X11 Mouse – Highlight Current Mouse Position

While I like Mikeserv's answer for cleverness, it has the downside that it will create a window which "steals" the focus and has to be clicked away. I also find it takes just slightly too long to start: about 0.2 to 0.3 seconds, which is just slightly too slow for a "smooth" experience.

I finally got around to digging into XLib, and clobbered together a basic C program to do this. The visual effect is roughly similar to what Windows (XP) has (from memory). It's not very beautiful, but it works ;-) It doesn't "steal" focus, starts near-instantaneous, and you can click "through" it.

You can compile it with cc find-cursor.c -o find-cursor -lX11 -lXext -lXfixes. There are some variables at the top you can tweak to change the size, speed, etc.

I released this as a program at https://github.com/arp242/find-cursor. I recommend you use this version, as it has some improvements that the below script doesn't have (such as commandline arguments and ability to click "through" the window). I've left the below as-is due to its simplicity.

/*
 * https://github.com/arp242/find-cursor
 * Copyright © 2015 Martin Tournoij <martin@arp242.net>
 * See below for full copyright
 */

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

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


// Some variables you can play with :-)
int size = 220;
int step = 40;
int speed = 400;
int line_width = 2;
char color_name[] = "black";


int main(int argc, char* argv[]) {
    // Setup display and such
    char *display_name = getenv("DISPLAY");
    if (!display_name) {
        fprintf(stderr, "%s: cannot connect to X server '%s'\n", argv[0], display_name);
        exit(1);
    }

    Display *display = XOpenDisplay(display_name);
    int screen = DefaultScreen(display);

    // Get the mouse cursor position
    int win_x, win_y, root_x, root_y = 0;
    unsigned int mask = 0;
    Window child_win, root_win;
    XQueryPointer(display, XRootWindow(display, screen),
        &child_win, &root_win,
        &root_x, &root_y, &win_x, &win_y, &mask);

    // Create a window at the mouse position
    XSetWindowAttributes window_attr;
    window_attr.override_redirect = 1;
    Window window = XCreateWindow(display, XRootWindow(display, screen),
        root_x - size/2, root_y - size/2,   // x, y position
        size, size,                         // width, height
        0,                                  // border width
        DefaultDepth(display, screen),      // depth
        CopyFromParent,                     // class
        DefaultVisual(display, screen),     // visual
        CWOverrideRedirect,                 // valuemask
        &window_attr                        // attributes
    );
    XMapWindow(display, window);
    XStoreName(display, window, "find-cursor");

    XClassHint *class = XAllocClassHint();
    class->res_name = "find-cursor";
    class->res_class = "find-cursor";
    XSetClassHint(display, window, class);
    XFree(class);

    // Keep the window on top
    XEvent e;
    memset(&e, 0, sizeof(e));
    e.xclient.type = ClientMessage;
    e.xclient.message_type = XInternAtom(display, "_NET_WM_STATE", False);
    e.xclient.display = display;
    e.xclient.window = window;
    e.xclient.format = 32;
    e.xclient.data.l[0] = 1;
    e.xclient.data.l[1] = XInternAtom(display, "_NET_WM_STATE_STAYS_ON_TOP", False);
    XSendEvent(display, XRootWindow(display, screen), False, SubstructureRedirectMask, &e);

    XRaiseWindow(display, window);
    XFlush(display);

    // Prepare to draw on this window
    XGCValues values;
    values.graphics_exposures = False;

    unsigned long valuemask = 0;
    GC gc = XCreateGC(display, window, valuemask, &values);

    Colormap colormap = DefaultColormap(display, screen);
    XColor color;
    XAllocNamedColor(display, colormap, color_name, &color, &color);
    XSetForeground(display, gc, color.pixel);
    XSetLineAttributes(display, gc, line_width, LineSolid, CapButt, JoinBevel);

    // Draw the circles
    for (int i=1; i<=size; i+=step) { 
        XDrawArc(display, window, gc,
            size/2 - i/2, size/2 - i/2,   // x, y position
            i, i,                         // Size
            0, 360 * 64);                 // Make it a full circle

        XSync(display, False);
        usleep(speed * 100);
    }
    XFreeGC(display, gc);
    XCloseDisplay(display);
}


/*
 *  The MIT License (MIT)
 * 
 *  Copyright © 2015 Martin Tournoij
 * 
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to
 *  deal in the Software without restriction, including without limitation the
 *  rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 *  sell copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 * 
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 * 
 *  The software is provided "as is", without warranty of any kind, express or
 *  implied, including but not limited to the warranties of merchantability,
 *  fitness for a particular purpose and noninfringement. In no event shall the
 *  authors or copyright holders be liable for any claim, damages or other
 *  liability, whether in an action of contract, tort or otherwise, arising
 *  from, out of or in connection with the software or the use or other dealings
 *  in the software.
 */