sub xline(x0 as int, y0 as int, x1 as int, y1 as int)
  inline DisplayGraphics_set_color(_ptr_main_module->m_gfx, CLR_WHITE);
  inline DisplayGraphics_draw_line(_ptr_main_module->m_gfx, x0, y0, x1, y1);
end sub

sub xpoint(x0 as int, y0 as int)
  inline DisplayGraphics_set_pixel(_ptr_main_module->m_gfx, x0, y0, CLR_WHITE);
end sub

sub xor_display
    inline int i;
    inline char *sptr = DisplayGraphics_get_page_ptr(_ptr_main_module->m_gfx, 0);
    inline for(i=0; i<4000; i++) sptr[i] ^=0xff;
    REDRAW SHOW
end sub

function sgn(x as int) as int
   if x<0 then sgn=-1
   if x>0 then sgn=1
   if x=0 then sgn=0
end function