Animated Images

world.ss

The teachpack provides two kinds of functions. The first four allow students to simulate a small world of animated drawings and games:

big-bang : Number Number Number World -> true
(big-bang width height n w) creates and shows a width x height canvas, starts the clock, makes it tick every n seconds, and makes w the first world

on-tick-event : (World -> World) -> true
(on-tick-event tock) calls tock on the current world for every clock tick; the result is the next world

on-key-event : (KeyEvent World -> World) -> true
(on-key-event react) calls react on every keystroke event, with a char or a symbol representing the keystroke, and the current world; the result is the next world

end-of-time : -> World
(end-of-time) stops the clock.

The rest are functions for creating scenes:

nw:rectangle : Number Number Mode Color -> Image
(nw:rectangle width height mode color) creates a width x height rectangle, solid or outlined, with its anchor in the NW corner

empty-scene : Number Number -> Scene
(empty-scene width height) creates a width x height "scene" (frame with origin in NW)

place-image : Image Number Number Scence -> Scene
(place-image image x y scene) places image at (x,y) into scene; (x,y) are comp. graph. coordinates

run-movie : (Listof Image) -> true
(run-movie loi) shows the list of images in loi, time-delayed

Finally, the teachpack also adds some one new form of syntax to the language:


   (update <expression> produce <expression>)

update the canvas of the world with the first expression; the result is the value of the second expression.

Both update and produce are new keywords.

The teachpack provides all the functions that image.ss provides.