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Dynamically Generating OpenGraph Images With Hugo 2024-02-19T04:12:27Z Using Hugo built-in functions to dynamically generate OpenGraph share images for every post. false true hugo-logo-wide.png Backstage
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I've lately seen some folks on social.lol posting about their various strategies for automatically generating Open Graph images for their Eleventy sites. So this weekend I started exploring how I could do that for my Hugo site1.

During my search, I came across a few different approaches using external services or additional scripts to run at build time, but I was hoping for a way to do this with Hugo's built-in tooling. I eventually came across a tremendously helpful post from Aaro titled Generating OpenGraph images with Hugo. This solution was exactly what I was after, as it uses Hugo's image functions to dynamically create a share image for each page.

I ended up borrowing heavily from Aaro's approach while adding a few small variations for my OpenGraph images.

  • When sharing the home page, the image includes the site description.
  • When sharing a post, the image includes the post title.
  • ... and if the post has a thumbnail2 listed in the front matter, that gets overlaid in the corner.

Here's how I did it.

New resources

Based on Aaro's suggestions, I used GIMP to create a 1200x600 image for the base. I'm not a graphic designer3 so I kept it simple while trying to match the site's theme.

I had to install the Fira Mono font Fira Mono .ttf to my ~/.fonts/ folder so I could use it in GIMP, and I wound up with a decent recreation of the little "logo" at the top of the page.

Red background with a command prompt displaying "[runtimeterror.dev] $" in white and red font.

That fits with the vibe of the site, and leaves plenty of room for text to be added to the image.

I also wanted to use that font later for the text overlay, so I stashed both of those resources in my assets/ folder:

File explorer window showing a directory structure with folders such as '.github/workflows', 'archetypes', 'assets' with subfolders 'css', 'js', and files 'FiraMono-Regular.ttf', 'og_base.png' under 'RUNTIMETERROR'.

OpenGraph partial

Hugo uses an internal template for rendering OpenGraph properties by default. I needed to import that as a partial so that I could override its behavior. So I dropped the following in layouts/partials/opengraph.html as a starting point:

// torchlight! {"lineNumbers": true}
<meta property="og:title" content="{{ .Title }}" />
<meta property="og:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}" />
<meta property="og:type" content="{{ if .IsPage }}article{{ else }}website{{ end }}" />
<meta property="og:url" content="{{ .Permalink }}" />
<meta property="og:locale" content="{{ .Lang }}" />

{{- if .IsPage }}
  {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
  <meta property="article:section" content="{{ .Section }}" />
  {{ with .PublishDate }}<meta property="article:published_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
  {{ with .Lastmod }}<meta property="article:modified_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
{{- end -}}

{{- with .Params.audio }}<meta property="og:audio" content="{{ . }}" />{{ end }}
{{- with .Params.locale }}<meta property="og:locale" content="{{ . }}" />{{ end }}
{{- with .Site.Params.title }}<meta property="og:site_name" content="{{ . }}" />{{ end }}
{{- with .Params.videos }}{{- range . }}
<meta property="og:video" content="{{ . | absURL }}" />
{{ end }}{{ end }}

To use this new partial, I added it to my layouts/partials/head.html:

{{ partial "opengraph" . }}

which is in turn loaded by layouts/_defaults/baseof.html:

  <head>
    {{- partial "head.html" . -}}
  </head>

So now the customized OpenGraph content will be loaded for each page.

Aaro's OG image generation

Aaro's code provided the base functionality for what I needed:

{{/* Generate opengraph image */}}
{{- if .IsPage -}}
  {{ $base := resources.Get "og_base.png" }}
  {{ $boldFont := resources.Get "/Inter-SemiBold.ttf"}}
  {{ $mediumFont := resources.Get "/Inter-Medium.ttf"}}
  {{ $img := $base.Filter (images.Text .Site.Title (dict
    "color" "#ffffff"
    "size" 52
    "linespacing" 2
    "x" 141
    "y" 117
    "font" $boldFont
  ))}}
  {{ $img = $img.Filter (images.Text .Page.Title (dict
    "color" "#ffffff"
    "size" 64
    "linespacing" 2
    "x" 141
    "y" 291
    "font" $mediumFont
  ))}}
  {{ $img = resources.Copy (path.Join .Page.RelPermalink "og.png") $img }}
  <meta property="og:image" content="{{$img.Permalink}}">
  <meta property="og:image:width" content="{{$img.Width}}" />
  <meta property="og:image:height" content="{{$img.Height}}" />

  <!-- Twitter metadata (used by other websites as well) -->
  <meta name="twitter:card" content="summary_large_image" />
  <meta name="twitter:title" content="{{ .Title }}" />
  <meta name="twitter:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end -}}"/>
  <meta name="twitter:image" content="{{$img.Permalink}}" />
{{ end }}

The resources.Get bits import the image and font resources to make them available to the images.Text functions, which add the site and page title texts to the image using the designated color, size, placement, and font.

The resources.Copy line moves the generated OG image alongside the post itself and gives it a clean og.png name rather than the very-long randomly-generated name it would have by default.

And then the <meta /> lines insert the generated image into the page's <head> block so it can be rendered when the link is shared on sites which support OpenGraph.

This is a great starting point for what I wanted to accomplish, but I made some changes to my opengraph.html partial to tailor it to my needs.

My tweaks

As I mentioned earlier, I wanted to have three slightly-different recipes for baking my OG images: one for the homepage, one for standard posts, and one for posts with an associated thumbnail. They all use the same basic code, though, so I wanted to be sure that my setup didn't repeat itself too much.

My code starts with fetching my resources up front, and initializing an empty $text variable to hold either the site description or post title:

{{ $img := resources.Get "og_base.png" }}
{{ $font := resources.Get "/FiraMono-Regular.ttf" }}
{{ $text := "" }}

For the site homepage, I set $text to hold the site description:

{{- if .IsHome }}
  {{ $text = .Site.Params.Description }}
{{- end }}

On standard post pages, I used the page title instead:

{{- if .IsPage }}
  {{ $text = .Page.Title }}
{{ end }}

If the page has a thumbnail parameter defined in the front matter, Hugo will use .Resources.Get to grab the image.

{{- with .Params.thumbnail }}
  {{ $thumbnail := $.Resources.Get . }}

{{% notice note "Resources vs resources" %}} The resources.Get function (little r) I used earlier works on global resources, like the image and font stored in the site's assets/ directory. On the other hand, the Resources.Get method (big R) is used for loading page resources, like the file indicated by the page's thumbnail parameter. {{% /notice %}}

Since I'm calling this method from inside a with block I use a $ in front of the method name to get the parent context. Otherwise, the leading . would refer directly to the thumbnail parameter (which isn't a page and so doesn't have the method available4).

Anyhoo, after the thumbnail is loaded, I use the Fit image processing method to scale down the thumbnail. It is then passed to the images.Overlay function to overlay it near the top right corner of the og_base.png image5.

  {{ with $thumbnail }}
    {{ $img = $img.Filter (images.Overlay (.Process "fit 300x250") 875 38 )}}
  {{ end }}
{{ end }}

Then I insert the desired text:

{{ $img = $img.Filter (images.Text $text (dict
  "color" "#d8d8d8"
  "size" 64
  "linespacing" 2
  "x" 40
  "y" 300
  "font" $font
))}}
{{ $img = resources.Copy (path.Join $.Page.RelPermalink "og.png") $img }}

All together now

After merging my code in with the existing layouts/partials/opengraph.html, here's what the whole file looks like:

// torchlight! {"lineNumbers": true}
{{ $img := resources.Get "og_base.png" }} <!-- [tl! **:2] -->
{{ $font := resources.Get "/FiraMono-Regular.ttf" }}
{{ $text := "" }}
<meta property="og:title" content="{{ .Title }}" />
<meta property="og:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end }}" />
<meta property="og:type" content="{{ if .IsPage }}article{{ else }}website{{ end }}" />
<meta property="og:url" content="{{ .Permalink }}" />
<meta property="og:locale" content="{{ .Lang }}" />
{{- if .IsHome }} <!-- [tl! **:2] -->
  {{ $text = .Site.Params.Description }}
{{- end }}

{{- if .IsPage }}
  {{- $iso8601 := "2006-01-02T15:04:05-07:00" -}}
  <meta property="article:section" content="{{ .Section }}" />
  {{ with .PublishDate }}<meta property="article:published_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
  {{ with .Lastmod }}<meta property="article:modified_time" {{ .Format $iso8601 | printf "content=%q" | safeHTMLAttr }} />{{ end }}
  {{ $text = .Page.Title }} <!-- [tl! ** ] -->
{{ end }}

{{- with .Params.thumbnail }} <!-- [tl! **:start] -->
  {{ $thumbnail := $.Resources.Get . }}
  {{ with $thumbnail }}
    {{ $img = $img.Filter (images.Overlay (.Process "fit 300x250") 875 38 )}}
  {{ end }}
{{ end }}

{{ $img = $img.Filter (images.Text $text (dict
  "color" "#d8d8d8"
  "size" 64
  "linespacing" 2
  "x" 40
  "y" 300
  "font" $font
))}}
{{ $img = resources.Copy (path.Join $.Page.RelPermalink "og.png") $img }} <!-- [tl! **:end] -->

<meta property="og:image" content="{{$img.Permalink}}">
<meta property="og:image:width" content="{{$img.Width}}" />
<meta property="og:image:height" content="{{$img.Height}}" />
<meta name="twitter:card" content="summary_large_image" />
<meta name="twitter:title" content="{{ .Title }}" />
<meta name="twitter:description" content="{{ with .Description }}{{ . }}{{ else }}{{if .IsPage}}{{ .Summary }}{{ else }}{{ with .Site.Params.description }}{{ . }}{{ end }}{{ end }}{{ end -}}"/>
<meta name="twitter:image" content="{{$img.Permalink}}" />

{{- with .Params.audio }}<meta property="og:audio" content="{{ . }}" />{{ end }}
{{- with .Site.Params.title }}<meta property="og:site_name" content="{{ . }}" />{{ end }}
{{- with .Params.videos }}{{- range . }}
<meta property="og:video" content="{{ . | absURL }}" />
{{ end }}{{ end }}

And it works! Black background with text "Dynamic Opengraph Images With Hugo", a command prompt "[runtimeterror.dev] $", and colorful hexagon shapes with "HUGO" letters.

I'm sure this could be further optimized by someone who knows what they're doing6. I'd really like to find a better way of positioning the thumbnail overlay to better account for different heights and widths. But for now, I'm pretty happy with how it works, and I enjoyed learning more about Hugo along the way.

  1. You're looking at it. ↩︎

  2. My current theme doesn't make use of the thumbnails, but a previous theme did so I've got a bunch of posts with thumbnails still assigned. And now I've got a use for them again! ↩︎

  3. Or a web designer, if I'm being honest. ↩︎

  4. Hugo scoping is kind of wild. ↩︎

  5. The overlay is placed using absolute X and Y coordinates. There's probably a way to tell it "offset the top-right corner of the overlay 20x20 from the top right of the base image" but I ran out of caffeine to figure that out at this time. Let me know if you know a trick! ↩︎

  6. Like Future John, perhaps? Past John loves leaving stuff for that guy to figure out. ↩︎