This test program uses OpenGL (Mesa) to simulate camera input,
and writes decoded Data Matrix streams to STDOUT.

The program is somewhat boring if you don't know that you can
right-click to cycle through the test images.  To add your own
images, just overwrite any image in the libdmtx/test/test_images
directory with another 256x256 PNG file.  If you want to add
brand new images then you will have to update the gFilename[] and
gFileCount variables at the top of gltest.c to include them.
