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<H1><A NAME="SECTION0020800000000000000000">
18.8 <tt class="module">gl</tt> --
<i>Graphics Library</i> interface</A>
</H1>
<P>
<p class='availability'>Availability: <span
class='platform'>IRIX</span>.</p>
<P>
This module provides access to the Silicon Graphics
<i>Graphics Library</i>.
It is available only on Silicon Graphics machines.
<P>
<b>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.
<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>
<dl><dd><pre class="verbatim">
lmdef(deftype, index, np, props)
</pre></dl>
<P>
is translated to Python as
<P>
<dl><dd><pre class="verbatim">
lmdef(deftype, index, props)
</pre></dl>
<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>
<dl><dd><pre class="verbatim">
getmcolor(i, &red, &green, &blue)
</pre></dl>
<P>
is translated to Python as
<P>
<dl><dd><pre class="verbatim">
red, green, blue = getmcolor(i)
</pre></dl>
<P>
</LI>
</UL>
<P>
The following functions are non-standard or have special argument
conventions:
<P>
<dl><dt><b><a name='l2h-3233'><tt class='function'>varray</tt></a></b> (<var>argument</var>)
<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><b><a name='l2h-3234'><tt class='function'>nvarray</tt></a></b> ()
<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><b><a name='l2h-3235'><tt class='function'>vnarray</tt></a></b> ()
<dd>
Similar to
<code>nvarray()</code>
but the pairs have the point first and the normal second.
</dl>
<P>
<dl><dt><b><a name='l2h-3236'><tt class='function'>nurbssurface</tt></a></b> (<var>s_k, t_k, ctl, s_ord, t_ord, type</var>)
<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><b><a name='l2h-3237'><tt class='function'>nurbscurve</tt></a></b> (<var>knots, ctlpoints, order, type</var>)
<dd>
Defines a nurbs curve.
The length of ctlpoints is
<code>len(<var>knots</var>) - <var>order</var></code>.
</dl>
<P>
<dl><dt><b><a name='l2h-3238'><tt class='function'>pwlcurve</tt></a></b> (<var>points, type</var>)
<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><b><a name='l2h-3239'><tt class='function'>pick</tt></a></b> (<var>n</var>)
<dd>
<dt><b><tt class='function'>select</tt></b> (<var>n</var>)
<dd>
The only argument to these functions specifies the desired size of the
pick or select buffer.
</dl>
<P>
<dl><dt><b><a name='l2h-3240'><tt class='function'>endpick</tt></a></b> ()
<dd>
<dt><b><tt class='function'>endselect</tt></b> ()
<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>
<dl><dd><pre class="verbatim">
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></dl>
<P>
<div class='seealso'>
<p class='heading'><b>See Also:</b></p>
<div class="seetext"><p>An interface to OpenGL is also available; see
information about David Ascher's
<b>PyOpenGL</b> online at
<a class="url" href="javascript:if(confirm('http://starship.python.net/crew/da/PyOpenGL/ \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address. \n\nDo you want to open it from the server?'))window.location='http://starship.python.net/crew/da/PyOpenGL/'" tppabs="http://starship.python.net/crew/da/PyOpenGL/">http://starship.python.net/crew/da/PyOpenGL/ <img src="offsite.gif" tppabs="http://www.python.org/doc/current/icons/offsite.gif"
border='0' class='offsitelink' height='15' width='17' alt='[off-site link]'
></a>. This may
be a better option if support for SGI hardware from before about
1996 is not required.</div>
</div>
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