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
• CONTRACT_SYMBOL
• ETHERSCAN_API_KEY
  • which can be obtained from your Etherscan account.

Then, just run yarn hardhat run deploy/asset.ts --network 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 quantity, bytes mintingBlob). Note that this is a different function signature to _mintFor in the previous example. 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 quantity,
        bytes calldata mintingBlob
    ) external override {
        // TODO: make sure only Immutable X can call this function
        // TODO: mint the token!
    }

}

Registration.sol & IMX.sol is for reference purposes if you choose to offer these functions in your own smart contracts and is not required if you only want to deploy an ERC721.

Verification with Etherscan should happen automatically within a few minutes of contract deployment, but if it fails you can run it manually, eg

yarn hardhat verify --network <network> <address> <args used in deployment>

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