#include <cvl/dap.h>
reverse_area(olda, newa, oldcolor, newcolor)
   struct dd_area *olda, *newa;
   PIXEL *oldcolor, *newcolor;
{
   int oldmode, newmode;
   ERRTYPE err;

   if (err = dd_rdset(olda, DD_WRITEMODE, &oldmode))
      errprnt(dd_err(err));
   switch (oldmode) {
      case DD_ASSIGN :
         newmode = DD_ASSIGN;
         *newcolor = 0;
      break;
      case DD_AND :
         newmode = DD_OR;
         *newcolor = ~(*oldcolor);
      break;
      case DD_OR :
         newmode = DD_AND;
         *newcolor = ~(*oldcolor);
      break;
      case DD_XOR :
         newmode = DD_XOR;
         *newcolor = *oldcolor;
      break;
   }
   *newa = *olda;
   if (err = dd_set(newa, DD_WRITEMODE, newmode))
      errprnt(dd_err(err));
}