x-clickthrough.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <X11/Xlib.h>
#include <X11/extensions/shape.h>
#include <X11/Xatom.h>

// Enable clickthrough, transparency, and always on top for a given window
//     x-clickthrough <windowid> <alpha (0-100)>
//
// alpha < 100 will enable window always on top and enable clickthrough
// alpha = 100 will disable window always on top and disable clickthrough 
//
// Compile with:
//     gcc x-clickthrough.c -o x-clickthrough -lX11 -lXext
//
// Examples:
//     x-clickthrough $(wmctrl -l | fzf | awk '{print $1}') 50
//     wmctrl -lx | awk '$3 ~ /mpv/ { print $1 }' | xargs -I {} x-clickthrough {} 50    # enable for all mpv windows
//     wmctrl -lx | awk '$3 ~ /mpv/ { print $1 }' | xargs -I {} x-clickthrough {} 100   # disable for all mpv windows


void setTransparency(Display *display, Window window, int level) {
    Atom opacityAtom = XInternAtom(display, "_NET_WM_WINDOW_OPACITY", False);
    unsigned long opacityValue = (unsigned long)((double)level / 100.0 * 0xffffffff);
    XChangeProperty(display, window, opacityAtom, XA_CARDINAL, 32, PropModeReplace, (unsigned char *)&opacityValue, 1);
}

void setAlwaysOnTop(Display *display, Window window, int enable) {
    Atom netWmStateAbove = XInternAtom(display, "_NET_WM_STATE_ABOVE", False);
    Atom netWmState = XInternAtom(display, "_NET_WM_STATE", False);

    XClientMessageEvent ev;
    memset(&ev, 0, sizeof(ev));

    ev.type = ClientMessage;
    ev.display = display;
    ev.window = window;
    ev.message_type = netWmState;
    ev.format = 32;
    ev.data.l[0] = enable ? 1 : 0;
    ev.data.l[1] = netWmStateAbove;
    ev.data.l[2] = 0;

    XSendEvent(display, DefaultRootWindow(display), False, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&ev);
    XSync(display, False);
}

void setClickthrough(Display *display, Window window, int enable) {
    if (enable) {
        XRectangle rect = {0, 0, 0, 0};
        Region region = XCreateRegion();
        XUnionRectWithRegion(&rect, region, region);
        XShapeCombineRegion(display, window, ShapeInput, 0, 0, region, ShapeSet);
        XDestroyRegion(region);
    } else {
        XShapeCombineMask(display, window, ShapeInput, 0, 0, None, ShapeSet);
    }
}

int main(int argc, char *argv[]) {
    if (argc < 3) {
        fprintf(stderr, "Usage: %s <windowid> <alpha (0-100)>\nSet alpha to 100 to disable clickthrough.\n", argv[0]);
        return 1;
    }
    
    Window window = strtoul(argv[1], NULL, 0);
    int level = atoi(argv[2]);
    
    Display *display = XOpenDisplay(NULL);
    if (display == NULL) {
        fprintf(stderr, "Failed to open display\n");
        return 1;
    }
    
    setTransparency(display, window, level);
    setClickthrough(display, window, level < 100);
    setAlwaysOnTop(display, window, level < 100);
    if (level == 100)
        XRaiseWindow(display, window);
    XCloseDisplay(display);
    return 0;
}

inspired by mpv-player/mpv#8949