How to evaluate the value of a variable ?

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glevalpoint1

GLEVALPOINT(3G) 						   OpenGL Manual						   GLEVALPOINT(3G)

NAME

       glEvalPoint - generate and evaluate a single point in a mesh

C SPECIFICATION

       void glEvalPoint1(GLint i);

       void glEvalPoint2(GLint i, GLint j);

PARAMETERS

       i
	   Specifies the integer value for grid domain variable i.

       j
	   Specifies the integer value for grid domain variable j (glEvalPoint2 only).

DESCRIPTION

       glMapGrid() and glEvalMesh() are used in tandem to efficiently generate and evaluate a series of evenly spaced map domain values.
       glEvalPoint can be used to evaluate a single grid point in the same gridspace that is traversed by glEvalMesh(). Calling glEvalPoint1 is
       equivalent to calling

	   glEvalCoord1(

				       i
				       .
				       /
				       u

				   +

				       u
				       1

			  );

       where / u = u 2 - u 1 n

       and n, u 1, and u 2 are the arguments to the most recent glMapGrid1() command. The one absolute numeric requirement is that if i = n, then
       the value computed from i . / u + u 1 is exactly u 2.

       In the two-dimensional case, glEvalPoint2, let

       / u = u 2 - u 1 n.PP / v = v 2 - v 1 m

       where n, u 1, u 2, m, v 1, and v 2 are the arguments to the most recent glMapGrid2() command. Then the glEvalPoint2 command is equivalent
       to calling

	   glEvalCoord2(

				  i
			       .
				  /
				     u

				 +

				     u
				     1

			      ,

				  j
			       .
				  /
				     v

				 +

				     v
				     1

			  );

       The only absolute numeric requirements are that if i = n, then the value computed from i . / u + u 1 is exactly u 2, and if j = m, then
       the value computed from j . / v + v 1 is exactly v 2.

ASSOCIATED GETS

       glGet() with argument GL_MAP1_GRID_DOMAIN

       glGet() with argument GL_MAP2_GRID_DOMAIN

       glGet() with argument GL_MAP1_GRID_SEGMENTS

       glGet() with argument GL_MAP2_GRID_SEGMENTS

SEE ALSO

       glEvalCoord(), glEvalMesh(), glMap1(), glMap2(), glMapGrid()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							   GLEVALPOINT(3G)

Shell Programming and Scripting