Overview of ERC721
Alternatively, we may store JSON metadata and token images on-chain. This is very expensive of course (saving data on-chain is the most expensive operation in Ethereum), but we can make it cheaper if we store templates. All tokens within a collection have similar metadata (mostly identical but image links and properties are different for each token) and visuals. For the latter, we can use SVG, which is an HTML-like format, and HTML is a good templating language.
When storing JSON metadata and SVG on-chain, the tokenURI function, instead of returning a link, would return JSON metadata directly, using the data URI scheme to encode it. SVG images would also be inlined, it won’t be necessary to make external requests to download token metadata and images.
NFT ManagerContract
NFT Renderer
Now we need to build an NFT renderer: a library that will handle calls to tokenURI in the NFT manager contract. It will render JSON metadata and an SVG for each minted token. As we discussed earlier, we’ll use the data URI format, which requires base64 encoding–this means we’ll need a base64 encoder in Solidity. But first, let’s look at what our tokens will look like.
Code
Check repo