path: root/xf86-input-joystick.tex

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\title{xf86-input-joystick}
\author{\textbf{Sascha Hlusiak}}
\logo{\includegraphics[width=1cm,height=1cm]{pics/X_Org_Logo.png}}
\titlegraphic{\includegraphics[width=3.6cm,height=3.6cm]{pics/logitech_1.png}}
%\institute{}
\date{XDC2012, Nürnberg}


%% ABSTRACT

%The joystick input module was part of the old XFree86 distribution, but the 
%driver was in a bad state until 2007, when development was pushed forward. It 
%first supported the Linux joystick kernel device only, later on support for 
%evdev devices was added, which added support for the driver to be hotplugged 
%by hal enabled server. A FreeBSD kernel backend is available as well, but 
%like Solaris, this is not a prominent system on workstations. Today the 
%joystick driver is well hotpluggable using udev and supports many features 
%and configuration possibilities, like generating mouse button events, pointer 
%movement or key strokes. Enabling the driver to act as both, a pointer and a 
%keyboard device, was particularly challenging. Having a second keyboard 
%device with a different keyboard layout was a problem too, but situation 
%improved with recent servers and XI2/MPX. Support for properties enable 3rd 
%party programs to be written that change the configuration of the device on 
%demand. Prominent target platforms are Linux on the PS3 or the XBox.




\begin{document}
\maketitle

\section*{Overview}
\subsection*{abstract}

\begin{frame}{abstract}
  \structure{xf86-input-joystick?}
  \begin{itemize}
    \item \textbf{not} meant for playing games under X
    \item input module for the X.Org server to handle classical joysticks
    \item can emit pointer movement and key events
    \item \textbf{control the cursor with a joystick}
  \end{itemize}
\end{frame}

\subsection*{overview}
\begin{frame}{overview}
  \tableofcontents
\end{frame}


\section{Basics}
\subsection{why joysticks}
\begin{frame}{why joysticks?}
  \begin{itemize}
    \item cheap remote control
    \begin{itemize}
      \item being lazy
      \item watching movies from couch
      \item control music
    \end{itemize}

    \item interactive kiosk systems
    \begin{itemize}
      \item replace fragile mouse/touchpad
    \end{itemize}

    \item console and media center systems
    \begin{itemize}
      \item Linux on XBox, PS2, ...
      \item \textit{Steam Big Picture} going there
    \end{itemize}
  \end{itemize}
\end{frame}


\subsection{physical joysticks}
\begin{frame}{classical joysticks}
  \begin{itemize}
    \item a lot of different hardware configurations
    \item easily 6 or more axes, different types
    \begin{itemize}
      \item directional pad
      \item hat switch
      \item analog sticks
    \end{itemize}
    \item bunch of buttons, easily 10 and more
    \item force feedback
  \end{itemize}
  \begin{center}
    \includegraphics[width=3.5cm,height=3.5cm]{pics/logitech_1.png}
  \end{center}
\end{frame}


\begin{frame}{why a joystick input module?}
  \begin{itemize}
    \item xorg-server knows pointers and keyboards
    \item \textbf{xf86-input-evdev} maps directly
    \item evdev only in Linux
    \item joysticks usually send absolute axis data \\
      $ \Rightarrow $ direct mapping useless \\
      $ \Rightarrow $ joystick specific event transformation needed
  \end{itemize}
  \scriptsize \vspace{1cm}
$$
  \underbrace{
  \left (
    \begin{matrix}
      \text{absolute axes} \\
      \text{buttons} \\
    \end{matrix}
  \right )
  }_{\text{joystick data}}
  \Rightarrow
  \underbrace{
    px(a_i) = \int_{t} f(a_i) \frac{\mathrm{px}}{\mathrm{s}}
  }_{\text{transformation}}
  \Rightarrow 
  \underbrace{
  \left (
    \begin{matrix}
      \text{pointer} \\
      \text{buttons} \\
      \text{keys} \\
    \end{matrix}
  \right )
  }_{\text{X events}}
$$
\end{frame}

\subsection{kernel level}
\begin{frame}{joysticks on kernel level}
  \structure{kernel device}
  \begin{itemize}
    \item usually Plug \& Play (USB)
    \item event driven $ \Rightarrow $ no polling
  \end{itemize}

  \structure{Linux}
  \begin{itemize}
    \item \texttt{/dev/input/js0} (joydev)
    \item \texttt{/dev/input/event0} (evdev)
  \end{itemize}

  \structure{(Free)BSD}
  \begin{itemize}
    \item \texttt{/dev/input/js0} (linux-js)
    \item \texttt{/dev/uhid0} (usbhid)
  \end{itemize}

  $ \Rightarrow $ lightweight abstraction layer
\end{frame}


\section{Details}
\subsection{mappings}
\begin{frame}{axis mappings}
  \structure{mapping mode}
  \begin{itemize}
   \item relative (analog)
   \item accelerated (D-Pad)
   \item absolute (analog)
  \end{itemize}

  \structure{mapping type}
  \begin{itemize}
    \item pointer movement
    \item scroll event
    \item key event sequence (e.g. cursor keys)
    \item none + raw valuator events (XI2)
  \end{itemize}
\end{frame}


\begin{frame}{button mappings}
  \begin{itemize}
    \item pointer click
    \item pointer movement (accelerated)
    \item scroll events (accelerated)
    \item key sequences (e.g. Alt+Tab)
    \begin{itemize}
     \item auto repeat applies
     \item keyboard layout applies
    \end{itemize}
    \item disable all events temporarily
    \begin{itemize}
      \item still allows playing games
    \end{itemize}
  \end{itemize}
\end{frame}


\subsection{configuration}
\begin{frame}{hotplugging and configuration}
  \begin{itemize}
    \item can be hotplugged through udev and \textit{xorg.conf.d}
    \begin{itemize}
      \item allows specific configuration
      \item easy pre-configuration through distributors
    \end{itemize}
    \item no EVIOCGRAB
    \begin{itemize}
      \item allows concurrent reads (e.g. for games)
      \item watch out when hotplugging \textbf{js0} \textit{and} \textbf{event0}
    \end{itemize}
    \item supports input device properties
    \begin{itemize}
      \item most configuration items can be changed at runtime
      \item TODO: frontend
    \end{itemize}
  \end{itemize}
\end{frame}


\begin{frame}{distribution default}
  \begin{itemize}
    \item mostly installed unintentionally \\
    $ \Rightarrow $ yields unexpected behaviour
    \begin{itemize}
     \item default should be disabled/floating
     \item make user aware to enable it during installation
	 \item popup from DE on hotplug event
     \item way to activate/deactivate it on the fly
    \end{itemize}

    \item no reasonable default configuration
    \begin{itemize}
      \item example configuration
      \item configuration wizard (\textit{xorg.conf.d})
      \item frontend for runtime configuration (properties, dynamic hotplugging)
    \end{itemize}
  \end{itemize}
\end{frame}


\subsection{pointer vs. keyboard}
\begin{frame}{pointer vs. keyboard}
  \begin{itemize}
    \item X.Org server strictly separates pointers and keyboards
    \item no hybrid input devices \\
    $ \Rightarrow $ xf86-input-joystick has to create two input devices
    \begin{itemize}
     \item properties only on pointer
     \item keyboard layout and autorepeat on keyboard
    \end{itemize}
  \end{itemize}
\end{frame}


\begin{frame}{keyboard configuration}
  \begin{itemize}
    \item user wants KeySyms (space, Return, XF86AudioPlay, ...)
    \item driver emits scancodes
    \begin{itemize}
      \item keyboard layout $ \Rightarrow $ unwanted indirection layer
      \item current layout unknown to driver
      \item no custom keyboard layout from within driver
    \end{itemize}
    \item different auto repeat rate possible \\
    $ \Rightarrow $ difficult to configure
  \end{itemize}
\end{frame}


\subsection{raw valuators}
\begin{frame}{raw valuator events}
  \begin{itemize}
    \item valuators 0 and 1 reserved for pointer movement
    \item optional raw valuators per axis
    \begin{itemize}
      \item useful for XI2 applications (e.g. gimp)
      \item less useful for games
    \end{itemize}
  \end{itemize}
\end{frame}


\section{Future}
\subsection{platforms}
\begin{frame}{platforms}
  \begin{itemize}
    \item focus on Linux
    \begin{itemize}
      \item end user desktop systems
      \item interactive kiosk systems
      \item console systems (XBox, PS2/3, ...)
      \item Wii remote? Kinect? \\
      $ \Rightarrow $ not classical joysticks \\
      $ \Rightarrow $ different module
    \end{itemize}
    \item support for Solaris, etc. possible \\
    $ \Rightarrow $ not attractive enough
  \end{itemize}
\end{frame}


\subsection{features}
\begin{frame}{force feedback}
  \begin{itemize}
    \item events from toolkit
    \item event infrastructure from client to server
  \end{itemize}
\end{frame}


\begin{frame}{possible features}
  \begin{itemize}
    \item most properties implemented
    \begin{itemize}
      \item still some work left
    \end{itemize}
    \item \textbf{xinput} only ``frontend'' for properties
    \begin{itemize}
      \item driver can deactivate/activate itself
      \item GTK/Qt frontend with support for ``profiles'' would be nice
    \end{itemize}
  \end{itemize}
\end{frame}



\section*{}
\subsection*{}
\begin{frame}
  \begin{center}
    \huge Thank you!
  \end{center}
\end{frame}


\end{document}