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
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
|
<HTML>
<HEAD>
<TITLE>Xlib programming: a short tutorial</TITLE>
</HEAD>
<BODY>
<H1>Xlib programming: a short tutorial</H1>
I haven't found anything very satisfying on the Web as an Xlib
tutorial. Many of them are too much Motif-oriented for my
taste. Furthermore, I answer questions about X programming almost
daily, so I've started to put together some small coursewares.
<H4>Important note:</H4> the example programs are written in C++, but
this is mainly for the ability to declare variables anywhere.
<HR>
Let's begin with a short story: the eternal story of the newbie at
Xlib writing his/her first program.
<P>
<I>
"Ok, I've to open a connection to the X server (whatever this means),
with XOpenDisplay, then create a window with XCreateWindow, then draw
a line with XDrawLine. Then, the program sleeps for ten seconds so I
can see the result. Sounds easy."
</I>
<P>
The poor newbie writes the program. And nothing happens. He then
calls his wizard friend.
<P>
<I>
-"Did you perform an XFlush after you've done everything ?<BR>
- No, why ?<BR>
- The requests stay in the client," </I>wizard doubletalk, thinks the
poor newbie<I>, " if you
don't."
</I>
<P>
The poor newbie changes the program. And nothing happens. He then
calls his wizard friend.
<P>
<I>
-"Did you map your window ?<BR>
- Did I do what ???<BR>
- Creating a window doesn't make it appear on the screen. You've to
map it with XMapWindow first.
</I>
<P>
The poor newbie changes the program. The window appears with nothing
in it (<A HREF="prog-1.cc">like this</A>). The poor newbie then calls
his wizard friend.
<P>
<I>
-"Did you wait for a MapNotify before drawing your line ?" </I>(more wizard doubletalk)<I><BR>
- "No, why ?</BR>
- X has a stateless drawing model, the content of the window may be lost
when the window isn't on the screen." </I>(overflow, why can't these
wizard guys speak just like you and me ?)<I> "You've to wait for a MapNotify
before drawing."
</I>
<P>
The poor newbie changes the program. Things are getting more and more
complex. Not as easy as it first seemed. A loop gets the events until a
MapNotify. The window appears with nothing
in it. The poor newbie then calls his wizard friend.
<P>
<I>
-"I got it, did you select the StructureNotifyMask on your window ?<BR>
- ???<BR>
- Just do it, and everything'll be fine.
</I>
<P>
The poor newbie fixes the program. And the miracle happens ! A line in the
window. Until now, the program looks like <A HREF="prog-2.cc">this</A>
(it is actually slighty more complex than the dialog may let you think).
<P>
Now you've learned at least 2 things:
<UL>
<LI> How to draw a line in a window with X.
<LI> Why some may need an X tutorial.
</UL>
Now, if you want to learn more and get a deeper understanding of the
program, go to <A HREF="2nd-program-anatomy.html">next lesson</A>.
<H4><A HREF="/gui/x/">More about X</A>.</H4>
<HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:ch.tronche@computer.org">ch.tronche@computer.org</A></ADDRESS>
</BODY>
</HTML>
|
