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Using VRF

Official documentation The usage tutorial is under Getting Started Look up the parameters for each network under Supported Networks

Sample Code​

Remix sample code

Triggering a Request and Generating a requestId​

uint256 requestId = s_vrfCoordinator.requestRandomWords(
    VRFV2PlusClient.RandomWordsRequest({
        keyHash: i_gasLane, // the maximum gas price tier
        subId: i_subscriptionId, // subscription id
        requestConfirmations: REQUEST_CONFIRMATIONS, // how many Chainlink nodes must confirm it
        callbackGasLimit: i_callbackGasLimit,  // the maximum gas the callback (fulfill) method may consume
        numWords: NUM_WORDS,               // the number of random words to request back
        extraArgs: VRFV2PlusClient._argsToBytes(
            VRFV2PlusClient.ExtraArgsV1({nativePayment: false})  // whether to pay with LINK or with eth
        )
    })
);

Detailed parameter explanations: https://docs.chain.link/vrf/v2-5/getting-started#contract-variables Note also that different networks impose maximum limits on certain parameters

Fulfilling the Random Words​

function fulfillRandomWords(
    uint256,
    uint256[] calldata randomWords
) internal override {
    uint256 indexOfWinner = (randomWords[0] % s_players.length);
    address payable winner = s_players[indexOfWinner];
    s_recentWinner = winner;
}

Operating Instructions​

Create a Subscription​

Dashboard: https://vrf.chain.link/ Click Create Subscription Fill in the corresponding information for email and program name, then click Create The wallet pops up to sign, then wait for confirmation

Add Funds​

Add LINK to the subscription

Add a Consumer​

Add our contract address to the subscription as a consumer

Faucet Address​

https://faucets.chain.link/sepolia

Installing Dependencies​

Chainlink VRF 2.5 project repository: https://github.com/smartcontractkit/chainlink-brownie-contracts

forge install /smartcontractkit/chainlink-brownie-contracts

My own forked repository: https://github.com/minner-fun/chainlink-brownie-contracts/tree/fix/vrfV2_5Mock Because the official V2_5Mock file throws a constructor-argument error, I made a small change and added an unused parameter to the constructor

// lib\chainlink-brownie-contracts\contracts\src\v0.8\vrf\mocks\VRFCoordinatorV2_5Mock.sol
constructor(uint96 _baseFee, uint96 _gasPrice, int256 _weiPerUnitLink) SubscriptionAPI(msg.sender) {
i_base_fee = _baseFee;
i_gas_price = _gasPrice;
i_wei_per_unit_link = _weiPerUnitLink;
setConfig();
}

//lib\chainlink-brownie-contracts\contracts\src\v0.8\vrf\dev\SubscriptionAPI.sol
constructor(address _sender) ConfirmedOwner(msg.sender) {
address sender = _sender;
}

Mock​

You need to deploy VRFCoordinatorV2_5Mock and LinkToken. Practical example

Creating a Subscription, Funding It, and Adding a Consumer​

When debugging on a local chain you need the full set of VRF functionality. Practical example

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