Identicon

The package implements flexible generation of identicons using the Juicy Pixels package. It’s reasonably fast for my taste, and since identicons are usually not bigger than 420 × 420 pixels, I think that sequential generation that JuicyPixels supports fits the task very well.

Quick start

To use the package you usually need the following set of imports (and a couple of language extensions for type level magic):

{-# LANGUAGE DataKinds     #-}
{-# LANGUAGE TypeOperators #-}

import Codec.Picture -- JuicyPixels
import Data.ByteString (ByteString) -- we use strict byte strings
import Data.Proxy
import Data.Word (Word8)
import Graphics.Identicon -- core definitions
import Graphics.Identicon.Primitive -- some visual primitives

You first write a type that has information about total number of bytes your identicon consumes and number of distinct visual components it has (it’s called “layers” in terminology of the package):

type MyIcon = Identicon 12 :+ Consumer 4 :+ Consumer 4 :+ Consumer 4

Here we have an identicon that needs 12 bytes to be generated. It has three consumers that take 4 bytes each and generate layers, i.e. visual objects (circles, squares, etc.).

The second step is to write implementation of every layer. We can use primitives available out-of-box, they live in the Graphics.Identicon.Primitive module:

myImpl :: Implementation MyIcon
myImpl = Identicon :+ a :+ a :+ a
  where
    a :: Word8 -> Word8 -> Word8 -> Word8 -> Layer
    a r g b n = rsym $ onGrid 3 3 n $
      gradientXY (edge . mid) black (PixelRGB8 r g b)

We could choose to code every layer differently, but since position and color of every layer are unlikely to be the same, this approach will work well too.

Every byte is available to layer-generating function as a distinct Word8 argument. The type system makes sure that:

• you consume exactly as many bytes as you promised in type of your identicon;

• you have as many layers as you described in type of your identicon;

• every function in your implementation has correct signature (i.e. it grabs as many Word8s as promised and produces a Layer in the end).

Mixing of layers and generation is handled by the library like this:

-- | Here is the function that generates your identicons. It's usually
-- convenient to wrap the 'renderIdenticon' function that comes with the
-- library.

genMyIdenticon
  :: Int               -- ^ Identicon width
  -> Int               -- ^ Identicon height
  -> ByteString        -- ^ Input (some sort of hash or something)
  -> Maybe (Image PixelRGB8)
     -- ^ Identicon, unless 'ByteString' is too short
genMyIdenticon = renderIdenticon (Proxy :: Proxy MyIcon) myImpl

For more information head straight to Haddocks. BTW, I have written a blog post about the package where I demonstrate some pictures generated with it.

License

Copyright © 2016 Mark Karpov

Distributed under BSD 3 clause license.