Opacity in a reparenting WM

Question

I'm writing a reparenting window manager for X11 (and have asked a number of questions about it here already). Right now, the issue I'm having isn't so much a bug to fix as much as a question on how to implement something.

Applications can request transparency, and if a compositor like xcompmgr or picom is running, they will provide it. However, this doesn't seem to work when I reparent the window; in this case the client window's background just shows a black background behind (maybe the frame window? but the background of that isn't black). I do indicate I have a frame by setting .NET_FRAME_EXTENTS.

What I've tried:

• It looks like awesomewm's code for opacity listens to a property notify with a .NET_WM_OPACITY. I don't get any PropertyNotify event when I change opacity of a window, despite selecting SubstructureRedirect|SubstructureNotify|PropertyChange on the root window.

Answer 1

You need to create your frame window with reparenting with depth=32 (ie: Made to work with transparency). Since you are already looking at AwesomeWM: It finds the right visual for this at startup and then creates all of its windows this way. That is only necessary since Lua code might want transparency. AFAIR, other WMs look at the program's window bit depth and create their frame window based on that.