gacha

Node Gacha

Given a database of items with variable drop rates, determine the odds of an item being dropped on a particular level.

npm install gacha

Eventually we'll offer a few systems of gacha. For now we only support "roguelike".

Roguelike Usage

var gacha = require('gacha');

var items = {
  "101": {
    "name": "Knife",
    "level": 1,
    "weight": 1.0,
    "spread": 1
  },
  "102": {
    "name": "Sword",
    "level": 2,
    "weight": 1.0,
    "spread": 2
  },
  "103": {
    "name": "Rapier",
    "level": 3,
    "weight": 3.0,
    "spread": 3
  }
};

var result = gacha.roguelike(items);

console.log(result); // Shown Below

// Which item should we spawn on level 3?
var random = Math.random() * result[3].total;

for (var i = 0; i < result[3].strata.length; i++) {
  if (random < result[3].strata[i]) {
    var id = result[3].lookup[i];
    console.log(items[id]);
    break;
  }
}

Result

{
  "0": {
    "lookup": [ "101", "102", "103" ],
    "strata": [ 0.24197072451914337, 0.3457475988742921, 0.4485344854101383 ],
    "total": 0.4485344854101383
  },
  "1": {
    "lookup": [ "101", "102", "103" ],
    "strata": [ 0.3989422804014327, 0.6186379251352939, 0.8551480729542124 ],
    "total": 0.8551480729542124
  },
  "2": {
    "lookup": [ "101", "102", "103" ],
    "strata": [ 0.24197072451914337, 0.5240655162930214, 0.9140048277385038 ],
    "total": 0.9140048277385038
  },
  "3": {
    "lookup": [ "102", "103" ],
    "strata": [ 0.2196956447338612, 0.6803545106956419 ],
    "total": 0.6803545106956419
  },
  "4": {
    "lookup": [ "102", "103" ],
    "strata": [ 0.10377687435514871, 0.493716185800631 ],
    "total": 0.493716185800631
  },
  "5": {
    "lookup": [ "103" ],
    "strata": [ 0.2365101478189184 ],
    "total": 0.2365101478189184
  },
  "6": {
    "lookup": [ "103" ],
    "strata": [ 0.1027868865358462 ],
    "total": 0.1027868865358462
  }
}