Get the latest tech news
Mixed DPI in X11
and the X Window System I'm writing this article because I'm getting tired of repeating the same concepts every time someone makes misinformed statements about the (lack of) support for mixed-DPI configurations in X11. It is my hope that anybody looking for information on the subject may be directed here, to get the facts about the actual possibilities offered by the protocol, avoiding the biased misinformation available from other sources.
In 1998, an extension to the core X11 protocol was devised to integrate multiple displays seamlessly, making them appear as a single X Screen, and thus allowing windows to freely move between them. This gives great flexibility on how to combine monitors (including overlaps, cloning, etc); the hidden cost is that all of the physical information that the core protocol would report about the virtual backend to its X Screen become essentially meaningless. For this reason, when the RANDR extension is enabled, the core protocol will synthetize ficticious physical dimensions for its X Screen, from the overall framebuffer size, assuming a “reference” pixel density of 96 DPI.
Or read this on Hacker News