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<H1><A NAME="SECTION0022800000000000000000">
20.8 <tt class="module">gl</tt> --
         <em>Graphics Library</em> interface</A>
</H1>

<P>
<A NAME="module-gl"></A>
<p class="availability">Availability: <span
 class="platform">IRIX</span>.</p>

<P>
This module provides access to the Silicon Graphics
<em>Graphics Library</em>.
It is available only on Silicon Graphics machines.

<P>
<span class="warning"><b class="label">Warning:</b>
Some illegal calls to the GL library cause the Python
interpreter to dump core.
In particular, the use of most GL calls is unsafe before the first
window is opened.</span>

<P>
The module is too large to document here in its entirety, but the
following should help you to get started.
The parameter conventions for the C functions are translated to Python as
follows:

<P>

<UL>
<LI>All (short, long, unsigned) int values are represented by Python
integers.
</LI>
<LI>All float and double values are represented by Python floating point
numbers.
In most cases, Python integers are also allowed.
</LI>
<LI>All arrays are represented by one-dimensional Python lists.
In most cases, tuples are also allowed.
</LI>
<LI>All string and character arguments are represented by Python strings,
for instance,
<code>winopen('Hi There!')</code>
and
<code>rotate(900, 'z')</code>.

</LI>
<LI>All (short, long, unsigned) integer arguments or return values that are
only used to specify the length of an array argument are omitted.
For example, the C call

<P>
<div class="verbatim"><pre>
lmdef(deftype, index, np, props)
</pre></div>

<P>
is translated to Python as

<P>
<div class="verbatim"><pre>
lmdef(deftype, index, props)
</pre></div>

<P>
</LI>
<LI>Output arguments are omitted from the argument list; they are
transmitted as function return values instead.
If more than one value must be returned, the return value is a tuple.
If the C function has both a regular return value (that is not omitted
because of the previous rule) and an output argument, the return value
comes first in the tuple.
Examples: the C call

<P>
<div class="verbatim"><pre>
getmcolor(i, &amp;red, &amp;green, &amp;blue)
</pre></div>

<P>
is translated to Python as

<P>
<div class="verbatim"><pre>
red, green, blue = getmcolor(i)
</pre></div>

<P>
</LI>
</UL>

<P>
The following functions are non-standard or have special argument
conventions:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5192' xml:id='l2h-5192' class="function">varray</tt></b>(</nobr></td>
  <td><var>argument</var>)</td></tr></table></dt>
<dd>
Equivalent to but faster than a number of
<code>v3d()</code>
calls.
The <var>argument</var> is a list (or tuple) of points.
Each point must be a tuple of coordinates
<code>(<var>x</var>, <var>y</var>, <var>z</var>)</code> or <code>(<var>x</var>, <var>y</var>)</code>.
The points may be 2- or 3-dimensional but must all have the
same dimension.
Float and int values may be mixed however.
The points are always converted to 3D double precision points
by assuming <code><var>z</var> = 0.0</code> if necessary (as indicated in the man page),
and for each point
<code>v3d()</code>
is called.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5193' xml:id='l2h-5193' class="function">nvarray</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Equivalent to but faster than a number of
<code>n3f</code>
and
<code>v3f</code>
calls.
The argument is an array (list or tuple) of pairs of normals and points.
Each pair is a tuple of a point and a normal for that point.
Each point or normal must be a tuple of coordinates
<code>(<var>x</var>, <var>y</var>, <var>z</var>)</code>.
Three coordinates must be given.
Float and int values may be mixed.
For each pair,
<code>n3f()</code>
is called for the normal, and then
<code>v3f()</code>
is called for the point.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5194' xml:id='l2h-5194' class="function">vnarray</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Similar to
<code>nvarray()</code>
but the pairs have the point first and the normal second.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5195' xml:id='l2h-5195' class="function">nurbssurface</tt></b>(</nobr></td>
  <td><var>s_k, t_k, ctl, s_ord, t_ord, type</var>)</td></tr></table></dt>
<dd>
Defines a nurbs surface.
The dimensions of
<code><var>ctl</var>[][]</code>
are computed as follows:
<code>[len(<var>s_k</var>) - <var>s_ord</var>]</code>,
<code>[len(<var>t_k</var>) - <var>t_ord</var>]</code>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5196' xml:id='l2h-5196' class="function">nurbscurve</tt></b>(</nobr></td>
  <td><var>knots, ctlpoints, order, type</var>)</td></tr></table></dt>
<dd>
Defines a nurbs curve.
The length of ctlpoints is
<code>len(<var>knots</var>) - <var>order</var></code>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5197' xml:id='l2h-5197' class="function">pwlcurve</tt></b>(</nobr></td>
  <td><var>points, type</var>)</td></tr></table></dt>
<dd>
Defines a piecewise-linear curve.
<var>points</var>
is a list of points.
<var>type</var>
must be
<code>N_ST</code>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5198' xml:id='l2h-5198' class="function">pick</tt></b>(</nobr></td>
  <td><var>n</var>)</td></tr></table></dt>
<dd>
<dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt class="function">select</tt></b>(</nobr></td>
  <td><var>n</var>)</td></tr></table></dt>
<dd>The only argument to these functions specifies the desired size of the
pick or select buffer.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-5200' xml:id='l2h-5200' class="function">endpick</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
<dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt class="function">endselect</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>These functions have no arguments.
They return a list of integers representing the used part of the
pick/select buffer.
No method is provided to detect buffer overrun.
</dl>

<P>
Here is a tiny but complete example GL program in Python:

<P>
<div class="verbatim"><pre>
import gl, GL, time

def main():
    gl.foreground()
    gl.prefposition(500, 900, 500, 900)
    w = gl.winopen('CrissCross')
    gl.ortho2(0.0, 400.0, 0.0, 400.0)
    gl.color(GL.WHITE)
    gl.clear()
    gl.color(GL.RED)
    gl.bgnline()
    gl.v2f(0.0, 0.0)
    gl.v2f(400.0, 400.0)
    gl.endline()
    gl.bgnline()
    gl.v2f(400.0, 0.0)
    gl.v2f(0.0, 400.0)
    gl.endline()
    time.sleep(5)

main()
</pre></div>

<P>
<div class="seealso">
  <p class="heading">See Also:</p>

  <dl compact="compact" class="seetitle">
    <dt><em class="citetitle"><a href="http://pyopengl.sourceforge.net/"
        >PyOpenGL: The Python OpenGL Binding</a></em></dt>
    <dd>An interface to OpenGL<a id='l2h-5202' xml:id='l2h-5202'></a> is also available;
            see information about the
            <strong>PyOpenGL</strong><a id='l2h-5203' xml:id='l2h-5203'></a> project online at
            <a class="url" href="http://pyopengl.sourceforge.net/">http://pyopengl.sourceforge.net/</a>.  This may be a
            better option if support for SGI hardware from before
            about 1996 is not required.</dd>
  </dl>
</div>

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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