XSelectInput(3)

📦
version 1.8.14 · 8 versions
, in alpine 3.24, arch rolling, nixos 26.05, nixpkgs unstable

💅 XSelectInput(3) — the "hey bestie, tell the server what u care about" era

okay so this is a page from the Xlib functions manual (the XLIB FUNCTIONS girlies, iykyk) and honestly? it's giving "select input events" and we're obsessed. let's get into it fr fr.

✨ SYNTAX ✨

int XSelectInput(Display *display, Window w, long event_mask);

no cap, that's the whole signature. three args, iconic behavior. 🎀

🌸 ARGUMENTS 🌸

  • display — specifies the connection to the X server. literally your lil link to the whole vibe.
  • event_mask — specifies the event mask. like, the actual menu of things u want reported. 💅
  • w — specifies the window whose events you are interested in. yes bestie, that window.

🦋 DESCRIPTION 🦋

so XSelectInput is the function that requests that the X server report the events associated with the specified event mask. periodt. u tell the server "hey, i wanna know when these things happen," and it says "bet."

initially, X will not report any of these events. like, zero. nothing. it's on silent mode until u say otherwise. 🙈

events are reported relative to a window. real "everything is about context" energy. if a window is not interested in a device event, it usually propagates to the closest ancestor that is interested — unless the do_not_propagate mask prohibits it. so basically the event floats up the family tree until someone claims it. the way that works is so satisfying tbh. 🧚

setting the event-mask attribute of a window overrides any previous call for the same window but not for other clients. so like, u can change your mind, but u can't change someone else's. mind ya business respectfully. 👑

multiple clients can select for the same events on the same window with the following restrictions:

  • multiple clients can select events on the same window because their event masks are disjoint. when the X server generates an event, it reports it to all interested clients. sharing is caring bestie. 🫶
  • only one client at a time can select CirculateRequest, ConfigureRequest, or MapRequest events, which are associated with the event mask SubstructureRedirectMask. exclusive access, no plus-ones. 💀
  • only one client at a time can select a ResizeRequest event, which is associated with the event mask ResizeRedirectMask. same energy. one at a time. ✋
  • only one client at a time can select a ButtonPress event, which is associated with the event mask ButtonPressMask. literally one. don't even try it. 😭

and then, the moment we've all been waiting for: the server reports the event to all interested clients. highkey the most equitable thing ever. 🌈

also important: XSelectInput can generate a BadWindow error. so like, do a vibe check on your window handle before u call this. 🔥

🎀 DIAGNOSTICS 🎀

  • BadWindow — a value for a Window argument does not name a defined Window. translation: that window does not exist bestie. it's giving "you tried to text a number that blocked you." 💀🙈

👑 SEE ALSO 👑

  • Xlib - C Language X Interface — the classic. the blueprint. read it if u want the full lore. 📚
ngl the propagation + multi-client rules are lowkey the whole personality of this function. respect the boundaries, select ur events, slay. 💅✨

kisses and X server blessings, this has been the libX11 1.8.14 edition of the page, dated X Version 11 — mwah, stay iconic bestie. 🌸🦋💖

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