Lighting

• Please insure when loading old scenes that the shop_lightpath points to a PxrCollect VOP.
• Pxr Std Lights When you migrate from RenderMan 20.x to 21.x, you cannot use Pxr Std lights (which are RSL lights) were deprecated in RenderMan 21. Create a new Pxr C++ light.  See Adding LightLights. After you add Pxr C++ lights and get "Invalid Light Handle" error.  Check your rendermn.ini and make sure you don't have RiOption for "int directlightingservices" turned off.  For C++ lights to work, it needs to be turned on. It is on by default

Shading

• The new material workflows requires that the most downstream VOP node is a PxrMaterialBuilder. 
• RSL (RenderMan Shading Language) support was removed in RenderMan 21. Materials (BxDFs) are C++ constructions and patterns should be OSL when possible.
• We accept the Houdini attribute names for use in shading by connecting a PxrPrimvar or PxrAttribute node to a parameter using the appropriate name.

Geometry

• Poorly tessellated (non-subdivision) surfaces may show artifacts when rendering like dark edges and outlines. It's recommended to render smooth subdivisions to avoid this artifact. You may also use polygons with no normals defined and then subdivide, RenderMan will compute the normals for you.

Rendering

• Since there have been improvements, it The RenderMan 21 ROP renders using the 21 Soho workflow. It is recommended to create use a new RenderMan RIS ROP to avoid any unexpected errorstake advantage of the interactive workflow in RenderMan 22.