Batch NFT reveal

This repository contains a gas-efficient implementation of an on-chain shuffling algorithm used to reveal NFTs in batches. The main benefits of this over other NFT randomization methods are:

• Makes the loop between buying and seeing your NFT revealed much faster, which improves experience
• Keeps attention up through the sale, as new NFTs keep being revealed, instead of just having a single peak of attention at start/reveal
• Reduces the need to have unrevealed NFTs up for sale, thus making it harder for people to get rarity sniped

For a survey of other ways to randomize NFTs, an analysis on them and an explanation of the algorithm used here, please read randomness.md.

Usage

1. Copy contracts/BatchReveal.sol into your project
2. Change TOKEN_LIMIT (maximum amount of tokens to be minted in your sale) and REVEAL_BATCH_SIZE (amount of tokens that to be revealed in each reveal)
3. Import BatchReveal into your contract, call setBatchSeed(randomNumber) to provide randomness for each batch, and modify tokenURI(id) to use getShuffledTokenId(id)

Please make sure that the following constraints are met:

• REVEAL_BATCH_SIZE can divide TOKEN_LIMIT (TOKEN_LIMIT % REVEAL_BATCH_SIZE = 0)
• Total amount of batches (calculated as TOKEN_LIMIT / REVEAL_BATCH_SIZE) should be equal or lower than 117, otherwise you might run into the gas limit

Examples

There are two production ready examples in the contracts/examples folder:

• Chainlink.sol uses chainlink's VRF as source of randomness.
• Blockhash.sol uses block hashes as source of randomness.

Apart from those, here's the most basic example (not suitable for production):

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/utils/Strings.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "../BatchReveal.sol";

contract Example is ERC721, BatchReveal {
    using Strings for uint256;

    string public baseURI;
    string public unrevealedURI;

    constructor(string memory _baseURI, string memory _unrevealedURI)
        ERC721("Mock NFT", "MNFT")
    {
        unrevealedURI = _unrevealedURI;
        baseURI = _baseURI;
    }

    function provideRandomness(uint randomNumber) public {
        setBatchSeed(randomNumber);
    }

    function tokenURI(uint256 id) public view override returns (string memory) {
        if(id >= lastTokenRevealed){
            return unrevealedURI;
        } else {
            return string(abi.encodePacked(baseURI, getShuffledTokenId(id).toString()));
        }
    }
}

License

All code has been licensed under CC0, just like tubby cats themselves.