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FLTK (pronounced "fulltick") stands for Fast Light Toolkit. It is a cross-platform C++ GUI toolkit for UNIX®/Linux® (X11), Microsoft® Windows®, and MacOS® X.

It provides modern GUI functionality without the bloat and supports 3D graphics via OpenGL® and its built-in GLUT emulation.

More information:

How to use

Login to Gadi with X11 (X-Windows) forwarding. Add the -Y option for Linux/Mac/Unix to your SSH command to request SSH to forward the X11 connection to your local computer. For Windows, we recommend to use MobaXterm ( as it automatically uses X11 forwarding.

Information about setting up MobaXterm and X-forwarding can be found in our connecting to Gadi page

You can check the versions installed in Gadi with a module query:

$ module avail fltk

We normally recommend using the latest version available and always recommend to specify the version number with the module command:

$ module load fltk/1.3.5

For more details on using modules see our software applications guide.

Start an interactive PBS job with the following command on Gadi.

It requests 1 CPU, 2 GiB memory, and 8 GiB local disk on a compute node on Gadi from the normal queue for its exclusive access for 30 minutes against the project a00. It also requests the system to enter the working directory once the job is started.

To change the number of CPU cores, memory, or jobfs required, simply modify the appropriate PBS resource requests in the qsub command below according to the information in our queue structure guide.

Note that if your application does not work in parallel, setting the number of CPU cores to 1 and changing the memory and jobfs accordingly is required to prevent the compute resource waste.

Also note that you must include -l storage=scratch/ab12+gdata/yz98 to the qsub command below if the job needs access to /scratch/ab12/ and /g/data/yz98/.

Details are found on our PBS directives page.

$ qsub -I -X -P a00 -q normal -l ncpus=1,mem=2GB,jobfs=8GB,walltime=00:30:00,wd

When the interactive job starts on Gadi, execute the followings commands:

# Load module, always specify version number.
$ module load fltk/1.3.5
$ ./fltk_program

To see the documentation of FLTK visit

Authors: Mohsin Ali
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