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Added how to use MetaObj together with text labels in ConTeXt
[http://www.ctan.org/tex-archive/graphics/metapost/contrib/macros/metaobj/ MetaObj] is a system for high-level object-oriented drawing based on [[MetaPost]] (from the [http://mirror.ctan.org/graphics/metapost/contrib/macros/metaobj/doc/momanual.pdf manual]).
When using text labels in embedded MetaPost code within ConTeXt, the whole MetaPost code is processed in two runs. This causes problems with MetaObj, because it doesn't expect this. See [http://archive.contextgarden.net/thread/20110118.121745.612f819e.en.html#20110118.121745.612f819e this mailing list thread] for details. The following example (from the manual, modified by Aditya Mahajan) shows how to avoid those problems.
<texcode>
\startMPinclusions[+]
input metaobj;
boolean flag; flag := false; % flag is false in the first run
\stopMPinclusions
\startMPdefinitions
vardef newSegment@# =
if not flag:
assignObj(@#, "Segment"); % this should be called only once
ObjPoint a, b;
ObjCode "@#b - @#a = (1cm, 2cm)";
fi;
enddef;
def drawSegment(suffix n) =
draw n.a -- n.b;
draw btex E etex shifted n.a;
enddef;
\stopMPdefinitions
\starttext
\startMPpage
newSegment.s;
s.a = origin;
drawObj(s);
newSegment.t;
if not flag:
rotateObj(t, 180); % we don't want the object rotated twice
fi;
t.a = s.a + (4cm, 1cm);
drawObj(t);
flag := true; % flag will be true after the first run
\stopMPpage
\stoptext
</texcode>
Just use "if not flag" constructions around anything that might cause trouble. Sometimes even the definition of relations (bindings) between objects will require precautions.
When using text labels in embedded MetaPost code within ConTeXt, the whole MetaPost code is processed in two runs. This causes problems with MetaObj, because it doesn't expect this. See [http://archive.contextgarden.net/thread/20110118.121745.612f819e.en.html#20110118.121745.612f819e this mailing list thread] for details. The following example (from the manual, modified by Aditya Mahajan) shows how to avoid those problems.
<texcode>
\startMPinclusions[+]
input metaobj;
boolean flag; flag := false; % flag is false in the first run
\stopMPinclusions
\startMPdefinitions
vardef newSegment@# =
if not flag:
assignObj(@#, "Segment"); % this should be called only once
ObjPoint a, b;
ObjCode "@#b - @#a = (1cm, 2cm)";
fi;
enddef;
def drawSegment(suffix n) =
draw n.a -- n.b;
draw btex E etex shifted n.a;
enddef;
\stopMPdefinitions
\starttext
\startMPpage
newSegment.s;
s.a = origin;
drawObj(s);
newSegment.t;
if not flag:
rotateObj(t, 180); % we don't want the object rotated twice
fi;
t.a = s.a + (4cm, 1cm);
drawObj(t);
flag := true; % flag will be true after the first run
\stopMPpage
\stoptext
</texcode>
Just use "if not flag" constructions around anything that might cause trouble. Sometimes even the definition of relations (bindings) between objects will require precautions.
