In this blog post, we are continuing to play with Haskell's diagrams library. We will write a literate Haskell program to generate an OpenGraph image.
Motivation
I am told that my Website pages should have OpenGraph images. So, I stopped worrying about not worrying about content, and I started worrying about not having an OpenGraph image.
So, let's do one.
Program
We will use the 3 Haskell packages for this Literate Haskell program like before: diagrams, diagrams-cairo and markdown-unlit.
Let's import a few modules.
import Diagrams.Backend.Cairo
import Diagrams.Prelude
import System.Environment (getArgs)
Now, our entry point what will render an OpenGraph image with size 1200x630
and extension .png
:
main :: IO ()
main = do
dir <- head <$> getArgs
logo <- loadLogo
render dir "og.png" (og "thenegation.com" "by Vehbi Sinan Tunalioglu" logo)
where
render dpath fname = renderCairo (dpath <> "/" <> fname) (mkSizeSpec2D (Just 1200) (Just 630))
This is how we will run our blog post:
runhaskell \
-pgmLmarkdown-unlit \
content/posts/2024-08-12_haskell-diagrams-og.lhs \
static/assets/media/posts/haskell-diagrams-og
Let's load my Website's logo image inside a Diagram B
value. We are scaling the diagram to 24
:
loadLogo :: IO (Diagram B)
loadLogo = do
(Right img) <- loadImageEmb "./static/android-chrome-512x512.png"
pure $ scaleUToX 24 $ image img
Let's create a function to clip a given image in a circle. We will use the clipBy
function to achieve this. Since our square image is scaled to 24
, We are using a circle with a radius of 12
:
mkAvatar :: Diagram B -> Diagram B
mkAvatar =
clipBy (circle 12)
Let's put some large text and then some smaller text under the avatar image to compose our OpenGraph image. Note that we use a canvas of 120x63
, which is proportional to the OpenGraph image size of 1200x630
and play with arbitrary colours:
og :: String -> String -> Diagram B -> Diagram B
og txtB txtS img =
logotype `atop` (rect 120 63 # fc (sRGB24read "#e4e4e7") # lw none)
where
logotype =
center $ vsep 9
[ mkAvatar img
, text txtB # bold # fontSizeL 6 # fc (sRGB24read "#09090b")
, text txtS # fontSizeL 4.27 # fc (sRGB24read "#18181b")
]
That's all! Let's see how PNG image looks like:
Wrap-Up
We have created an OpenGraph image for my Website. The next challange will be to add my blog post title and description to the image dynamically. I am not sure how to do that yet, especially with flowing text.
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