<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><title>The Ghostscript library</title><!-- $Id: Lib.htm,v 1.43 2005/10/20 19:46:23 ray Exp $ --><!-- Originally: lib.txt --><link rel="stylesheet" type="text/css" href="gs.css" title="Ghostscript Style"></head> <body><!-- [1.0 begin visible header] ============================================ --> <!-- [1.1 begin headline] ================================================== --> <h1>The Ghostscript Library</h1> <!-- [1.1 end headline] ==================================================== --> <!-- [1.2 begin table of contents] ========================================= --> <h2>Table of contents</h2> <blockquote><ul><li><a href="#GS_library">The Ghostscript library</a><li><a href="#PS_operator_API">PostScript operator API</a><ul><li><a href="#Patterns">Patterns</a><li><a href="#Lower_level_API">Lower-level API</a></ul><li><a href="#Visual_trace">Visual Trace instructions</a><li><a href="#Full_example">A full example</a></ul></blockquote> <!-- [1.2 end table of contents] =========================================== --> <!-- [1.3 begin hint] ====================================================== --> <p>For other information, see the <a href="Readme.htm">Ghostscriptoverview</a>. <!-- [1.3 end hint] ======================================================== --> <hr> <!-- [1.0 end visible header] ============================================== --> <!-- [2.0 begin contents] ================================================== --> <h2><a name="GS_library"></a>The Ghostscript library</h2> <p>This document describes the Ghostscript library, a set of proceduresto implement the graphics and filtering capabilities that are primitiveoperations in the PostScript language and in Adobe Portable Document Format(PDF). <p>Ghostscript is actually two programs: a language interpreter, and agraphics library.  The library provides, in the form of C procedures, allthe graphics functions of the language, that is, approximately thosefacilities listed in section 8.1 of the <cite>PostScriptLanguage Reference Manual</cite>, starting with thegraphics state operators.  In addition, the library provides somelower-level graphics facilities that offer higher performance in exchangefor less generality. <hr> <h2><a name="PS_operator_API"></a>PostScript operator API</h2> <p>The highest level of the library, which is the one that most clients willuse, directly implements the PostScript graphics operators with proceduresnamed <b><tt>gs_XXX</tt></b>, for instance <b><tt>gs_moveto</tt></b> and<b><tt>gs_fill</tt></b>.  Nearly all of these procedures take graphicsstate objects as their first arguments, such as <blockquote><b><tt>int gs_moveto(gs_state *, double, double);</tt></b></blockquote> <p>Nearly every procedure returns an integer code which is &gt;= 0 for asuccessful return or &lt;0 for a failure.  The failure codes corresponddirectly to PostScript errors, and are defined in<b><tt>gserrors.h</tt></b>. <p>The library implements all the operators in the following sections of the<cite>PostScript Language Reference Manual</cite>, with the indicatedomissions and with the APIs defined in the indicated <b><tt>.h</tt></b>files.  A header of the form <b><em>A.h(B.h)</em></b> indicates that<b><em>A.h</em></b> is included in <b><em>B.h</em></b>, so<b><em>A.h</em></b> need not be included explicitly if <b><em>B.h</em></b>is included.  Operators marked with * in the "omissions" column are notimplemented directly; the library provides lower-level procedures that canbe used to implement the operator. <p>There are slight differences in the operators that return multiple values,since C's provisions for this are awkward.  Also, the control structure forthe operators involving callback procedures (<b><tt>pathforall</tt></b>,<b><tt>image</tt></b>, <b><tt>colorimage</tt></b>,<b><tt>imagemask</tt></b>) is partly inverted: the client calls a procedureto set up an enumerator object, and then calls another procedure for eachiteration.  The <b><tt>...show</tt></b> operators,<b><tt>charpath</tt></b>, and <b><tt>stringwidth</tt></b> also use aninverted control structure. <blockquote><table cellpadding=0 cellspacing=0><tr valign=bottom>	<th align=left>Section<br>(operators)	<td>&nbsp;&nbsp;	<th align=left>Headers	<td>&nbsp;&nbsp;	<th align=left>Omissions<tr>	<td colspan=5><hr><tr valign=top>	<td>Graphics state -- device-independent	<td>&nbsp;	<td><b><tt>gscolor.h</tt></b>(<b><tt>gsstate.h</tt></b>)<br><b><tt>gscolor1.h</tt></b><br><b><tt>gscolor2.h</tt></b><br><b><tt>gscspace.h</tt></b><br><b><tt>gshsb.h</tt></b><br><b><tt>gsline.h</tt></b>(<b><tt>gsstate.h</tt></b>)<br><b><tt>gsstate.h</tt></b>	<td>&nbsp;	<td>&nbsp;<tr>	<td>&nbsp;<tr valign=top>	<td>Graphics state -- device-dependent	<td>&nbsp;	<td><b><tt>gscolor.h</tt></b>(<b><tt>gsstate.h</tt></b>)<br><b><tt>gscolor1.h</tt></b><br><b><tt>gscolor2.h</tt></b><br><b><tt>gsht.h</tt></b>(<b><tt>gsht1.h</tt></b>,<b><tt>gsstate.h</tt></b>)<br><b><tt>gsht1.h</tt></b><br><b><tt>gsline.h</tt></b>(<b><tt>gsstate.h</tt></b>)	<td>&nbsp;	<td>&nbsp;<tr>	<td>&nbsp;<tr valign=top>	<td>Coordinate system and matrix	<td>&nbsp;	<td><b><tt>gscoord.h</tt></b><br><b><tt>gsmatrix.h</tt></b>	<td>&nbsp;	<td><b><tt>*matrix</tt></b>, <b><tt>*identmatrix</tt></b>, <b><tt>*concatmatrix</tt></b>, <b><tt>*invertmatrix</tt></b><tr>	<td>&nbsp;<tr valign=top>	<td>Path construction	<td>&nbsp;	<td><b><tt>gspath.h</tt></b><br><b><tt>gspath2.h</tt></b>	<td>&nbsp;	<td><b><tt>*arct</tt></b>, <b><tt>*pathforall</tt></b>, <b><tt>ustrokepath</tt></b>, <b><tt>uappend</tt></b>, <b><tt>upath</tt></b>, <b><tt>ucache</tt></b><tr>	<td>&nbsp;<tr valign=top>	<td>Painting	<td>&nbsp;	<td><b><tt>gsimage.h</tt></b><br><b><tt>gspaint.h</tt></b><br><b><tt>gspath2.h</tt></b>	<td>&nbsp;	<td><b><tt>*image</tt></b>, <b><tt>*colorimage</tt></b>, <b><tt>*imagemask</tt></b>, <b><tt>ufill</tt></b>, <b><tt>ueofill</tt></b>, <b><tt>ustroke</tt></b><tr>	<td>&nbsp;<tr valign=top>	<td>Form and pattern	<td>&nbsp;	<td><b><tt>gscolor2.h</tt></b>	<td>&nbsp;	<td><b><tt>execform</tt></b><tr>	<td>&nbsp;<tr valign=top>	<td>Device setup and output	<td>&nbsp;	<td><b><tt>gsdevice.h</tt></b>	<td>&nbsp;	<td><b><tt>*showpage</tt></b>, <b><tt>*set</tt></b>/<b><tt>currentpagedevice</tt></b><tr>	<td>&nbsp;<tr valign=top>	<td>Character and font	<td>&nbsp;	<td><b><tt>gschar.h</tt></b><br><b><tt>gsfont.h</tt></b>	<td>&nbsp;	<td>*(all the <b><tt>show</tt></b> operators), <b><tt>definefont</tt></b>, <b><tt>undefinefont</tt></b>, <b><tt>findfont</tt></b>, <b><tt>*scalefont</tt></b>, <b><tt>*makefont</tt></b>, <b><tt>selectfont</tt></b>, <b><tt>[Global]FontDirectory</tt></b>, <b><tt>Standard</tt></b>/<b><tt>ISOLatin1Encoding</tt></b>, <b><tt>findencoding</tt></b></table></blockquote> <p>The following procedures from the list above operate differently from theirPostScript operator counterparts, as explained here: <dl><dt><b><tt>gs_makepattern(gscolor2.h)</tt></b><dd>Takes an explicit current color, rather than using the current color inthe graphics state.  Takes an explicit allocator for allocating the patternimplementation.  See below for more details on<b><tt>gs_makepattern</tt></b>.</dl> <dl><dt><b><tt>gs_setpattern(gscolor2.h)</tt></b><dt><b><tt>gs_setcolor(gscolor2.h)</tt></b><dt><b><tt>gs_currentcolor(gscolor2.h)</tt></b><dd>Use <b><tt>gs_client_color</tt></b> rather than a set of colorparameter values.  See below for more details on<b><tt>gs_setpattern</tt></b>.</dl> <dl><dt><b><tt>gs_currentdash_length/pattern/offset(gsline.h)</tt></b><dd>Splits up <b><tt>currentdash</tt></b> into three separate procedures.</dl> <dl><dt><b><tt>gs_screen_init/currentpoint/next/install(gsht.h)</tt></b><dd>Provide an "enumeration style" interface to <b><tt>setscreen</tt></b>.(<b><tt>gs_setscreen</tt></b> is also implemented.)</dl> <dl><dt><b><tt>gs_rotate/scale/translate(gscoord.h)</tt></b><dt><b><tt>gs_[i][d]transform(gscoord.h)</tt></b><dd>These always operate on the graphics state CTM.  The correspondingoperations on free-standing matrices are in <b><tt>gsmatrix.h</tt></b> andhave different names.</dl> <dl><dt><b><tt>gs_path_enum_alloc/init/next/cleanup(gspath.h)</tt></b><dd>Provide an "enumeration style" implementation of<b><tt>pathforall</tt></b>.</dl> <dl><dt><b><tt>gs_image_enum_alloc(gsimage.h)</tt></b><dt><b><tt>gs_image_init/next/cleanup(gsimage.h)</tt></b><dd>Provide an "enumeration style" interface to the equivalent of<b><tt>image</tt></b>, <b><tt>imagemask</tt></b>, and<b><tt>colorimage</tt></b>.  In the <b><tt>gs_image_t</tt></b>,<b><tt>ColorSpace</tt></b> provides an explicit color space, rather thanusing the current color space in the graphics state;<b><tt>ImageMask</tt></b> distinguishes <b><tt>imagemask</tt></b> from<b><tt>[color]image</tt></b>.</dl> <dl><dt><b><tt>gs_get/putdeviceparams(gsdevice.h)</tt></b><dd>Take a <b><tt>gs_param_list</tt></b> for specifying or receiving theparameter values.  See <b><tt>gsparam.h</tt></b> for more details.</dl> <dl><dt><b><tt>gs_show_enum_alloc/release(gschar.h)</tt></b><dt><b><tt>gs_xxxshow_[n_]init(gschar.h)</tt></b><dt><b><tt>gs_show_next(gschar.h)</tt></b><dd>Provide an "enumeration style" interface to writing text.  Note thatcontrol returns to the caller if the character must be rasterized.</dl> <p>This level of the library also implements the following operators from othersections of the Manual: <blockquote><table cellpadding=0 cellspacing=0><tr valign=bottom>	<th align=left>Section<br>(operators)	<td>&nbsp;&nbsp;	<th align=left>Headers	<td>&nbsp;&nbsp;	<th align=left>Operators<tr>	<td colspan=5><hr><tr valign=top>	<td>Interpreter parameter	<td>&nbsp;	<td><b><tt>gsfont.h</tt></b>	<td>&nbsp;	<td><b><tt>cachestatus</tt></b>, <b><tt>setcachelimit</tt></b>, <b><tt>*set/currentcacheparams</tt></b><tr valign=top>	<td>Display PostScript	<td>&nbsp;	<td><b><tt>gsstate.h</tt></b>	<td>&nbsp;	<td><b><tt>set/currenthalftonephase</tt></b></table></blockquote> <p>In order to obtain the full PostScript Level 2 functionality listed above,<b><tt>FEATURE_DEVS</tt></b> must be set in the makefile to include at least the following: <blockquote><b><tt>FEATURE_DEVS=patcore.dev cmykcore.dev psl2core.dev dps2core.dev ciecore.dev path1core.dev hsbcore.dev</tt></b></blockquote> <p>The <b><tt>*lib.mak</tt></b> makefiles mentioned below do not alwaysinclude all of these features. <p>Files named <b><tt>gs*.c</tt></b> implement the higher level of thegraphics library.  As might be expected, all procedures, variables, andstructures available at this level begin with "<b><tt>gs_</tt></b>".Structures that appear in these interfaces, but whose definitions may behidden from clients, also have names beginning with "<b><tt>gs_</tt></b>",that is, the prefix, not the implementation, reflects at what level theabstraction is made available. <h3><a name="Patterns"></a>Patterns</h3> <p>Patterns are the most complicated PostScript language objects that thelibrary API deals with.  As in PostScript, defining a pattern color andusing the color are two separate operations. <p><b><tt>gs_makepattern</tt></b> defines a pattern color.  Its arguments are as follows: <blockquote><table cellpadding=0 cellspacing=0><tr valign=top>	<td><b><tt>gs_client_color *</tt></b>	<td>&nbsp;&nbsp;&nbsp;	<td>The resulting <b><tt>Pattern</tt></b> color is stored here.  This is different from PostScript, which has no color objects <em>per se</em>, and hence returns a modified copy of the dictionary.<tr valign=top>	<td><b><tt>const gs_client_pattern *</tt></b>	<td>&nbsp;	<td>The analogue of the original <b><tt>Pattern</tt></b> dictionary, described in detail just below.<tr valign=top>	<td><b><tt>const gs_matrix *</tt></b>	<td>&nbsp;	<td>Corresponds to the matrix argument of the <b><tt>makepattern</tt></b> operator.<tr valign=top>	<td><b><tt>gs_state *</tt></b>	<td>&nbsp;	<td>The current graphics state.<tr valign=top>	<td><b><tt>gs_memory_t *</tt></b>	<td>&nbsp;	<td>The allocator to use for allocating the saved data for the	    <b><tt>Pattern</tt></b> color.  If this is	    <b><tt>NULL</tt></b>, <b><tt>gs_makepattern</tt></b> uses the	    same allocator that allocated the graphics state.  Library	    clients should probably always use <b><tt>NULL</tt></b>. </table></blockquote> <p>The <b><tt>gs_client_pattern</tt></b> structure defined in<b><tt>gscolor2.h</tt></b> corresponds to the <b><tt>Pattern</tt></b>dictionary that is the argument to the PostScript language<b><tt>makepattern</tt></b> operator.  This structure has one extra member,<b><tt>void&nbsp;*client_data</tt></b>, which is a place for clients tostore a pointer to additional data for the <b><tt>PaintProc</tt></b>; thisprovides the same functionality as putting additional keys in the<b><tt>Pattern</tt></b> dictionary at the PostScript language level.  The<b><tt>PaintProc</tt></b> is an ordinary C procedure that takes asparameters a <b><tt>gs_client_color&nbsp;*</tt></b>, which is the<b><tt>Pattern</tt></b> color that is being used for painting, and a<b><tt>gs_state&nbsp;*</tt></b>, which is the same graphics state thatwould be presented to the <b><tt>PaintProc</tt></b> in PostScript.Currently the <b><tt>gs_client_color&nbsp;*</tt></b> is always the currentcolor in the graphics state, but the <b><tt>PaintProc</tt></b> should notrely on this.  The <b><tt>PaintProc</tt></b> can retrieve the<b><tt>gs_client_pattern&nbsp;*</tt></b> from the<b><tt>gs_client_color&nbsp;*</tt></b> with the<b><tt>gs_getpattern</tt></b> procedure, also defined in<b><tt>gscolor2.h</tt></b>, and from there, it can retrieve the<b><tt>client_data</tt></b> pointer. <p>The normal way to set a <b><tt>Pattern</tt></b> color is to call<b><tt>gs_setpattern</tt></b> with the graphics state and with the<b><tt>gs_client_color</tt></b> returned by <b><tt>gs_makepattern</tt></b>.After that, one can use <b><tt>gs_setcolor</tt></b> to set further<b><tt>Pattern</tt></b> colors (colored, or uncolored with the sameunderlying color space); the rules are the same as those in PostScript.Note that for <b><tt>gs_setpattern</tt></b>, the<b><tt>paint.values</tt></b> in the <b><tt>gs_client_color</tt></b> must befilled in for uncolored patterns; this corresponds to the additionalarguments for the PostScript <b><tt>setpattern</tt></b> operator in theuncolored case. <p>There is a special procedure <b><tt>gs_makebitmappattern</tt></b> for creating bitmap-basedpatterns.  Its API is documented in <b><tt>gscolor2.h</tt></b>; its implementation, in<b><tt>gspcolor.c</tt></b>, may be useful as an example of a pattern using a particularlysimple <b><tt>PaintProc.</tt></b> <h3><a name="Lower_level_API"></a>Lower-level API</h3> <p>Files named <b><tt>gx*.c</tt></b> implement the lower level of the graphicslibrary.  The interfaces at the <b><tt>gx</tt></b> level are less stable,and expose more of the implementation detail, than those at the<b><tt>gs</tt></b> level: in particular, the <b><tt>gx</tt></b> interfacesgenerally use device coordinates in an internal fixed-point representation,as opposed to the <b><tt>gs</tt></b> interfaces that use floating pointuser coordinates.  Named entities at this level begin with<b><tt>gx_</tt></b>. <p>Files named <b><tt>gz*.c</tt></b> and <b><tt>gz*.h</tt></b> are internal tothe Ghostscript implementation, and are not designed to be called byclients. <hr> <h2><a name="Visual_trace"></a>Visual Trace instructions</h2> <p>Visual Trace instructions may be inserted in code to provide debug output ina graphical form. Graphics Library doesn't provide a rasterisation of theoutput, because it is platform dependent. Instead this, client applicationshpuld set <b><tt>vd_trace0</tt></b> external variable to Graphics Library,passing a set of callbacks which provide the rasterization. <p>Visual Trace instructions are defined in <b><tt>vdtrace.h</tt></b>.Debug output must be opened with <b><tt>vd_get_dc</tt></b> instruction,which obtains a drawing context for the debug output, and must be closedwith <b><tt>vd_release_dc</tt></b> instruction. After opening the output,scale, origin and shift to be set for mapping the debugee coordinate spaceto window coordinate space. Than painting instructions to be used.Painting may be either immediate or indirect. <p>Indirect painting uses <b><tt>vd_beg_path</b></tt> beforeline output and <b><tt>vd_end_path</b></tt> after line output,to store a path into a temporary storage. After this <b><tt>vd_stroke</b></tt> may be used for stroking the path,or <b><tt>vd_fill</b></tt> may be used for filling the region inside the path. <p>Immediate painting happens when path construction instructions areinvolved without <b><tt>vd_beg_path</b></tt> and <b><tt>vd_end_path</b></tt>.In this case lines and curves are being drawed immediately, when a path constructioninstruction is executed. <p>The following table explains the semantics of Visual Trace instructions.<p> <table cellpadding=0 cellspacing=0><tr><th colspan=5 bgcolor="#CCCC00"><hr><font size="+1">Visual Trace instructions</font><hr><tr>	<th align=left>Instruction        <td>&nbsp;&nbsp;	<th align=left>Function        <td>&nbsp;&nbsp;	<th align=left>Parameters<tr>	<td colspan=5><hr><tr>	<td><b><tt>vd_get_dc</tt></b>        <td>&nbsp;&nbsp;	<td>Obtain drawing context        <td>&nbsp;&nbsp;	<td><b><tt>-T</tt></b> option flag value, for which the subsequent output is enabled.<tr>	<td><b><tt>vd_release_dc</tt></b>        <td>&nbsp;&nbsp;	<td>Release drawing context        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_enabled</tt></b>        <td>&nbsp;&nbsp;	<td>Is trace currently enabled ?        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_size_unscaled_x</tt></b>        <td>&nbsp;&nbsp;	<td>Get the horizontal size of the output window in pixels.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_size_unscaled_y</tt></b>        <td>&nbsp;&nbsp;	<td>Get the vertical size of the output window in pixels.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_size_caled_x</tt></b>        <td>&nbsp;&nbsp;	<td>Get the horizontal size of the output window in debuggee coordinate units.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_size_caled_y</tt></b>        <td>&nbsp;&nbsp;	<td>Get the vertical size of the output window in debuggee coordinate units.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_scale_x</tt></b>        <td>&nbsp;&nbsp;	<td>Get the horizontal scale.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_scale_y</tt></b>        <td>&nbsp;&nbsp;	<td>Get the vertical scale.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_origin_x</tt></b>        <td>&nbsp;&nbsp;	<td>Get the horizontal position of the draft origin in debuggee coordinate space.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_get_origin_y</tt></b>        <td>&nbsp;&nbsp;	<td>Get the vertical position of the draft origin in debuggee coordinate space.        <td>&nbsp;&nbsp;	<td><tr>	<td><b><tt>vd_set_scale(s)</tt></b>        <td>&nbsp;&nbsp;	<td>Set isotripic scale.        <td>&nbsp;&nbsp;	<td>Debugee space to window space mapping scale, same for both dimentions.<tr>	<td><b><tt>vd_set_scaleXY(sx,sy)</tt></b>        <td>&nbsp;&nbsp;	<td>Set anisotripic scale.        <td>&nbsp;&nbsp;	<td>Debugee space to window space mapping scale, one for each dimention.<tr>	<td><b><tt>vd_set_origin(x,y)</tt></b>        <td>&nbsp;&nbsp;	<td>Set the draft origin.        <td>&nbsp;&nbsp;	<td>Origin of the draft in debugee space.<tr>	<td><b><tt>vd_set_shift(x,y)</tt></b>        <td>&nbsp;&nbsp;	<td>Set the draft position.        <td>&nbsp;&nbsp;	<td>Position of the draft origin in window space (in pixels).<tr>	<td><b><tt>vd_set_central_shift</tt></b>        <td>&nbsp;&nbsp;	<td>Set the draft position to window center.        <td>&nbsp;&nbsp;	<td>

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