1. how to get a mask for gus/ ground/ or whatever object u wanna mask out:
<1>.save your lighting file as a other one.
for example: i wanna a mask for gus in shot9, so i saved out my lighting file as other file called 'shot9_mask'.
<2>.create slim shaders with diffuse color of white or black. have the object u wanna mask out attached with color different than other objects.
Remove all the lights u already have, and create a new RendermanEnvLight with color: white; intensity: 1.0; sample: 512, max v: 2.0.
for example: in shot 9 I wanna mask out gus. so I give him a black color, other set to white color in shader. and then this is my render:
(1).u need to have the correct displacement attachment to the object. Other wise the mask u render out won't match the outline of your object in the beauty pass. I have already make the some of the surface shader on gus so u guys don't need to remake it. it's in assets/lights/12.0_lights/12.0_lights.proj/slim/palettes/shot12SnowAndBg.splt.
you can find those shaders by open your slim, and File/Open Palette. then open the file above, u will see some black surface shaders for different parts of gus in that palette.
Ask me if u dont know which one is supposed to be attached to which object (u guys have my number right~? lol)
(2) about the snow ground. first make sure u have the effect on it. second, when u make white surface shader for it. make sure change the ' object size' of ur slim shade to 200. otherwise it won't get the correct displacement.
<3>After u have the mask, then u can put gus and env in different render layer, which will also help speed up the render. and Then comp them together. like this:
<4>.If u need to create Zdepth pass for comp atmosphere effect of DOF. I have a way to cheat it.
save your mask file as another one call. 'XXX_Zdepth.ma' (Opppps, so many files >_<)
(1). connect all the diffuse color of all you surface shader to this mixcolor node: assets/lights/09.0_lights/mixColor_forZdepth.slim (the folder is really messy right now, sorry about that...). and in the SL_box, u can the value of float d to control how far it face into black.
(2). give your sky plane a black shader.
(3). in your renderman control, create a output pass called : 'DiffuseColor'. set it to TIFF. (that's the frame u want for your Zdepth render)
here is an example for shot9's Zdepth pass (I only render the Depth pass for my Env, cuz gus will be in focus all the time)
<5>.Final Comp with another fog layer in front of everything, together with LightWrap & EdgeBlur: