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Avatars & identicons

Summary. Every account gets a distinctive avatar with no upload and no server storage: a two-tone gradient deterministically derived from the public key, with the Grin mark or the person’s initial on top. The derivation is byte-identical across platforms.

Motivation

Faces make a contact list scannable. But hosting user images means storage, moderation, and a privacy leak (who fetched whose picture, from where). Goblin sidesteps all of it: an avatar is a pure function of the pubkey, computed on the device. Same key → same avatar, on every platform, forever, so you recognize a contact by their colors even before a name resolves.

How it works

The pubkey (normalized to lowercase hex) is hashed with SHA-256; bytes of that hash choose two hues, a blend offset, and a gradient angle (HSL→RGB, all in f64 so independent ports produce identical bytes). The result is rendered as an SVG gradient. On top:

  • a letter (the contact’s initial) for named users, or
  • the Grin mark for anonymous keys.

When a contact does publish a picture in their Nostr profile, Goblin can render that instead; otherwise the deterministic gradient is the fallback, so there is always an avatar. The eight theme avatar pairs supply complementary ink colors so initials stay legible.

Reference

  • goblin/src/gui/views/goblin/identicon.rs: to_hex_seed(), gradient_params() (SHA-256 → hues/angle), gradient_bg_svg(), gradient_avatar_svg() (gradient + Grin mark), GRIN_PATH, LOGO_FRAC, LOGO_OPACITY.
  • goblin/src/gui/views/goblin/widgets.rs: avatar(), gradient_avatar(), gradient_letter_avatar(), avatar_any() (dispatch to the best available avatar).
  • Picture handling/processing: goblin/src/nostr/avatar.rs (format sniff, square-crop, resize, metadata strip).

References