81 lines
2.8 KiB
TypeScript
81 lines
2.8 KiB
TypeScript
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import type { Cue } from "./data";
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/**
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* How one node looks at one instant. The animation functions below produce
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* these, and Transect.tsx only draws them, so adding a property here (a colour,
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* a stroke, a glow) is the only change the drawing needs to follow.
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*/
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export type NodeLook = {
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radius: number;
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opacity: number;
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};
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/**
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* A node that is not being sung. Radius is in map units (the page's pixels),
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* so nodes grow with the camera's zoom. (The page itself uses 3 at 0.85.)
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*/
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export const RESTING: NodeLook = { radius: 2.5, opacity: 0.9 };
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/** A node while its line is sung: the page's selected mark. */
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export const LIT: NodeLook = { radius: 7, opacity: 1 };
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const clamp01 = (v: number) => Math.min(1, Math.max(0, v));
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/** Slightly slower lighting up and switching off. Relatively slower decay. */
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const LIGHT_UP_S = 0.12;
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const SWITCH_OFF_S = 0.5;
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/** Blend two looks; p = 0 is `from`, p = 1 is `to`. */
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export const mixLooks = (from: NodeLook, to: NodeLook, p: number): NodeLook => ({
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radius: from.radius + (to.radius - from.radius) * p,
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opacity: from.opacity + (to.opacity - from.opacity) * p,
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});
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/**
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* A node being switched on.
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* @param elapsedS seconds since its line started (0 at the lyric timestamp)
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* @param from the look it starts from
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*/
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export const lightUp = (elapsedS: number, from: NodeLook = RESTING): NodeLook =>
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mixLooks(from, LIT, clamp01(elapsedS / LIGHT_UP_S));
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/**
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* A node being switched off.
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* @param elapsedS seconds since its line ended (0 at the next lyric timestamp)
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* @param from the look it had when it was switched off
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*/
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export const switchOff = (elapsedS: number, from: NodeLook = LIT): NodeLook =>
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mixLooks(from, RESTING, clamp01(elapsedS / SWITCH_OFF_S));
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/** Longest a node holds fully lit, after lighting up, before it switches off. */
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export const MAX_LIT_S = 0.9;
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/**
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* When a cue's nodes start switching off: when the line ends, or once they have
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* lit up and held for MAX_LIT_S, whichever comes first, so a long line does not
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* keep a node lit for too long.
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*/
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export const switchOffAt = (cue: Cue): number =>
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Math.min(cue.stopS, cue.startS + LIGHT_UP_S + MAX_LIT_S);
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/**
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* The look of a node at time `t`, given the cue that lights it (or none).
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* Before the line: resting. Then lighting up until switchOffAt(). After that:
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* switching off, starting from however far the light-up got, so a short line
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* never jumps.
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*/
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export const nodeLookAt = (cue: Cue | undefined, t: number): NodeLook => {
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if (!cue || t < cue.startS) {
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return RESTING;
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}
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const offS = switchOffAt(cue);
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if (t < offS) {
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return lightUp(t - cue.startS);
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}
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return switchOff(t - offS, lightUp(offS - cue.startS));
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};
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/** Whether a look is anything other than resting (drawn on top if so). */
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export const isAwake = (look: NodeLook): boolean =>
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look.radius !== RESTING.radius || look.opacity !== RESTING.opacity;
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