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<h1><font color="#0000A0">Controls:
buttons, sliders, toggles, and menus</font></h1>
</div></td>
<td width="24%"><a href="controls.html"><img src="images/controls.jpg" alt="controls" width="267" height="250" /></a><a href="arrow.html"></a></td>
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<p class="Normal">You can create buttons, sliders, toggle switches, and pull-down menus to
control your program. You import these capabilities with this statement:</p>
<div>
<p class="program"> from visual.controls import *</p>
</div>
<p class="Normal">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 class="Normal">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 visual.controls import *<br />
<br />
def change(): # Called by controls
when button clicked<br />
if b.text == 'Click me':<br />
b.text = 'Try again'<br />
else:<br />
b.text = 'Click me'<br />
<br />
c = controls() # Create controls window<br />
# Create a button in the controls window:<br />
b = button( pos=(0,0), width=60, height=60, <br />
text='Click
me', action=lambda: change() )<br />
while True:<br />
c.interact()
# Check for mouse; drive actions<br />
</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>
<p class="program"> c = controls(title='Controlling the Scene',<br />
x=0, y=400, width=300, height=300,
range=50)</p>
</div>
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<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">display </span><span class="Normal">Every
controls window has the attribute <span class="attribute">display</span>;
sphere(display=c.display) will place a sphere in the controls window
named c.</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), slider (depends on slider min and max), or menu
(the text just selected on the menu). The value of a toggle
or slider (but not a menu) 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 the header at the top of a menu</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>
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