FlashPrint visual glitch on Linux (Debian testing)
In addition to open source niceties of OpenGL, you need to will often need to install and update the drivers for your GPU.  If you do not wish to or cannot utilize your GPU (it'll cost u in performance), look for options to turn off hardware acceleration or use a purely "software renderer" type setting.  I don't know if FlashPrint has such settings, but i do know that OpenGL can do some screwy stuff if you lack correct Nvidia drivers (and have an nvidia gpu).