5 World Operations

Every canvas comes with an associated world. A client program can set the world, start the world’s clock, stop the world’s clock, and deal with tick events (the clock ticks) and keyboard inputs (keyevents).

((init-world viewport) v) → void?

viewport : viewport?

v : any/c

Sets the initial value of viewport’s world to v.

((set-on-tick-event   viewport)             secs             update-callback)   →   void?

viewport : viewport?

secs : real?

update-callback : (any/c . -> . any/c)

For viewport, sets update-callback to be invoked to transform the world value every secs seconds. Only one callback is installed at a time.

((stop-tick viewport)) → void?

viewport : viewport?

Stops updating viewport’s world via a callback installed with set-on-tick-event.

((set-on-key-event viewport) key-callback) → void?

viewport : viewport?

key-callback : (any/c any/c . -> . any/c)

Sets key-callback as the function to call whenever a key event is received for viewport. The key-callback is given a key event and the current world, and it produces an updated world.