25 lines
874 B
TypeScript
25 lines
874 B
TypeScript
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/**
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* Slideshow speeds for the lightbox (#473).
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*
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* Three speeds and off, cycled by one key, so a gallery can be left running at
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* an exhibition, a fair booth or on a second screen without the viewer growing
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* a control of its own.
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*/
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/** Seconds between advances, slowest last. `null` is off. */
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export const SLIDESHOW_SPEEDS = [null, 3, 5, 10] as const;
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export type SlideshowSpeed = (typeof SLIDESHOW_SPEEDS)[number];
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/**
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* The next speed in the cycle: off → 3s → 5s → 10s → off.
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*
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* An unrecognised value returns the first speed, so the cycle can always be
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* re-entered rather than sticking.
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*/
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export function nextSlideshowSpeed(current: SlideshowSpeed): SlideshowSpeed {
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const position = SLIDESHOW_SPEEDS.indexOf(current);
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if (position === -1) return SLIDESHOW_SPEEDS[1];
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return SLIDESHOW_SPEEDS[(position + 1) % SLIDESHOW_SPEEDS.length];
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}
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