30.1 Write a title card🔗ℹ

(define welcome

(slide #:id 'welcome #:layout 'title

[title "Solving equations"]

[subtitle "Keep both sides equal."]))

The names title and subtitle are part of the slide syntax. They are not variables you must define.

A slide is a description with no duration of its own. Draw it directly with slide->pict:

> (slide->pict welcome)

A plain slide lowered to an ordinary Scene has duration zero. The documentation build checks that statement:

> (scene-duration (slide->scene welcome))

0

30.2 Make a clip🔗ℹ

A slide clip gives the slide a timed presentation. hold-slide makes a clip that keeps the populated card unchanged for a chosen duration.

(define held-title

(hold-slide welcome #:duration 3))

A clip retains its authored duration when lowered to an ordinary Scene:

> (scene-duration (slide->scene held-title))

3

30.3 Reveal the title, then the subtitle🔗ℹ

For changes within the card, use build-slide. A beat is a named interval in the clip. Beats run one after another. An action describes a change within a beat. reveal-slot is an action that makes content appear.

Here, both slots start hidden. The title takes 0.4 seconds to fade in during a one-second beat. The subtitle starts in the next beat.

(define opening

(build-slide welcome #:initial 'hidden

(beat 'heading #:duration 1

(reveal-slot 'title #:duration 0.4))

(beat 'explanation #:duration 3

(reveal-slot 'subtitle #:duration 0.5))))

The clip lasts four seconds. The action durations fit inside their beats; they are not added to the beat durations:

> (scene-duration (slide->scene opening))

4

Hidden slots keep their places, so the subtitle does not move when the title appears.

30.4 Give individual bullets names🔗ℹ

bullets makes a list whose items can be targeted separately. The item names are not printed. A selector such as '(body identity) means the item named identity inside the body slot.

(define card

(slide #:id 'layout-title+body #:layout 'title+body

[title "Explain one idea"]

[body

(bullets

[structure "Choose a layout."]

[identity "Name what matters."]

[timing "Reveal it at the right moment."])]))

(define clip

(build-slide card #:initial 'hidden

(beat 'heading #:duration 0.7

(reveal-slot 'title))

(beat 'structure #:duration 0.9

(reveal-slot '(body structure)))

(beat 'identity #:duration 0.9

(reveal-slot '(body identity)))

(beat 'timing #:duration 0.9

(reveal-slot '(body timing)))

(beat 'read #:duration 1.6)))

The five frames show the empty start, heading, and three settled bullet states. The last beat simply leaves the completed list on screen.

To inspect a named boundary directly, ask slide->pict for that point in the clip:

> (slide->pict clip #:at '(identity end))

30.5 Actions within a beat🔗ℹ

Two actions in one beat start together. Add #:at to delay one relative to the start of that beat. For example, this body reveal starts half a second later:

(define delayed-card

(build-slide

(slide #:layout 'title+body

[title "One beat"]

[body "The body starts later."])

#:initial 'hidden

(beat 'show #:duration 2

(reveal-slot 'title #:duration 0.4)

(reveal-slot 'body #:at 0.5 #:duration 0.4))))

conceal-slot fades content out; it does not free layout space. emphasize-slot briefly enlarges visible content and restores its size. The slot entrance and exit effects are 'fade and 'instant; the slide transition effects in the next chapter are a different vocabulary.

Continue with Put slides together. Complete standalone programs for the main examples are "scribblings/examples/first-slide.rkt" and "scribblings/examples/builds.rkt".