Exemple minimal

Suite =E0 mon post pr=E9c=E9dent, je me suis concentr=E9 sur les fonction=
s xval,=20
yval ... dans 3d.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
input 3dgeom;
drawing_scale:=3D15cm;

vardef def_Repere(expr inst)=3D
  new_obj_points(inst,2);
  set_Repere_points(inst);
enddef;

vardef set_Repere_points(expr inst)=3D
set_point(1)(1,1,0);set_point(2)(-1,1,0);
enddef;

vardef draw_Repere(expr inst)=3D
draw_line(1,2);
  if xval(1)<.5 : message "x < 0,5" fi;
  if yval(1)<.5 : message "y < 0,5" fi;
enddef;
=20

assign_obj("OIJK","Repere");

beginfig(1);
set_point_(Obs)(4,6,4);
Obs_phi:=3D90;
Obs_dist:=3D2;
point_of_view_obj("OIJK",1,Obs_phi);
reset_obj("OIJK");
draw_obj("OIJK");
endfig;
end.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

et voil=E0 le log :

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
This is MetaPost, Version 0.641 (MiKTeX 2.4) (preloaded mem=3Dplain=20
2005.5.14)  25 JUN 2005 07:08
**exmini.mp
(exmini.mp (C:\texmf\metapost\threed\3dgeom.mp=20
(C:\texmf\metapost\threed\3d.mp
*** 3d,          v1.34 (c) D. Roegel, 17 August 2003 ***
(C:\texmf\metapost\threed\3dgeom.mp (C:\texmf\metapost\threed\3d.mp)
(C:\texmf\metapost\threed\3dutil.mp
*** 3dutil,   v1.34 (c) D. Roegel 17 August 2003 ***)
*** 3dgeom,   v1.34 (c) D. Roegel 17 August 2003 ***))
(C:\texmf\metapost\threed\3dutil.mp)
*** 3dgeom,   v1.34 (c) D. Roegel 17 August 2003 ***)
x < 0,5
y < 0,5 [1] )
1 output file written: exmini.1

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Que faut-il comprendre ? Merci de m'=E9clairer.

Jean-Michel