Mental Ray and Maya, its a love hate relationship, both need each other but its like a bad marriage. :p
Anyway, here is a quick run through of getting mip_matteshadow to work for catching shadows casted by mental ray lights, such as the native IBL. Usebackground shader will not work for MR specific lights.
– First you must enable your MIP shaders, Just pop this in your MEL command and run “optionVar -intValue MIP_SHD_EXPOSE 1;”
– find the mip_matteshadow material in the hypershade and assign it to the floor plane
– Open the assigned mip_matteshadow material and make sure the you’ve got shadows ticked. ( its OK by default )
Next the tricky part, we have to tell maya to recognise the alpha of the matteshadow for the background
– Create a mip_rayswitch_environment
– Connect it to the “background” channel of mip_matteshadow
– create a mib_color_alpha
– set the factor of mib_color_alpha to 0.0
– connect it to the “background” channel of mip_rayswitch_environment ( note its different to the top one )
– Next, you can connect your IBL image into the Environment channel of mip_rayswitch_environment or a mip_cameramap ( this has no alpha contribution BUT you need it to for reflections etc, you can leave it blank for just shadow catching )
OK Phew, now we need to work on the camera. ( if you are using IBL or camera maping reflections etc )
– create another mip_rayswitch_environment and connect it to the mental ray environment shader of the render camera
– create a mib_color_alpha
– set the factor of mib_color_alpha to 0.0
– connect it to the “background” channel of mip_rayswitch_environment
– connect the IBL or mirrorball to the “environment” channel ( this is very important )
Well that should be it, when you render, you should see your image on a black background and your shadow included in the alpha of your image. š
