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Version: 0.4.1

Complex Animations

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

Callback-Style Functions​

To overcome the limitations of styled and layout 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)

  In subslide #self.subslide,

  test #uncover("2-")[uncover] function,

  and test #only("2-")[only] function,

  #pause

  and paused text.
])

image

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.
])

image

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.