a>() without arguments shows a gallery of the stock
patterns. The following patterns are supported:
</p><dl><dt>
Wedge
</dt><dd><p>
The image of a wedge.
</p></dd><dt>
Cone
</dt><dd><p>
The image of a cone.
</p></dd><dt>
SmoothChecker
</dt><dd><p>
A checkerboard with Gaussian filtering on top. Use the
option-value pair 'sigma', SIGMA to specify the standard
deviation of the smoothing and the pair 'step', STEP to specfity
the checker size in pixels.
</p></dd><dt>
ThreeDotsSquare
</dt><dd><p>
A pattern with t