Video constants

        #define VIDEO            0x10
        #define MODE             *((byte far *) 0x449lu)
        #define PAGE             *((byte far *) 0x462lu)
        #define PAGELEN          *((unsigned int far *) 0x44Clu)
        #define VIDOFFSET        *((unsigned int far *) 0x44Elu)
        #define ROWCOUNT         *((byte far *) 0x484lu)
        #define CHARHEIGHT       *((unsigned int far *) 0x485lu)
        #define CURSOR_UNDERBAR       (MODE==7)?0x0B0C:0x0607
        #define CURSOR_HALFBLOCK      (MODE==7)?0x070C:0x0407

    Shadow constants

        #define SHADOW_TL   0x0080
        #define SHADOW_T    0x0040
        #define SHADOW_TR   0x0020
        #define SHADOW_R    0x0010
        #define SHADOW_BR   0x0008
        #define SHADOW_B    0x0004
        #define SHADOW_BL   0x0002
        #define SHADOW_L    0x0001

        #define SHADOW_TOP      (SHADOW_TL|SHADOW_T|SHADOW_TR)
        #define SHADOW_BOTTOM   (SHADOW_BL|SHADOW_B|SHADOW_BR)
        #define SHADOW_LEFT     (SHADOW_TL|SHADOW_L|SHADOW_BL)
        #define SHADOW_RIGHT    (SHADOW_TR|SHADOW_R|SHADOW_BR)