Drop a detail pass that changes nothing when it sits between two others

Capture sharpening at a scale too coarse to draw its radius emits one pass
with an empty body (`nothing_to_sharpen`), so that a chain still ends in
something that performs the output transform. At fit on any modern sensor
that is most of the time. When another neighbourhood operation follows it
- dehaze, clarity, texture - the pass is not last and does nothing: it
reads the rgba16float intermediate and writes the same texels to the other
one. It still cost a full render-sized read and write every frame:

  scene                           before     after
  sharpen+clarity 2560x1600 fit   18.66 ms   14.16 ms
  sharpen+clarity 3840x2160 fit   37.93 ms   27.88 ms
  every operation 2560x1600 fit   71.80 ms   67.24 ms
  clarity alone   2560x1600 fit   14.23 ms   14.20 ms  (control)
  sharpen+clarity 2560x1600 1:1   23.01 ms   22.97 ms  (control: resolves)

(Laptop RTX 3050 held at 420/810 MHz by its power cap, synthetic 60 MP
source, median of five alternated runs of forty frames each.)

`compose_detail_with` now drops such a pass where dropping it is exact:
not the last pass, whose output transform would otherwise move onto the
previous pass's f32 result and round differently; and not a pass right
after a reduced one, because a full-resolution pass is what closes the
reduced chain for the operation after it. `DetailPass::is_identity` says
what "changes nothing" means: full size, nothing bound at binding 3, and a
body with no code in it.

The rgba8 output is bit-identical: every scene above hashed the same
before and after, and the sharpen+clarity frame hashes the same as clarity
on its own, which is the claim in one line. A new dr-pipeline test pins
the three cases - dropped ahead of another operation, kept when last, kept
when alone.

This commit is contained in:

dtourolle

2026-09-26 07:10:41 -04:00

parent 1dc7b45cfe

commit d430ec9528

2 changed files with 107 additions and 5 deletions

docs/dev/traceability.md

+5 -5

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