Nodes aspectors

Cycles aplica una sèrie d’optimitzacions de node aspector tant en temps de compilació com d’execució. En explotar-los és factible dissenyar complicats grups de nodes estil «Uber Shader» que incorrin en un sobretemps de revelat mínim per a funcionalitats no utilitzades.

Node Optimizations

Com a primer pas en la preparació d’un node aspector per a l’execució, Cycles expandeix tots els grups de nodes, com si fes ús d’una eina de Desagrupar, i descarta els elemtns que són només de la IU com ara marcs i nodes de redirecció.

After that, it applies some obvious transformations, for example, it can (the list is not exhaustive):

  • Replace the following nodes with the constant result of their evaluation, if all their inputs are determined to be constant:

    RGB, Value, Mix RGB, Math, Vector Math, RGB to BW, Gamma, Bright Contrast, Invert, Separate/Combine RGB/XYZ/HSV, Blackbody, RGB Curves, Vector Curves, Color Ramps.

  • Detect Mix RGB, Math and Vector Math nodes that become no-op (without Clamp) or evaluate to 0 as a result of addition, subtraction, multiplication, division or dot/cross product with a known constant 0 or 1 input, and replace with the appropriate input link or constant result.

  • Elimineu els nodes Mesclar RGB (sense Retenir) i Mesclar aspector quan se sap que el Factor és 0 o 1 reemplaçant amb el valor d’ingressió o enllaç apropiat.

  • Eliminate no-op Mix RGB (except Color Burn, Color Dodge, Lighten, or enabled Clamp), Invert, RGB Curves and Vector Curves nodes with known zero Factor.

  • Elimineu els nodes aspectors Emissiu i Rerefons que no emeten cap llum, i afegiu nodes Aspectors amb una o ambdós arguments d’ingressió sense ocupar.

  • Eliminate Bump with constant Height input, using its Normal input or Geometry Normal instead. This is useful for implementing node group inputs that default to normal via routing through a no-op Bump before doing math.

  • Replace Attribute nodes of the View Layer type with the evaluated attribute value (it is constant within the whole Render Layer).

  • Combine multiple copies of the same node with the same inputs into only one instance.

Finally, any nodes that end up not connected either directly or indirectly to the Output node are removed.

Run-Time Optimizations

When executing shaders, a special optimization is applied to Mix Shader nodes. If Factor evaluates to 0 or 1, any nodes that are only reachable via the unused branch of the mix are not evaluated.

This can substantially reduce the performance cost of combining multiple materials in one shader with a Color Attribute, texture, or other input used as a switch.

Open Shading Language

If Open Shading Language is chosen as the rendering backend, node shaders are translated to OSL code and then compiled and executed by the OSL runtime. In the process it applies its own extensive set of optimizations, both at compile time and run-time.

Open Shading Language can optimize out Script nodes if their outputs are unused or constant, even if their OSL shaders have side effects like debug tracing and message passing, which may be confusing. For that reason message passing with setmessage and getmessage should generally not be used for passing information forward in the graph; explicitly passing information through sockets should be preferred.