scribblealloc, recognize – character recognition


#include <u.h>
#include <libc.h>
#include <draw.h>
#include <scribble.h>
Scribble *scribblealloc(void);
Rune      recognize(Scribble *);


The scribble library implements simple character recognition. All characters are drawn using a single stroke of the pen (mouse button 1) as on a palmtop computer.

The library is not really intended for standalone use. Its primary use is by the scribble graphical control (see control(2)).

Scribblealloc allocates and returns an appropriately initialized Scribble structure:
#define    CS_LETTERS        0
#define    CS_DIGITS         1
#define    CS_PUNCTUATION     2
struct Scribble {
/* private state */
Point        *pt;
int          ppasize;
Stroke       ps;
Graffiti     *graf;
int          capsLock;
int          puncShift;
int          tmpShift;
int          ctrlShift;
int          curCharSet;

This structure encodes the points making up the stroke to be recognized, as well as the character group in which the stroke should be searched.

There are three such groups: letters, digits, and punctuation. The current group is encoded in the curCharSet field of the Scribble structure. Special strokes are recognized to switch between groups. In addition, the charater recognized is influenced by mode parameters and modifies them. These are identified by the capsLock, puncShift, tmpShift, and ctrlShift fields of the Scribble structure. When puncShift is non–zero, the character is recognized in the punctuation character set. Similarly, when the character recognized is printable and ctrlShift is set, the associated control character is returned as if the control key were depressed, and when the character is a letter and capsLock or tmpShift is set, the upper–case version is returned. The puncShift and tmpShift flags are turned off once a character has been recognized; the others are left set.

The character to be recognized is encoded as an array of pen_points in the ps field. To allow easy drawing of the stroke as it is drawn, the pt and ppasize fields are available to the application code for storing an array of points for a call to poly (see draw(2)).

Recognize recognizes the character provided in the ps field of the Scribble structure; it returns the rune or zero if nothing was recognized.

/sys/lib/scribble/classifiers contains the stroke definitions.


This library is adapted from software reproduced by permission:

Graffiti.c is based on the file Scribble.c copyrighted by Keith Packard:
Copyright © 1999 Keith Packard

Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of Keith Packard not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission. Keith Packard makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

Portions of the software Copyright © 1994 by Sun Microsystems Computer Company.

Portions of the software Copyright © 2000 by Compaq Computer Corporation.

Keyboard and prompter in bitsyload(1), draw(2), control(2)