Graphic character

ISO/IEC 646

In ASCII (specified in ISO/IEC 646), graphic characters are contained in rows 2 through 7 of the code table. However, two of the characters in these rows, namely the space character SP at row 2 column 0 and the delete character DEL (also called the rubout character) at row 7 column 15, require special mention.

The space is considered to be both a graphic character and a control character in ISO 646. It can be considered as a character with a visible form or, in contexts such as teleprinters, a control character that advances the print head without printing a character.

The delete character is strictly a control character, not a graphic character. This is true not only in ISO 646, but also in all related standards including Unicode. However, many other character sets deviate from ISO 646, and as a result a graphic character might occupy the position originally reserved for the delete character.

Unicode

In Unicode, Graphic characters are those with General Category Letter, Mark, Number, Punctuation, Symbol or Zs=space. Other code points (General categories Control, Zl=line separator, Zp=paragraph separator) are Format, Control, Private Use, Surrogate, Noncharacter or Reserved (unassigned).

{{anchor|Spacing character|Non-spacing character}}Spacing and non-spacing characters

Most graphic characters are spacing characters, which means that each instance of a spacing character has to occupy some area in a graphic representation. For a teletype or a typewriter this implies moving of the carriage after typing of a character. In the context of monospace typefaces (or computer fonts), each spacing character occupies one rectangular character box of equal sizes.. If a text is rendered using proportional fonts, widths of character boxes are not equal, but are positive.

There exist also non-spacing graphic characters. Most of the non-spacing characters are modifiers (called combining characters in Unicode), such as diacritical marks. Although non-spacing graphic characters are uncommon in traditional code pages, there are many such in Unicode. A combining character has its distinct mark, but it applies to a character box of another character, a spacing one. In some historical systems such as typewriters, this was implemented as 'backspace and overstrike'.

Note that not all modifiers are non-spacing the Unicode block "Spacing Modifier Letters" list a number of others.

Notes

References

References

1. (20 May 2014). "The Computer Graphics Metafile: Butterworth Series in Computer Graphics Standards". Elsevier Science.
2. https://www.unicode.org/versions/Unicode5.2.0/ch02.pdf#G25564 Chapter 2, table 2.3