/*
   This file contains documentation for GG that doesn't fit in the source code.
*/

/** \page design Design
    \section design_purpose Purpose 
    GG is designed to achieve several goals:
    - Platform-independence: GG should be buildable on any platform that supports OpenGL
    - Driver-independence: GG should be a standalone GUI framework that does not require any particular application framework;
    though SDL and Ogre drivers are supplied, GG should be usable with any driver code the user wishes to supply
    - Easy extensibility: new controls and GUI behavior should be easy to incorporate
    - Complete graphical control for the user/designer: the user should not be limited by the author's lack of artistic skill!
    - Independence of UI elements from the source code: GG UI elements should be configurable as text files, so that UI design 
    and alteration should not require a recompilation
    - Overall time efficiency: an application with a reasonable number of GG UI elements should not slow down significantly 
    because of the rendering or handling of those elements
    - Overall space efficiency: each GG UI element should have a reasonably small data size
    - Efficient mixture of 2D and 3D graphical elements: it should be appropriate to use GG in any frame-based 3D application, 
    even a realtime 3D video game
    - Simplicity of use: GG UI elements should be able to send arbitrary messages when manipulated by the user; there should be 
    no message passing hierarchy imposed on the user

    \section design_features Features
    GG has the following features and services:
    - Communication of UI controls via signals and slots
    - Support for 2D-, 3D-, and mixed-mode rendering
    - Managment of textures and fonts
    - Serialization of UI elements

    \section nonfeatures Non-Features
    - GG is not fully threadsafe, due to its use of signals and slots
    - No sound support is provided
*/

/** \page architecture Architecture
    \section arch_rendering Rendering Overview

    GG uses OpenGL to render its graphics.  It is assumed that the entire GUI
    is being redrawn multiple times each second, as part of a high-framerate
    application.  Each GG UI element is drawn using calls to OpenGL.
    Therefore, each element can be rendered as a pre-rendered pixmap, flat 2D
    texture or sprite, or even a fully 3D rendering; the complexity of the
    graphics used to represent the UI elements is only limited by the target
    rendering hardware and the user's skill.

    \section arch_main_loop_integration Integration With Application Render Loop

    GG supplies a render loop in the form of GUI::Run().  For many
    applications, this default render loop is sufficient.  However, for users
    who are integrating GG with an existing application that already has its
    own render loop, there is another way.  See the GG::EventPump
    documentation for info on how you can update GG's GUI once per frame from
    your application's render loop.

    \section arch_UI_overview UI Overview
    \subsection arch_input_events Input Events

    GG is organized as a layer on top of an existing user input framework.  GG
    has no way of determining that a mouse click, mouse move, or any other
    user input event, has taken place.  To use GG, one must subclass off of
    the abstract class GG::GUI, and define several of GG::GUI's pure virtual
    functions.  These functions poll the underlying operating system or input
    framework, and generate GG input messages from them.  Such messages are
    mouse moves and clicks, key presses and releases, joystick movement,
    etc. GG maintains internal state as to what part of the GUI is being
    dragged, clicked, etc.

    \subsection arch_UI_overview_example Example:

    Suppose the user clicks the left mouse button at screen position (50, 37).
    GG will receive a message from the underlying application framework that a
    left mouse click has occurred; it then determines what UI element is under
    that screen location, if any.  If it turns out there is a button under
    that spot, GG sets internal state indicating that the left mouse button is
    being held down, and that it is over the button.  GG then sends a message
    to the button that it is depressed.  The button sets its own internal
    state and returns.  All processing is complete for this input; the next
    time the button is redrawn, it knows to draw itself in a depressed state.
    Very little computation is involved in processing a single user input
    event.  GG's performance is therefore usually limited only by the
    application-defined processing that is associated with manipulating the
    controls (e.g., a button click may trigger disk IO).

    \subsection arch_UI_element_conns UI Element Connections

    GG UI elements are connected using signals and slots, using the
    Boost.Signals library.  This allows arbitrary connections between one
    control and another, and between a control and any other code; there is no
    hierarchy of passed messages as there is in some other GUIs, and no
    type-unsafe callbacks are used.  Refer to the \ref sigs_n_slots
    documentation for details.

    \subsection arch_gui_services GG::GUI Services

    The singleton GG::GUI object is globally available through a static member
    function, GG::GUI::GetGUI().  This allows all code in the application to
    rely on GG::GUI for certain essential services.  GUI-specific services
    include registering windows into the GUI, registering windows as
    always-on-top or modal windows, moving windows up or down in the z-order
    layers of the GUI, removing windows from the GUI, getting mouse state
    (position and button depression), setting mouse delay repeat (see GG::GUI
    for a description of this), entering and exiting from an orthographic
    projection (2D) rendering mode.  Most of these services must be provided
    by the user when subclassing from GG::GUI; if either of SDLGUI or OgreGUI
    is used, these services are already implemented.

    <p>

    GG::GUI does a variety of things for the user, some of which are not
    strictly necessary for the core GUI functionality.  GG::GUI provides
    limited timing info via FPS() and DeltaT().  These are provided to
    indicate how fast the GUI is rendering, and how long it has been since the
    last frame was rendered.  There is also a font manager, an
    application-wide font "pool", from which the user can request fonts.  The
    font pool loads and stores the fonts as needed by the application, and
    multiple requests for the same font at the same size will result in the
    creation of only one font object.  A texture manager exists which does a
    similar job with textures.  If the user wants to programmatically create
    textures, she can also add them to the texture pool, provide a name, and
    request that texture as many times as needed.  OpenGL texture objects are
    used as the underlying texture rendering method.  */

/** \page sigs_n_slots Signals and Slots
    \section sigs_n_slots_definition Sig-who? Slo-what?

    If you've never been exposed to the signals and slots pattern before, it
    can be a little confusing.  Simply put, a slot is a function or function
    object that is "listening" for a signal.  A slot "listening" to a certain
    signal is said to be connected to that signal.  When a signal is emitted,
    all slots that are connected to that signal are called (since they are all
    functions/function objects).  If a signal is emitted to which no slots are
    connected, nothing happens.

    \section sigs_n_slots_motivation Motivation for the Signals and Slots Pattern
    \subsection prob The Problem

    Originally, GG used a very simple strategy for passing messages between
    windows/controls.  The method was to call a Command() function, which
    passed to the callee an integer representing the type of message (button
    click, scroll, or whatever), an ID number associated with the calling
    control, and a single integer parameter.  It could have been made more
    general and even less typesafe by replacing the int parameter with a void
    pointer, but in either case it suffers from two huge limitations.  First,
    the type of message and the parameter must be known to both caller and
    callee; this means that, for example, the user must keep track of the
    integer value representing a button click message, and make sure that
    separate sections of code are using the same value to represent it.
    Second, any code that doesn't contain a control, but that wants to know
    about button pushes, scrolling scrollbars, etc., must deal with that
    control's parent (or break encapsulation).  This creates a lot of chains
    of passed messages, and a large number of kludges to get messages to the
    sections of code that need them.

    \subsection sigs_n_slots_soln The Solution

    Now, each control emits a signal every time a significant event occurs.
    If no processing needs to be associated with such an event, its signal
    need not be connected to anything.  Futhermore, no matter how many modules
    need to react to a certain signal, they can all be connected.

    \section sigs_n_slots_use Using Signals and Slots
    \subsection sigs_n_slots_connecting Connecting Signals To Slots

    There are two types of connections between signals and slots.  The first
    type of connection is between a signal and a slot, which may be a functor
    (which in turn may be a boost::bind object), a free function or a static
    member function or function object.  Just call Connect(sig, slot).  The
    second type is between a signal and a non-static member function.  In this
    case, the call to Connect() requires a third parameter: a pointer to the
    object whose member function is to be called.  For instance, if I have a
    class Foo and an object foo1 of class Foo, I cannot call foo1.bar() by
    simply knowing the address of bar().  I need to call Connect(sig,
    &Foo::bar, &foo1) so that the signal knows which object's bar() to call.
    Both versions of Connect() return a connection object.  By keeping this
    connection object, you can later disconnect() the connection you made.  In
    addition, signal-signal connections are possible.  Calling Connect(sig1,
    sig2) forwards all sig1's signal emissions to sig2.  This is provided as a
    convenience to avoid having to write dummy forwarding functions that do
    this.

    \subsection sigs_n_slots_emitting Emitting Signals

    To emit a signal from a signal object "sig", just use its function call
    operator ("operator()"), like this: "sig();"

    \subsection disconnecting Disconnecting Signals and Slots

    If you kept the connection object returned by Connect(), a
    connection_obj.disconnect() call will disconnect the associated signal and
    slot.  Also, consider this: what happens if a signal A is connected to a
    slot consisting of a member function of object B, B is deleted, and then
    A() is called?  A segfault, unless the B's class inherits from
    boost::trackable, which auto-disconnects slots in its destructor.  GG::Wnd
    is derived from boost::trackable, so all GG::Wnd-derived classes should
    handle such situations gracefully.  See the Boost tutorial below for
    details.  \see http://boost.org/doc/html/signals.html for a tutorial on
    other aspects of signals and slots; you can create connections that have
    scope, control the order of the invocation of multiple slots that are
    called by a signal, and combine the return values of such slots (take the
    first return value, the last, the average of all of them, etc.).  */

/** \page text_handling Text Handling
    \section text_handling_unicode_support Unicode Support

    GG supports Unicode characters.  All strings that are rendered as text in
    GG are considered to be UTF-8 encoded.  GG uses the utfcpp library
    (http://utfcpp.sourceforge.net) to handle conversions from UTF-8 encoded
    strings to Unicode code points.  A detail that you must know about utfcpp
    is that it throws exceptions on invalid input.  Any time you pass a string
    to a GG function, you run the risk of generating an exception if the
    string is not UTF-8 encoded.  Note that ISO-8859-1 (commonly called
    "Latin-1"), Windows-1252, and other common single-byte encodings are not
    usable as UTF-8 strings.

    \section text_handling_all_chars_considered_utf8 All Characters Are Considered UTF-8 Encoded

    Yes, all characters!  Even if you call GG::Font::RenderGlyph() with a char
    parameter, that char had better conform to UTF-8 requirements for a valid
    codepoint (in particular, it's value must be in the range [0x0, 0x7f]).

    \section text_handling_font_support Font Support

    Be sure to use a TrueType font capable of rendering the character sets you
    need for whatever language(s) you need to support.  Note that due to the
    large number of Unicode characters and the space requirements of using
    textured fonts, GG::Font requires you to supply it with the Unicode
    character sets you want at construction time.  A useful pattern for
    constructing a GG::Font with the right character set coverage is to use
    UnicodeCharsetsToRender().  You simply pass it a string containing
    representative characters, and it returns a set of GG::UnicodeCharsets
    that covers all the characters in the string.

    \section text_handling_user_input User Input

    Unicode characters can be input by the user, as long as the input driver
    handles Unicode input.  The SDL reference driver does.  The Ogre OIS input
    plugin does not.  GG will convert any Unicode input to a multibyte UTF-8
    sequence before adding it to a user-editable string (e.g. as in a
    GG::Edit).

*/

/** \page drag_n_drop Drag and Drop
    \section drag_n_drop_basics Basics

    GG has drag and drop support that allows you to potentially drag any
    GG::Wnd and drop it onto any other GG::Wnd.  The results of this drop
    depend on the two GG::Wnd's involved.  Each GG::Wnd has a
    GG::Wnd::DragDropDataType() method that returns a string describing what
    kind of data the GG::Wnd represents.  The string can be a MIME type, or
    any arbitrary string the user likes.  During the dragging portion of the
    operation, a GG::Wnd under the cursor has its GG::Wnd::DropsAcceptable()
    member called, in which it can examine the data type string and other
    relevant aspects of each dragged GG::Wnd and decide whether or not to
    accept it.  On the drop, the GG::Wnd under the cursor has its
    GG::Wnd::AcceptDrops() method called with those GG::Wnd's it has
    previously deemed accepted in GG::Wnd::DropAcceptable().  GG::Wnd's
    accepted by the drop target are removed from their original parent, if
    any, through a call to GG::Wnd::ChildrenDraggedAway().

    Note that only GG::Wnd's with non-empty GG::Wnd::DragDropDataType() may be
    dragged and dropped.  Within those GG::Wnd's, there are two categories: 1)
    GG::Wnd's with GG::Wnd::Dragable() true and those without.  A
    GG::Wnd::Dragable() GG::Wnd moves across the screen normally when dragged.
    A Non-GG::Wnd::Dragable() GG::Wnd does not move when drag-and-dropped;
    instead, it is rendered in place, and an additional copy of it is rendered
    as if the cursor were dragging it.

    \section drag_n_drop_advanced Advanced Use

    There is an extensive set of notification functions that may be called
    during a drag and drop operation.  The drop target and the orginal parent
    of the dragged GG::Wnd(s), if any, may be notified of various events or
    queried (e.g. GG::Wnd::DropsAcceptable()).  Additionally,
    GG::Wnd::GetDragDropRenderingState() indicates whether a GG::Wnd is being
    dragged, whether it is over a valid drop target, etc.  See the GG::Wnd
    documentation for details.

*/

/** \page building Building GG
    \section building_reqs Requirements
    GG requires GCC 3.4 or later, or MSVC++ 8.0 SP1 or later.  Note that both are available for free download.
    <p>
    GG relies on a few other open-source libraries:
    - FreeType 2 - http://www.freetype.org
    - Boost >= 1.36 - http://www.boost.org

    Image loading library/libraries:
    Either:
    - DevIL 1.6.1 - http://openil.sourceforge.net

    Or, at least one of:
    - libpng - http://www.libpng.org/pub/png/libpng.html
    - libjpeg - http://www.ijg.org
    - libtiff - http://www.libtiff.org

    Optional libraries for input drivers:
    - SDL >= 1.2 - http://www.libsdl.org
    - Ogre >= 1.4 - http://ogre3d.org

    GG's documentation relies on Doxygen
    (http://www.stack.nl/~dimitri/doxygen). If you have Doxygen installed in a
    standard location, the docs will be built automatically.  Otherwise, from
    the GG/doc directory, run Doxygen; the documentation will appear in the
    GG/doc/GG directory.
    <br>

    \section howto_build How To Build GG

    \subsection howto_build_all_platforms All Platforms

    You will need to first build the buildable portions of the Boost
    libraries.  See http://boost.org/more/getting_started/index.html for
    details on building Boost.  There are often pre-built binaries available
    for download for the latest Microsoft C++ compiler.  You will also need to
    decide whether to use DevIL, or GG's built-in image loading code (built-in
    is the default).  The built-in image loader only supports PNG, JPEG, and
    TIFF formats, using a modified version of Boost.GIL from Boost 1.37.
    DevIL supports more image formats, but is less portable.  If you choose
    not to use DevIL, you must make at least one of the PNG, JPEG, and TIFF
    format-specific libraries available instead.

    GG uses CMake to generate makefiles, MSVC and XCode projects files, etc.
    Here is the quick-and-dirty info on using CMake.  Download and install
    CMake if necessary, of course.  You run ccmake (Linux) or cmake-gui
    (Windows or Mac OS X) to set the build options, such as whether to use
    DevIL, whether to build static or dynamic libs, etc.  It's really
    straightforward, and the end result of using CMake is that you get to use
    make, Visual Studio's IDE, XCode projects, or whatever CMake-supported
    build tool you like.  It supports just about everything.

    \subsection howto_build_unix Unix

    To build GG, you will need to have CMake installed.  The headers and built
    binaries for the libraries you intend to use should be available in your
    include and link paths, respectively.  just run cmake from the command
    line, and the defaults will probably work for you just fine.  If you need
    to configure the build in some way, run ccmake next.  Once you've picked
    your options, hit 'c' for configure, then 'g' for generate.

    You can let CMake know about any nonstandard paths to these headers and
    library binaries by running ccmake, then toggling on advanced mode by
    hitting 't', then filling in what CMake couldn't find.  For example, if
    you want to use your own zlib, you can point CMake at it by setting
    ZLIB_INCLUDE_DIR and ZLIB_LIBRARY from the advanced mode.  Other than
    cases like this, you shouldn't need to use the advanced mode.

    Once this is done, Unix users can simply type
    \verbatim
      make
      make install [as root, if necessary]\endverbatim

    \subsection howto_build_win32_microsoft Windows

    First off, try to avoid building GG altogether by downloading a Windows
    installer containing pre-built GG binaries and headers from the
    SourceForge download page.

    If you want to build GG, you will need to have CMake installed, even if
    you want to use the Visual Studio IDE.  Run cmake-gui, and select the
    top-level GG folder for the "Where is the source code" field, and wherever
    you want the build products to go for the "Where to build the binaries"
    field (these can be the same place if you like).  Next, hit the Configure
    button.  If the config step succeeds (unlikely ;) ), hit "Generate".  Be sure
    to select the generator you want -- I think Borland CodeBuilder is the
    default, if you can believe that.  After this, you should be able to
    launch your favorite IDE, or build using nmake, or whatever, from the
    "Where to build the binaries" folder.

    If the config step fails, which is very likely, select the "Advanced
    View" in the view drop-list, and fill in the paths to headers and libs
    that CMake couldn't find.  For instance, you'll probably need to fill in
    FREETYPE_INCLUDE_DIR_freetype2, FREETYPE_INCLUDE_DIR_ft2build, and
    FREETYPE_LIBRARY with the paths to the freetype2 folder, the path to the
    ft2build.h header, and the path to the FreeType link library,
    respectively.  The fields you need to fill in will contain {field
    name}-NOTFOUND.  Note that some fields are optional, e.g. those related to
    DevIL.

    \subsection howto_build_macos Mac OS X

    As of this writing, GG builds fine on Mac OS X.  As for the generation of
    XCode projects and makefiles, I'm not so certain, since I don't have
    access to a Mac OS X box.
 */

/** \page brief_tour A Brief Tour

    In a library as diverse in functionality as GG, it can be difficult even
    to figure out what the library has to offer.  This "tour" is designed to
    provide a brief overview of the various features of GG not covered
    elsewhere, and to point users to the more detailed information elsewhere
    in the documentation.  The topics are covered in no particular order.

    First off, it should be noted that there is a lot of general overview-type
    documentation in the GG::Wnd and GG::GUI detailed documentation.  Many of
    the things mentioned below are covered there in more detail.

    \section tour_event_filters Event Filters

    Event filtering allows one to use a GG::Wnd to intrusively handle the
    events sent to another GG::Wnd.  This can be useful, for example, in a
    control (the parent) that is composed of multiple controls (the children),
    but which needs to handle certain events uniformly.  Perhaps right-clicks
    should always bring up a context menu, for instance.  Without event
    filtering, each child control would have to explicitly forward its
    right-clicks instead of processing them normally, which would in turn
    require subclassing.  Event filters remove the need for such subclassing.
    \see The GG::Wnd description, GG::Wnd::EventFilter(),
    GG::Wnd::InstallEventFilter(), and GG::Wnd::RemoveEventFilter().

    \section tour_layouts Layouts

    GG::Layout encapsulates the relative arrangement of child GG::Wnd's in the
    client area of a GG::Wnd, so that positioning such children requires less
    hand-coding.  \see The GG::Wnd description.

    \section tour_browse_info The Browse-Info System

    Like "tooltips", but more general.  You can have any non-interactive GUI
    elements you like inside of a GG::BrowseInfoWnd, and the contents of the
    GG::BrowseInfoWnd can vary, for example to provide increasing amounts of
    info over time.  \see The GG::Wnd description.

    \section tour_style_factory The Style Factory

    Many of the control classes reuse other controls to do part of their work.
    For instance, GG::Scroll uses a pair of GG::Button objects for its up and
    down (or left and right) buttons.  If a user wishes to use a custom
    subclass of GG::Button throughout an application, how is she to get
    GG::Scroll to create GG::Button's of the right type?  The answer is that
    all controls created by GG are requested from a GG::StyleFactory.  \see
    The GG::Wnd description and the GG::GUI description.

    \section tour_plugins Plugins

    Plugins (dynamically loaded shared libraries/DLLs not linked into the
    application when it is built) can be created and used with GG.  Plugins
    provide a GG::StyleFactory, and a default font name and size.  \see
    GG::PluginInterface.

    \section tour_standard_dialogs Standard Dialogs

    Three standard dialogs are provided:
    - A color selection dialog, GG::ColorDlg;
    - A file(s)/directory selection dialog, GG::FileDlg; and
    - A general-purpose message dialog containing at most three buttons, GG::ThreeButtonDlg.

    \section tour_cursor_rendering Cursor Rendering

    GG can optionally render a cursor.  By default, GG assumes that the
    underlying system is rendering the cursor, and so does not attempt to do
    so.  \see GG::GUI::RenderCursor(), GG::GUI::GetCursor(),
    GG::GUI::SetCursor(), and GG::Cursor.

    \section tour_flags Flags

    GG uses format flags, window creation flags, and several other types of
    bit-flag sets in various places.  These bit-flag sets are not
    interoperable.  This is designed as a workaround to problems inherent to
    C++ enums, such as implicit conversion to integral types, which in turn
    leads to comparability of arbitrary enumeration values from different
    enumerations.  For instance, it is impossible (due to a compile-time
    error) to accidentally pass the (nonsensical) flag GG::FORMAT_NONE to the
    \a flags parameter of GG::Wnd::Wnd().  With built-in C++ enums, this would
    not be caught by the compiler.  GG provides two classes, GG::Flags and
    GG::FlagSpec, that allow the user to extend the sets of flags used in GG,
    if user-created subclasses should require more flags than the ones GG
    provides.

    \section tour_text_formatting_tags Text Formatting Tags

    Text rendered by GG can make use of text formatting tags, similar to those
    used in HTML documents (e.g. \<i><i>italicized text here</i>\</i>).  GG
    defines numerous tags that control text justification, text color,
    bolding, underlining, italicizing, etc.  Users can also add their own
    tags.  Though GG does not associate any semantics with user-defined tags,
    it will treat them as tags, meaning they will be automatically be removed
    from the text as it appears when rendered.  \see The GG::Font description.

    \section tour_keyboard_accelerators Keyboard Accelerators

    Keyboard accelerators may be established that emit signals on (and
    possibly filter out) keystrokes.  Accelerators can include a modifier
    specification, so for instance Ctrl-K, Alt-K, and K may be created as
    different accelerators.  Each accelerator has an associated signal to
    which arbitrarily many slots can be connected.  \see The GG::GUI
    description.

    \section tour_user_input_drivers User Input Drivers

    Two input drivers are currently available for use with GG -- one for <a
    href="http://libsdl.org">SDL</a> and one for <a
    href="http://ogre3d.org">Ogre</a>.  Note that Ogre does not have built-in
    support for user input.  As of this writing, it uses another library
    called <a href="http://sourceforge.net/projects/wgois">OIS</a>.  An Ogre
    plugin that provides OIS support is also provided in src/Ogre/Plugins.
    \see GG::SDLGUI, GG::OgreGUI, GG::OgreGUIInputPlugin, and OISInput.

    \section tour_timers Timers

    Timers are available to which slots can be connected.  A timer fires its
    signal after at least T time has elapsed, where T is a user-provided time
    interval.  Note the use of "at least".  Timers are only evaluated during
    GG's normal processing loop, so if the application is cycling slowly (due
    to heavy processing, etc.), timers can fire arbitrarily less frequently
    than desired.

    \section tour_event_pumps Event Pumps

    GG abstracts out the inner loop that processes events and renders frames
    into a class called GG::EventPump.  Most users will never need to use
    event pumps, but those users writing a new input driver will.  Note that
    if you are integrating GG with an existing application that has its own
    render loop, you will almost certainly need to use GG::EventPump.  See the
    GG::EventPump documnentation for details.

*/

/** \page tutorials Tutorials
    \section tut_using Using the Tutorials
    The following tutorials are available in the tutorial directory.  They are built by default when you build GG.
    \section tut_1 Tutorial 1: Minimal (minimal.cpp)
    This is the minimal interesting GG application, and uses one of the default input drivers, SDL.
    \section tut_2 Tutorial 2: Controls (controls.cpp)
    This builds upon Tutorial 1 by adding one of every type of Control, and connecting some signals and slots.
*/

/** \mainpage GG Documentation Overviews
    \section Overviews
    -# \ref design
    -# \ref architecture
    -# \ref sigs_n_slots
    -# \ref text_handling
    -# \ref drag_n_drop
    -# \ref brief_tour
    -# \ref building
    -# \ref tutorials
*/
