Isle-Slingers/js/physics/aim/index.js

/* ISLE SLINGERS -- physics/aim/index.js (submodule: aim)
 * Modularization pass (behavior-neutral split of the original
 * js/core.js monolith). Installs its units into ONE shared physics scope `P`
 * that every physics submodule sees -- the same single-scope semantics the
 * monolith had. Must load before js/physics/index.js (the aggregator that
 * attaches the public ISLE_CORE API). Surface installed: aimVector, trajectory.
 */
(function (root, factory) {
  var part = factory();
  if (typeof module !== 'undefined' && module.exports) module.exports = part;
  else (root.ISLE_PHYSICS_PARTS = root.ISLE_PHYSICS_PARTS || []).push(part);
})(typeof globalThis !== 'undefined' ? globalThis : this, function () {
  'use strict';
  return function (P) {
  P.aimVector = function(g, sling, drag) {
    var dx = sling.x - drag.x, dy = sling.y - drag.y;
    var len = Math.sqrt(dx * dx + dy * dy);
    if (len < P.MIN_PULL) return null;
    var cl = Math.min(len, P.MAX_PULL);
    var v = cl * P.LAUNCH_POWER;
    return { vx: (dx / len) * v, vy: (dy / len) * v, pull: cl };
  }

  // Pure P.trajectory preview: identical integrator + substepping as the live
   // sim (2x 1/120 per output point), so the dotted preview matches the real
   // flight exactly. Gravity + drag only; stops at the ground.
   P.trajectory = function(g, sx, sy, vx, vy, steps) {
     var pts = [];
     var x = sx, y = sy, i, sub;
     for (i = 0; i < steps; i++) {
       for (sub = 0; sub < 2; sub++) {
         var dt = 1 / 120;
         var nvy = vy + P.GRAVITY * dt;
         x += vx * dt;
         y += (vy + nvy) * 0.5 * dt;
         vx *= P.AIR_DRAG;
         vy = nvy;
       }
       if (y > P.WORLD.ground - 18) { pts.push({ x: x, y: P.WORLD.ground - 18, last: true }); break; }
       pts.push({ x: x, y: y, last: false });
     }
     return pts;
   }
  };
});