# film The clock, the shot table and the palettes of GREEN SKY. Every other slice talks to this module and to nothing else. ## The clock A fixed **1/24 s per rendered frame**, ignoring the real frame delta. The film is therefore byte-identical on every run whatever the frame rate, so it can be recorded a frame at a time and retimed on the host. Film.FPS 24 Film.FIXED_DT 1/24 Film.DURATION 122 seconds `scenes/main.scene`'s entrypoint calls `Film.build()` once on load and `Film.tick()` once per frame. There is no cutscene, no coroutine timeline and no `task.wait` chain anywhere in the demo. ## The shot table `Film.SHOTS` — eighteen entries, `{ n, seconds, act, name, brief }`. `seconds` is the only timing authority in the film; `greensky/camera` owns where each set-up stands. Shot numbers are stable and are never renumbered, because every slice keys off them. Film.shotAt(t) -> the shot on screen at t, and seconds into it Film.shotStart(n) -> when shot n begins ## Registering a slice local Film = require("greensky.film") local M = {} function M.build() end -- once, on scene load function M.update(c) end -- every frame Film.register("pan", M, 10) -- lower order ticks first The context `c` every update receives: | field | meaning | |---|---| | `t` / `u` | film seconds, and 0..1 across the whole film | | `dt` | always `FIXED_DT` | | `frame` | integer frame counter from 0 | | `shot` / `shotT` / `shotU` | the shot on screen, and progress through it | | `cut` | true on the first frame of a new shot | | `act` | 1, 2 or 3 | | `storm` / `flood` / `clear` | the three progressions, 0..1 | `Film.arcAt(t)` gives those last three at any time, so a slice can ask what act III looks like without waiting for it. ## Two palettes, and they are not the same thing **`Film.PALETTE`** is the **light** — what the sun, the sky and the ambient are doing in the world, per act, plus the discharge. `greensky/sky` reads it every frame. **`Film.PAL`** is the **photograph taken of that light** — the response of the camera's negative, per act. `greensky/camera` reads it every frame and writes it into the `gs_grade` post-process pass. Its fields are `ev` (exposure compensation in stops), `exposure`, `contrast`, `pivot`, `saturation`, `vignette`, `vigInner`, `grain`, and the ASC-CDL triplets `lift` (offset, moves the blacks), `gain` (slope, the whites) and `gamma` (power, the mids). Both carry `dry`, `storm`, `clear` and `flash`, and both are interpolated by the same `c.storm` / `c.clear` ramps, so the light and the photograph of it always agree about which act it is. `Film.mixGrade(a, b, x)` mixes two `Film.PAL` entries. Every `gain` in `Film.PAL` is at or below 1 on purpose: the post chain is display-referred and hard-clipped at 1.0, so a gain above 1 clips the image rather than opening it up. Level lives in `ev`, in stops. ## The site `Film.SITE` — the numbers more than one slice needs about the place: pan radius, runway length and width, hangar position, cloud base and top, the cloud volume's horizontal extent, where the storm enters and leaves, and how deep the flood gets. Everything must live inside 8 km of every camera station, because the far plane is hard-fixed at 8000. ## Curves Film.ramp(t, a, b) smoothstep, 0 before a and 1 after b Film.lerp(a, b, x) Film.mix3(a, b, x) mix two {r, g, b} Film.clamp01(x) ## Files film.module/init.luau this module ../design/spec.md read this before changing any of it ../design/shotlist.md the eighteen shots as written

# gliders Three sailplanes over the salt pan, and the whole 122 seconds of flying they do. KILO is the lead ship the film keeps returning to; BRAVO and CHARLIE are already airborne when the film opens and join KILO for the last pass. They are the demo's only scale reference — a 15-metre wing against a 4.5-kilometre cloud. ## What it provides ```lua local Gliders = require("greensky.gliders") Gliders.SHIPS -- { "KILO", "BRAVO", "CHARLIE" } Gliders.poseAt(ship, t) -- -> position {x,y,z}, forward {x,y,z} Gliders.poseFull(ship, t) -- + speed, yaw, pitch, bank, rates, load Gliders.posAt(ship, t) -- -> x, y, z Gliders.tipAt(ship, side, t) -- a wingtip, side = -1 port / +1 starboard ``` Every one of them is a **pure function of film time**. They answer for any `t` in `0 .. Film.DURATION`, they read no entity, and they do not care whether the slice has been ticked — which is what lets the camera slice call `poseAt` from inside its own update to frame and ride a ship. `greensky/camera` uses this for shots 3, 9 and 12. ## How a ship is animated One authored key table per ship, evaluated as a monotone cubic Hermite spline. Everything else is a derivative of it, so there is no second animation to keep in sync and no way for the attitude to disagree with the path: | what | from | |---|---| | forward | normalised `dp/dt` | | pitch | `asin(forward.y)` | | bank | `atan(speed * dyaw/dt / g)` — a real coordinated turn | | ailerons | `dbank/dt`, opposite sides | | elevator | `dpitch/dt` | | rudder | `dyaw/dt` | | wing flex | load factor `1/cos(bank)` | | wingtip vapour | load factor, gated by humidity | Rates are read over a 0.75 s window. A cubic spline's second derivative ripples inside every segment, so a turn rate read at velocity resolution makes a steady thermal turn look like a shiver; 0.75 s is also about how long an aircraft takes to change bank, so the smoothing is the physics rather than a cover for it. On top of the path — never in it — the cell throws the ships about from the gust front to the last of the rain, and the pilots work against it. The route the camera reads stays exactly where it was authored. ## Where they are | film time | KILO | |---|---| | 0 – 6.4 | parked at the west end of the strip, nose east, one wingtip a hand off the concrete | | 6.4 – 12.4 | the ground roll: 130 m of concrete, wing level by t = 10.4 | | 12.4 | rotation and lift-off | | 12.4 – 17.5 | climb-out, easing right off the centreline | | 17.5 – 39.2 | the thermal: a 110 m circle at 30 m/s, 42 degrees of bank, climbing 12 m/s | | 39.2 – 55 | east along the gust front, through the 700 m cloud base at exactly t = 55 | | 55 – 76 | inside the mass, climbing to 1,370 m, then turning north and coming down | | 76 – 99 | out into the rain, descending across the pan | | 99 – 106 | a hard diving turn, wings coming level pointing due south | | 106 – 122 | the low pass: 68 m/s, 90 m off the flood, all three ships in line | BRAVO and CHARLIE fly their own thermals — wider and tighter respectively, at their own altitudes — until KILO leaves the turn at t = 39.2. All three exit on the same heading, and from there the wingmen hold a station on KILO that eases into their slot in the final line. ## The airframe Twelve entities under each ship's root, built nose along **+Z**, span along **±X**, up along **+Y**. Fuselage, nose, canopy, two wing panels with 3.5 degrees of dihedral, two ailerons, a tailplane, a fin, a rudder, and a wingtip entity each side carrying a `TrailRenderer` for the vapour. The root's rotation is `yaw(+Y) * pitch(+X) * roll(+Z)`, composed with `Transform.quatFromAxisAngle` and `Transform.quatMul`. This pass is a greybox: one flat material, no textures, silhouette only.