tools-make/Documentation/faq.texi

\input texinfo   @c -*-texinfo-*-
@c A FAQ for GNUstep

@node Top, Compatibility, (dir), (dir)
@chapter GNUstep Frequently Asked Questions with Answers

Last updated @today{}.
Please send corrections to @email{gnustep-maintainer@@gnu.org}. Also look
at the user FAQ for more user oriented questions.

@menu
* Compatibility::               
* Compiling and Developing::    
* GNU Objective C Compiler and Runtime::  
* GNUstep Base Library::        
* GNUstep GUI Library::         
* GNUstep DisplayGhostScript Server::  
@end menu

@c ****************************************************************
@c Compiling
@node Compatibility, Compiling and Developing, Top, Top
@section Compatibility

@menu
* Is it easy to port OPENSTEP and Rhapsody programs to GNUstep?::  
* Can I transfer archived data from GNUstep to Cocoa?::  
* Does distributed objects work between GNUstep and Cocoa?::  
* Is there an Interface Builder for GNUstep?::  
* Can I use my original NIB files?::  
* Can one use the hybrid "Objective-C++"::  
* Is there a plan to support Java/YellowBox Bindings?::  
* What if I compile GNUstep under OPENSTEP/MacOS X?::  
* Is the Objective C API for GTK related?::  
* How about implementing parts of the Application Kit with GTK?::  
@end menu

@node Is it easy to port OPENSTEP and Rhapsody programs to GNUstep?, Can I transfer archived data from GNUstep to Cocoa?, Compatibility, Compatibility
@subsection Is it easy to port OPENSTEP and Rhapsody programs to GNUstep?

It is probably easy for simple programs. There are some portability
tools
to make this easier (@url{http://www.gnustep.org/resources/source_port.html}),
or rewrite the Makefiles yourself.  You will also have to
translate the NIB files (if there are any) to GNUstep model files using
the nib2gmodel program (from @url{ftp://ftp.gnustep.org/pub/gnustep/dev-apps}).

@node Can I transfer archived data from GNUstep to Cocoa?, Does distributed objects work between GNUstep and Cocoa?, Is it easy to port OPENSTEP and Rhapsody programs to GNUstep?, Compatibility
@subsection Can I transfer archived data from GNUstep to Cocoa?

Apple's archiving format is proprietary and not documented, so this
poses a problem for anyone wanting to implement compatibility with it.
However, even if we reverse engineered the format, there are enough
differences between the class and ivar layouts to make this sort of
compatibility difficult. Not to mention the fact that we would
constantly have to keep up with the changes Apple made. Also Apple's
archiving format, as far as we know, would not be compatible between
different machines because of endiness issues, although GNUstep doesn't
have this problem.

Your best bet is to implement your own archiving format that would work
both with GNUstep and Cocoa. Fortuneatly, you don't have to start from
scratch, since this has been essentially done for you in the nib2gmodel
tool, which has an archiver that works both on GNUstep and Cocoa. It
might be nice to split this off into a separate project to make it
easier for other people to do the same thing.

@node Does distributed objects work between GNUstep and Cocoa?, Is there an Interface Builder for GNUstep?, Can I transfer archived data from GNUstep to Cocoa?, Compatibility
@subsection Does distributed objects work between GNUstep and Cocoa?

See the answer to the previous question (on archive compatibility) for
why this won't work either.

@node Is there an Interface Builder for GNUstep?, Can I use my original NIB files?, Does distributed objects work between GNUstep and Cocoa?, Compatibility
@subsection Is there an Interface Builder for GNUstep?

There is an Interface Builder for GNUstep called Gorm, but it is
in alpha release, so it may not work perfectly. You can download it from
the ftp site or via http.
The Project Manager ProjectCenter is also available.

@node Can I use my original NIB files?, Can one use the hybrid "Objective-C++", Is there an Interface Builder for GNUstep?, Compatibility
@subsection  Can I use my original NIB files?

 No - NeXT/Apple never documented their nib format, so GNUstep supports
both the 'gmodel' format (which stores information as text
(property-lists) and can therefore be edited 'by hand') and binary
archive format (which can be edited by Gorm).  There IS a conversion
tool called nib2gmodel that can be compiled under OPENSTEP to convert
OPENSTEP nib files to GNUstep gmodel files.

@node Can one use the hybrid "Objective-C++", Is there a plan to support Java/YellowBox Bindings?, Can I use my original NIB files?, Compatibility
@subsection  Can one use the hybrid "Objective-C++"

No. at present the GNU compiler (gcc) does not support
"Objective-C++". Apple has submitted patches for this, but it is up to
the GCC steering commitee to decide if they want to add them. If you
would like to see this, please politely and respectfully lobby them at
@email{gcc@@gnu.org}.

@node Is there a plan to support Java/YellowBox Bindings?, What if I compile GNUstep under OPENSTEP/MacOS X?, Can one use the hybrid "Objective-C++", Compatibility
@subsection  Is there a plan to support the Java/YellowBox Bindings?

Yes. The GNustep Java library/bridge called JIGS is available now.  JIGS
is a free (LGPL) Java Interface for GNUstep; it can automatically wrap
Objective-C libraries based on GNUstep, making them accessible directly
to the Java programmer as if they were Java libraries. As a side effect,
it is also possible to use the whole engine in the reverse way: JIGS
provides a high level API to allow Objective-C programmers to start java
virtual machines inside GNUstep Objective-C code and access java objects
in the java virtual machine transparently, as if they were objective-C
objects.

@node What if I compile GNUstep under OPENSTEP/MacOS X?, Is the Objective C API for GTK related?, Is there a plan to support Java/YellowBox Bindings?, Compatibility
@subsection  What if I compile GNUstep under OPENSTEP/MacOS X?

GNUstep uses the X-windows display postscript extension.
The interface to that is not the same as the interface to the
OPENSTEP/MacOS-X windows server.  While someone could write a
backend library to provide the interface, nobody has bothered to
date.

Also, the GNUstep base library is still being ported to Darwin.

@node Is the Objective C API for GTK related?, How about implementing parts of the Application Kit with GTK?, What if I compile GNUstep under OPENSTEP/MacOS X?, Compatibility
@subsection  Is the Objective C API for GTK related?

  No.  GNUstep applications provide their GUI via the OpenStep
API, which provides fully object-oriented access to GUI manipulation.

  The object-oriented nature of the libraries and language make it much easier
for new users to create their own subclasses rather than simply using the
supplied widgets as in other frameworks.

@node How about implementing parts of the Application Kit with GTK?,  , Is the Objective C API for GTK related?, Compatibility
@subsection  How about implementing parts of the Application Kit with GTK?

  Yes and No - The GNUstep architecture provides a single,
platform-independent, API for handling all aspects of GUI interaction
(implemented in the gstep-gui library), with a backend architecture
that permits you to have different display models (display postscript,
X-windows, win32, berlin ...) while letting you use the same code
for printing as for displaying. Use of GTK in the frontend gui
library would remove some of those advantages without adding any.

That being said, a backend library could be implemented using gtk
if anyone wanted to do so.  Since the frontend library handles most
of the work involved in implementing the OpenStep API, the backend
is a relatively thin layer and the advantages of GTK over direct
xlib or win32 calls is likely to be minimal.  If/when GTK is ported
to more systems, a backend written using it could be a valuable
asset - volunteers are, as always, wecome.


@c ****************************************************************
@c Compiling
@node Compiling and Developing, GNU Objective C Compiler and Runtime, Compatibility, Top
@section Compiling and Developing

@menu
* How can I get started programming?::  
* How can I help with GNUstep?::  
* Helping develop GNUstep::     
* Helping document GNUstep::    
* How do I update the task list?::  
* How do I start writing tests?::  
* How do I start writing applications?::  
* How can I help with the GNUstep website?::  
* Why doesn't GDB support Objective-C?::  
@end menu

@node How can I get started programming?, How can I help with GNUstep?, Compiling and Developing, Compiling and Developing
@subsection  How can I get started programming?

  Good question.  Read the tutorials at the GNUstep web site. Also look at
Apple's documentation (pointers in the Resources section on the GNUstep web
site.

@node How can I help with GNUstep?, Helping develop GNUstep, How can I get started programming?, Compiling and Developing
@subsection  How can I help with GNUstep?

@enumerate
@item Write/debug library code 
@item Write documentation 
@item Update the task list and library headers 
@item Write applications
@end enumerate

Let people know what you are doing.  Break your project up into
the smallest units you can.  Feed back frequent updates to the
maintainers.  Ask questions in the discussion mailing list.

Do remember that any changes beyond a few lines of code (or
documentation) require a disclaimer or copyright assignment to the
Free Software Foundation before they can be incorporated into the
project.  Get in touch with the maintainer of the library you are
working on about this.

Don't start with large-scale reorganisation of anything - instead,
get a general idea in mind of what you want to do, and proceed as
much as possible with incremental changes that don't break anything
- that way you can make those incremental changes available to the
rest of the community at frequent intervals.

Don't be afraid to give up - there is no shame in finding out that
you have take on too large/complex a project.  It's much better to
'resign' and take on a smaller job than to just stop without telling
anyone.

Please document the code you add or change (using autogsdoc comments
that begin with a slash and two asterices). But PLEASE, do not copy from
the Apple documentation or any other copyrighted documentation.


@node Helping develop GNUstep, Helping document GNUstep, How can I help with GNUstep?, Compiling and Developing
@subsection  Helping develop GNUstep

There is plenty of unimplemented stuff in the gui library and
backend libraries that volunteers can work on - just browse through
the code and see if it conforms to the documentation.

Specific tasks are noted in the developers section on the GNUstep
website.

Once you have coded something, you could always write a testcase
and documentation for it :-)

@node Helping document GNUstep, How do I update the task list?, Helping develop GNUstep, Compiling and Developing
@subsection  Helping document GNUstep

All class documentation is written directly in the source code itself
and translated using the autogsdoc program. See the source code and
documentation for autogsdoc for information on documenting the classes.

Newcomers could write documentation for individual classes by
comparing the OpenStep specification, the MacOS-X documentation,
and the GNUstep source.  Documentation should clearly note where
individual methods are specific to OpenStep, MacOS-X or are GNustep
extensions.

More experienced people could write documentation on general
programming topics, and tutorials for new users.

Anyone willing to write documentation, either tutorials for using
GNUstep, or reference documentation for individual classes, should
either write it in gsdoc or as plain ascii text for someone else to
format into gsdoc.

GNUstep documentation should have copyright assigned to the Free
Software Foundation.

@node How do I update the task list?, How do I start writing tests?, Helping document GNUstep, Compiling and Developing
@subsection  How do I update the task list?

 The task list (@url{http://savannah.gnu.org/pm/?group_id=99}) is 
supposed to tell people what jobs are waiting to be done. Feel free to
add to it or update the tasks that are there (you need to create a login
for yourself first).

One job of major importance that pretty much anyone can do is to
look for jobs to add to the task list.  In the case of methods from
the OpenStep specification or the MacOS-X documentation not being
present in the GNUstep libraries, it is also helpful to add the
method prototypes to the library header files.

Send any changes or additions to @email{bug-gnustep@@gnu.org}.

A beginner can look through the MacOS-X documentation, the OpenStep
specification and the GNUstep source and contribute task items.

If a class or method is in MacOS-X and OpenStep but is not in
GNUstep - it's a high priority TODO and should at least be added
to the GNUstep headers and a dummy version added to the source with
a FIXME comment.

If a class or method is in MacOS-X but not OpenStep or GNUstep -
it's a low priority TODO.  It should be added to the GNUstep headers
bracketed in @code{#ifndef STRICT_OPENSTEP}

If a class or method is in OpenStep but not in MacOS-X or GNUstep
- it's a low priority TODO.  It should be added to the GNUstep
headers bracketed in @code{#ifndef STRICT_MACOS_X}

There are a couple of people working on this already, so it's a
good idea to get in touch with Adam or Richard to coordinate efforts.

@node How do I start writing tests?, How do I start writing applications?, How do I update the task list?, Compiling and Developing
@subsection  How do I start writing tests?

 You can write testcases - where the libraries fail tests, you
could either fix the problem, or add it to the task list.

To write testcases, you need to use anonymous CVS to install the
latest GNUstep snapshots you can find. Then checkout the 'tests'
module from CVS.  In the 'tests' directory, you will find a
regression testing framework.
In order to use this you will also need a recent (v 1.3.2 or later) copy of
Guile (you can get this from a GNU ftp site) and will need to check-out,
built, and installed the 'guile' package from the GNUstep CVS repository.

@node How do I start writing applications?, How can I help with the GNUstep website?, How do I start writing tests?, Compiling and Developing
@subsection  How do I start writing applications?

 You can either look at the links on the GNUstep website for
applications that have been started, and email their owners to
volunteer to help, or you can start your own project.

@node How can I help with the GNUstep website?, Why doesn't GDB support Objective-C?, How do I start writing applications?, Compiling and Developing
@subsection  How can I help with the GNUstep website?

 Talk to Adam Fedor @email{fedor@@gnu.org}, the maintainer.

The GNUstep website is kept as a CVS module, but the largest portions
of it (the FAQ and the Documentation) are actually
generated from files in the individual GNUstep packages.

If you want to update the FAQ or documentation  - grab
the latest snapshot of the GNUstep core you can find, update it
from the CVS repository, and work with the contents of the appropriate
documentation directory.

If you want to work on other parts of the website, you can grab a copy
of the website via anonymous CVS. See
@url{http://savannah.gnu.org/cvs/?group_id=99} for instructions on how
to do that.

The main task with the website is to figure out which bits are
out-of-date (or wrong) and update/mark-as-outdated as required.

@node Why doesn't GDB support Objective-C?,  , How can I help with the GNUstep website?, Compiling and Developing
@subsection Why doesn't GDB support Objective-C?

Apple has submitted their patches to make GDB work with Objective-C
programs, and the GDB maintainer has said that he is interested in
integrating them. Now it appears that that there is just a lack of
time and priority to get this done. You can ask about or lobby for this - 
see @url{http://sources.redhat.com/gdb/}.

There are patches available on the gnustep web site if you want
to compile your own gdb (see @url{http://www.gnustep.org/pub/gnustep/patches}).


@c -------------------------------------------------------------------

@node GNU Objective C Compiler and Runtime, GNUstep Base Library, Compiling and Developing, Top
@section GNU Objective C Compiler and Runtime

@menu
* What is the Objective C Runtime?::  
* Does it allow a mixture of Objective C and C++::  
* Where can I find more information?::  
@end menu

@node What is the Objective C Runtime?, Does it allow a mixture of Objective C and C++, GNU Objective C Compiler and Runtime, GNU Objective C Compiler and Runtime
@subsection What is the Objective C Runtime?

The Objective C Runtime Library provides C functions and data structures
required to execute an Objective C program. 

The GNU Objective C Runtime Library offers everything NeXT's runtime
does, including Categories, Protocols, @samp{+poseAs:}, thread-safety,
class initialization on demand, delayed loading of classes, and
initialization of static instances (such as @@""-style string objects). 

It also has several improvements over NeXT's implementation:

@itemize @bullet

@item NeXT's runtime requires an extra function call (objc_msgSend) for
each message that is sent; (the function looks up the receiving
instance's implementation of the method).  GNU's implementation is
faster because it does not use an extra function call.  Instead, it
inlines a short piece of code that makes two pointer hops into a method
dispatch table; because the code is inlined, it does not incur the
overhead of a function call.

@item When running in thread-safe mode, NeXT's runtime must aquire a
global mutual exclusion lock every time a message is sent; this is
extremely slow.  GNU's runtime, amazingly, sends messages just as fast
in thread-safe mode as it does in single-thread mode---the code path
does not contain even a single extra instruction!  The GNU runtime only
needs locks when certainly structures are written, not read; the
structures are written relatively infrequently: only at class
initialization and when @samp{+poseAs:} is called.

@item GNU's runtime provides ``selector-types'' along with each
selector; NeXT's does not.  A selector-type is a string that describes
the C variable types for the method's return and argument values.  Among
other uses, selector-types is extrememly helpful for fast distributed
objects implementations, (see GNUstep Base Library Section, below).

@item Many of the GNU functions have different names than their
corresponding NeXT functions; the GNU names conform to the GNU coding
standards.

@end itemize

@node Does it allow a mixture of Objective C and C++, Where can I find more information?, What is the Objective C Runtime?, GNU Objective C Compiler and Runtime
@subsection Does it allow a mixture of Objective C and C++?

No.  
See @pxref{Can one use the hybrid "Objective-C++"}

@node Where can I find more information?,  , Does it allow a mixture of Objective C and C++, GNU Objective C Compiler and Runtime
@subsection Where can I find more information?

The FAQ associated with the newsgroup @samp{comp.lang.objective-c}
contains more information about GNU Objective C.

@c ------------- GNU Compiler and Objective C Runtime Library -------

@node GNUstep Base Library, GNUstep GUI Library, GNU Objective C Compiler and Runtime, Top
@section GNUstep Base Library

@menu
* What is the GNUstep Base Library?::  
* What is base's current state of development?::  
* What are the features of GNU Distributed Objects?::  
@end menu

@node What is the GNUstep Base Library?, What is base's current state of development?, GNUstep Base Library, GNUstep Base Library
@subsection What is the GNUstep Base Library?

The GNUstep Base Library is a library of general-purpose, non-graphical
Objective C objects.  For example, it includes classes for strings,
object collections, byte streams, typed coders, invocations,
notifications, notification dispatchers, moments in time, network ports,
remote object messaging support (distributed objects), event loops, and
random number generators.

It provides functionality that aims to implement the non-graphical
portion of the OpenStep standard (the Foundation library).  

@node What is base's current state of development?, What are the features of GNU Distributed Objects?, What is the GNUstep Base Library?, GNUstep Base Library
@subsection What is its current state of development?

GNUstep base is currently stable and implements probably 99% of the
functionality of the OpenStep classes and most all of the new Carbon
classes.
Normal work can already be done using the library since the
missing 1 percent are the least-often-used features or are simply not
up to date with the latest Carbon spec.

@node What are the features of GNU Distributed Objects?,  , What is base's current state of development?, GNUstep Base Library
@subsection What are the features of GNU Distributed Objects?

GNU Distributed Objects has many of the features of other distributed
objects implementations, but, since it is free software, it can be
ported to platforms for which other distributed objects implementations
are not available.

[NOTE: The GNU distributed object facilities have the same ease-of-use
as NeXT's; be warned, however, that they are not compatible with each
other.  They have different class heirarchies, different instance
variables, different method names, different implementation strategies
and different network message formats.  You cannot communicate with a
NeXT NSConnection using a GNU NSConnection.  

Here are some differences between GNU distributed objects and NeXT's
distributed objects: NeXT NSDistantObject asks it's remote
target for the method encoding types and caches the results; GNU
NSDistantObject gets the types directly from the local GNU "typed selector"
mechanism if the information is known locally and only queries the remote
target or caching encoding types when using a method that is not known to
the local process.  The NSProxy for the remote root object always has name 0
and, once set, you cannot change the root object of a NSConnection; the GNU
Proxy for the remote root object has a target address value just like
all other Proxy's, and you can change the root object as many times as
you like. ].

@c --------------------------GNUstep Base Library----------------------

@node GNUstep GUI Library, GNUstep DisplayGhostScript Server, GNUstep Base Library, Top
@section GNUstep GUI Library

@menu
* What is the GUI Library?::    
* Explain the organization of the front- and back-ends::  
* What is the current state of development of the front-end?::  
* What is the current state of development of the X/DPS back-end?::  
@end menu

@node What is the GUI Library?, Explain the organization of the front- and back-ends, GNUstep GUI Library, GNUstep GUI Library
@subsection What is the GUI Library?

The GNUstep GUI Library is a library of objects useful for writing
graphical applications.  For example, it includes classes for drawing
and manipulating graphics objects on the screen: windows, menus,
buttons, sliders, text fields, and events.  There are also many
peripheral classes that offer operating-system-independent interfaces to
images, cursors, colors, fonts, pasteboards, printing.  There are also
workspace support classes such as data links, open/save panels,
context-dependent help, spell checking.

It provides functionality that aims to implement the @samp{AppKit}
portion of the OpenStep standard.  However the implementation has
been written to take advantage of GNUstep enhancements wherever possible.


@node Explain the organization of the front- and back-ends, What is the current state of development of the front-end?, What is the GUI Library?, GNUstep GUI Library
@subsection Explain the organization of the front- and back-ends

The GNUstep GUI Library is divided into a front- and back-end.  The
front-end contains the majority of implementation, but leaves out the
low-level drawing and event code.  A back-end can override whatever
methods necessary in order to implement low-level drawing event
receiving.  Different back-ends will make GNUstep available on various
platforms.  The default GNU back-end will run on top of X Windows.
Other back-ends could allow GNUstep to run on OpenGL and WIN32
graphics/event platforms.  Much work will be saved by this clean
separation between front- and back-end, because it allows different
platforms to share the large amount of front-end code.

@node What is the current state of development of the front-end?, What is the current state of development of the X/DPS back-end?, Explain the organization of the front- and back-ends, GNUstep GUI Library
@subsection What is the current state of development of the front-end?

Many of the classes are well implemented, if not thouroughly tested.
See the GNUstep web sites and read status information contained in the
distribution for the most up-to-date information.

@node What is the current state of development of the X/DPS back-end?,  , What is the current state of development of the front-end?, GNUstep GUI Library
@subsection What is the current state of development of the X/DPS back-end?

It works, but is slow and buggy. A lot of work could be done.

@c ------------------------- GNUstep GUI Library -----------------------

@node GNUstep DisplayGhostScript Server,  , GNUstep GUI Library, Top
@section GNUstep DisplayGhostScript Server

@menu
* What is the Display Ghostscript Server?::  
* What is DGSs current state of development?::  
* What is the relationship between the Display Ghostscript Server and X Windows?::  
@end menu

@node What is the Display Ghostscript Server?, What is DGSs current state of development?, GNUstep DisplayGhostScript Server, GNUstep DisplayGhostScript Server
@subsection What is the Display Ghostscript Server?

It is a free implementation of a Display PostScript server based on the
GNU Ghostscript program developed by Aladdin Enterprises and now owned by artofcode LLC.

@node What is DGSs current state of development?, What is the relationship between the Display Ghostscript Server and X Windows?, What is the Display Ghostscript Server?, GNUstep DisplayGhostScript Server
@subsection What is its current state of development?

GNU contracted with Aladdin Enterprises to add some key features to GNU
Ghostscript so it could be used as a DPS server. This work has mostly
been done, although Aladdin did not completely finish the work that they
were contracted for.  (Because the work took longer than specified and
was not completed, Aladdin agreed to waive approximately $10,000 in
promised fees for the work that was actually done and delivered.)  DGS
works fairly well with a single context.  Alpha channel and compositing
currently doesn't work.

@node What is the relationship between the Display Ghostscript Server and X Windows?,  , What is DGSs current state of development?, GNUstep DisplayGhostScript Server
@subsection What is the relationship between the Display Ghostscript Server and X Windows?

Display Ghostscript runs on top of X Windows.

@c ------------------ GNUstep DisplayGhostScript Server ---------------

@format
All trademarks mentioned on in this FAQ belong to their owners.
@end format

@bye
\bye