[PATCH] Icon layout incorrect

[Ian Wienand <ianw gelato unsw edu au>]

Hi,

In bug #161512 Sebastien Bacher requested
> could you send this patch the nautilus-list for review ? The nautilus
> maintainers use mainly the list to review patches.

When getting _NET_WORKAREA information, a length value of G_LONGMAX is
passed to gdk_property_get().  Internally, gdk_property_get()
increments this value, causing it to wrap around to zero.  Thus the
property call doesn't fail, but doesn't return any useful information.

This manifests in the icon layout being slightly askew, as noted by
David Mosberger @
http://lists.debian.org/debian-ia64/2004/12/msg00034.html

A suggested patch is attached,

-i
ianw gelato unsw edu au
http://www.gelato.unsw.edu.au

--- nautilus-2.8.2/src/file-manager/fm-desktop-icon-view.c	2004-06-10 00:14:55.000000000 +1000
+++ nautilus-2.8.2-fixed/src/file-manager/fm-desktop-icon-view.c	2004-12-17 13:08:31.187503033 +1100
@@ -163,6 +163,7 @@
 net_workarea_changed (FMDesktopIconView *icon_view,
 		      GdkWindow         *window)
 {
+	long *nworkareas = NULL;
 	long *workareas = NULL;
 	GdkAtom type_returned;
 	int format_returned;
@@ -174,23 +175,57 @@
 
 	icon_container = get_icon_container (icon_view);
 
+	/* Find the number of desktops so we know how long the
+	 * workareas array is going to be (each desktop will have four
+	 * elements in the workareas array describing
+	 * x,y,width,height) */
 	gdk_error_trap_push ();
 	if (!gdk_property_get (window,
-			       gdk_atom_intern ("_NET_WORKAREA", FALSE),
+			       gdk_atom_intern ("_NET_NUMBER_OF_DESKTOPS", FALSE),
 			       gdk_x11_xatom_to_atom (XA_CARDINAL),
-			       0, G_MAXLONG, FALSE,
+			       0, 4, FALSE,
 			       &type_returned,
 			       &format_returned,
 			       &length_returned,
-			       (guchar **) &workareas)) {
+			       (guchar **) &nworkareas)) {
+		g_warning("Can not caclulate _NET_NUMBER_OF_DESKTOPS");
+	}
+	if (gdk_error_trap_pop()
+	    || nworkareas == NULL
+	    || type_returned != gdk_x11_xatom_to_atom (XA_CARDINAL)
+	    || format_returned != 32)
+		g_warning("Can not calculate _NET_NUMBER_OF_DESKTOPS");
+	
+	/* Note : gdk_property_get() is broken (API documents admit
+	 * this).  As a length argument, it expects the number of
+	 * _bytes_ of data you require.  Internally, gdk_property_get
+	 * converts that value to a count of 32 bit (4 byte) elements.
+	 * However, the length returned is in bytes, but is calculated
+	 * via the count of returned elements * sizeof(long).  This
+	 * means on a 64 bit system, the number of bytes you have to
+	 * request does not correspond to the number of bytes you get
+	 * back, and is the reason for the workaround below.
+	 */ 
+	gdk_error_trap_push ();
+	if ((*nworkareas < 1) 
+	    || !gdk_property_get (window,
+				  gdk_atom_intern ("_NET_WORKAREA", FALSE),
+				  gdk_x11_xatom_to_atom (XA_CARDINAL),
+				  0, ((*nworkareas) * 4 * 4), FALSE,
+				  &type_returned,
+				  &format_returned,
+				  &length_returned,
+				  (guchar **) &workareas)) {
+		g_warning("Can not get _NET_WORKAREA");
 		workareas = NULL;
 	}
 
 	if (gdk_error_trap_pop ()
 	    || workareas == NULL
 	    || type_returned != gdk_x11_xatom_to_atom (XA_CARDINAL)
-	    || (length_returned % 4) != 0
+	    || ((*nworkareas) * 4 * sizeof(long)) != length_returned
 	    || format_returned != 32) {
+		g_warning("Can not determine workarea, guessing at layout");
 		nautilus_icon_container_set_margins (icon_container,
 						     0, 0, 0, 0);
 	} else {
@@ -200,6 +235,9 @@
 			icon_container, screen, workareas, length_returned / sizeof (long));
 	}
 
+	if (nworkareas != NULL)
+		g_free (nworkareas);
+
 	if (workareas != NULL)
 		g_free (workareas);
 }

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