The projection modes of the various PROJECT2 commands do not provide to differ between lines in front and hidden lines.

The trick is to do the projection twice. Second with special pen an line type settings before. The example below offers a differenced appearance:

• Einfach: Simple graphical box
• Aufsicht: One projection
• Detailiert: Darstellung mit verdeckten Linien

! ZweiD= Parameter to select the grade of details
! hiddenLT= Linetype (name) for hidden line
! StiftLV= Pen for hidden lines
! scale= factor for scale independant linetype

IF ZweiD="Einfach" THEN
  !»» display simple crossed box
  RECT2 -a/2,-b/2,a/2,b/2
  LINE2 -a/2,-b/2,a/2,b/2
  LINE2 a/2,-b/2,-a/2,b/2
  !»» or
  ! RECT2 0,0,a,b
  ! LINE2 0,0,a,b : LINE2 0,b,a,0
  ELSE

  !»» Projection of the view
  LINE_TYPE 1  !»» or SYMB_LINE
  PROJECT2 3,270,2
  IF ZweiD="Detailiert" THEN
    !»» Projection of the hidden lines
    !»» Check first for linetype and pen.
    hiddenLT="Verdeckte Teile"  !»» or "Miniatur", or "Hidden3D"
    IF IND(LINE_TYPE,hiddenLT) THEN
      LINE_TYPE hiddenLT
      ELSE
      scale=100/GLOB_SCALE/10000
      DEFINE LINE_TYPE hiddenLT 1,2,0.7*scale,1.2*scale
      LINE_TYPE hiddenLT
      ENDIF
    IF StiftVL>0 THEN PEN StiftVL
    PROJECT2 3,270,1
    PEN SYMB_VIEW_PEN
    ENDIF
  ENDIF

VALUES "ZweiD" "Einfach","Aufsicht","Detailiert"