FR-DEV-3f asks for look emulation and proposes HaldCLUT import to inherit
the free film-simulation ecosystem. This takes the other road for the
stocks where the measurements exist: run the physics.
A stock here is its manufacturer's own datasheet -- spectral sensitivity,
characteristic curves, dye densities. Light exposes three emulsion layers,
the layers develop to densities, the densities are dyes that absorb, and
what is left is what reaches the eye. A colour negative comes out orange
and upside down because that is what a colour negative is; it becomes a
photograph when a paper profile prints it, with the enlarger's filtration
solved rather than dialled.
What that buys over a LUT is that the parameters stay physical. Opening up
a stop moves the picture along the film's real characteristic curve,
shoulder and all, instead of scaling a number baked at one exposure. The
data cost runs the other way too: a stock is 17 kB of published
measurements where one HaldCLUT is 800 kB of one person's grade.
It looks like it needs a spectral integration per pixel. It does not, and
that is the whole design:
- Exposure is a 3x3 matrix. The reconstructed scene spectrum is linear
in the sRGB triple, so the integral collapses into nine numbers,
exactly -- no approximation.
- The characteristic curve is three 1D functions, sampled exactly.
- Everything after that -- dye absorption, the print through the
negative, the paper, the viewing illuminant, the adaptation -- takes
exactly three numbers in, so it bakes into one 32^3 lookup.
Per pixel: a matrix multiply, three curve taps, one fetch. Splitting the
curve out of the 3D lookup rather than baking one LUT over exposure is
measured, not assumed: the curve carries the sharp shape and the dye
mixing is smooth, so folding them together would need three times the
resolution for the same error. At 32^3 the worst error is 0.003 in linear
sRGB, under one 8-bit code value, and a test says so.
No wgpu dependency, deliberately, and the same isolation argument dr-lens
makes: the model is plain f32 with a documented layout, so every property
worth asserting is asserted on the CPU. Binding it to a texture is dr-gpu's
job and is not done here yet.
The expected values in tests/ came from a Python prototype running against
a different colour-science stack. Agreement to three decimals is evidence
about the model rather than about one implementation of it -- a transposed
matrix or a mispasted observer row would pass every unit test and fail
that one.
Profiles are converted from spektrafilm by Andrea Volpato, CC BY-SA 4.0.
The converter is in the tree and runnable, so what was changed from
upstream is auditable rather than taken on trust; profiles/CHANGELOG.txt
records it, including the one deliberate deviation -- Mallett & Yuksel's
1 kB basis instead of Hanatos's 4 MB table, which costs accuracy at the
gamut edge and saves four megabytes.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The icon was already embedded and had been all along: `app.slint` sets it and
`build.rs` compiles it into the binary with `EmbedFiles`. That is not what a
Wayland compositor looks at. It ignores a client-set icon entirely, matches
the surface's `app_id` against installed `.desktop` files, and takes the icon
from the one whose basename agrees. Nothing set an app id and no desktop entry
existed, so GNOME had nothing to resolve and drew the placeholder.
Both halves are needed and neither substitutes for the other: the embedded
icon is what X11 and the window itself use, and the desktop entry is what the
overview, the dash and alt-tab use.
The app id, the `.desktop` basename and the installed icon's filename are one
string in three places — `paris.tourolle.darkroom`, the same reverse-DNS name
the Android manifest already uses, because it is one application. Change one
without the others and the icon disappears again with nothing logged, so each
file says so where the string appears.
The PKGBUILD builds from the checkout rather than a release tarball, so
`makepkg -si` installs what is being worked on. Install verified by inspection
of the built package: binary, desktop entry, and the icon under
hicolor/256x256 by the name the entry asks for.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Establishes the v0.1 foundations on both platforms:
- dr-types: SourceRef (never a filesystem path — Android SAF has none),
Format, Availability, Validator with ETag quote normalisation
- dr-gpu: wgpu device, compute pass writing a storage texture, resize
- dr-ui: Slint shell with FR-UI-1 adaptive layout, computed in Rust to
avoid a binding loop
- docker/android: pinned toolchain, verified producing API 28 ARM binaries
Measured the cost of the temporary CPU readback path (dr-gpu bench):
compute is 0.06-0.28ms across sizes while readback is 0.63-7.43ms, so
readback is 90-96% of frame time and scales with area. Recorded in
ARCH §6.1 — this is why spike S1 is the priority.
Mitigations pending S1: reuse the staging buffer, apply at most one
resize per frame, and cap render resolution at 2048 on the long edge.
10 tests passing; core crates cross-compile for aarch64-linux-android.
dtourolleandClaude Opus 5