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GEL README, Andreas Bærentzen, February 2006.
==========
 
This README describes the GEL project. GEL stands for Geometry and Linear 
Algebra which are the constituents we will mostly put into this library.
 
There are a good many tools for computational geometry processing: A
voxel grid and a simple triangle mesh data structure. There is also halfedge 
 
based polygonal mesh data structure called HMesh. There is a very
useful data structure known as a k-D tree and many other things. 
 
Also found are two packages for linear algebra: CGLA is strictly for
small vectors and matrices. LinAlg is a Lapack wrapper for slightly
larger problems. At this point, it is fairly simple. 
 
Finally there are some utilities in Util: Getting command line
arguments, hash table classes, a 2D grid class, a resource manager and
other miscellany. 
 
GEL is intended for use both under a  variety of unix platforms (Linux
and OSX in particular) and  under windows. This README is mostly for
unix users. Windows users should also consult README_MSVC
 
Dependencies: GEL depends on the Developers Image Library DevIL,
Lapack, and OpenGL and GLUT. However, most of GEL does not require
these dependencies. In particular, you do not need DevIL except if you
want the OBJ viewer example program.
 
Who made GEL
==========
 
GEL is mostly the work of Andreas Bærentzen, but other people
contribute. In particular, Jeppe Frisvad, Bjarke Jakobsen, Henrik
Aanæs, and Bent D. Larsen. We are all from Informatics and
Mathematical Modelling, a department of the Technical University of
Denmark. 
 
Regarding LICENSE.
==========
 
I was considering putting GEL under the LGPL. But it is a long complex
text. The longer any kind of document, the more chances for loopholes
in my opinion. Instead, I list a few simple rules below. The most
important one is that if you want to use GEL for some purpose, and it
is not crystal clear whether it is against the rules, contact me. As
for the rules:
 
You are allowed to use GEL for academic or commercial purposes. In
particular, you are welcome to give GEL to students as a basis for 
academic work or to use it for your own applications.
 
The biggest limitation that I want to impose is that you cannot repackage
GEL in any way. You are not allowed to distribute another library which
contains GEL or parts of GEL unless you make it clear that this other
library contains GEL. You are also not allowed to redistribute GEL in a
changed form. If you want changes to be made, contact me.
 
Of course, neither I nor my employer will give you any money or be
held responsible in any way, under any circumstances what so ever - no
matter what sort of damage GEL might inflict upon you. Not that I can
foresee GEL causing you any damage :-) 
 
If anything is unclear, please contact me. In fact, if you want to use
GEL for a bigger project, I'd appreciate an email to jab@imm.dtu.dk
 
In a project such as this, it is almost impossible to completely avoid
building upon fragments of other peoples source code. GEL includes an
obj loader based on work by Nate Robins. Some pieces of source code
from Graphics Gems have also been used. All of this amounts to only a
small fraction of the GEL source code and it should not be in
violation of any license. Should you disagree, contact me, and I will
rectify the situation.
 
----------------------------------------------------------------------
1. INTRODUCTION
----------------------------------------------------------------------
 
In the following, I discuss the structure of the source code and how to
add new directories to the framework. 
 
The idea is that this framework should be a) simple to use and b) let 
people easily compile the same source code under various unix platforms.
A seperate configuration is kept for each combination of OS, architecture, 
and compiler. It is possible to specify targets release or debug.
 
Source files are compiled in build directories, and separate build 
directories are kept for each unique combination of 
 
os architecture compiler target
 
such as
 
Linux_i686_g++3_debug
 
this makes it easier to work in a heterogenous environment or to 
experiment with seperate compilers or just to switch between debug mode 
and optimized.
 
To see how to use the framework, you may skip to section 5.
 
----------------------------------------------------------------------
2. DIRECTORY STRUCTURE
----------------------------------------------------------------------
 
The directories under the root of the source tree (where you find this 
README) are
 
src        - Source code for GEL libraries
apps       - Source code for applications
apps       - Source code for test programs
doc        - Documentation
bin        - Executables
lib        - Libraries
makefiles  - As the name suggests, makefiles
 
src contains a number of subdirectories each of which represents a 
link library. apps  also contains subdirectories, however each of these
is supposed to contain source code for an executable.
 
----------------------------------------------------------------------
3. FILE NAMES
----------------------------------------------------------------------
 
source files are *.c or *.cpp depending on whether it is C or C++
header files are named *.h
 
----------------------------------------------------------------------
4. MAKEFILES
----------------------------------------------------------------------
 
Some defintions:
----------------
 
The PLATFORM is a string concatenation of the os cpu and compiler, e.g.
 
Linux_i686_g++
 
The TARGET is either `debug' or `release'. By default it is debug. It is
recommended that you do _not_ hardwire your own default into the makefiles
as I did for many years. It seems better to define the variable when running
make, using "make TARGET=release" or by setting the target variable in the
environment.
 
 
Make'ing from the source root
-----------------------------
 
Just typing
> make 
 
from the root of the source tree will cause first every library and
then every application to be remade. However, there are several
targets.
 
make all			 - equivalent to "make lib shared test app"
 
make lib       - make all libraries
 
make shared    - For the current target platform combination, a shared library
								 is created by stringing together the compiled static libraries
 
make app       - make all applications
 
make clean     - clean all library directories and app directories.
                 this removes only files pertaining to the current
                 platform and target (release/debug). This also
                 removes generated libraries. 
 
make distclean - cleans and completely removes all build directories. 
 
make platform  - copies a template to OS_CPU_COMPILER.mk in the
                 makefiles directory. Use this only if you know what you
								 are doing.
 
make install   - Copies header files and libraries to the appropriate place
							   which is PREFIX=/usr/local by default. The libraries which
								 are copied are either the debug or release versions depending
								 on the active target. 
 
								 Install does not install applications since many are little
								 test programs that do not belong in your path.
 
 
Make'ing in subdirectories
--------------------------
 
Go to a subdirectory of src, say src/somedir. 
Here you have the following options:
 
make
make lib
make clean
 
The first two invocations are identical and will rebuild all sourcefiles and
put them in a library directory. The latter will remove all object and
dependency files (but only for the current platform
(e.g. Linux_i686_g++_debug) The default target is lib.
 
Go to a subdirectory of apps, say apps/somedir. 
Here you have the following options:
 
make
 
or
 
make app
 
will recompile the source files in the current directory and build the 
programs. This is the default target. When compiled, the application is
moved to wherever/GEL/bin
 
make force
 
does the same but tries first to recompile all libraries that the 
applications in somedir depend on. This is the safe way to recompile,
but it takes a few seconds more, so if you are sure the libraries are
up to date, just go make.
 
make clean
 
works like above. 
 
Makefiles in subdirectories under apps should generally be edited.
When create by `make makefiles' the Makefile in apps/somedir looks
like this 
 
PROGRAMS 	= prog1 prog2
OWN_LIBS 	= Lib1 Lib2
LIBS			= ${GLLIBS} ${XLIBS} -lm -lz -lexpat
 
Add something like this
 
PROGRAMS 	= prog1 prog2
OWN_LIBS 	= Lib1 Lib2
LIBS			= ${GLLIBS} ${XLIBS} -lm -lz -lexpat
 
where prog1 and prog2 are programs you wish to create. These must 
correspond to source files with the same name and suffix .cpp. In
other words, 
 
prog1.cpp 
prog2.cpp
 
must exist (and contain a main function)
 
Lib1 and Lib2 are libraries that must also be in the directory structure,
i.e. under src there are subdirectories 
 
src/Lib1
src/Lib2
 
the files in these subdirectories will be compiled and put in library 
files named libLib1.a under lib. More precisely it will be put here:
 
lib/PLATFORM_TARGET/
 
PLATFORM and TARGET are defined above. Another library directory are for
precompiled libraries whose source code is not a part of this tree. Put
such libraries here:
 
lib/PLATFORM/
 
this directory is created by 
 
make platform from the source root.
 
----------------------------------------------------------------------
5. CONFIGURATION
----------------------------------------------------------------------
 
When you add a new project to this framework, you should go through
the following steps:
 
Add directories for libraries under src. E.g. add 
 
mkdir src/somelib
 
Then add directories for applications:
 
mkdir apps/someapp
 
Copy appropriate source files to these directories and then edit
 
makefiles/config.mk
 
to tell us which compiler to use (leave blank to use default) 
 
Finally, from the source root type 
 
make platform
 
Depending on your compiler you may now have to edit the makefile called
 
makefiles/PLATFORM.mk 
 
to set special compile flags. No go 
 
make makefiles
 
Finally you are all set. Go
 
make
 
 
----------------------------------------------------------------------
6. DEPENDENCIES IN GEL
----------------------------------------------------------------------
 
Each directory under src represents a library. There are some dependencies
between these libraries.
 
 
 
lib						depends on
-----------------------------------
CGLA 					nothing 
 
Util 					CGLA
 
LinAlg 				CGLA
 
Geometry 			LinAlg, CGLA
 
HMesh					CGLA, Util, Geometry, LinAlg (indirectly)
 
GLGraphics		Everything (since it contains general rendering
							facilities)
 
 
----------------------------------------------------------------------
7. TODO
----------------------------------------------------------------------
 
- No real testing of blended C and C++.
- No dependency computation for .c 
 
 
 
 
 
 
 
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