Graph Unit 
                               BitBlt Operators 

      PURPOSE:  BitBlt operators for PutImage and SetWriteMode to determine
                the method to be used for screen updates.

      REMARKS:  Use these BitBlt operators with PutImage and SetWriteMode:

                       Const
                          CopyPut   = 0;  { MOV }
                          XORPut    = 1;  { XOR }

                    Use these BitBlt operators with PutImage only:

                       Const
                          OrPut     = 2;  { OR  }
                          AndPut    = 3;  { AND }
                          NotPut    = 4;  { NOT }