[lttv.git] / lttv / doc / developer / developer_guide / html / x50.html

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>2.3. Using the reading context</A
></H1
><P
>&#13;If you have read the tutorials about writing a text and a graphic module, you
should be fairly ready to use the information provided to your hook by the
reading API.
</P
><P
>&#13;The data structures of the reading context are based on the gobject, a
object-oriented library from the glib. Some evolved types that are found in the
context also comes from the "glib" (GArray, GHashTable and so on). For detailed
information about "gobjects" and the "glib", see the <A
HREF="http://www.gtk.org"
TARGET="_top"
>www.gtk.org</A
> website. They provide a complete
API reference about the data types they provide.
</P
><P
>&#13;The reading context is object oriented. It is described by the lttv/tracecontext.h
header. Is can be illustrated with this UML class diagram :
</P
><P
>&#13;<DIV
CLASS="mediaobject"
><P
><IMG
SRC="lttv-context.png"
ALIGN="center"><DIV
CLASS="caption"
><P
>Linux Trace Toolkit Viewer Reading Context Class Diagram</P
></DIV
></P
></DIV
>
</P
><P
>&#13;Though, for performance's sake, navigating through it is not as encapsulated as
it could. Consider the class attributes to be all public (no get/set functions).
Sometimes, iteration upon a specific element can be uneasy. For example, you may
have to get the number of tracefiles in a trace from the "vt" field of the trace
context to be able to iterate over all the tracefiles contained by the trace.
</P
><P
>&#13;To facilitate the common operations on the reading context, LTTV now provides a
header that consists of simple macros : lttv/contextmacros.h. It gives an object
look-and-feel to the context classes. Simple "GET" macros can be used to easily
access the different fields are iterate over the elements (and get the total
number of elements too).
</P
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Commit	Line	Data
7cb02901	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
	2	<HTML
	3	><HEAD
	4	><TITLE
	5	>Using the reading context</TITLE
	6	><META
	7	NAME="GENERATOR"
	8	CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
	9	REL="HOME"
	10	TITLE="Linux Trace Toolkit Viewer Developer Guide"
	11	HREF="index.html"><LINK
	12	REL="UP"
	13	TITLE="How to use the Linux Trace Toolkit Viewer's Reading Context"
	14	HREF="c40.html"><LINK
	15	REL="PREVIOUS"
	16	TITLE="Why an event driven trace reader ?"
	17	HREF="x46.html"><LINK
	18	REL="NEXT"
	19	TITLE="Linux Trace Toolkit Viewer Graphical Module Tutorial"
	20	HREF="c67.html"></HEAD
	21	><BODY
	22	CLASS="sect1"
	23	BGCOLOR="#FFFFFF"
	24	TEXT="#000000"
	25	LINK="#0000FF"
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	27	ALINK="#0000FF"
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	31	SUMMARY="Header navigation table"
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	53	WIDTH="80%"
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	55	VALIGN="bottom"
	56	>Chapter 2. How to use the Linux Trace Toolkit Viewer's Reading Context</TD
	57	><TD
	58	WIDTH="10%"
	59	ALIGN="right"
	60	VALIGN="bottom"
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	64	>Next</A
65	></TD
66	></TR
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68	><HR
69	ALIGN="LEFT"
70	WIDTH="100%"></DIV
71	><DIV
72	CLASS="sect1"
73	><H1
74	CLASS="sect1"
75	><A
76	NAME="AEN50"
77	>2.3. Using the reading context</A
78	></H1
79	><P
80	> If you have read the tutorials about writing a text and a graphic module, you
81	should be fairly ready to use the information provided to your hook by the
82	reading API.
83	</P
84	><P
85	> The data structures of the reading context are based on the gobject, a
86	object-oriented library from the glib. Some evolved types that are found in the
87	context also comes from the "glib" (GArray, GHashTable and so on). For detailed
88	information about "gobjects" and the "glib", see the <A
89	HREF="http://www.gtk.org"
90	TARGET="_top"
91	>www.gtk.org</A
92	> website. They provide a complete
93	API reference about the data types they provide.
94	</P
95	><P
96	> The reading context is object oriented. It is described by the lttv/tracecontext.h
97	header. Is can be illustrated with this UML class diagram :
98	</P
99	><P
100	> <DIV
101	CLASS="mediaobject"
102	><P
103	><IMG
104	SRC="lttv-context.png"
105	ALIGN="center"><DIV
106	CLASS="caption"
107	><P
108	>Linux Trace Toolkit Viewer Reading Context Class Diagram</P
109	></DIV
110	></P
111	></DIV
112	>
113	</P
114	><P
115	> Though, for performance's sake, navigating through it is not as encapsulated as
116	it could. Consider the class attributes to be all public (no get/set functions).
117	Sometimes, iteration upon a specific element can be uneasy. For example, you may
118	have to get the number of tracefiles in a trace from the "vt" field of the trace
119	context to be able to iterate over all the tracefiles contained by the trace.
120	</P
121	><P
122	> To facilitate the common operations on the reading context, LTTV now provides a
123	header that consists of simple macros : lttv/contextmacros.h. It gives an object
124	look-and-feel to the context classes. Simple "GET" macros can be used to easily
125	access the different fields are iterate over the elements (and get the total
126	number of elements too).
127	</P
128	></DIV
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130	CLASS="NAVFOOTER"
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132	ALIGN="LEFT"
133	WIDTH="100%"><TABLE
134	SUMMARY="Footer navigation table"
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136	BORDER="0"
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146	ACCESSKEY="P"
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165	>Next</A
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172	VALIGN="top"
173	>Why an event driven trace reader ?</TD
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176	ALIGN="center"
177	VALIGN="top"
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179	HREF="c40.html"
180	ACCESSKEY="U"
181	>Up</A
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193	>