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GLEVALMESH(3G)				  OpenGL Manual 			   GLEVALMESH(3G)

NAME
       glEvalMesh - compute a one- or two-dimensional grid of points or lines

C SPECIFICATION
       void glEvalMesh1(GLenum mode, GLint i1, GLint i2);

PARAMETERS
       mode
	   In glEvalMesh1, specifies whether to compute a one-dimensional mesh of points or
	   lines. Symbolic constants GL_POINT and GL_LINE are accepted.

       i1, i2
	   Specify the first and last integer values for grid domain variable i.

C SPECIFICATION
       void glEvalMesh2(GLenum mode, GLint i1, GLint i2, GLint j1, GLint j2);

PARAMETERS
       mode
	   In glEvalMesh2, specifies whether to compute a two-dimensional mesh of points, lines,
	   or polygons. Symbolic constants GL_POINT, GL_LINE, and GL_FILL are accepted.

       i1, i2
	   Specify the first and last integer values for grid domain variable i.

       j1, j2
	   Specify the first and last integer values for grid domain variable j.

DESCRIPTION
       glMapGrid() and glEvalMesh are used in tandem to efficiently generate and evaluate a
       series of evenly-spaced map domain values.  glEvalMesh steps through the integer domain of
       a one- or two-dimensional grid, whose range is the domain of the evaluation maps specified
       by glMap1() and glMap2().  mode determines whether the resulting vertices are connected as
       points, lines, or filled polygons.

       In the one-dimensional case, glEvalMesh1, the mesh is generated as if the following code
       fragment were executed:

	   glBegin( type );
	   for ( i = i1; i <= i2; i += 1 )
	      glEvalCoord1(

				   i
				.
				/\
				   u

			       +

				   u
				   1

			);
	   glEnd();

       where

       /\ u = u 2 - u 1 n

       and n, u 1, and u 2 are the arguments to the most recent glMapGrid1() command.  type is
       GL_POINTS if mode is GL_POINT, or GL_LINES if mode is GL_LINE.

       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, glEvalMesh2, let .cp /\ u = u 2 - u 1 n

       /\ 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, if mode is GL_FILL, the glEvalMesh2 command is equivalent to:

	   for ( j = j1; j < j2; j += 1 ) {
	      glBegin( GL_QUAD_STRIP );
	      for ( i = i1; i <= i2; i += 1 ) {
		 glEvalCoord2(

				  i
			       .
				  /\
				     u

				 +

				     u
				     1

			      ,

				  j
			       .
				  /\
				     v

				 +

				     v
				     1

			  );
		 glEvalCoord2(

				  i
			       .
				  /\
				     u

				 +

				     u
				     1

			      ,

					      j
					   +
					      1

			       .
				  /\
				     v

				 +

				     v
				     1

			  );
	      }
	      glEnd();
	   }

       If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to:

	   for ( j = j1; j <= j2; j += 1 ) {
	      glBegin( GL_LINE_STRIP );
	      for ( i = i1; i <= i2; i += 1 )
		 glEvalCoord2(

				  i
			       .
				  /\
				     u

				 +

				     u
				     1

			      ,

				  j
			       .
				  /\
				     v

				 +

				     v
				     1

			  );
	      glEnd();
	   }

	   for ( i = i1;  i <= i2; i += 1 ) {
	      glBegin( GL_LINE_STRIP );
	      for ( j = j1; j <= j1; j += 1 )
		 glEvalCoord2(

				  i
			       .
				  /\
				     u

				 +

				     u
				     1

			      ,

				  j
			       .
				  /\
				     v

				 +

				     v
				     1

			  );
	      glEnd();
	   }

       And finally, if mode is GL_POINT, then a call to glEvalMesh2 is equivalent to:

	   glBegin( GL_POINTS );
	   for ( j = j1; j <= j2; j += 1 )
	      for ( i = i1; i <= i2; i += 1 )
		 glEvalCoord2(

				  i
			       .
				  /\
				     u

				 +

				     u
				     1

			      ,

				  j
			       .
				  /\
				     v

				 +

				     v
				     1

			  );
	   glEnd();

       In all three cases, 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.

ERRORS
       GL_INVALID_ENUM is generated if mode is not an accepted value.

       GL_INVALID_OPERATION is generated if glEvalMesh is executed between the execution of
       glBegin() and the corresponding execution of glEnd().

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
       glBegin(), glEvalCoord(), glEvalPoint(), 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				   GLEVALMESH(3G)
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