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<TITLE> Description of Objects in VPython</TITLE>
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<h1 CLASS="Heading-1"> <font color="#0000A0">Controls: buttons, sliders, toggles,
and menus</font></h1>
</DIV>
<DIV>
<p>You can create buttons, sliders, toggle switches, and pull-down menus to
control your program. You import these capabilities with this statement:</p>
<div>
<h2 class="program0"> from visual.controls import *</h2>
</div>
<p>Importing from <span class="attribute">visual.controls</span> makes available
all Visual objects plus the controls module. To use the control features,
you create a special controls window and add control objects to that window,
specifying what actions should take place when the controls are manipulated.
For example, an action associated with a button might be the execution of
a function to change the color of a Visual object. After creating the controls,
you repeatedly call an interact routine to check for user manipulation of
the controls, which trigger actions. For a detailed example, see the VPython
demo program <span class="attribute">controlstest.py</span>. </p>
<p>Here is a small example. All it does is change the button text when you click
the button. The Python construction "lambda:" is required for the
controls module to have the correct context ("namespace") for calling
the specified routine.</p>
<p class="program">from visu<span class="program">al.controls import *</span></p>
<p class="program"> </p>
<p class="program"><span class="program">def change(): # Called by controls
when button is clicked</span></p>
<p class="program"><span class="program"> if b.text ==
'Click me':</span></p>
<p class="program"><span class="program"> b.text
= 'Try again'</span></p>
<p class="program"><span class="program"> else:</span></p>
<p class="program"><span class="program"> b.text
= 'Click me'</span></p>
<p class="program"> </p>
<p class="program"><span class="program">c = controls() # Create controls window</span></p>
<p class="program"><span class="program"># Create a button in the controls window:</span></p>
<p class="program"><span class="program">b = button( pos=(0,0), width=60, height=60,
</span></p>
<p class="program"><span class="program"> text='Click
me', action=lambda: change() )</span></p>
<p class="program"><span class="program">while 1:</span></p>
<p class="program"><span class="program"> c.interact()
# Check for mouse ev</span>ents and drive specified actions</p>
</div>
<P CLASS="attributes"> </P>
<p class="Normal"><font color="#0000A0">Controls window</font></p>
<p class="attributes"> <span class="attribute">controls()</span> Creates a controls
window with the specified attributes, and returns it. For example, the following
creates a controls window 300 by 300, located at (0,400) with respect to the
upper left corner of the screen, with 'Controlling the Scene' in the title bar,
and a range of 50 (window coordinates from -50 to +50 in x and y):</p>
<DIV>
<H2 CLASS="program0"> c = controls(title='Controlling the Scene',</H2>
<P CLASS="program"> x=0, y=400, width=300, height=300,
range=50)</P>
</DIV>
<DIV></DIV>
<DIV>
<DIV>
<P CLASS="Normal"><font color="#0000A0">Controls window parameters</font></P>
<P CLASS="attributes"> <span class="attribute">x</span>, <span class="attribute">y</span>
Position of the window on the screen (pixels from upper left)</P>
<P CLASS="attributes"> <span class="attribute">width</span>, <span class="attribute">height</span>
Width and height of the display area in pixels.</P>
<P CLASS="attributes"> <span class="attribute">title</span> Text in the control
window's title bar.</P>
<P CLASS="attributes"><span class="attribute">range</span> The extent of the
region of interest away from the center along each axis. The default is
100. The center of a controls window is always (0,0).</P>
<p class="attributes"> <span class="attribute"></span></p>
<P CLASS="Normal"><font color="#0000A0">Control objects</font></P>
<P CLASS="Normal">After creating a controls window, you can create the following
control objects that will appear in that window:</P>
<p class="attributes"> <span class="attribute"><b>button</b></span> A button
to click.</p>
<p class="attributes"> <span class="attribute"><b>slider</b></span> Drag a
slider to enter a numeric value graphically.</p>
<p class="attributes"> <span class="attribute"><b>toggle</b></span> Click
on the handle to flip a toggle switch.</p>
<p class="attributes"><span class="attribute"><b>menu</b></span> A pull-down
menu of options.</p>
<P CLASS="Normal">Control objects have the following attributes:</P>
<p class="attributes"> <span class="attribute">pos</span><span class="attribute"></span>
Position of the control (center of button or toggle, one end of slider,
upper left corner of menu title)</p>
<p class="attributes"> <span class="attribute">color</span> Gray by default</p>
<p class="attributes"> <span class="attribute">width</span><span class="attribute"></span>
Width of button, toggle, or menu</p>
<p class="attributes"> <span class="attribute">height</span> Height of button,
toggle, or menu</p>
<p class="attributes"><span class="attribute">axis</span> Axis for slider,
pointing from <span class="attribute">pos</span><span class="attribute"></span>
to other end (as for cylinder or arrow)</p>
<p class="attributes"> <span class="attribute">length</span> Length of slider
(in direction of axis)</p>
<p class="attributes"> <span class="attribute">min, max</span> Minimum and
maximum values for a slider</p>
<p class="attributes"> <span class="attribute">value</span> Value of toggle
(0 or 1) or slider (depends on slider min and max). The value of a toggle
or slider can be set as well as read. If you set the value of a toggle or
slider, the control moves to the position that corresponds to that value.</p>
<p class="attributes"> <span class="attribute">text</span> Text to display
on a button, or menu title</p>
<p class="attributes"> <span class="attribute">text0</span> Text to display
below a toggle switch (associated with toggle value = 0)</p>
<p class="attributes"> <span class="attribute">text1</span> Text to display
above a toggle switch (associated with toggle value = 1)</p>
<p class="attributes"> <span class="attribute">action</span> Specify Python
statement to be executed when a control is manipulated</p>
<p class="attributes"> <span class="attribute">items</span> For menus only,
list of menu items to choose from. Here is how to add a menu item to a menu
named m1:</p>
<p class="program"> m1.items.append(
('Red', lambda: cubecolor(color.red)) )</p>
<p class="attributes"></p>
<p class="attributes"> This adds to the pull-down menu an item 'Red' which
when chosen will pass the value color.red to the subroutine cubecolor().
The Python construction "lambda:" is required for the controls
module to have the correct context ("namespace") for calling the
specified routine.</p>
<P CLASS="Normal"> </P>
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