How to override hard-coded equation colors?

Questions
1

Hello Typst Community,

I have been working with text color transformations and came across an interesting challenge. I have a function that changes text colors recursively:

#let to-gray(self: none, it) = {
  show text: it => text(gray, it)
  it
}

Using this function, I can overwrite hard-coded text colors like this:

#to-gray[
  this was a #text(red)[red] text.
]

However, I noticed that this function does not change the colors of equations. I know that we can change the color of any text, including equations, with:

#set text(gray)

And to change the color of equations specifically, we can use:

#show math.equation: set text(gray)

However, both don’t overwrite the hard-coded colors. I am looking for a way to achieve the same effect as #to-gray for equations. Why does #set work for equations, but #show does not?

Thank you in advance for your help!

1 Like
2

Hi. I think the issue here is that math mode is not exactly the same as text mode, and recently there is a push for it to be even more separate. IMO, there should be some easy way to override the text color in math mode, so maybe you should create an issue, if there isn’t one already open.

To be able to override the text color in both modes, here is a very limited solution:

#let to-gray(it) = {
  let styled = text(red)[].func()
  show text: text.with(gray)
  show math.equation: it => {
    if it.has("label") { return it }
    let fields = it.fields()
    _ = fields.remove("body")
    let body = it
      .body
      .children
      .map(x => if x.func() == styled { x.child } else { x })
      .map(text.with(gray))
      .join()
    [#math.equation(..fields, body)<a>]
  }
  it
}

#to-gray[
  this was a #text(red)[red] text.

  $ x = text(#green, y) $
]

Without force override, it’s much more simple:

#let to-gray(it) = {
  set text(gray)
  show math.equation: text.with(gray)
  it
}

But ultimately, if you don’t have a practical application for this, you shouldn’t force Typst to do what it wasn’t designed for. The ability to make a smaller scope with new style is a very powerful feature that can be used in many different ways. While making it impossible to override some settings no matter what is definitely a niche use case. The simplest solution that comes to mind is to just not change text color inline, then it becomes very easy:

#let to-gray(it) = {
  set text(gray)
  show math.equation: text.with(gray)
  it
}

#to-gray[
  this is a text.

  $ x = y $
]

// Or

#[
  #show: to-gray

  this is a text.

  $ x = y $
]

If you can share your use case, I might be able to help you with a better approach.

P.S. I the title should be more about overriding text color, recursiveness isn’t really what it’s about, IMO.

2 Likes
3

Thank you for your quick response.

I wanted to use this function in Touying, a slide-making library for presentations.
Touying supports dynamic slides, and we want to change the colors or make elements transparent until they are revealed as the slides progress.

The method used in Touying is essentially the same as my to-gray function combined with the ordinary set text(gray).
However, presentation slides often have many colored texts and equations, and their colors are usually specified manually, so I needed some overriding functionality.

4

So you want to replace the hiding function with the function that just makes text gray until uncovered?

If so, then the actual question would be “How to replace the cover function in Touying with a text color change” or something along those lines. This way, people that are familiar with the library can notice the question and might have an answer for it. Otherwise, the question sounds very broad and not very practical.

I mean, it works, so it might be enough for you.

code 
#let to-gray(it) = {
  let styled = text(red)[].func()
  show text: text.with(gray)
  show math.equation: it => {
    if it.has("label") { return it }
    let fields = it.fields()
    _ = fields.remove("body")
    if "label" in fields { _ = fields.remove("label") }
    let body = it
      .body
      .children
      .map(x => if x.func() == styled { x.child } else { x })
      .map(text.with(gray))
      .join()
    [#math.equation(..fields, body)<a>]
  }
  it
}

#import "@preview/touying:0.6.1": *
#import themes.metropolis: *
#show: metropolis-theme.with(
  config-methods(cover: (self: none, body) => to-gray(body)),
  config-common(
    slide-fn: slide.with(
      setting: body => {
        // Fix moving list items when using pause
        // https://discord.com/channels/1054443721975922748/1280244268769873950/1319729269353746604
        let spacing = 0.75em
        set par(spacing: spacing)
        set list(spacing: spacing)
        body
      },
    ),
  ),
)

== Testing cover function
List:
- one #pause
- $x = text(#green, y)$ #pause
- #text(green)[three]
1 Like
5

Actually, I am the person who implemented the color-changing cover and transparentize function. I received an issue report stating that the equation color is not changing. I struggled to find a solution and finally came here to ask for this functionality, as I thought it was not a question specific to Touying.

2 Likes
6

Well, since the problem originated from that library, it makes sense that it’s related to that library, because the chance that someone would do this outside of it, is probably very low. I guess then you should open an issue about it, because as it is right now, I don’t think there is a good solution for it. Because using the half-broken solution that I showed isn’t really a great idea for a public package. Unless some experimental flag is added.

1 Like
7

Thank you for your reply and thoughtful feedback. I will rethink the functionality based on your insights.

Separately, I’d like to ask about the behavior of ‘set’, ‘show’, and ‘show-set’ in another thread, purely out of personal interest and to deepen my understanding.

Thank you again for your help!

1 Like