Installation: npm install @imtbl/imx-contracts or yarn add @imtbl/imx-contracts.

Immutable X is the only NFT scaling protocol that supports minting assets on L2, and having those assets be trustlessly withdrawable to Ethereum L1. To enable this, before you can mint on L2, you need to deploy an IMX-compatible ERC721 contract as the potential L1 home for these assets. Luckily, making an ERC721 contract IMX-compatible is easy!

In the test environment, deploying an ERC721 contract which is compatible with Immutable X is extremely easy. First, update the .env file, setting CONTRACT_OWNER_ADDRESS, CONTRACT_NAME, and CONTRACT_SYMBOL. Then, just run yarn run simple-deploy-ropsten.

If you're starting from scratch, simply deploy a new instance of Asset.sol and you'll have an L2-mintable ERC721 contract. Set the _imx parameter in the contract constructor to either the Public Test or Production addresses as above.

If you already have an ERC721 contract written, simply add Mintable.sol as an ancestor, implement the _mintFor function with your internal mint function, and set up the constructor as above:

import "@imtbl/imx-contracts/contracts/Mintable.sol";

contract YourContract is Mintable {

    constructor(address _imx) Mintable(_imx) {}

    function _mintFor(
        address to,
        uint256 id,
        bytes calldata blueprint
    ) internal override {
        // TODO: mint the token using your existing implementation
    }

}

To enable L2 minting, your contract must implement the IMintable.sol interface with a function which mints the corresponding L1 NFT. This function is mintFor(address to, uint256 id, bytes blueprint). The "blueprint" is the immutable metadata set by the minting application at the time of asset creation. This blueprint can store the IPFS hash of the asset, or some of the asset's properties, or anything a minting application deems valuable. You can use a custom implementation of the mintFor function to do whatever you like with the blueprint.

Your contract also needs to have an owner() function which returns an address. You must be able to sign a message with this address, which is used to link this contract your off-chain application (so you can authorise L2 mints). A simple way to do this is using the OpenZeppelin Ownable contract (npm install @openzeppelin/contracts).

import "@imtbl/imx-contracts/contracts/Mintable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract YourContract is IMintable, Ownable {

    function mintFor(
        address to,
        uint256 id,
        bytes calldata blueprint
    ) external override {
        // TODO: make sure only Immutable X can call this function
        // TODO: mint the token!
    }

}

Deploy to ropsten, change to dev/mainnet if required

yarn deploy-registration --network ropsten

If validation fails you can run it manually, eg

yarn hardhat verify --network mainnet 0x72a06bf2a1CE5e39cBA06c0CAb824960B587d64c 0x5FDCCA53617f4d2b9134B29090C87D01058e27e9

Run yarn compile. The output can be found in the artifacts/typechain folder.