Overview

Starting with 23.3, Current RenderMan can bake integrator results to images or points clouds.

Potential applications include transferring pre-computed global illumination for real-time realtime playback or optimising optimizing render times for large static assets.

Additional details are provided in the baking app note.

Limitations

The current implementation comes with a number of important limitations:

• Baking is non-incremental. 
  • This limitation excludes integrators that can not be setup to render in a single increment, like PxrVCM.
  • PxrPathTracer, PxrDirectLighting, PxrOcclusion and PxrVisualizer are compatible.
• Baking is incompatible with curves.
• Baking cannot be used with sample filters or display filters
• Each baking display can use at most one RGBA display channel.
  • Use multiple display drivers to output multiple signals.
• All images are baked at the same resolution.
• No breakpointing / stop-and-resume during baking
• There is no separate irradiance output
  

  • As a workaround, we suggest baking illumination and albedo: dividing the illumination by the albedo gives the irradiance.

...

Two views of a single point cloud with direct illumination on the box and the two teapots (baked with the PxrDirectLighting integrator).

Two This example shows two point clouds with global illumination (baked using the PxrPathTracer integrator): one for the box and one for a teapot.

Finally, we can render an image using these global illumination point clouds as textures.
The 3D point clouds can be read in an OSL shader using the texture3d() function (For a more cache-friendly 3D texture format, the point clouds can be converted into brick maps using the `brickmake' utility program.)

Multiple outputs, arbitrary output variables, LPEs

Similar to raytrace rendering, \textit{light path expressions} (LPEs) may be used to isolate different components of global illumination while baking. The data that can be baked is very general: if an integrator can splat it, then the illumination baker can write it to a display driver.

For example, the view-independent components of global illumination can be precomputed. As a simple example, here we declare direct diffuse and indirect diffuse outputs:

DisplayChannel "color directDiffuse" "string source" ["color lpe:C<RD>[LO]"]
DisplayChannel "color indirectDiffuse" "string source" ["color lpe:C<RD>.+[LO]"]
Display "<identifier:object>DirectDiffuse.tif" "tiff" "directDiffuse"
Display "+<identifier:object>IndirectDiffuse.tif" "tiff" "indirectDiffuse"

Similarly, the albedo user lobe may be rendered with an albedo LPE:

Option "lpe" "string user2" ["Albedo,DiffuseAlbedo,SubsurfaceAlbedo,HairAlbedo"]
DisplayChannel "color albedo" "string source" ["color lpe:overwrite;C(U2L)|O"]
Display "+<identifier:object>Albedo.tif" "tiff" "albedo"

The images below shows albedo, direct diffuse, and indirect diffuse for the  Cornell box with two spheres.