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).
procedure
((init-world viewport) v) → void?
viewport : viewport? v : any/c
Sets the initial value of viewport’s world to v.
procedure
((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.
Stops updating viewport’s world via a callback installed with
set-on-tick-event.
procedure
((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.