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<TITLE> Description of Objects in VPython</TITLE>
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<DIV>
<H1 CLASS="Heading-1"> <font color="#0000A0">Additional Attributes</font></H1>
</DIV>
<DIV>
<P CLASS="Normal"> The following attributes apply to all VPython objects:</P>
<P CLASS="attributes"> <span class="attribute">visible</span> If false (0),
object is not displayed; e.g. <span class="attribute">ball.visible = 0</span><EM CLASS="program"><BR>
</EM> Use <span class="attribute">ball.visible = 1</span> to make the ball
visible again.</P>
<P CLASS="attributes"><span class="attribute">frame</span> Place this object
into a specified frame, as in <span class="attribute">ball = sphere(frame
= f1)</span> </P>
<P CLASS="attributes"> <span class="attribute">display</span> When you start
a VPython program, for convenience Visual creates a display window and names
it <span class="attribute">scene</span>. By default, objects you create go
into that display window. You can choose to put an object in a different display
like this: </P>
</DIV>
<blockquote>
<blockquote>
<DIV><span class="program (unavailable)"><b> scene2
= display( title = "Act IV, Scene 2" ) </b></span></DIV>
<DIV><b><span class="program (unavailable)"> rod
= cylinder( display = scene2 )</span></b> </DIV>
<blockquote>
<DIV class="attributes">The function <font color="#FF0000">display.get_selected()</font>
returns a reference to the display in which objects are currently being
created.</DIV>
</blockquote>
</blockquote>
</blockquote>
<DIV>
<P CLASS="attributes"><span class="attribute">__class__</span> Name of the class
of object. For example, <span class="attribute">ball.__class__ is sphere</span>
is true if <span class="attribute">ball</span> is a sphere object. There are
two underscores before and after the word <span class="attribute">class</span>.
In a list of visible objects provided by <a href="display.html">scene.objects</a>,
if <span class="attribute">obj</span> is in this list you can determine the
class of the object with <span class="attribute">obj.__class__</span>. </P>
<P CLASS="attributes"><span class="attribute">__copy()__</span> Makes a copy
of an object. There are two underscores before and after the <span class="attribute">copy()</span>.
Without any arguments, this results in creating a second object in the exact
same position as the first, which is probably not what you want. The <font color="#FF0000">__copy__()</font>
function takes a list of keyword=value argument pairs which are applied to
the new object before making it visible. For example, to clone an object from
one display to another, you would execute: <font color="#FF0000">new_object
= old_object.__copy__( display=new_display)</font>. Restriction: If the original
object is within a frame, and the new object is on a different display, you
must supply both a new display and a new frame for the new object (the new
frame may be None). This is due to the restriction that an object may not
be located within a frame that is in a separate display. The attribute <font color="#FF0000">__members__</font>
used to give a list of all the object's attributes but is no longer available
in VPython. Its main use was in copying objects.</P>
<blockquote>
<p>Here is an example that uses the __copy()__ function. The following routine
copies all of the Visual objects currently existing in one display into
a previously defined second display:</p>
</blockquote>
</DIV>
<blockquote>
<DIV>
<p><b><span class="program (unavailable)">def clone_universe( new_display,
old_display):<br>
# Create a dictionary of
frames in the old display<br>
# to the corresponding frames
in the new display.<br>
frames = dict()<br>
# Initialize the lookup
dictionary<br>
for obj in old_display.objects:<br>
if
obj.__class__ == frame:<br>
frames[obj]
= obj.__copy__( frame=None, display=new_display)<br>
# For each old reference
frame that was within another reference frame,<br>
# place the new reference
frame within the appropriate frame in the new<br>
# display. Here old is an
object and new is its frame in the new display.<br>
for old, new in frames.iteritems():<br>
if
old.frame:<br>
new.frame
= frames[old.frame]<br>
# Copy over the universe.<br>
for obj in old_display.objects:<br>
if
obj.__class__ == frame:<br>
#
Already taken care of above.<br>
continue<br>
if
obj.frame:<br>
#
Then initialize with the corresponding reference frame in the new<br>
#
display.<br>
obj.__copy__(
display=new_display, frame=frames[obj.frame])<br>
else:<br>
#
Don't need to care about the frame attribute, since it is None.<br>
obj.__copy__(
display=new_display)</span></b></p>
</DIV>
</blockquote>
<DIV>
<P CLASS="Normal">See <a href="display.html">Controlling One or More Visual
Display Windows</a> for more information on creating and manipulating display
objects.</P>
<P CLASS="Normal"> </P>
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