If you are familiar with Renderman you are most probably familiar with the concept of render passes and their use. However my Blender Renderman exporter (with matt ebb’s Blender/3delight exporter and the RibMosaic project I start to feel that there is a need to give my project a name to prevent confusion). Offers a different use for render passes as a side effect: Preview passes.
The easiest way to set up a preview pass is to just create another render pass with the same settings as your main pass (that’s a bit cumbersome, the “copy pass” operator is on its way)
but lower the resolution,
the Pixel Samples,
max trace depth, photon count, etc. and in the world TAB activate “override ShadingRate” and raise that way up.
If you have Light Shaders or surface shaders with expensive raytrace shadeops you may even add an extra pass to them as well and link the new pass to your preview render pass and then lower the samples settings for your shaders.
The last thing you need to do is in the “Render” Panel in the render TAB disable “Export All Passes”.
Now you can easily switch between your preview pass to get a fast approximation and the beauty pass to render the full blown high resolution version over night