id: film_sim
order: 190
# What this node is *about* is not written here, and cannot be: a `rust:` node
# publishes its own descriptor, so `attributes:` in this file would be read,
# validated and then ignored. See `Attribute::Effect` on `FilmSim`'s descriptor
# in `../src/ops/film_sim.rs`.
rust: FilmSim

why_rust: |
  It carries a stock's measured tables — an exposure matrix, three
  characteristic curves and a density lookup — which are not parameters and
  which no `uniforms:` expression could produce. Its neutral is "no stock
  loaded" rather than a set of values, and it is the one node that declares
  `Operation::renders`, so while a stock is loaded the composer emits it in
  the view transform's place instead of the default sigmoid.

placement: |
  Last, in the view transform's place (D19, FR-DEV-3j), after every other
  operation and after the detail stage.

  Before D19 it sat at order 25, after white balance and exposure, and every
  decision below it acted on the film's output, as though the frame had been
  scanned and then worked on. That put a display-referred rendering in the
  middle of the chain, which is what D19 removes: every operation is now handed
  the scene, and the film is the last thing that happens to the picture — an
  edit is a decision about the exposure the negative receives. `Stage::View`
  is what puts it there; this number only places it in the panel's order.