wrlib: move fixed angle rotation code to dedicated functions

The function RRotateImage contains code to handle efficiently the 4 simple
angles 0, 90, 180 and 270 degrees, which makes it a long function.

This patch separate the code for the different cases into dedicated
functions so the main function's code ends up being simple (aka: easier to
understand/review/maintain).

As a side effect, the function for the 180 degree function is not static
because it can be reused to flip an image both horizontally and vertically.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

wrlib/rotate.h

@@ -0,0 +1,30 @@
+/*
+ * Raster graphics library
+ *
+ * Copyright (c) 2014 Window Maker Team
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Library General Public
+ *  License along with this library.
+ */
+
+#ifndef WRASTER_ROTATE_H
+#define WRASTER_ROTATE_H
+
+
+/*
+ * Returns a new image, rotated by 180 degrees
+ */
+RImage *wraster_rotate_image_180(RImage *source);
+
+
+#endif