Things can get really complicated with x11 when you have processes running on remote machines or using XEmbed. With XEmbed, what may look like a single window

Things can get really complicated with x11 when you have processes running on remote machines or using XEmbed. With XEmbed, what may look like a single window is actually multiple windows all managed by different processes with their own render loops. Speaking of XEmbed, many years ago, we had an application that ran complicated visualization pipelines. We wanted to add a modern GUI around it to configure it and provide interaction. We didn't have the ability to rewrite the original application, so we wrote a Gtk GUI and used XEmbed to embed the other process in it, then used a unix socket to send commands back and forth. To the user, it was seamless and worked really well!