|The Finite Element ToolKit|
Developed by the MCP Research Group
at the UCSD Center for Computational Mathematics
SG User's Guide
Table of Contents
SG is an unstructured simplex mesh OpenGL display and manipulation tool for use with the finite element research codes MC and PLTMG. SG provides OpenGL-based graphics over UNIX and INET sockets on UNIX/X-based systems, Win32-based systems, and other systems. It can also be used with MCLite as a replacement for MATLAB's builtin graphics for polygons. SG can read Geomview OFF files and OpenInventor files for polygonal surface descriptions, and it can also read PDB files for molecule descriptions. SG looks and acts somewhat like Geomview, and it mimics most of the basic features and controls of Geomview for displaying polygonal 2-manifolds.
SG is designed to mimic the well-known Geomview program from the University of Minnesota's geometry center, and it uses one of Geomview's input file formats (the "OFF" format). Although SG it is quite a bit simpler than Geomview, it has three advantages when compared to Geomview. First, it can take input directly from files, UNIX pipes, UNIX domain sockets, and INET sockets (Geomview cannot take input from INET sockets). Second, it can produce provably correct PostScript renderings of meshes (Geomview uses a baricenter-based front-to-back ordering for the Painter's algorithm, which often fails for complex meshes; SG uses a linear programming approach which is mathematically guaranteed to work if the picture is paintable with the Painter's algorithm). Third, it will build and run on Win32 platforms such as Windows 2000, Windows NT, and Windows 98. (Some may actually view this as a disadvantage.) In the case of Win32, SG uses the WINSOCK API for INET socket access. The window-system specific connection to X11 or Win32 is made through "WGL" extensions to Win32 under NT, or using the SGI "GLw" widget set on X11 platforms. The graphics in SG is done in an entirely platform-independent manner using OpenGL. This portability is due to SG having been built on top of a portable low-level abstraction library called MALOC (Minimal Abstraction Layer for Object-oriented C). MALOC was written primarily to support the development of MC, but is now also used for SG. Both MALOC and SG are now both used by Randy Bank in the development of his software package PLTMG.
Quaternion-based Trackball Rotator
SG is a polygonal manifold display and manipulation tool. It can also display PDB (Protein DataBase) data as a collection of intersecting triangulated spheres of appropriate color and radii. It is basically a trackball rotator, although one can also scale and translate the object being displayed. The manipulation is done with a combination of the mouse and the keyboard. The rotator is quaternion-based, following the trackball example in Mark Kilgard's OpenGL programming book. The rotator avoids gimbal lock, rotation instability, and other degeneracies through the use of a projection ball and quaternions. The hysteresis problem usually present in rotators is removed by employing Ken Shoemake's non-accumulation trick from his famous Arcball example in one of the Graphics Gems. (I.e., when you move the mouse back to the starting point in a rotation, the object resumes its original position.)
SG can generate a very high-quality Postscript rendering of any displayed scene, with (provably) correct logical rendering order of the polygon primitives, through the use of builtin routine called SGps. SGps generates Postscript output from an arbitrary OpenGL scene, by using the feedback buffer mechanism in OpenGL. SGps is similar to Seth Teller's PSGL, and to Gary Wu's PSOGL, but it does not use the same baricentric depth quicksorting of the polygons, which is prone to incorrect rendering orders for complex scenes. Instead, SGps is based on a linear programming approach developed jointly with R. Bank. If a scene can be rendered by the Painter's Algorithm, then SGps is guaranteed to find a logically correct painting order, and it will then use the Painter's Algorithm to render the scene correctly in Postscript.
Here are some examples illustrating the Geomview-compatible OFF input format tha t SG employs: tri, tet. The portability of SG is attained by the use of a low-level abstraction library called MALOC. The MALOC library must be installed before installing SG. Similar to MALOC, SG is easily buildable from source on any UNIX-like system, and uses a GNU autoconf build environment.
Information and Resources
Detailed information about SG can be found in the User's Guide and Programmers's Guide.
While SG is itself a self-contained software package, it is one of several components of FETK (the Finite Element ToolKit). FETK consists of the following components written in Clean OO C:
MALOC is self-contained, and requires only an ANSI-C compiler on a UNIX or Win32 platform. PUNC, GAMer, SG, and MC are also self-contained, but rely on MALOC having been previously installed on the platform. Additional features of MC are enabled if PUNC is available, but PUNC is not required to build MC. The MC eXtension libraries MCX are constructed on top of MALOC and MC, and in order install and use MCX one must first correctly configure and install both MALOC and MC. MCX is made up of a number of individual libraries developed by members of our group, or contributed by one of a number of colleagues. More information about FETK can be found on the FETK website:
SG is copyrighted, but is redistributable in source and binary form under the following license. The SG source can be downloaded from the FETK Download Page.
In case you are having trouble with X11 on your MacOSX Leopard machine, here are some precompiled binaries:
Frequently Asked Questions
What is SG and what does SG stand for?
See the Overview.
How to I obtain a copy of the SG source code?
See the Obtaining SG section.
I managed to get a copy of "sg-VERSION.[i386|src|tar].[rpm|gz]"; how do I now install SG?
See the Installation Instructions.
You gave me a "patch.gz" file to fix a bug in SG; how do I apply the patch?
To apply patches to upgrade SG to a new version, you first obtain the patch from me or my webpage as a single file with a name like "patch.gz". You apply the patch after you have unpacked the sg.tgz file as described above. To apply the patch, cd into the directory containing the root SG directory (called "sg" after unpacking sg.tgz) and execute the "patch" program as follows (the patch program exists on most UNIX machines):
Patch files are simply the output from a recursive "diff" that are used to represent all differences between two directory trees. For example, to create a patch representing the changes from version 1.0 of SG (in directory sg_1.0 for example) to version 1.1 of SG (e.g. in directory sg_1.1), I would normally type the following:
I really don't know what I'm doing; how to I get more documentation for SG?
The User's Guide and the Programmers's Guide contain all of the SG documentation.
Why did you develop SG? There are many other mesh viewer packages, right?
Yes, there are. Geomview is awesome. However, we often want to display the mesh in a calculation on a local workstation, while running the calculation on a larger remote (possibly parallel) machine. For large complex meshes, opening up a remote X display is extremely slow (the X libraries may not even exist on the large number crucher). By running SG on the local machine, our numerical codes on the remote machine can send polygons in binary XDR format directly to an INET socket on the local machine. This is extremely fast, even for very large datasets. Finally, we often need to run visualization tools natively on Win32 platforms.
There are a couple of things we didn't like about Geomview, which we made different in SG. For example, the rotator in Geomview exhibits hysteresis in the sense that if you return the mouse to its original location when rotating, the object doesn't actually return to its original position. SG on the other hand uses a quaternion-based trackball rotator, and uses a rotation non-accumulation trick due to Ken Shoemake to avoid this type of hysteresis (the particular trick can be found in one of the Graphics Gems volumes). The PostScript generation mentioned above was another reason for writing SG.
What is in all of these subdirectories? Where exactly is "SG"?
SG consists of several (class) libraries from which you will call routines to handle your application. You will need to write a main driver program (and any supporting routines you need) and then link to the libraries. Alternatively, you can build the SG tools "sg" and "mcsg" by doing a "./configure ; make ; make install" in the tools subdirectory. These two tools process and display polygon data, and have functionality and behavior similar to Geomview. If you are simply after these two tools, then you don't need to actually use the libraries and headers that get installed when you configure/make/make install the SG libraries. However, the in order to successfully configure/make/make install the tools sg and mcsg, you must first succesfully configure/make/make install the SG libraries.
As described in the file "INSTALL", you will build all of the libraries in one shot for your particular architecture, along with various test programs to verify that the various pieces are functioning correctly. The libraries end up in "sg/lib", and the header files are in subdirectories in "sg/inc".
The following directory tree is created when you unpack the SG "sg.tgz" distribution file by following the instructions in the INSTALL document:
sg | ------------------------ / | | | \ config doc examples src tools
The src directory has the additional subdirectory structure:
src | ------------------------------ / | | | | | | \ aaa_inc aaa_lib base gl glu glw ogl vgl
Within each library source directory is an additional subdirectory, "sg". The "sg" subdirectory contains public headers for the library, representing the library API; these headers will be installed in the specified header install directory during the install procedure after building SG. (The OpenGL library subdirectories gl, glu, and glw contain additional OpenGL-specific API files in additional subdirectories.)
The following is a brief description of each subdirectory of the package.
sg - The entire SG package sg/config - GNU Autoconf scripts and non-unix config files sg/doc - SG documentation sg/examples - Complex examples and data files for using SG sg/src - SG source code (all source and headers) sg/src/aaa_inc - Header installation tools sg/src/aaa_lib - Library installation tools sg/src/*/sg - The SG headers (API) sg/src/base - Source for M. Holst's BASE (SG foundation headers) sg/src/ogl - Source for M. Holst's OGL (OpenGL rotator kernel) sg/src/vgl - Source for M. Holst's VGL (Virtual openGL) sg/src/gl - Source files for dubset of B. Paul's MesaGL sg/src/glu - Source files for dubset of B. Paul's MesaGLU sg/src/glw - Source files for dubset of B. Paul's MesaGLw sg/tools - Some binary tools for use with SG
Okay, I seem to have installed SG correctly; how do I actually use it now?
Using the SG code is very simple; just type "./mcsg" without arguments and you get a list of all of the options. The socket bridging tool functions similarly; typing "./mcbridge" without arguments gives you a list of all of the possible options. The remaining tool "sg" is a motif version of "mcsg" with similar functionality, but with a more sophisticated button layout.
What is the class hierarchy? How are the various libraries related?
Detailed information on the class relationships can be found in the Programmers's Guide. The following directed graph shows the class library dependencies. (This tends to evolve as MC is developed.)
MALOC ==> base ==> ogl ==> vgl ==> sg /\ /\ || || OpenGL ===> gl => glu || || Window System =========> wgl/glw
Wait! I have a bunch of other questions, such as:
Available distribution formats
SG is distributed in both binary format (as a binary RPM file sg-VERSION.i386.rpm for i386-based versions of Linux) and in source format (as a source RPM file sg-VERSION.src.rpm and as a gzipped tar file "sg-VERSION.tar.gz").
Installation using the binary RPM file
The following rpm command will install all of the SG headers and libraries into /usr/local/include and /usr/local/lib, and will install the SG documentation into /usr/share/doc/packages/sg:
rpm -Uvh sg-VERSION.i386.rpm
Installation and rebuilding from sources using the source RPM file
The following rpm command will unpack the source rpm file "sg-VERSON.src.rpm" into the SG gzipped tar file containing the sources called "sg-VERSION.tar.tar.gz" and into a small RPM spec file called "sg-VERSON.spec":
rpm -Uvh sg-VERSION.src.rpmThe sources can then be unpacked and built using the directions for the gzipped tar file below. Alternatively, the following rpm command will do these steps for you:
rpm -bp sg-VERSION.spec
Rebuilding binary and source RPM files from the gzipped tar file
The SG sources contain the RPM spec file "sg-VERSON.spec" in the root source directory; as a result, rebuilding the RPM files from sources can be done using the rpm command:
rpm -ta sg-VERSION.tar.gzThe result will be the corresponding source and binary rpm files, named "sg-VERSON.src.rpm" and "sg-VERSION.i386.rpm". Normally, these files are written to /usr/src/redhat/SRPMS and /usr/src/redhat/RPMS respectively, but you must be logged in as root for these to work. The destination directories can be overriden using arguments to the rpm program (see the rpm manpage).
Installation and building from sources using the gzipped tar file
The following command will unpack SG into a number of subdirectories and files on any UNIX machine (and on any WinNT machine with the GNU-Win32 tools gzip and tar).
gzip -dc sg.tgz | tar xvf -
Building the package using the GNU "configure" shell script and "make"
The "configure" shell script in the "sg" directory (the toplevel directory created when you unpacked the SG tgz file) will build the entire package. This is a standard GNU autoconf-generated configuration script. For a list of the possible configuration options, type:
You should be able to build SG by simply typing:
./configure make make install
However, it is often advantageous to keep the original source directory pristine; the configure script can actually be run outside the source tree, which will keep all files created by the build outside the source tree. (This idea is related to the section below describing how to build binaries for multiple architectures at the same time using the same source tree, and requires that your version of make has the VPATH facility, such as GNU make.) For example, I build SG in a separate directory from the source tree as follows:
gzip -dc sg.tgz | tar xvf - mkdir sg_build cd sg_build ../sg/configure make make install
Building binaries for multiple architectures in the same source directory
If you have a version of "make" that supports the VPATH facility (such as any recent version of GNU make), then you can build the package for multiple architectures in the same source directory (in fact, you can do the compiles at the same time without collisions). This is very useful if you have your home directory on an NFS volume that you share among multiple architectures, such as SGI, Linux, etc. To build SG for all the systems at the same time, you simply make an additional subdirectory in the main SG directory for each architecture, copy "configure" into it, "cd" into the subdirectory, and then install as above. For example, on a linux machine you would do the following:
mkdir linux cp configure linux/. cd linux ./configure make make install
If you mount the same NFS home directory on for example an OpenStep box, you could at the same time do the following:
mkdir next cp configure next/. cd next ./configure make make install
Again, both builds can actually be done outside the source tree rather than in a subdirectory of the source tree, as described in the previous section.
Building shared libraries rather than static libraries
(MIKE: give an overview of libtool.)
Rebuilding the configure script and the Makefile.in files
If for some reason you actually need to rebuild the configure script or the Makefile.in files using the GNU autoconf suite, you should read the block of documentation at the top of the configure.in file. The commentary I put there explains exactly how the GNU autoconf suite must be used and in what order, and exactly what files are produced at each step of the process. A script called "bootstrap" which automates this process is located in the config subdirectory of the SG source tree.
Below is some platform-specific build/usage information for SG.
What you end up with
Once the build completes via the "configure;make;make install" procedure above with no errors, the SG library (libsg.a and/or libsg.so) is installed into the specified installation directory. You can also build some useful tools that employ the SG library by cd-ing into the "tools" subdirectory and repeating the "configure;make;make install" procedure. Once the tools build completes, you will end up with:
mcsg - Core socket OpenGL tool ([GLw | WGL] + [X | Win32] + OpenGL) mcbridge - A socket bridging tool (FILE/PIPE/UNIX/INET) sg - A Motif version of mcsg (Motif + X + OpenGL)
If the SG tools work like they were designed, you won't need any more information to use the tools. If you want to know more about the details of the algorithms in SG, or about the implementation details such as the socket graphics, have a look at the Programmer's Guide.
Getting SG to find your installation of GL/GLU/GLw/Motif/Etc
If your installation of OpenGL (libGL, libGLU, libGLw and headers) and/or Motif is located in an unusual directory, then the configuration script may have trouble finding the libraries or the headers. The configure script prints out the state of affairs quite clearly as to whether it found the libraries and the headers. If you have the libraries and configure is not finding them, then here are several possible solutions, each of which usually works. They are listed in preferred order (i.e. you should try Solution 1 first, and if that doesn't work try Solution 2, and so on).
Note that you DO NOT need Motif in order to build SG; if you DO have Motif, then the additional Motif-based tool "sg" is built. Without Motif libraries on your system, you still get the base socket graphics tool "mcsg" and the socket bridging tool "mcbridge". ("sg" is somewhat fancier than "mcsg", but "mcsg" has all of the core functionality of the Motif tool.) On a Win32 machine such as Windows NT, you will also end up with both "mcsg" and "mcbridge".
SG (Socket Graphics) was conceived, designed, and implemented over several years by Michael Holst, beginning with an initial implementation in 1994. Various colleagues have contributed ideas and/or code to SG (see the credits list below).
SG (Socket Graphics) Copyright (C) 1994-2010 Michael Holst TELE: (858) 534-4899 Department of Mathematics FAX: (858) 534-5273 UC San Diego, AP&M 5739 EMAIL: email@example.com La Jolla, CA 92093 USA WEB: http://ccom.ucsd.edu/~mholstSG was designed to be a portable networked visualization tool for use in the development of MC (Manifold Code), an adaptive multilevel finite element package also developed by Michael Holst. It is also used by Randy Bank as the primary visualization tool for PLTMG. Both SG and MC are written on top of a low-level abstraction layer called MALOC (Minimal Abstraction Layer for Object-oriented C), also developed by Michael Holst. SG was developed almost entirely on a home-grown 90Mhz Pentium PC running various flavors of Linux and [Free|Net|Open]BSD, using primarily GNU, BSD, and other free software development tools. Most of the development occurred during the hours of 10pm to 2am on a daily basis for several years, under heavy influence of Starbuck's coffee, with helpful advice provided by Mac and Mochi (two cats knowledgable in socket programming and numerical analysis).
SG was released under the GNU GPL (GNU General Public License) beginning with the initial implementation in 1994, and continues to be released under this license. What this means is that like all GNU software, SG is freely redistributable in source code form following the rules outlined in the text of the GNU GPL. You should have received a copy of the GNU GPL with this distribution of SG; a copy can be found here. If you did not receive a copy of the GNU GPL, please write to me and also write to: The Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Software included in the SG source code package
A complete roadmap to the source code forming the SG package can be found above. While the core SG classes were developed primarily by Michael Holst, some additional software is currently included with SG:
sg/src/vgl/vglm.c - Motif Variant of vgl (joint Bank/Holst effort) sg/src/vgl/oglps.c - Perfect PS generation (joint Bank/Holst effort) sg/src/gl/* - B. Paul's MesaGL (the GL library) sg/src/glu/* - B. Paul's MesaGLU (the GLU library) sg/src/glw/* - SGI's OpenGL widgets (the GLw library)The extra conditionally-build libraries provide the complete OpenGL capability that SG requires in order to function, if these libraries are not available on the particular platform. Under normal circumstances, these three libraries will not have to be built; the OpenGL API they provide is completely software-based, and will be slower than native hardware-accelerated OpenGL which is normally available on modern PCs, Macs, and SGI platforms.
Below is a credits list for the people that have contributed to SG in one way or another. The fields below follow the credits file format used in the Linux kernel CREDITS file to allow for easy manipulation via shell scripts. The fields are as follows:
N: name of contributor E: email address W: web address P: PGP key ID and fingerprint D: description of primary contributions S: snail-mail address
N: Michael Holst E: firstname.lastname@example.org W: http://ccom.ucsd.edu/~mholst P: 1024/0xB5212DCD D: sg/* -- The package structure D: sg/acconfig.h -- The platform abstraction information D: sg/configure.in -- The GNU autoconf/automake structure D: sg/config/* -- The GNU autoconf/automake shell scripts D: sg/doc/* -- The package documentation D: sg/examples/* -- The package examples D: sg/src/aaa_inc/* -- Library header build structure D: sg/src/aaa_lib/* -- Static and shared library build structure D: sg/src/base/* -- M. Holst's SG Foundation headers D: sg/src/ogl/* -- M. Holst's OpenGL-based trackball rotator D: sg/src/vgl/* -- M. Holst's window system abstraction layer D: sg/src/gl/* -- The libGL wrapper D: sg/src/glu/* -- The libGLU wrapper D: sg/src/glw/* -- The libGLw wrapper D: sg/tools/* -- Tools built on the libraries S: Department of Mathematics S: UC San Diego, AP&M 5739 S: La Jolla, CA 92093 USA N: Randolph E. Bank E: email@example.com D: sg/src/vgl/vglm.c -- Vglm Class (Motif variant; joint w/ Holst) D: sg/src/ogl/oglps.c -- OglPS Class (Perfect PS; joint w/ Holst) S: Department of Mathematics S: UC San Diego S: La Jolla, CA 92093 USA N: Steve Bond E: firstname.lastname@example.org D: sg/sg.spec -- RPM support (for building src/binary RPMs) S: Department of Mathematics S: UC San Diego S: La Jolla, CA 92093 USA
Contacting the Author
If you have questions or comments about SG, please feel free to contact me at email@example.com.
This version of SG is distributed under the following guidelines:
The GPL (GNU General Public License) below is copyrighted by the Free Software Foundation. However, the instance of software that it refers to, my package in this case, is copyrighted by myself as the author of the package. Any additional software that I distribute with my software is copyrighted by the authors of those pieces of software (see the individual source files for author information). ---Michael Holst
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If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances. It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice. This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License. 8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. 9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. NO WARRANTY 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. (one line to give the program's name and a brief idea of what it does.) Copyright (C) 19yy < name of author > This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. < signature of Ty Coon >, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.