diff --git a/common/rfb/ColourCube.h b/common/rfb/ColourCube.h
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+/* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
+ * 
+ * This 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 2 of the License, or
+ * (at your option) any later version.
+ * 
+ * This software 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 this software; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
+ * USA.
+ */
+//
+// ColourCube - structure to represent a colour cube.  The colour cube consists
+// of its dimensions (nRed x nGreen x nBlue) and a table mapping an (r,g,b)
+// triple to a pixel value.
+//
+// A colour cube is used in two cases.  The first is internally in a viewer
+// when it cannot use a trueColour format, nor can it have exclusive access to
+// a writable colour map.  This is most notably the case for an X viewer
+// wishing to use a PseudoColor X server's default colormap.
+//
+// The second use is on the server side when a client has asked for a colour
+// map and the server is trueColour.  Instead of setting an uneven trueColour
+// format like bgr233, it can set the client's colour map up with a 6x6x6
+// colour cube.  For this use the colour cube table has a null mapping, which
+// makes it easy to perform the reverse lookup operation from pixel value to
+// r,g,b values.
+
+#ifndef __RFB_COLOURCUBE_H__
+#define __RFB_COLOURCUBE_H__
+
+#include <rfb/Pixel.h>
+#include <rfb/ColourMap.h>
+
+namespace rfb {
+
+  class ColourCube : public ColourMap {
+  public:
+    ColourCube(int nr, int ng, int nb, Pixel* table_=0)
+      : nRed(nr), nGreen(ng), nBlue(nb), table(table_), deleteTable(false)
+    {
+      if (!table) {
+        table = new Pixel[size()];
+        deleteTable = true;
+        // set a null mapping by default
+        for (int i = 0; i < size(); i++)
+          table[i] = i;
+      }
+    }
+
+    ColourCube() : deleteTable(false) {}
+
+    virtual ~ColourCube() {
+      if (deleteTable) delete [] table;
+    }
+
+    void set(int r, int g, int b, Pixel p) {
+      table[(r * nGreen + g) * nBlue + b] = p;
+    }
+
+    Pixel lookup(int r, int g, int b) const {
+      return table[(r * nGreen + g) * nBlue + b];
+    }
+
+    int size()      const { return nRed*nGreen*nBlue; }
+    int redMult()   const { return nGreen*nBlue; }
+    int greenMult() const { return nBlue; }
+    int blueMult()  const { return 1; }
+
+    // ColourMap lookup() method.  Note that this only works when the table has
+    // the default null mapping.
+    virtual void lookup(int i, int* r, int* g, int* b) {
+      if (i >= size()) return;
+      *b = i % nBlue;
+      i /= nBlue;
+      *g = i % nGreen;
+      *r = i / nGreen;
+      *r = (*r * 65535 + (nRed-1)   / 2) / (nRed-1);
+      *g = (*g * 65535 + (nGreen-1) / 2) / (nGreen-1);
+      *b = (*b * 65535 + (nBlue-1)  / 2) / (nBlue-1);
+    }
+
+    int nRed;
+    int nGreen;
+    int nBlue;
+    Pixel* table;
+    bool deleteTable;
+  };
+}
+#endif