▼ |  | Graphics: Legacy Library

1 | Basic Commands
2 | Position Operations
3 | Color Operations
4 | Draw, Clear, and Flip Operations
5 | World Operations
6 | Miscellaneous Operations
7 | An Example
8 | A More Complicated Example
9 | Protecting Graphics Operations
10 | Mouse Operations
11 | Keyboard Operations
12 | Flushing
13 | Graphics Library as a Unit

On this page:

init-world
set-on-tick-event
stop-tick
set-on-key-event

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### 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.

> procedure ((stop-tick viewport)) → void?
> viewport : viewport?

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.
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