Clarify licenses

- add license headers to everything
- convert a few files from public domain or LGPL2.1+ to GPL2+
- some archaeology to clarify which files are from which library

5 files changed, 13 insertions, 5 deletions

diff --git a/src/widgets/gimp/CMakeLists.txt b/src/widgets/gimp/CMakeLists.txt
index aa886cc67..0c8686cdd 100644
--- a/src/widgets/gimp/CMakeLists.txt
+++ b/src/widgets/gimp/CMakeLists.txt
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
 set(gimpwidgets_SRC
 	gimpcolorwheel.c
 	ruler.cpp
diff --git a/src/widgets/gimp/gimpcolorwheel.c b/src/widgets/gimp/gimpcolorwheel.c
index 51d2c7e1c..87f17eac6 100644
--- a/src/widgets/gimp/gimpcolorwheel.c
+++ b/src/widgets/gimp/gimpcolorwheel.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
 /* HSV color selector for GTK+
  *
  * Copyright (C) 1999 The Free Software Foundation
diff --git a/src/widgets/gimp/gimpcolorwheel.h b/src/widgets/gimp/gimpcolorwheel.h
index 41a38c842..e79fc1575 100644
--- a/src/widgets/gimp/gimpcolorwheel.h
+++ b/src/widgets/gimp/gimpcolorwheel.h
@@ -1,3 +1,7 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+/** @file
+ * HSV color selector for GTK+
+ */
 /* HSV color selector for GTK+
  *
  * Copyright (C) 1999 The Free Software Foundation
@@ -5,7 +9,7 @@
  * Authors: Simon Budig <Simon.Budig@unix-ag.org> (original code)
  *          Federico Mena-Quintero <federico@gimp.org> (cleanup for GTK+)
  *          Jonathan Blandford <jrb@redhat.com> (cleanup for GTK+)
- * 
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU Lesser General Public License as published by
  * the Free Software Foundation; either version 3 of the License, or
diff --git a/src/widgets/gimp/ruler.cpp b/src/widgets/gimp/ruler.cpp
index f4f1a2f29..a0dd19dc5 100644
--- a/src/widgets/gimp/ruler.cpp
+++ b/src/widgets/gimp/ruler.cpp
@@ -1,8 +1,9 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
 /*
  * Customized ruler class for inkscape.  Note that this is a fork of
  * the GimpRuler widget from GIMP: libgimpwidgets/gimpruler.c.
- * The GIMP code is released under the GPL 3.  The GIMP code itself
- * is a fork of the now-obsolete GtkRuler widget from GTK+ 2.
+ * The GIMP code was released under the LGPL3+ (which is GPL3 plus extra permissions that may be ignored).
+ * The GIMP code itself is a fork of the now-obsolete GtkRuler widget from GTK+ 2.
  *
  * Major differences between implementations in Inkscape and GIMP are
  * as follows:
@@ -26,7 +27,7 @@
  *
  * Copyright (C) 1999-2011 authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v3+. Read the file 'COPYING' for more information.
  */
 
 #include <cstring>
diff --git a/src/widgets/gimp/ruler.h b/src/widgets/gimp/ruler.h
index ed529d082..5e9b1ee16 100644
--- a/src/widgets/gimp/ruler.h
+++ b/src/widgets/gimp/ruler.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 #ifndef __SP_RULER_H__
 #define __SP_RULER_H__
 
@@ -10,7 +11,7 @@
  *
  * Copyright (C) 1999-2002 authors
  *
- * Released under GNU GPL, read the file 'COPYING' for more information
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
  */
 
 #include <gtk/gtk.h>