Skip to main content

Cover Function

As you already know, both uncover and #pause use the cover function to conceal content that is not visible. So, what exactly is the cover function here?

Default Cover Function: hide​

The cover function is a method stored in s.methods.cover, which is later used by uncover and #pause.

The default cover function is the hide function. This function makes the internal content invisible without affecting the layout.

Updating the Cover Function​

In some cases, you might want to use your own cover function. In that case, you can set your own cover function using:

config-methods(cover: (self: none, body) => hide(body))

hack: handle enum and list​

You will find that the existing cover function cannot hide the mark of enum and list, refer to here, so you can hack:

config-methods(cover: (self: none, body) => box(scale(x: 0%, body)))

Semi-Transparent Cover Function​

Touying supports a semi-transparent cover function, which can be enabled by adding:

config-methods(cover: utils.semi-transparent-cover.with(alpha: 85%))

You can adjust the transparency through the alpha: .. parameter.

Warning

Note that the transparent-cover here does not preserve text layout like hide does because it adds an extra layer of box, which may disrupt the original structure of the page.

Internals

The utils.semi-transparent-cover method is defined as:

#let semi-transparent-cover(self: none, constructor: rgb, alpha: 85%, body) = {
  cover-with-rect(
    fill: update-alpha(
      constructor: constructor,
      self.page.fill,
      alpha,
    ),
    body,
  )
}

It creates a semi-transparent rectangular mask with the same color as the background to simulate the effect of transparent content. Here, constructor: rgb and alpha: 85% indicate the background color's construction function and transparency level, respectively.