The teachpack assumes working knowledge of the basic image manipulation primitives and introduces a special kind of image: a scene.
|(define (focus-at-0-0 i)|
|(and (= (pinhole-x i) 0) (= (pinhole-y i) 0)))|
|(and/c image? focus-at-0-0)|
The teachpack can display only Scenes, which are images whose pinholes are at position (0 ,0).
|(empty-scene width height) → Scene|
|width : natural-number/c|
|height : natural-number/c|
Creates a width x height Scene.
|(place-image img x y s) → Scene|
|img : image?|
|x : number?|
|y : number?|
|s : Scene|
Creates a scene by placing img at (x ,y) into s; (x ,y) are comp. graph. coordinates, i.e., they count right and down from the upper-left corner.