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/**
* Returns true if the specified GLU core- or extension-function can be
* successfully used through this GLU instance. By "successfully" we mean
* that the function is both <i>callable</i> on the machine running the
* program and <i>available</i> on the current display.<P>
*
* A GLU function is <i>callable</i> if it is a GLU core- or extension-function
* that is supported by the underlying GLU implementation. The function is
* <i>available</i> if the OpenGL implementation on the display meets the
* requirements of the GLU function being called (because GLU functions utilize
* OpenGL functions). <P>
*
* Whether or not a GLU function is <i>callable</i> is determined as follows:
* <ul>
* <li>If the function is a GLU core function (i.e., not an
* extension), <code>gluGetString(GLU_VERSION)</code> is used to determine the
* version number of the underlying GLU implementation on the host.
* then the function name is cross-referenced with that specification to
* see if it is part of that version's specification.
*
* <li> If the function is a GLU extension, the function name is
* cross-referenced with the list returned by
* <code>gluGetString(GLU_EXTENSIONS)</code> to see if the function is one of
* the extensions that is supported by the underlying GLU implementation.
* </ul>
*
* Whether or not a GLU function is <i>available</i> is determined as follows:
* <ul>
* <li>If the function is a GLU core function then the function is first
* cross-referenced with the GLU specifications to find the minimum GLU
* version required to <i>call</i> that GLU function. Then the following table
* is consulted to determine the minimum GL version required for that version
* of GLU:
* <ul>
* <li> GLU 1.0 requires OpenGL 1.0
* <li> GLU 1.1 requires OpenGL 1.0
* <li> GLU 1.2 requires OpenGL 1.1
* <li> GLU 1.3 requires OpenGL 1.2
* </ul>
* Finally, <code>glGetString(GL_VERSION)</code> is used to determine the
* highest OpenGL version that both host and display support, and from that it
* is possible to determine if the GL facilities required by the GLU function
* are <i>available</i> on the display.
*
* <li> If the function is a GLU extension, the function name is
* cross-referenced with the list returned by
* <code>gluGetString(GLU_EXTENSIONS)</code> to see if the function is one of
* the extensions that is supported by the underlying GLU implementation.
* </ul>
*
* <b>NOTE:</b>The availability of a function may change at runtime in
* response to changes in the display environment. For example, when a window
* is dragged from one display to another on a multi-display system, or when
* the properties of the display device are modified (e.g., changing the color
* depth of the display). Any application that is concerned with handling
* these situations correctly should confirm availability after a display
* change before calling a questionable OpenGL function. To detect a change in
* the display device, please see {@link
* GLEventListener#displayChanged(GLDrawable,boolean,boolean)}.
*
* @param gluFunctionName the name of the OpenGL function (e.g., use
* "gluNurbsCallbackDataEXT" to check if the <code>
* gluNurbsCallbackDataEXT(GLUnurbs, GLvoid)</code> extension is available).
*/
public boolean isFunctionAvailable(String gluFunctionName);
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