1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
|
<!-- vim:tabstop=4:shiftwidth=4:noexpandtab:textwidth=80
-->
<sect1 id="kernel_part_cxref">
<title>CXRef</title>
<para>
CXRef class wrapps Xpdf <classname>XRef</classname> class and provides additional functionality
with same interface (see <xref linkend="wrapper"/>. It provides with
protected interface for making changes and internally stores changed
objects. When object should be fetched (<classname>fetch</classname>
method is called), it will check whether this object is already changed
and if so, uses changed value. Otherwise delegates to <classname>XRef</classname> original
implementation (this logic is kept in all methods defined in XRef).
</para>
<para>
CXRef inherits from <classname>XRef</classname> and so can be polymorphicaly used in xpdf code
and this code doesn't need any changes to use CXref functionality.
Aditional interface enables changes, but as we want to keep this making
changes under control so it is protected and so accessible only for its
inheritance descendants.
</para>
<para>
Added functionality includes:
<itemizedlist>
<listitem>
new indirect objects creation - creates new pdf object and
associates it with reserved reference.
</listitem>
<listitem>
changing of already existing indirect objects.
<classname>changeObject</classname> method which changes object
with given reference with given object.
</listitem>
<listitem>
changing of document trailer - add, remove or change elements of
<xref linkend="trailer"/>.
</listitem>
<listitem>
checking for type safety - checks whether given object can
safely replace original value (in document or currently saved
form) according types. Type safe change is consider such change,
when new value type is either same as old type, or dereferenced
types (if any of types is reference) or if original value is
CNull, then new value may have arbitrary type.
</listitem>
<listitem>
reopen functionality - <classname>reopen</classname> method which
is responsible for document content reopen with <xref linkend="crossref_table"/>
at specified position. This is then used to change current
revision of document, where cross reference table position is
specific for desired revision.
</listitem>
</itemizedlist>
</para>
<para>
For more information about CXref usage, please see <xref linkend="kernel_part_layers_ch"/>.
</para>
<mediaobject>
<imageobject>
<imagedata fileref="kernel/images/cxref.png" format="PNG"/>
</imageobject>
<caption><para>CXref class scheme</para></caption>
</mediaobject>
</sect1>
|
