Erna - a Typst library to scale and align rows of images

vmartel08 · September 5, 2026, 8:11am

I may be mistaken but perhaps have a look at How to provide assets (image files) with a template so that they could eventually be overwritten? - #2 by vmartel08

tad-lispy · September 5, 2026, 9:27am

Yes, that’s what I have in mind.

tad-lispy · September 15, 2026, 6:55am

Erna 0.2.0 is out!

This version addresses the issue where passing a relative path to an image results in wrong absolute path resolution. The solution is to pass content, not paths to images, like this:

#import "@preview/erna:0.2.0"

#erna.multiple-rows(
    gutter: 20pt,
    (
        image("opossums-in-a-row.jpg"),
        image("opossum-in-a-tree.jpg"),
    ),
    (
        image("baby-opossum.webp"),
        image("ninja-opossum.jpg"),
        image("opossum-with-teeth.jpg"),
    ),
)

This opened another issue: what if a user passes content that is not an image. After some tinkering, this is now possible and seems to work correctly. So now Erna can lay out any kind of content, or at least many different kinds, like images, shapes, text, etc. Here is a simple example:

#import "@preview/erna:0.2.0"

#erna.multiple-rows(
    gutter: 20pt,
    (
        image("opossums-in-a-row.jpg"),
        image("opossum-in-a-tree.jpg"),
    ),
    (
        rect[
            I think\
            opossums are\
            _really_ cool
        ],
        image("ninja-opossum.jpg"),
    ),
    (
        image("baby-opossum.jpeg"),
        image("opossum-with-teeth.jpg"),
    ),
)

A few more elaborate examples are in the preview document.

Handling content other than images was complicated by this bug:

github.com/typst/typst

Weird behaviour of `scale(5pt, …)` in constrained space

opened 07:11AM - 21 Jul 25 UTC

YDX-2147483647

bug layout

### Description If a content cannot fit into a container, then [`scale`](https:…//typst.app/docs/reference/layout/scale/)-ing the content with an absolute factor may lead to weird result. (Here _absolute_ means the factor is a `length`, rather than `ratio` or `auto`.) - container width: 2 pt - scale factor: 5 pt - content width: 10 pt ⇒ result width: 25 pt <img width="100" alt="Image" src="https://github.com/user-attachments/assets/82cee6a3-abf5-4cf6-b60a-2560a47d0836" /> ```typ #block(width: 2pt, stroke: gray, scale(x: 5pt, box( width: 10pt, height: 10pt, fill: orange.transparentize(50%), ))) // For reference #grid(columns: 2, align: horizon, line(length: 10pt), [#10pt]) ``` This usage is common in tables: <img width="300" alt="Image" src="https://github.com/user-attachments/assets/633af1f0-1545-4878-9eba-6e416a873802" /> <details> <summary>Code</summary> ```typ #set page(height: auto, width: auto, margin: (right: 1em + 20pt, rest: 1em)) #set raw(lang: "typc") #let test-box = box.with( height: 10pt, width: 10pt, fill: orange.transparentize(50%), ) A #10pt box: #test-box(baseline: 20%) #table( columns: (auto, 12pt), align: (start, center + horizon), inset: (x: 5pt, y: 7pt), stroke: 0.5pt, [Put in a column \ #text(0.8em)[(width: #12pt, inset-x: #5pt)]], test-box(), [Apply `scale(5pt, …)`], scale(5pt, test-box()), [It becomes #25pt × #5pt?], test-box(width: 25pt, height: 5pt), [Retry `scale(50%, …)`], scale(50%, test-box()), [Now the desired #5pt box], test-box(width: 5pt, height: 5pt), ) ``` </details> ### My attempt It looks like in typst 0.13.1, the result size is determined by: ```typ #let calc-result-size(available-size, content-size, scale-abs) = { let scale-ratio = scale-abs / calc.min(available-size, content-size) content-size * scale-ratio } ``` ![Image](https://github.com/user-attachments/assets/079b2761-72af-4700-997c-2442d4867afa) <details> <summary>Code</summary> ```typ #let calc-result-height(available: 0pt, content: 0pt, scale-abs: 0pt) = { // Here `0pt` are only placeholders. This function only expects positive lengths. let scale-ratio = scale-abs / calc.min(available, content) content * scale-ratio } #let scale-abs = 10pt #let content-height = 10pt #let available-heights = (20pt, 15pt, 10pt, 8pt, 4pt, 2pt, 1pt, 0.5pt) #assert.eq(type(scale-abs), length) #let it = scale(scale-abs, box( fill: orange.transparentize(50%), width: 10pt, height: content-height, )) #set page(width: auto, height: auto, margin: 1em) A #content-height square: #box(width: 10pt, height: content-height, fill: purple, baseline: 20%) #let raw-repr(it) = raw(repr(it), lang: "typc") #table( columns: 2 + available-heights.len(), align: (x, _) => if x > 0 { center } else { start } + horizon, stroke: (x, y) => if y > 0 { (top: 0.5pt) } + if x > 0 { (left: 0.5pt) }, [*Height of \ available space*], $+oo$, ..available-heights.map(raw-repr), [ *Height of* \ #raw( lang: "typc", ```typc scale( {scale-abs}, box(height: {content-height}) )``` .text .replace("{scale-abs}", repr(scale-abs)) .replace("{content-height}", repr(content-height)), ) ], grid( align: horizon, columns: 4, column-gutter: 2pt, raw-repr(content-height), box(width: 0.5pt, height: content-height, fill: black), it, ), ..available-heights.map(h => { let result = calc-result-height( available: h, content: content-height, scale-abs: scale-abs, ) grid( align: horizon, columns: 4, column-gutter: 2pt, raw-repr(result), box(width: 0.5pt, height: result, fill: black), box(height: h, stroke: gray, it), ) }), ) ``` </details> https://github.com/typst/typst/blob/b790c6d59ceaf7a809cc24b60c1f1509807470e2/crates/typst-layout/src/transforms.rs#L100-L127 ### Links Related: #3148, which is a bug about `reflow: true`. These two bugs can somewhat mix together. Background: [How does `scale` work within grids? - Questions - Typst Forum](https://forum.typst.app/t/how-does-scale-work-within-grids/5137?u=y.d.x). ### Reproduction URL _No response_ ### Operating system Web app ### Typst version - [x] I am using the latest version of Typst

Eventually I found a workaround, but it took me some time to understand what’s going on.

Because Erna is not only about images now, I renamed the two functions:

erna.image-row → erna.row
erna.image-rows → erna.multiple-rows

I hope this also makes the difference between them more clear.

Overall, what started as an annoying bug, resulted in a substantial expansion of useful features. I’m quite pleased with the result. The Typst community is very friendly. Thanks to everyone involved! Please let me know if you find Erna useful or have any questions.

Marcono1234 · September 22, 2026, 4:32pm

In Typst 0.15.0 the path type was added. It is resolved relative to where it is called (e.g. user code) and can also be passed to packages, allowing them to read the file.

That would solve your issue. However, your approach of supporting any content for Erna 0.2.0 is probably even better because it allows customizing how the images are loaded, or as you mention even using arbitrary non-image content.

As side note: It looks like your package currently publicly exports your complete implementation, including seemingly internal functions such as aspect-ratio or solve. You can avoid that by placing your implementation in a separate type Typst file and then only importing (and effectively re-exporting) only the public API in the entrypoint Typst file, see also packages/docs/typst.md at main · typst/packages · GitHub.