e81a954787
Now vaguely follows the tree structure of "src", with the exception of directories that described subsystems spanning more than one "kit" or "server" (e.g. "media", "midi", "bluetooth") -- these have been left as their own top-level directory within docs/develop.
150 lines
7.7 KiB
Plaintext
150 lines
7.7 KiB
Plaintext
<BASE HREF="http://bedriven.be-in.org/articles/input_server/II_035-an%20introduction%20to%20the%20input%20server.html"><table border=1 width=100%><tr><td><table border=1 bgcolor=#ffffff cellpadding=10 cellspacing=0 width=100% color=#ffffff><tr><td><font face=arial,sans-serif color=black size=-1>This is <b><font color=#0039b6>G</font> <font color=#c41200>o</font> <font color=#f3c518>o</font> <font color=#0039b6>g</font> <font color=#30a72f>l</font> <font color=#c41200>e</font></b>'s <a href="http://www.google.com/help/features.html#cached"><font color=blue>cache</font></a> of <A HREF="http://bedriven.be-in.org/articles/input_server/II_035-an%20introduction%20to%20the%20input%20server.html"><font color=blue>http://bedriven.be-in.org/articles/input_server/II_035-an%20introduction%20to%20the%20input%20server.html</font></a>.<br>
|
|
<b><font color=#0039b6>G</font> <font color=#c41200>o</font> <font color=#f3c518>o</font> <font color=#0039b6>g</font> <font color=#30a72f>l</font> <font color=#c41200>e</font></b>'s cache is the snapshot that we took of the page as we crawled the web.<br>
|
|
The page may have changed since that time. Click here for the <A HREF="http://bedriven.be-in.org/articles/input_server/II_035-an%20introduction%20to%20the%20input%20server.html"><font color=blue>current page</font></a> without highlighting.</font><br><br><center><font size=-2><i>Google is not affiliated with the authors of this page nor responsible for its content.</i></font></center></td></tr>
|
|
<tr><td>
|
|
<table border=0 cellpadding=0 cellspacing=0><tr><td><font face=arial,sans-serif color=black size=-1>These search terms have been highlighted: </font></td><td bgcolor=#ffff66><B><font face=arial,sans-serif color=black size=-1>hiroshi </font></B></td><td bgcolor=#A0FFFF><B><font face=arial,sans-serif color=black size=-1>lockheimer </font></B></td></tr></table>
|
|
<font face=arial,sans-serif color=black size=-1>These terms only appear in links pointing to this page: <B>input_server </B></font>
|
|
</td></tr></table></td></tr></table>
|
|
<hr>
|
|
<HTML>
|
|
<HEAD><TITLE>Be Newsletter, Volume II, Issue 35</TITLE></HEAD>
|
|
<BODY BGCOLOR="#FFFFFF">
|
|
|
|
<HR><Center><B>Be Newsletter, Volume II, Issue 35; September 2, 1998</B></CENTER><HR>
|
|
|
|
|
|
<FONT SIZE=+1><B><A NAME="Insight"></A>BE ENGINEERING INSIGHTS: <p>An Introduction to the Input Server</B></FONT>
|
|
<br><B>By <B style="color:black;background-color:#ffff66">Hiroshi </B><B style="color:black;background-color:#A0FFFF">Lockheimer</B> <A HREF="mailto:hiroshi@be.com"><B style="color:black;background-color:#ffff66">hiroshi</B>@be.com</A></B>
|
|
<P>One of the many upcoming changes in the BeOS is in the world
|
|
of input devices and events. The Input Server, slated to
|
|
debut in R4, is a server that deals with all things "input."
|
|
Specifically, it serves three functions: manages input
|
|
devices such as keyboards and mice; hosts a stream of events
|
|
that those devices generate; and dispatches those events
|
|
that make it through the stream.
|
|
|
|
|
|
<P>
|
|
<b>Managing Input Devices</b>
|
|
|
|
|
|
<P>The Input Server is a pretty dumb piece of software. (Cue to
|
|
Alex: roll your eyes and say, "What do you expect <B style="color:black;background-color:#ffff66">Hiroshi</B>,
|
|
you wrote it.") On its own, the server doesn't know how a
|
|
keyboard or a mouse works; it relies on <CODE>BInputServerDevice</CODE>
|
|
add-ons to tell it.
|
|
|
|
|
|
<P><CODE>BInputServerDevice</CODE> is a base class from which all input
|
|
device add-ons must derive. It provides the basic framework
|
|
of virtual hook functions and non-virtual member functions
|
|
that the Input Server uses to communicate with an add-on,
|
|
and that the add-on can use to talk back to the server. To
|
|
give a sneak peak of the API, some of the virtuals include
|
|
<CODE>InitCheck()</CODE>, <CODE>Start()</CODE>, <CODE>Stop()</CODE>, and <CODE>Control()</CODE>. The common
|
|
sequence of the life of an input device is this:
|
|
|
|
<ol>
|
|
|
|
<li> The Input Server loads an add-on and constructs its
|
|
<CODE><CODE>BInputServerDevice</CODE></CODE>-derived object.
|
|
|
|
|
|
<P><li> The Input Server calls <CODE>InitCheck()</CODE> on the object. The
|
|
object determines whether it is capable of doing its job
|
|
-- that is, generating input events.
|
|
|
|
|
|
<P><li> This task may involve the object sniffing around for
|
|
hardware it can drive, or looking for a kernel device
|
|
driver in <CODE>/dev</CODE>. If the object is happy, it registers with
|
|
the Input Server any input device(s) it finds, and
|
|
returns <CODE>B_NO_ERROR</CODE>. An error return causes the Input
|
|
Server to promptly destruct the object and unload the
|
|
add-on.
|
|
|
|
|
|
<P><li> At some point in time, someone will tell the input
|
|
devices registered with the Input Server to <CODE>Start()</CODE>. The
|
|
system automatically starts keyboards and mice at boot
|
|
time. Any other type of device (an "undefined" input
|
|
device that the system doesn't have any special knowledge
|
|
about) can be started by an application using new API in
|
|
the Interface Kit.
|
|
|
|
|
|
<P><li> A registered device, whether it has been started or
|
|
not, may be <CODE>Control()</CODE>-ed at any time. Think of Control()
|
|
as the <CODE>ioctl()</CODE> equivalent in input device parlance.
|
|
Examples of system-defined control messages include
|
|
keymap changes and mouse speed changes.
|
|
</ol>
|
|
|
|
<P>
|
|
<b>Generating Input Events</b>
|
|
|
|
|
|
<P>Once a <CODE>BInputServerDevice</CODE>-derived object's input device is
|
|
up and running, its primary task is to generate input
|
|
events. These events are expressed as BMessages. For
|
|
example, a keyboard input device will most likely generate
|
|
<CODE>B_KEY_DOWN</CODE> and <CODE>B_KEY_UP</CODE> messages. Similarly, a mouse input
|
|
device will probably generate <CODE>B_MOUSE_UP</CODE>, <CODE>B_MOUSE_DOWN</CODE>, and
|
|
<CODE>B_MOUSE_MOVED</CODE> events.
|
|
|
|
|
|
<P>There is nothing that prevents an input device from putting
|
|
arbitrary data in any of the <CODE>BMessages</CODE> it generates. So, for
|
|
example, a tablet may generate the aforementioned mouse
|
|
events with extra data such as pressure and proximity. Any
|
|
information packed into the <CODE>BMessages</CODE> is delivered
|
|
unmolested by the input server.
|
|
|
|
|
|
<P>When an event is ready to be shipped off, an input device
|
|
enqueues it into the Input Server's event stream. Some
|
|
<CODE>BHandler</CODE> (most likely a <CODE>BView</CODE>) down the line eventually
|
|
receives the event by way of the usual hook functions such
|
|
as <CODE>KeyDown()</CODE>, <CODE>MouseDown()</CODE>, and <CODE>MouseMoved()</CODE>.
|
|
|
|
|
|
<P>
|
|
<b>The Input Event Stream</b>
|
|
|
|
|
|
<P>The Input Server's event stream is open for inspection and
|
|
alteration by anyone in the system. This is achieved through
|
|
another set of add-ons called <CODE>BInputServerFilter</CODE>. Like
|
|
<CODE>BInputServerDevice</CODE>, <CODE>BInputServerFilter</CODE> is a base class for input filter add-ons to the Input Server.
|
|
|
|
|
|
<P>An input filter add-on is privy to all the events that pass
|
|
through the Input Server's event stream. A filter may
|
|
inspect, alter, generate, or completely drop input events.
|
|
It's similar in some ways to the Interface Kit's
|
|
<CODE>BMessageFilter</CODE>, but much more low-level. A
|
|
<CODE>BInputServerFilter</CODE> sees all events that exist in the system;
|
|
<CODE>BMessageFilters</CODE> are associated with a specific <CODE>BLooper</CODE> and
|
|
thus see only the events targeted to its <CODE>BLooper</CODE>. Also,
|
|
filters in the Input Server can generate additional events
|
|
in place of, or in addition to, the original input event
|
|
that it was invoked with.
|
|
|
|
|
|
<P>
|
|
<b>Conclusion</b>
|
|
|
|
|
|
<P>With the introduction of loadable input device objects, the
|
|
Input Server enables the BeOS to be used with a wide variety
|
|
of input devices (and more than one of them at once too).
|
|
And with the advent of input filters, the Input Server opens
|
|
the door to a new class of tricks, hacks, and (gulp) pranks
|
|
for the creative developer. It's going to be fun.
|
|
|
|
|
|
<P>
|
|
|
|
</BODY>
|
|
</HTML>
|