How to use a different cover function for text and math in Touying

Questions
1

As noted in Touying’s tutorial, its utils.semi-transparent-cover cover function doesn’t always preserve page structure. This is especially obvious when using math and alignment tabs. Example:

#import "@preview/touying:0.6.1": *
#import themes.simple: *

#show: simple-theme.with(aspect-ratio: "16-9")

= Hello

== Page with text

#lorem(25) #pause

#lorem(25)

== Page with math

$
  f(x) pause &= 3x \
  f(x) pause &= 5x + 6
$
#pause
$ g(x) = 1 $

Given this limitation, I would like to use use.semi-transparent-cover for text but not for math. I assumed this would be a common issue but cannot find anything that achieves this. I tried the following to achieve this:

Attempt 1

#let has-equation(body) = body.func() == math.equation or (body.has("children") and body.children.any(i => i.func() == math.equation))

#show: simple-theme.with(
  aspect-ratio: "16-9",
  config-methods(cover: 
    (self:none, body) => if has-equation(body) {
      hide(body)
    } else {
      utils.semi-transparent-cover(self:self, alpha: 85%, body)
    }
  )
)

This works for full equations but not when pause is used within math mode.

Attempt 2

#show math.equation: it => {
  show: simple-theme.with(
    aspect-ratio: "16-9",
    config-methods(cover: utils.semi-transparent-cover.with(alpha: 85%))
  )
  it
}

This gives the error maximum show rule depth exceeded. Hint: check whether the show rule matches its own output. Not sure where the recursion is occurring, this error doesn’t make sense to me.

Attempt 3

If I try to put this before the math:

#show: simple-theme.with(
  aspect-ratio: "16-9",
  config-methods(cover: (self:none, body) => hide(body))
)

…and this after:

#show: simple-theme.with(
  aspect-ratio: "16-9",
  config-methods(cover: utils.semi-transparent-cover.with(alpha: 85%))
)

It causes a lot of issues downstream, adding extra pages inexplicably throughout.

Is the only way to handle this through the callback approach?

2

I figured out a solution using a state:

#let should-hide = state("cover-count", false)
#let hide-now-on() = context should-hide.update(true)
#let shade-now-on() = context should-hide.update(false)
#let cover-it(self:none, it) = context if should-hide.get() {hide(it)} else {utils.semi-transparent-cover(it, self:self, alpha:85%)}

#show: simple-theme.with(
  aspect-ratio: "16-9",
  config-methods(cover: cover-it)
)

Then I can just use the two defined functions to switch between the two types of covering.