Question

I’m writing a application that put docks in the right side of the screen, like this:

I can reserve space in the side of the screen by using the _NET_WM_STRUT_PARTIAL, so that the maximized windows won’t overlap the docks.

In the image, you can see that there is a top panel. The problem is that the docks will overlap the panel. Is there a way to either find out the size of the panel, or to make a way that the panel will reduce to open space to the docks?

I’m using Xlib, by the way.

Answer 1

By using the good hint given by Havoc P, I was able to formulate this code, that returns the height of a top docking panel:

#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <limits.h>
#include <stdlib.h>
#include <stdio.h>

static Display* display;

// looks for the maximum "docking height" of all children of this window
static int top_panel_height(Window window)
{
    int height = 0;     // maximum height
    Window w;
    Window* children;
    unsigned int n_children;

    XQueryTree(display, window, &w, &w, &children, &n_children);

    // looks for each one of the children
    int i;
    for(i=0; i<n_children; i++)
    {
        // this is the property we're looking for
        Atom strut = XInternAtom(display, "_NET_WM_STRUT_PARTIAL", 
                False);
        Atom type_return;
        int actual_type;
        unsigned long nitems, bytes;
        unsigned char* data = NULL;

        // load window attributes (we only want to know about the
        //                         windows where y = 0)
        XWindowAttributes xwa;
        XGetWindowAttributes(display, window, &xwa);

        // load the property _NET_WM_STRUT_PARTIAL
        int s = XGetWindowProperty(display, window, strut, 0, LONG_MAX, 
                False, 
                XA_CARDINAL, &type_return, &actual_type,
                &nitems, &bytes, (unsigned char**)&data);
        if(s == Success)
        {
            Atom *state = (Atom *) data;
            // state[2] contains the "dock height"
            if(xwa.y == 0 && nitems > 0 && state[2])
                if(state[2] > height)
                    height = state[2];
        }

        // recursively, traverse the tree of all children of children
        int children_max_height = top_panel_height(children[i]);
        if(children_max_height > height)
            height = children_max_height;
    }

    return height;
}


int main()
{
    display = XOpenDisplay(NULL);
    Window root = RootWindow(display, DefaultScreen(display));

    printf("%d\n", top_panel_height(root));

    return 0;
}

It might not be pretty, but it works 🙂