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<TITLE> Description of Objects in VPython</TITLE>
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<H1 CLASS="Heading-1"> <font color="#0000A0">The arrow Object</font></H1>
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<DIV>
<P CLASS="Normal">
<IMG SRC="VisualRef-2.gif" ALIGN="RIGHT">
The arrow object has a straight box-shaped shaft with an arrowhead at one end. The following statement will display an arrow pointing parallel to the x axis:</P>
<DIV>
<H2 CLASS="program0">
pointer = arrow(pos=(0,2,1), axis=(5,0,0), shaftwidth=1)</H2>
<P CLASS="Normal"> The arrow object has the following attributes and default
values, like those for cylinders: <span class="attribute">pos<font color="#000000">
(0,0,0)</font></span>, <span class="attribute">x</span><span class="attribute"><font color="#000000">
(0)</font></span>, <span class="attribute">y<font color="#000000">(0)</font></span>,
<span class="attribute">z<font color="#000000">(0)</font></span>, <span class="attribute">axis<font color="#000000">
(1,0,0)</font></span>, <span class="attribute">length<font color="#000000">
(1)</font></span>, <span class="attribute">color<font color="#000000"> (1,1,1)
which is color.white</font></span>, <span class="attribute">red<font color="#000000">
(1)</font></span>, <span class="attribute">green<font color="#000000"> (1)</font></span>,
<span class="attribute">blue<font color="#000000"> (1)</font></span>, and
<span class="attribute">up<font color="#000000"> (0,1,0)</font></span>.
The <span class="attribute">up</span> attribute is significant for arrow
because the shaft and head have square cross sections, and setting the <EM CLASS="program">
</EM><span class="attribute">up</span> attribute rotates the arrow about
its axis. Additional arrow attributes:</P>
<P CLASS="attributes"> <span class="attribute">shaftwidth</span> By default, shaftwidth
= 0.1*(length of arrow)</P>
<P CLASS="attributes"> <span class="attribute">headwidth</span> By default, headwidth
= 2*shaftwidth</P>
<P CLASS="attributes"> <span class="attribute">headlength</span> By default, headlength
= 3*shaftwidth</P>
<P CLASS="Normal"> Assigning any of these attributes to 0 makes it use defaults
based on the size of the arrow. If <span class="attribute">headlength</span>
becomes larger than half the length of the arrow, or the shaft becomes thinner
than 1/50 the length, the entire arrow is scaled accordingly.</P>
<P CLASS="Normal">This default behavior makes the widths of very short arrows
shrink, and the widths of very long arrows grow (while displaying the correct
total length). If you prefer that <span class="attribute">shaftwidth</span>
and <span class="attribute">headwidth</span> not change as the arrow gets
very short or very long, set <span class="attribute">fixedwidth = 1</span>.
In this case the only adjustment that is made is that <span class="attribute">headlength</span>
is adjusted so that it never gets longer than half the total length, so
that the total length of the arrow is correct. This means that very short,
thick arrows look similar to a thumbtack, with a nearly flat head.</P>
<P CLASS="Normal">Note that the <span class="attribute">pos</span> attribute
for cylinder, arrow, cone, and pyramid corresponds to one end of the object,
whereas for a box, sphere, or ring it corresponds to the center of the object.
</P>
<P CLASS="Normal"> </P>
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<b class="navlabel">Next:</b> <a class="sectref" HREF="cone.html">The cone Object</A>
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