Proportionally scale arbitrary canvas to a fixed width

[noahjutz]

I'm looking for a canvas-agnostic solution for scaling any canvas to a fixed width (e. g. the page width), such that the leftmost visible element borders to the left edge of the canvas and rightmost element borders to the right edge of the canvas. The canvas should vertically scale proportionally, so the aspect ratio is maintained.

Or, more simply put, I want to resize my graphs like you would in any image editing software:

Screencast.from.2024-08-19.17-40-14.webm

Canvases can be scaled to the parent's size by using a relative unit as its length (e. g. 10%), but I would like a solution that works independently of the canvas' content bounds; using length: 10%, for example, would impose the limitation of having a fixed 10 units horizontally available.

The set-viewport transformation function allows for mapping arbitrary bounds to a fixed width, but this requires manually passing the bounds of the content - a task that could be automated. To complicate matters further, you'd have to measure variably sized shapes like content somehow.

One potential solution might be to resolve the position of each element, caching the min and max x and y values, and somehow retroactively applying a transformation based on those values. But maybe there's a much more simple solution I'm missing.

[johannes-wolf]

Something like:

#import "@preview/cetz:0.2.2"
#set page(width: 12cm, height: 10cm)

#let scale-to(body, target-width: 1) = {
  (ctx => {
    import cetz.draw: *

    let (ctx: _, drawables, bounds) = cetz.process.many(ctx, cetz.util.resolve-body(ctx, body))
    
    let bounds = cetz.vector.sub(bounds.high, bounds.low)
    let ratio = bounds.at(1) / bounds.at(0)

    return cetz.process.many(ctx, {
      group({
        set-viewport((0, 0, 0), (target-width, target-width * ratio, 1), bounds: bounds,)
        body
      })
    })
  },)
}

#place(rect(width: 10cm, height: 8cm))

#cetz.canvas(length: 10cm, {
  import cetz.draw: *

  scale-to({
    circle((2,1), fill: red)
    rotate(300deg)
    rect((0,0), (rel: (2, 2)), fill: blue)
  })
})

Gives:

But as you have mentioned, finding the right scaling with unscaled content in the canvas is non-trivial.

[johannes-wolf]

You could also apply scaling to the content by modifying the .body field of drawable with .type == "content".

[johannes-wolf]

Alternative: Use Typst' naitve scale() function:

#place(rect(width: 10cm, height: 8cm))

#let c = cetz.canvas({
  import cetz.draw: *

  circle((1,1), fill: red)
  content((5,0), [Some test text is here. \ What do you think?])
  rotate(280deg)
  rect((1,3), (rel: (2, 2)), fill: blue)
})

#place(context {
  let (width, height) = measure(c)
  scale(10cm / width * 100%, place(c))
})

The downside is, that it scales the stroke-width of your canvas.