colour: specialise the cast function

Makefile.am

@@ -18,6 +18,7 @@ UTIL_FILES   =		\
     bitwise.hpp		\
     colour.cpp		\
     colour.hpp		\
+    colour.ipp		\
     coord.hpp		\
     coord/base.hpp	\
     coord/init.hpp	\

colour.hpp

@@ -31,6 +31,11 @@ namespace util {
     template <size_t S, typename T>
     struct colour : public coord::base<S,T,colour,coord::rgba> {
         using coord::base<S,T,util::colour,coord::rgba>::base;
+        using base_t = coord::base<S,T,util::colour,coord::rgba>;
+
+        template <typename U>
+        colour<S,U>
+        cast (void) const;
 
         static const colour WHITE;
         static const colour BLACK;
@@ -49,4 +54,6 @@ namespace util {
     std::ostream& operator<< (std::ostream&, util::colour<S,T>);
 }
 
+#include "colour.ipp"
+
 #endif

colour.ipp

@@ -0,0 +1,36 @@
+/*
+ * This file is part of libgim.
+ *
+ * libgim is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * libgim 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with libgim.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2010-2015 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifdef __UTIL_COLOUR_IPP
+#error
+#endif
+#define __UTIL_COLOUR_IPP
+
+template <size_t S, typename T>
+template <typename U>
+util::colour<S,U>
+util::colour<S,T>::cast (void) const
+{
+    colour<S,U> ret;
+    std::transform (this->begin (),
+                    this->end (),
+                    ret.begin (),
+                    renormalise<T,U>);
+    return ret;
+}

test/colour.cpp

@@ -10,4 +10,12 @@ main (int, char**)
     CHECK_EQ (util::colour4f::WHITE.g, 1.f);
     CHECK_EQ (util::colour4f::WHITE.b, 1.f);
     CHECK_EQ (util::colour4f::WHITE.a, 1.f);
+
+    // Check casting works between intergral and floating formats
+    {
+        util::colour4f f (1);
+        util::colour<4,uint8_t> u (255);
+        CHECK_EQ (f.cast<uint8_t> (), u);
+        CHECK_EQ (u.cast<float> (), f);
+    }
 }