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Correct the explanation of glyphs and glyph table.

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Richard M. Stallman 2002-09-14 17:36:44 +00:00
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lispref/display.texi
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@ -3380,17 +3380,36 @@ are defined in the library @file{disp-table}.
@cindex glyph
A @dfn{glyph} is a generalization of a character; it stands for an
image that takes up a single character position on the screen. Glyphs
are represented in Lisp as integers, just as characters are.
are represented in Lisp as integers, just as characters are. Normally
Emacs finds glyphs in the display table (@pxref{Display Tables}).
@cindex glyph table
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable @code{glyph-table}.
A glyph can be @dfn{simple} or it can be defined by the @dfn{glyph
table}. A simple glyph is just a way of specifying a character and a
face to output it in. The glyph code for a simple glyph, mod 524288,
is the character to output, and the glyph code divided by 524288
specifies the face number (@pxref{Face Functions}) to use while
outputting it. (524288 is
@ifnottex
2**19.)
@end ifnottex
@tex
$2^{19}$.)
@end tex
@xref{Faces}.
On character terminals, you can set up a @dfn{glyph table} to define
the meaning of glyph codes. The glyph codes is the value of the
variable @code{glyph-table}.
@defvar glyph-table
The value of this variable is the current glyph table. It should be a
vector; the @var{g}th element defines glyph code @var{g}. If the value
is @code{nil} instead of a vector, then all glyphs are simple (see
below). The glyph table is not used on windowed displays.
vector; the @var{g}th element defines glyph code @var{g}.
If a glyph code is greater than or equal to the length of the glyph
table, that code is automatically simple. If the value of
@code{glyph-table} is @code{nil} instead of a vector, then all glyphs
are simple. The glyph table is not used on graphical displays, only
on character terminals. On graphical displays, all glyphs are simple.
@end defvar
Here are the possible types of elements in the glyph table:
@ -3403,24 +3422,13 @@ but not under a window system.
@item @var{integer}
Define this glyph code as an alias for glyph code @var{integer}. You
can use an alias to specify a face code for the glyph; see below.
can use an alias to specify a face code for the glyph and use a small
number as its code.
@item @code{nil}
This glyph is simple. The glyph code mod 524288 is the character to
output, and the glyph code divided by 524288 specifies the face number
(@pxref{Face Functions}) to use while outputting it. (524288 is
@ifnottex
2**19.)
@end ifnottex
@tex
$2^{19}$.)
@end tex
@xref{Faces}.
This glyph is simple.
@end table
If a glyph code is greater than or equal to the length of the glyph
table, that code is automatically simple.
@defun create-glyph string
@tindex create-glyph
This function returns a newly-allocated glyph code which is set up to