Complex Animations

Thanks to the syntax provided by Polylux, we can also use only, uncover, and alternatives in Touying.

Mark-Style Functions

We can use mark-style functions, which are very convenient to use.

At subslide #touying-fn-wrapper((self: none) => str(self.subslide)), we can

use #uncover("2-")[`#uncover` function] for reserving space,

use #only("2-")[`#only` function] for not reserving space,

#alternatives[call `#only` multiple times \u{2717}][use `#alternatives` function #sym.checkmark] for choosing one of the alternatives.

However, this does not work in all cases, for example if you put uncover into the context expression, you will get an error.

Callback-Style Functions

To overcome the limitations of layout functions mentioned earlier, Touying cleverly implements always-effective only, uncover, and alternatives using callback functions. Specifically, you need to introduce these three functions as follows:

#slide(repeat: 3, self => [
  #let (uncover, only, alternatives) = utils.methods(self)

  At subslide #self.subslide, we can

  use #uncover("2-")[`#uncover` function] for reserving space,

  use #only("2-")[`#only` function] for not reserving space,

  #alternatives[call `#only` multiple times \u{2717}][use `#alternatives` function #sym.checkmark] for choosing one of the alternatives.
])

Notice that we no longer pass a content block but instead pass a callback function with a self parameter. Later, we extract only, uncover, and alternatives functions from self using:

#let (uncover, only, alternatives) = utils.methods(self)

We then call these functions in subsequent steps.

Here's an interesting fact: the self.subslide of type int indicates the current subslide index, and in fact, the only, uncover, and alternatives functions rely on self.subslide to determine the current subslide index.

Warning

We manually specify the repeat: 3 parameter, indicating the display of 3 subslides. We need to do this manually because Touying cannot infer how many subslides only, uncover, and alternatives should display.

only

The only function means it "appears" only on selected subslides. If it doesn't appear, it completely disappears and doesn't occupy any space. In other words, #only(index, body) is either body or none.

The index can be an int type or a str type like "2-" or "2-3". For more usage, refer to Polylux.

uncover

The uncover function means it "displays" only on selected subslides; otherwise, it will be covered by the cover function but still occupies the original space. In other words, #uncover(index, body) is either body or cover(body).

The index can be an int type or a str type like "2-" or "2-3". For more usage, refer to Polylux.

You may also have noticed that #pause actually uses the cover function, providing a more convenient syntax. In reality, their effects are almost identical.

alternatives

The alternatives function displays a series of different content in different subslides. For example:

#slide(repeat: 3, self => [
  #let (uncover, only, alternatives) = utils.methods(self)

  #alternatives[Ann][Bob][Christopher]
  likes
  #alternatives[chocolate][strawberry][vanilla]
  ice cream.
])

As you can see, alternatives can automatically expand to the most suitable width and height, a capability that only and uncover lack. In fact, alternatives has other parameters, such as start: 2, repeat-last: true, and position: center + horizon. For more usage, refer to Polylux.