Visualise document evolution

[davystrong]

Motivation

I'd like to be able to sweep through the evolution of a document to find the cause of "layout did not converge" errors.

This is being discussed here along with some options for integrating detection into the compiler. However, actually generating different versions of the document for visual debugging may be more appropriate as an IDE feature.

Description

Some way of switching the number of iterations used by the compiler for the preview. A dropdown or slider in the preview window would be great. Changing the number of iterations shouldn't change the position at which the document is displayed.

Examples/Questions

• Previewing a document with a state feedback loop should display the final version of the document, along with a warning (at the top of the window?) that the layout didn't converge. The warning should include a dropdown or slider to select previous iterations of the document. Changing the value of the slider/dropdown should immediately display the other version, without confirmation.
• How should the value be selected? I was thinking of a slider or a dropdown, but increment/decrement buttons could work too.

[Myriad-Dreamin]

typst doesn't expose the argument to control max number of layout iterations, so we cannot add it without patching typst. However, some naive out-of-box idea could be some function helper that reduce chances to iterate layout, lets say some helper consume-layout-iteration(n: int) has been invented, we can generate such documents by sys.inputs along with the helper:

In your document,

#consume-layout-iteration(int(sys.inputs.at("x-max-layout-iter", default: 0)))

And produces documents by:

seq 0 5 | xargs -I {} typst compile --input=x-max-layout-iter={} main.typ main-iter-{}.pdf

[davystrong]

@Myriad-Dreamin thanks for getting back so quickly! I'm not sure I understand, are you saying there is a way of creating a consume-layout-iteration function? I can't think of any way because some state updates will occur even if, for example, I insert an invalidating state update at the start of the document.

[davystrong]

Actually, I believe that my previous comment is wrong. If I don't output the document, I don't think any state updates occur. Therefore, something like this at the start of the file works:

#let MAX-ITERS = 2

#show: document => context {
  let iters = counter("__iterations")
  if iters.final().first() != 5 - MAX-ITERS {
    iters.update(iters.final().first() + 1)
  } else {
    iters.update(5 - MAX-ITERS)
    document
  }
}

and you can check the number of iterations with a separate counter (obviously this second code snippet will never converge):

#context {
  let iters = counter("__iterations_view")
  for i in range(iters.final().first() + 1) {
    iters.step()
  }
  [#(iters.final().first() + 1)]
}

[laurmaedje]

typst doesn't expose the argument to control max number of layout iterations, so we cannot add it without patching typst.

I'll add a compiler API for this soon. We also want to add a debugging UI for this to the web app.