From 2e758f78c151b35b316c3286c83e14a435242486 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bert=20M=C3=BCnnich?= <ber.t@posteo.de>
Date: Sun, 2 Feb 2014 14:56:01 +0100
Subject: [PATCH] Check if window manager supports fullscreen; related to issue
 #128

---
 window.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 window.h |  1 +
 2 files changed, 44 insertions(+)

diff --git a/window.c b/window.c
index faea963..8086a4c 100644
--- a/window.c
+++ b/window.c
@@ -54,6 +54,9 @@ static int barheight;
 
 Atom atoms[ATOM_COUNT];
 
+static Bool fs_support;
+static Bool fs_warned;
+
 void win_init_font(Display *dpy, const char *fontstr)
 {
 	int n;
@@ -102,6 +105,36 @@ unsigned long win_alloc_color(win_t *win, const char *name)
 	return col.pixel;
 }
 
+void win_check_wm_support(Display *dpy, Window root)
+{
+	int format;
+	long offset = 0, length = 16;
+	Atom *data, type;
+	unsigned long i, nitems, bytes_left;
+	Bool found = False;
+
+	while (!found && length > 0) {
+		if (XGetWindowProperty(dpy, root, atoms[ATOM__NET_SUPPORTED],
+		                       offset, length, False, XA_ATOM, &type, &format,
+		                       &nitems, &bytes_left, (unsigned char**) &data))
+		{
+			break;
+		}
+		if (type == XA_ATOM && format == 32) {
+			for (i = 0; i < nitems; i++) {
+				if (data[i] == atoms[ATOM__NET_WM_STATE_FULLSCREEN]) {
+					found = True;
+					fs_support = True;
+					break;
+				}
+			}
+		}
+		XFree(data);
+		offset += nitems;
+		length = MIN(length, bytes_left / 4);
+	}
+}
+
 #define INIT_ATOM_(atom) \
 	atoms[ATOM_##atom] = XInternAtom(e->dpy, #atom, False);
 
@@ -150,6 +183,9 @@ void win_init(win_t *win)
 	INIT_ATOM_(_NET_WM_ICON);
 	INIT_ATOM_(_NET_WM_STATE);
 	INIT_ATOM_(_NET_WM_STATE_FULLSCREEN);
+	INIT_ATOM_(_NET_SUPPORTED);
+
+	win_check_wm_support(e->dpy, RootWindow(e->dpy, e->scr));
 }
 
 void win_update_sizehints(win_t *win)
@@ -379,6 +415,13 @@ void win_toggle_fullscreen(win_t *win)
 	if (win == NULL || win->xwin == None)
 		return;
 
+	if (!fs_support) {
+		if (!fs_warned) {
+			warn("window manager does not support fullscreen");
+			fs_warned = True;
+		}
+		return;
+	}
 	win->fullscreen = !win->fullscreen;
 
 	memset(&ev, 0, sizeof(ev));
diff --git a/window.h b/window.h
index b9e064d..ec71319 100644
--- a/window.h
+++ b/window.h
@@ -36,6 +36,7 @@ enum {
 	ATOM__NET_WM_ICON,
 	ATOM__NET_WM_STATE,
 	ATOM__NET_WM_STATE_FULLSCREEN,
+	ATOM__NET_SUPPORTED,
 	ATOM_COUNT
 };