11.1 Move one part of a diagram🔗ℹ

Put related Visuals in a group, then address a child by its Visual path. The destination is in the group’s local coordinates.

(define recipe-dot

(circle #:id 'dot #:center (vec2 -1 0) #:radius 1/2

#:fill "dodgerblue" #:stroke "navy"))

(define recipe-tile

(rectangle #:id 'tile #:center (vec2 1 0) #:width 1 #:height 1

#:fill "gold" #:stroke "sienna"))

(define recipe-pair

(group (list recipe-dot recipe-tile) #:id 'pair #:center (vec2 1 0)))

(define grouped-scene

(scene-add (make-scene) recipe-pair))

(define child-moves

(scene-play grouped-scene

(move-to '(pair dot) (vec2 -1 2))

#:duration 2))

Here is the completed movement. The documentation build evaluates the displayed scene->pict call; it only scales the resulting Pict for the page.

> (scene->pict child-moves 2)

> (scene-duration child-moves)

2

> (visual-position (scene-state-ref (scene-sample child-moves 2) '(pair dot)))

(vec2 -1 2)

Do not confuse a Visual path such as '(pair dot) with a geometric movement route. For the longer explanation, see Move one child inside a group.

11.2 Start the second animation later🔗ℹ

Use timed when two requests share one play clip but start at different times.

(define delay-dot

(circle #:id 'delay-dot #:center (vec2 -3 1) #:radius 1/2))

(define delay-tile

(rectangle #:id 'delay-tile #:center (vec2 -3 -1) #:width 1 #:height 1))

(define delay-start

(scene-add (make-scene) delay-dot delay-tile))

(define delayed-scene

(scene-play delay-start

(timed (move-to 'delay-dot (vec2 3 1))

#:start 0 #:duration 2)

(timed (move-to 'delay-tile (vec2 3 -1))

#:start 1/2 #:duration 2)

#:duration 5/2))

At 3/2 seconds both objects are moving, but the second one started later:

> (scene->pict delayed-scene 3/2)

> (scene-duration delayed-scene)

5/2

The outer duration includes the delay. For two non-overlapping steps, two ordinary scene-play calls are usually simpler. See Delay the second start.

11.3 Bring a faded object back🔗ℹ

First decide whether the object is transparent or absent. fade-to changes opacity but keeps the target in the Scene; fade-out removes it.

(define restore-dot

(circle #:id 'restore-dot #:center origin #:radius 1/2))

(define restore-start

(scene-add (make-scene) restore-dot))

(define invisible

(scene-play restore-start (fade-to 'restore-dot 0) #:duration 1))

(define removed

(scene-play restore-start (fade-out 'restore-dot) #:duration 1))

Before comparing invisible and absent states, here is the object they start with:

> (scene->pict restore-start 0)

> (scene-state-has? (scene-sample invisible 1) 'restore-dot)

#t

> (scene-state-has? (scene-sample removed 1) 'restore-dot)

#f

Restore the first with another opacity animation. Reintroduce the second with fade-in:

(define visible-again

(scene-play invisible (fade-to 'restore-dot 1) #:duration 1))

(define reintroduced

(scene-play removed (fade-in restore-dot) #:duration 1))

> (scene-state-has? (scene-sample visible-again 2) 'restore-dot)

#t

> (scene-state-has? (scene-sample reintroduced 2) 'restore-dot)

#t

See Hide an object, or remove it for the visual comparison.

11.4 Reveal a mathematical graph🔗ℹ

Construct the curve first, leave it out of the initial Scene, and introduce it with create.

(define graph-axes

(axes #:id 'graph-axes

#:x-range (axis-range -3 3 1)

#:y-range (axis-range -2 2 1)

#:x-length 7 #:y-length 9/2

#:stroke "navy"))

(define graph-curve

(function-graph graph-axes

(lambda (x) (- (/ (* x x) 4) 1))

#:id 'graph-curve

#:sample-count 81

#:stroke "crimson"))

(define graph-drawing

(scene-play (scene-add (make-scene) graph-axes)

(create graph-curve)

#:duration 2))

The completed reveal looks like this:

> (scene->pict graph-drawing 2)

> (scene-duration graph-drawing)

2

> (scene-state-has? (scene-sample graph-drawing 2) 'graph-curve)

#t

Do not add graph-curve before calling create. See Draw a graph for sampling and axis geometry.

11.5 Inspect a frame without making a movie🔗ℹ

When you want a picture rather than the semantic state, scene->pict is the direct route. It samples both the Scene and its ordinary camera at the same time; no frame directory or encoder is involved.

> (scene->pict graph-drawing 1)

Use scene-sample separately when you also need to inspect the semantic state:

(define middle-state (scene-sample graph-drawing 1))

> (scene-state? middle-state)

#t

> (pict? (scene->pict graph-drawing 1))

#t

A 3D camera inside view3d is part of that view instead of the ordinary Scene camera.