For other information, see the Ghostscript overview.
Ghostscript can use the character rasterizer provided by the underlying operating system and window system; specifically, Adobe Type Manager (ATM) or a TrueType rasterizer under MS Windows, or the facilities provided by X Windows. This ability augments, but does not replace, Ghostscript's own Type 1 rasterizer: Ghostscript may still use its own rasterizer for very large characters, characters that are clipped or transformed in unusual ways, and for output to devices other than the screen.
Ghostscript connects to these platform facilities through a driver-like interface called the xfont (external font) interface. Current xfont implementations are associated directly with device drivers; in a future release, Ghostscript may separate them, so that (for example) it will be possible to use the platform rasterizer when writing to a file.
Please note that from this point, this file is likely to be useful only to a small number of Ghostscript porters and implementors.
| Type | Declared / defined in | Represents | ||
|---|---|---|---|---|
gs_char
| gsccode.h
| A character code that appears in a string. Currently it is always a single byte, but composite fonts or Unicode may require it to be wider in the future. | ||
gs_glyph
| gsccode.h
| A character name like "period" or "epsilon". From
the xfont implementation's point of view, it is just a handle;
when necessary, Ghostscript provides a
gs_proc_glyph_name_t procedure to
convert it to a string name.
| ||
gs_proc_glyph_name_t
| gsccode.h
| A procedure that maps a gs_glyph to
its string name; see the char_xglyph procedure.
| ||
gx_xglyph
| gsxfont.h
| A character or glyph code that can be used with a
specific platform font. Normally it will be a character code
that the implementation of render_char will
turn into a 1-character string and give to the platform's
"display string" operation.
| ||
gx_xfont_procs
| gsxfont.h, gxxfont.h
| The xfont analogue of
gx_device_procs, the type of the
procedure record that defines an xfont implementation.
| ||
gx_xfont
| gsxfont.h, gxxfont.h
| The gxfont analogue of gx_device,
the type of the basic structure for an xfont.
| ||
(encoding_index)
| Not really a type, although it probably should be:
an int used to indicate the
Encoding used by a font. Defined values are
| |||
All the procedures that return int results return 0 on
success, or an appropriate negative error code for error conditions; these
error codes are defined in gserrors.h. The relevant ones
are the same as for drivers, and as with drivers,
if an implementation procedure returns an error, it should use the
return_error macro -- defined in gx.h,
which is automatically included by gdevprn.h but not by
gserrors.h -- rather than a simple return
statement, for instance
return_error(gs_error_VMerror);
lookup_fontgx_xfont *(*lookup_font)(P7(gx_device *dev,
const byte *fname, uint len, int encoding_index,
const gs_uid *puid, const gs_matrix *pmat,
const gs_memory_procs *mprocs))
UniqueID, and matrix, and return
an xfont, or NULL if no suitable xfont exists. Use
mprocs to allocate the xfont and any subsidiary data
structures. The matrix is the FontMatrix concatenated with
the CTM, so (roughly speaking) the font size in pixels is
pmat -> yy × 1000 for a normal
Type 1 font.
Note that this is the only implementation procedure that does not take an
xfont * as its first argument. In fact, callers of
lookup_font must use the get_xfont_device
driver procedure to get the correct device to pass as the first argument to
lookup_font.
char_xglyphgx_xglyph (*char_xglyph)(P5(gx_xfont *xf, gs_char chr,
int encoding_index, gs_glyph glyph,
gs_proc_glyph_name_t glyph_name))
glyphshow, chr may be
gs_no_char; for an ordinary show operation,
if the character code is invalid, glyph may be
gs_no_glyph.
char_metricsint (*char_metrics)(P5(gx_xfont *xf, gx_xglyph xg,
int wmode, gs_int_point *pwidth,
gs_int_rect *pbbox))
render_charint (*render_char)(P7(gx_xfont *xf, gx_xglyph xg,
gx_device *target, int x, int y, gx_color_index color,
int required))
copy_mono operation. If required is false,
the procedure should return an error if the rendering operation would be
expensive, since in this case Ghostscript has already cached the bitmap and
metrics from a previous call with required=true. If the
operation cannot be done, return 1.
releaseint (*release)(P2(gx_xfont *xf,
const gs_memory_procs *mprocs))
mprocs is not NULL, also free any storage
allocated by lookup_font (including the xfont itself).
Copyright © 2000-2006 Artifex Software, Inc. All rights reserved.
This software is provided AS-IS with no warranty, either express or implied. This software is distributed under license and may not be copied, modified or distributed except as expressly authorized under the terms of that license. Refer to licensing information at http://www.artifex.com/ or contact Artifex Software, Inc., 7 Mt. Lassen Drive - Suite A-134, San Rafael, CA 94903, U.S.A., +1(415)492-9861, for further information.
Ghostscript version 8.64, 3 February 2009