File: annotated.c

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tinywm 1.3-9
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/* TinyWM is written by Nick Welch <mack@incise.org>, 2005.
 *
 * This software is in the public domain
 * and is provided AS IS, with NO WARRANTY. */

/* much of tinywm's purpose is to serve as a very basic example of how to do X
 * stuff and/or understand window managers, so i wanted to put comments in the
 * code explaining things, but i really hate wading through code that is
 * over-commented -- and for that matter, tinywm is supposed to be as concise
 * as possible, so having lots of comments just wasn't really fitting for it.
 * i want tinywm.c to be something you can just look at and go "wow, that's
 * it?  cool!"  so what i did was just copy it over to annotated.c and comment
 * the hell out of it.  ahh, but now i have to make every code change twice!
 * oh well.  i could always use some sort of script to process the comments out
 * of this and write it to tinywm.c ... nah.
 */

/* most X stuff will be included with Xlib.h, but a few things require other
 * headers, like Xmd.h, keysym.h, etc.
 */
#include <X11/Xlib.h>

#define MAX(a, b) ((a) > (b) ? (a) : (b))

int main()
{
    Display * dpy;
    Window root;
    XWindowAttributes attr;

    /* we use this to save the pointer's state at the beginning of the
     * move/resize.
     */
    XButtonEvent start;

    XEvent ev;


    /* return failure status if we can't connect */
    if(!(dpy = XOpenDisplay(0x0))) return 1;

    /* you'll usually be referencing the root window a lot.  this is a somewhat
     * naive approach that will only work on the default screen.  most people
     * only have one screen, but not everyone.  if you run multi-head without
     * xinerama then you quite possibly have multiple screens. (i'm not sure
     * about vendor-specific implementations, like nvidia's)
     *
     * many, probably most window managers only handle one screen, so in
     * reality this isn't really *that* naive.
     *
     * if you wanted to get the root window of a specific screen you'd use
     * RootWindow(), but the user can also control which screen is our default:
     * if they set $DISPLAY to ":0.foo", then our default screen number is
     * whatever they specify "foo" as.
     */
    root = DefaultRootWindow(dpy);

    /* you could also include keysym.h and use the XK_F1 constant instead of
     * the call to XStringToKeysym, but this method is more "dynamic."  imagine
     * you have config files which specify key bindings.  instead of parsing
     * the key names and having a huge table or whatever to map strings to XK_*
     * constants, you can just take the user-specified string and hand it off
     * to XStringToKeysym.  XStringToKeysym will give you back the appropriate
     * keysym or tell you if it's an invalid key name.
     *
     * a keysym is basically a platform-independent numeric representation of a
     * key, like "F1", "a", "b", "L", "5", "Shift", etc.  a keycode is a
     * numeric representation of a key on the keyboard sent by the keyboard
     * driver (or something along those lines -- i'm no hardware/driver expert)
     * to X.  so we never want to hard-code keycodes, because they can and will
     * differ between systems.
     */
    XGrabKey(dpy, XKeysymToKeycode(dpy, XStringToKeysym("F1")), Mod1Mask, root,
            True, GrabModeAsync, GrabModeAsync);

    /* XGrabKey and XGrabButton are basically ways of saying "when this
     * combination of modifiers and key/button is pressed, send me the events."
     * so we can safely assume that we'll receive Alt+F1 events, Alt+Button1
     * events, and Alt+Button3 events, but no others.  You can either do
     * individual grabs like these for key/mouse combinations, or you can use
     * XSelectInput with KeyPressMask/ButtonPressMask/etc to catch all events
     * of those types and filter them as you receive them.
     */
    XGrabButton(dpy, 1, Mod1Mask, root, True, ButtonPressMask, GrabModeAsync,
            GrabModeAsync, None, None);
    XGrabButton(dpy, 3, Mod1Mask, root, True, ButtonPressMask, GrabModeAsync,
            GrabModeAsync, None, None);

    for(;;)
    {
        /* this is the most basic way of looping through X events; you can be
         * more flexible by using XPending(), or ConnectionNumber() along with
         * select() (or poll() or whatever floats your boat).
         */
        XNextEvent(dpy, &ev);

        /* this is our keybinding for raising windows.  as i saw someone
         * mention on the ratpoison wiki, it is pretty stupid; however, i
         * wanted to fit some sort of keyboard binding in here somewhere, and
         * this was the best fit for it.
         *
         * i was a little confused about .window vs. .subwindow for a while,
         * but a little RTFMing took care of that.  our passive grabs above
         * grabbed on the root window, so since we're only interested in events
         * for its child windows, we look at .subwindow.  when subwindow ==
         * None, that means that the window the event happened in was the same
         * window that was grabbed on -- in this case, the root window.
         */
        if(ev.type == KeyPress && ev.xkey.subwindow != None)
            XRaiseWindow(dpy, ev.xkey.subwindow);
        else if(ev.type == ButtonPress && ev.xbutton.subwindow != None)
        {
            /* now we take command of the pointer, looking for motion and
             * button release events.
             */
            XGrabPointer(dpy, ev.xbutton.subwindow, True,
                    PointerMotionMask|ButtonReleaseMask, GrabModeAsync,
                    GrabModeAsync, None, None, CurrentTime);

            /* we "remember" the position of the pointer at the beginning of
             * our move/resize, and the size/position of the window.  that way,
             * when the pointer moves, we can compare it to our initial data
             * and move/resize accordingly.
             */
            XGetWindowAttributes(dpy, ev.xbutton.subwindow, &attr);
            start = ev.xbutton;
        }
        /* the only way we'd receive a motion notify event is if we already did
         * a pointer grab and we're in move/resize mode, so we assume that. */
        else if(ev.type == MotionNotify)
        {
            int xdiff, ydiff;

            /* here we "compress" motion notify events.  if there are 10 of
             * them waiting, it makes no sense to look at any of them but the
             * most recent.  in some cases -- if the window is really big or
             * things are just acting slowly in general -- failing to do this
             * can result in a lot of "drag lag."
             *
             * for window managers with things like desktop switching, it can
             * also be useful to compress EnterNotify events, so that you don't
             * get "focus flicker" as windows shuffle around underneath the
             * pointer.
             */
            while(XCheckTypedEvent(dpy, MotionNotify, &ev));

            /* now we use the stuff we saved at the beginning of the
             * move/resize and compare it to the pointer's current position to
             * determine what the window's new size or position should be.
             *
             * if the initial button press was button 1, then we're moving.
             * otherwise it was 3 and we're resizing.
             *
             * we also make sure not to go negative with the window's
             * dimensions, resulting in "wrapping" which will make our window
             * something ridiculous like 65000 pixels wide (often accompanied
             * by lots of swapping and slowdown).
             *
             * even worse is if we get "lucky" and hit a width or height of
             * exactly zero, triggering an X error.  so we specify a minimum
             * width/height of 1 pixel.
             */
            xdiff = ev.xbutton.x_root - start.x_root;
            ydiff = ev.xbutton.y_root - start.y_root;
            XMoveResizeWindow(dpy, ev.xmotion.window,
                attr.x + (start.button==1 ? xdiff : 0),
                attr.y + (start.button==1 ? ydiff : 0),
                MAX(1, attr.width + (start.button==3 ? xdiff : 0)),
                MAX(1, attr.height + (start.button==3 ? ydiff : 0)));
        }
        /* like motion notifies, the only way we'll receive a button release is
         * during a move/resize, due to our pointer grab.  this ends the
         * move/resize.
         */
        else if(ev.type == ButtonRelease)
            XUngrabPointer(dpy, CurrentTime);
    }
}