11 Keyboard Operations

▼ |  | 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:

get-key-press
ready-key-press
key-value

Racket
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## 11 Keyboard Operations🔗ℹ

The graphics library contains functions that report key presses from the keyboard. The functions get-key-press and ready-key-press return a “key-press descriptor,” and then key-value takes the descriptor and returns a character or symbol (usually a character) representing the key that was pressed. Key presses are buffered and returned in the same order in which they occurred. Thus, the descriptors returned by get-key-press and ready-key-press may be from presses that occurred long before these functions were called.

> procedure (get-key-press viewport) → key-press?
> viewport : viewport?

Returns the next key press in the viewport, waiting for a key press if necessary.

> procedure (ready-key-press viewport) → key-press?
> viewport : viewport?

Returns the next key press in the viewport or returns #f if none is available. Unlike get-key-press, ready-key-press always returns immediately.

> procedure (key-value key-press) → (or/c char? symbol?)
> key-press : key-press?

Returns a character or special symbol for the key that was pressed. For example, the Enter key generates #\return, and the up-arrow key generates 'up. For a complete list of possible return values, see get-key-code.
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