.MtlWrapper.shadows = True
        o.vray.MtlWrapper.alpha_contribution = -1
        o.name = matte + o.name if o.name[:6] != matte else o.name