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<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN">
<HTML
><HEAD
><TITLE
>The Procedural Database</TITLE
><META
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PROCEDURAL-DATABASE"
>The Procedural Database</A
></H1
><P
>The procedural database is a registry of things gimp and its
plugins can do. When you install a procedure for your plugin, you
are extending the procedural database.</P
><P
>The procedural database is self documenting, in that when
you install a procedure in it, you also add documentation for it,
its parameters and return values.</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="GIMP-PYTHON-MODEL"
>The Gimp-Python Model</A
></H2
><P
>In Gimp-Python, the procedural database is represented by
the object <TT
CLASS="PARAMETER"
><I
>gimp.pdb</I
></TT
>. In most of my
plugins, I make an assignment from <TT
CLASS="PARAMETER"
><I
>gimp.pdb</I
></TT
>
to <TT
CLASS="PARAMETER"
><I
>pdb</I
></TT
> for convenience.</P
><P
>You can query the procedural database with
<TT
CLASS="PARAMETER"
><I
>pdb</I
></TT
>'s method <TT
CLASS="FUNCTION"
><B
>query</B
></TT
>. Its
specification is:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
>pdb.query(name, [blurb, [help, [author, [copyright, [date, [type]]]]]])</PRE
></TD
></TR
></TABLE
><P
>Each parameter is a regular expression that is checked
against the corresponding field in the procedural database. The
method returns a list of the names of matching procedures. If
<TT
CLASS="FUNCTION"
><B
>query</B
></TT
> is called without any arguments, it will
return every procedure in the database.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PDB-PROCEDURES"
>Procedural Database Procedures</A
></H2
><P
>Procedures can be accessed as procedures, or by treating
<TT
CLASS="PARAMETER"
><I
>pdb</I
></TT
> as a mapping objest. As an example,
the probedure <TT
CLASS="FUNCTION"
><B
>gimp_edit_fill</B
></TT
> can be
accessed as either <TT
CLASS="FUNCTION"
><B
>pdb.gimp_edit_fill</B
></TT
> or
<TT
CLASS="FUNCTION"
><B
>pdb['gimp_edit_fill']</B
></TT
>. The second form is
mainly for procedures whose names are not valid Python names (eg
in script-fu-..., the dashes are interpreted as minuses).</P
><P
>These procedure objects have a number of attribute:</P
><P
></P
><DL
><DT
>proc_name</DT
><DD
><P
>The name of the procedure.</P
></DD
><DT
>proc_blurb</DT
><DD
><P
>A short peice of information about the procedure.</P
></DD
><DT
>proc_help</DT
><DD
><P
>More detailed information about the procedure.</P
></DD
><DT
>proc_author</DT
><DD
><P
>The author of the procedure.</P
></DD
><DT
>proc_copyright</DT
><DD
><P
>The copyright holder for the procedure (usually the
same as the author).</P
></DD
><DT
>proc_date</DT
><DD
><P
>The date when the procedure was written.</P
></DD
><DT
>proc_type</DT
><DD
><P
>The type of procedure. This will be one of
PROC_PLUG_IN, PROC_EXTENSION or PROC_TEMPORARY.</P
></DD
><DT
>nparams</DT
><DD
><P
>The number of parameters the procedure takes.</P
></DD
><DT
>nreturn_vals</DT
><DD
><P
>The number of return values the procedure gives.</P
></DD
><DT
>params</DT
><DD
><P
>A description of parameters of the procedure. It
takes the form of a tuple of 3-tuples, where each 3-tuple
describes a parameter. The items in the 3-tuple are a
parameter type (one of the PARAM_* constants), a
name for the parameter, and a description of the
parameter.</P
></DD
><DT
>return_vals</DT
><DD
><P
>A description of the return values. It takes the
same form as the <TT
CLASS="LITERAL"
>params</TT
>
attribute.</P
></DD
></DL
><P
>A procedure object may also be called. At this point,
Gimp-Python doesn't support keyword arguments for PDB
procedures. Arguments are passed to the procedure in the normal
method. The return depends on the number of return values:</P
><P
></P
><UL
><LI
><P
>If there are zero return values,
<TT
CLASS="LITERAL"
>None</TT
> is returned.</P
></LI
><LI
><P
>If there is only a single return value, it is
returned.</P
></LI
><LI
><P
>If there are more return values, then they are
returned as a tuple.</P
></LI
></UL
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="MORE-INFORMATION"
>More Information</A
></H2
><P
>For more information on invoking PDB procedures, please
see the example plugins. For information on individual
procedures, please see the PDB Browser plugin (in the Xtns
menu). It alows you to peruse to the database
interactively.</P
></DIV
></DIV
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