precision-game/js/behaviours/sine_y.mjs

import { register_behaviour } from "./core.mjs";

import * as entity from "../entity.mjs";
import { underride } from "../underride.mjs";



register_behaviour("sine_y", {
	tick: (enemy, deltatime) => {
		const {x} = entity.get_pos(enemy);

		const meta = entity.get_meta(enemy);
		const age = meta.get("age");

		// `movement_speed` is in hertz and `Math.sin` input is in radians.
		const age_factor = meta.get("movement_speed") * Math.PI * 2;
		const offset = meta.get("offset") * Math.PI * 2;
		const y = meta.get("center_y") + Math.sin(age * age_factor + offset) * meta.get("movement_scale");

		entity.set_pos(enemy, x, y);
	},
	init: (enemy, params = {}) => {
		params = underride(params, {
			movement_scale: 100,
			movement_speed: 1/4,
			offset: 0,
		});

		const {y} = entity.get_pos(enemy);

		const meta = entity.get_meta(enemy);

		meta.set("center_y", y);

		meta.set("movement_scale", params.movement_scale);
		meta.set("movement_speed", params.movement_speed);
		meta.set("offset", params.offset);
	},
});