Empty or transparent window with Xlib showing border lines only

Question

Is there a way to create a window with Xlib which only display the border lines, title, close button and that you can move with the mouse? The content of the window must be empty (or "totally transparent", although "transparency" sounds more like an effect I don't need). Basically the window should show the background area.

Carner

Answer 1

I'm not sure if it is what you want, but following code creates an X window with transparent background but still using the window decoration of your window manager.

It will only work though if your X11 and graphics hardware configuration supports visuals with a depth of 32 bit.

#include <X11/Xlib.h>
#include <X11/Xutil.h>

int main(int argc, char* argv[])
{
    Display* display = XOpenDisplay(NULL);

    XVisualInfo vinfo;
    XMatchVisualInfo(display, DefaultScreen(display), 32, TrueColor, &vinfo);

    XSetWindowAttributes attr;
    attr.colormap = XCreateColormap(display, DefaultRootWindow(display), vinfo.visual, AllocNone);
    attr.border_pixel = 0;
    attr.background_pixel = 0;

    Window win = XCreateWindow(display, DefaultRootWindow(display), 0, 0, 300, 200, 0, vinfo.depth, InputOutput, vinfo.visual, CWColormap | CWBorderPixel | CWBackPixel, &attr);
    XSelectInput(display, win, StructureNotifyMask);
    GC gc = XCreateGC(display, win, 0, 0);

    Atom wm_delete_window = XInternAtom(display, "WM_DELETE_WINDOW", 0);
    XSetWMProtocols(display, win, &wm_delete_window, 1);

    XMapWindow(display, win);

    int keep_running = 1;
    XEvent event;

    while (keep_running) {
        XNextEvent(display, &event);

        switch(event.type) {
            case ClientMessage:
                if (event.xclient.message_type == XInternAtom(display, "WM_PROTOCOLS", 1) && (Atom)event.xclient.data.l[0] == XInternAtom(display, "WM_DELETE_WINDOW", 1))
                    keep_running = 0;

                break;

            default:
                break;
        }
    }

    XDestroyWindow(display, win);
    XCloseDisplay(display);
    return 0;
}

Reduplication

I tried this code on Raspberry Pi3.. XMatchVisualInfo returns 1, so no error and visual was found. But no transparency. What can it be? On PC with ubuntu works with transparency fine. – Electrolyse

My system supports transparent windows (using transset from a terminal applies transparency to any window), yet the root depth on my system appears to be only 24. Is setting a depth of 32 really required? – Oran

Besides hardware and X, it is necessary to have a screen compositor, such as xcompmgr, compton, etc. running in the background. Lubuntu does not run this by default; install one to run upon startup. You can usually tell if your OS is already running a compositor if the edge of your windows has funky dropshadows shading what's underneath, or if your windows fly in from the side. xcompmgr has been recommended by others, as being lightweight. – Champagne