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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 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 ways to do that for my Hugo site.

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.
  • ... but if the post has a thumbnail1 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 designer2 so I kept it simple while trying to match the theme, font, and colors used on the site.

I had to install the Fira Mono font Fira Mono .ttf to my ~/.fonts/ folder so I could use it in GIMP.

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>

Aaro's OG image generation

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

{{/* 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 into the post bundle directory 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 made some changes in 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 the description or 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 %}}

And since I'm calling this method from inside a with branch I have to put a $ in front of the method. Otherwise, the leading . would refer directly to the thumbnail parameter (which isn't a page and so doesn't have the method available3).

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

  {{ 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 doing4. 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. 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! ↩︎

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

  3. Hugo scoping is kind of wild. ↩︎

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