43.1 Complete source🔗ℹ

scribblings/examples/moving-circle.rkt

#lang racket/base

(require animate)

(provide disc initial movement animation)

;; doc: object begin

(define disc

(circle #:id 'moving-circle

#:center (vec2 -3 0)

#:radius 3/4

#:fill "dodgerblue"

#:stroke "navy"

#:stroke-width 3))

;; doc: object end

;; doc: scene begin

(define initial

(scene-add (make-scene) disc))

;; doc: scene end

;; doc: motion begin

(define movement

(scene-play initial

(move-to 'moving-circle (vec2 3 0))

#:duration 1))

;; doc: motion end

;; doc: hold begin

(define animation (scene-wait movement 1/2))

;; doc: hold end

43.2 How the program is organized🔗ℹ

disc is the original Visual. initial puts it in a Scene without adding time. movement adds one second of motion; animation adds the final half-second hold. These are separate values, so the program can inspect the starting Scene without undoing the movement.

The movie uses animation, not just movement. Its total duration is 1.5 seconds. The final hold gives the viewer time to see the completed move.

43.3 Render the movie🔗ℹ

43.4 Try one change🔗ℹ

Change the destination in move-to, or change the duration of the move. Keep a final hold. To see a still while editing in DrRacket, evaluate (scene->pict animation 1).

See Quick Start: a moving circle for the explanation of each constructor and Save frames and make a video for the difference between rendering and encoding.