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Asymptote FAQ - Section 5
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Asymptote FAQ - Section 5 <br>
Questions about arrows
</h1>

<ul>
<li><a href="#doublearrows" rel=subdocument>Q5.1. How do I draw two arrows at arbitrary positions along a
path?</a>
<li><a href="#reversearrow" rel=subdocument>Q5.2. How do I reverse the direction of an arrowhead?</a>
<li><a href="#reversearrow" rel=subdocument>Q5.3. How do I change the size of all arrows?</a>
<li><a href="#arrowhead" rel=subdocument>Q5.4. Can I create other arrowhead styles?</a>
</ul><hr>

<h2><A name="doublearrows">
Question 5.1.  How do I draw two arrows at arbitrary positions along a
path?
</A></h2>

Assuming that at least one of the arrowheads is to be filled, you can
do this: <pre>
size(200); 
path g = (0,0)..(1,3)..(3,0); 
draw(g,Arrow(Relative(0.9))); 
add(arrow(g,invisible,FillDraw(black),Relative(0.5))); 
add(arrow(reverse(g),invisible,FillDraw(white,black),Relative(0.9))); 
</pre>
If both of the arrowheads are to be drawn with filltype NoFill,
one will need to create a specialized version of the arrow routine in 
<code>plain_arrows.asy</code>: <pre>
void arrow(frame f, arrowhead arrowhead=DefaultHead,
           path g, pen p=currentpen, real size=0,
           real angle=arrowangle, filltype filltype=arrowhead.defaultfilltype,
           position position=EndPoint, bool forwards=true,
           margin margin=NoMargin, bool center=false);
</pre>

<h2><A name="reversearrow">
Question 5.2.  How do I reverse the direction of an
arrowhead?
</A></h2>

Simply reverse the direction of the path. 
<pre>
path g=((0,0)--(5cm,0));
draw(reverse(g),Arrow(Relative(0.55)));
</pre>

<h2><A name="reversearrow">
Question 5.3.  How do I change the size of all
arrows?
</A></h2>

To override the arrowsize you can give every Arrow drawing attribute a
real size argument. If you want to do this globally, you can override the
pen-dependent arrowsize function like this:
<pre>
DefaultHead.size=new real(pen p=currentpen) {return 2mm;};
</pre>

<h2><A name="arrowhead">
Question 5.4.  Can I create other arrowhead
styles?
</A></h2>

Yes, you can build custom arrowheads like this (see the predefined
arrowhead styles in <code>plain_arrows.asy</code> for further examples):  <pre>
arrowhead DotHead;
DotHead.head=new path(path g, position position=EndPoint, pen p=currentpen,
                      real size=0, real angle=arrowangle) {
  if(size == 0) size=DotHead.size(p);
  bool relative=position.relative;
  real position=position.position.x;
  if(relative) position=reltime(g,position);
  path r=subpath(g,position,0);
  pair x=point(r,0);
  real t=arctime(r,size);
  pair y=point(r,t);
  return circle(0.5(x+y),0.5size);
};

size(100);
draw((0,0)..(1,1)..(2,0),Arrow(DotHead));
dot((2,0),red);
</pre>
If you submit your alternate arrowheads to the Forum or the Patch 
Tracking System, we'll consider including them in a future release. 
<hr>
Next: <a href="section6.html" rel=precedes>Questions about 2D graphs</a>.<br>
Back: <a href="section4.html" rev=precedes>Questions about labels</a>.<br>
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<address>
<A href="http://asymptote.sourceforge.net">Asymptote</A> 
- 24 March 2017
</address><br>
Extracted from Asymptote Frequently Asked Questions,
Copyright &copy; 2017 .
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