# grade FURROW's photograph, as pure functions of one number: `t`, the seconds of film elapsed. Nothing in here touches an entity or keeps a clock, so it is safe to require from anywhere and it answers the same twice. ```lua local grade = require("furrow.grade") grade.dust(t) -- 0 at shot 1, 1 at shot 24. The film's whole arc. grade.air(t) -- every PhysicalAtmosphere field, plus groundAlbedo/sunColor grade.sun(t) -- the sun's colour and intensity (its DIRECTION never moves) grade.ambient(t) -- the sky dome's colour and intensity grade.fog(t) -- HeightFog settings; density 0 through Act I grade.lensFx(t) -- flare, halo, streak, grain grade.shutter() -- a 180-degree shutter, constant grade.exposure(t) -- AutoExposure, on a half-stop leash grade.grade(t) -- the seven knobs of the fullscreen grade pass grade.dof(t) -- the lens for the set-up the film is on, racks included grade.shotAt(t) -- which set-up, and how far through it ``` `furrow.Look` is the only thing that pushes these at the renderer. Other slices are welcome to read `grade.dust(t)` — the SAND slice in particular, so airborne density and air density agree instead of drifting. ## The arc The sun never moves. The air does. `film.clarity(t)` runs 0.04 to 1.00 and `grade.dust` rebases it so every curve here reads 0 at shot 1 and 1 at shot 24. The largest single-frame change in any of these channels, measured across the whole 181 seconds at the film's own 1/24 s step, is about 1% of that channel's range — the arc is continuous, not stepped. | | shot 1 | shot 24 | |---|---|---| | `aerial` | 0.15 | 1.00 | | `mie` | 0.20 | 18.0 | | `rayleigh` | 0.95 | 0.06 | | `skyIntensity` | 0.55 | 0.85 | | sun | white, 4.0 | 1.0/0.60/0.30, 2.05 | | ambient | cool blue-violet, 0.55 | warm brown, 1.15 | | fog density | 0 (passes released) | 0.017 | | grain | 0.014 | 0.040 | | contrast / saturation | 1.10 / 1.16 | 0.94 / 0.92 | ## Three numbers that were measured, not reasoned about - **`mie` ramps to 18, not to 2.5.** At 2.5 the zenith of this scene is still frankly blue. The brown-out does not read until the Mie term buries the Rayleigh one. - **`skyIntensity` starts at 0.55.** At 1.0 the noon horizon clips to a flat band of pure white across the frame. `skyIntensity` scales the sky alone and leaves aerial perspective on the geometry untouched, which is why it is the right knob and `exposure` is not. - **The flare threshold starts at 2.6, not the default 0.75.** At noon on gypsum most of the frame is above 0.75, and the lens-optics pass at that threshold flares the GROUND. At 2.6 only the solar disc reaches it. ## The grade pass `GRADE_WGSL` is a fullscreen post-process registered from inline WGSL rather than from a `.shader` asset, so it lives exactly as long as the component that registered it and leaves nothing in the world tree. The frame arriving at it is already display-referred, so it does not tonemap — it rolls the top end off above 0.80, then does contrast, saturation, a split tone, a shadow lift and a vignette. A second tonemap here was tried and takes a correct noon down to dusk.

# filmClock <!-- zero:scaffolded-readme --> <!-- Replace the line below with what this module provides and who consumes it, then delete both comment lines. --> TODO: describe this module.