Numbering¶

The example deck for this page is numbering.typ (HTML, PDF presentation, PDF handouts). It illustrates the three numbering functions in one deck.

A number on a slide can be useful for the audience: someone who wants to ask a question about a specific subslide needs a way to reference it. Animo gives a deck three functions to build such a handle, and it is up to you how to use these functions to format and position (sub)slide numbers.

The Slide Number¶

numbered: on #slide decides whether a slide is counted. A title or section slide is typically numbered: false. It says nothing about whether a number is shown.

slide-number() and slide-count() read that counter. Both are context functions and hand back plain integers, so anything can be computed from them.

#context [Slide #slide-number() of #slide-count()]

On a slide that numbered: false leaves out, slide-number() is none rather than the number of the slide before it, so one footer can serve a whole deck:

#let footer = context {
  let number = slide-number()
  if number != none {
    place(bottom + right, [#number / #slide-count()])
  }
}

Navigation does not use this counter. A presenter walks through a title slide whether or not it carries a number, so the position in the deck, as referenced by the URL, is counted separately over every slide.

The Subslide Number¶

A subslide number is a callback rather than a counter. The HTML output renders one rendering per epoch, and a rendering covers every state that shares its content, so a number written into it would be one number for a whole run of subslides.

per-subslide lays its callback out once per subslide, stacks the renderings in a container the size of the largest of them, and the browser shows the one belonging to the subslide on screen. A page of a paged output knows its own single state, so it just carries that state's rendering. Despite these different mechanisms, all three output types agree.

#per-subslide(it => [#it.number of #it.count])

The callback receives the subslide numbers, one dictionary of four, listed in the Reference. number counts from one, where the URL fragment addresses state 0 of a slide: the fragment is an address, while the number is what the audience reads on the slide. step and steps count every subslide of every slide, unnumbered slides included, because they measure the talk rather than its numbering. They are named for the presenter's steps, and a step is the transition from one subslide to the next, so steps counts subslides rather than transitions.

A callback may return none, which lays nothing out for that subslide. This writes a number only where it carries information:

#per-subslide(it => if it.count > 1 [ (#it.number/#it.count)])

A Progress Bar¶

step and steps are what an indicator spanning the whole talk is measured against, and the callback returns content, so the indicator can be anything typst draws.

#per-subslide(
  it => rect(width: 100% * (it.step - 1) / (it.steps - 1), height: 4pt, fill: blue),
  wrap: block,
)

A rendering that states a ratio needs a container width to be a ratio of, and only a filling container has one. The rect above is block-level, so auto chooses the filling block as well, and wrap: block states the requirement rather than changing the outcome. The argument is needed for a rendering that is inline and states a ratio, such as a bar drawn as box(width: 100% * f, ..). A stack of inline renderings measures them unbounded, where a 100% width resolves to zero, so such a bar lays out with no width at all.

Where a Number Goes¶

Animo has no header or footer machinery, so a recurring element is a wrapper around #slide that fills one of the two outer layers.

Put it in the overlay. An overlay is one rendering per slide, where the body is one rendering per epoch, so a stack of one rendering per subslide is paid for once in an overlay and once per epoch in the body. The overlay also belongs to the viewport, so a pan leaves it where it is, where a footer placed in the body travels with the canvas.

What a Handout Shows¶

A handout page carries the number of the state it kept, which is not the number of the page it is. A slide whose third subslide is the one the handout keeps shows "3 of 3" on a page that may be the seventh of the handout. Someone who noted a number during the talk looks for that number, rather than for the position of the page within the handout.

What This Costs¶

A stack is one rendering per subslide, so it is the only construct in Animo whose cost grows with a slide's states rather than with its epochs. For a number that is a few glyphs it is a few percent of a deck. See What a Number Costs for empirical tests.