Day night cycle

common/time.ts

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+// the day and night cycle. world time counts ticks since 06:00 of day 1, it never wraps around
+import { TICKS_PER_SECOND } from "./constants.ts";
+
+// 30 minutes of day, 06:00 to 18:00
+export const DAY_TICKS = 30 * 60 * TICKS_PER_SECOND;
+// 10 minutes of night, 18:00 to 06:00
+export const NIGHT_TICKS = 10 * 60 * TICKS_PER_SECOND;
+export const CYCLE_TICKS = DAY_TICKS + NIGHT_TICKS;
+// dusk right after sunset and dawn right before sunrise, so the whole day is bright
+export const TWILIGHT_TICKS = 60 * TICKS_PER_SECOND;
+
+// in game hours are longer during the day than at night, since both halves are 12 hours
+const DAY_TICKS_PER_HOUR = DAY_TICKS / 12;
+const NIGHT_TICKS_PER_HOUR = NIGHT_TICKS / 12;
+// from midnight to 06:00, to count days from midnight
+const TICKS_BEFORE_SIX = 6 * NIGHT_TICKS_PER_HOUR;
+
+// named times of day, as ticks into the cycle
+export const TIMES_OF_DAY: Record<string, number> = {
+	day: 0,
+	noon: 6 * DAY_TICKS_PER_HOUR,
+	sunset: DAY_TICKS,
+	night: DAY_TICKS + TWILIGHT_TICKS,
+	midnight: DAY_TICKS + 6 * NIGHT_TICKS_PER_HOUR,
+};
+
+// ticks into the current cycle, 0 is 06:00
+export function time_of_day(time: number): number {
+	return ((time % CYCLE_TICKS) + CYCLE_TICKS) % CYCLE_TICKS;
+}
+
+export function is_day(time: number): boolean {
+	return time_of_day(time) < DAY_TICKS;
+}
+
+// the day number, starting at 1 and going up at midnight, and the time on a 24 hour clock
+export function clock(time: number): { day: number; hour: number; minute: number } {
+	const t = time_of_day(time);
+	const hours = t < DAY_TICKS ? 6 + t / DAY_TICKS_PER_HOUR : 18 + (t - DAY_TICKS) / NIGHT_TICKS_PER_HOUR;
+	const total_minutes = Math.floor(hours * 60) % (24 * 60);
+	return {
+		day: Math.floor((time + TICKS_BEFORE_SIX) / CYCLE_TICKS) + 1,
+		hour: Math.floor(total_minutes / 60),
+		minute: total_minutes % 60,
+	};
+}
+
+// like "Day 3, 14:05"
+export function format_clock(time: number): string {
+	const { day, hour, minute } = clock(time);
+	return `Day ${day}, ${String(hour).padStart(2, "0")}:${String(minute).padStart(2, "0")}`;
+}
+
+// how much daylight there is, 1 all day and 0 in the middle of the night, fading through dusk and dawn.
+// time can be fractional, for drawing between ticks
+export function daylight(time: number): number {
+	const t = time_of_day(time);
+	if (t < DAY_TICKS) return 1;
+	const into_night = t - DAY_TICKS;
+	const until_day = CYCLE_TICKS - t;
+	const fade = Math.min(1, into_night / TWILIGHT_TICKS, until_day / TWILIGHT_TICKS);
+	return 1 - smoothstep(fade);
+}
+
+function smoothstep(x: number) {
+	return x * x * (3 - 2 * x);
+}