Add aspect ratio support to the resize directive

Feature Request

I find myself wanting to resize images to multiple different sizes and formats for responsive and lazy loaded images, but always want to keep the same aspect ratio.

Ideally I could do something like this:

./assets/awesome-image.jpg?width=300;600;900&height=169;338;506

and imagetools would magically know I want that to be three 16:9 images. Not surprisingly, I actually get back 9 images with all permutations of widths and heights.

Proposed Transform

It’d be nice if we could specify either an aspect ratio and either width or height along the lines of

./assets/awesome-image.jpg?width=300;600;900&aspect=1.77777777

Existing Workaround

There is a workaround here so this is more of a convenience request than anything else. I can just split this out into three separate imports each specifying exactly one width and height.

[JonasKruckenberg]

Just opened a discussion for potentially adopting more ideas from services like Cloudinary!

[tony-sull]

I was going to propose that the API mirrored an existing popular one (like Cloudinary has).

Yep that makes total sense. It looks like the two main differences are that they have a shorthand ar for the aspect ratio parameter, and they value can be either a string like 16:9 or a float.

I should have a little time this morning, I’ll add that in and submit another PR once it’s tested