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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
				⋅
				Δ
				   u

			       +

				   u
				   1

			);
	   glEnd();

       where

       Δ 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 ⋅ Δ u + u 1 is exactly u 2.

       In the two-dimensional case, glEvalMesh2, let .cp Δ u = u 2 - u 1 n

       Δ 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
			       ⋅
				  Δ
				     u

				 +

				     u
				     1

			      ,

				  j
			       ⋅
				  Δ
				     v

				 +

				     v
				     1

			  );
		 glEvalCoord2(

				  i
			       ⋅
				  Δ
				     u

				 +

				     u
				     1

			      ,

					      j
					   +
					      1

			       ⋅
				  Δ
				     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
			       ⋅
				  Δ
				     u

				 +

				     u
				     1

			      ,

				  j
			       ⋅
				  Δ
				     v

				 +

				     v
				     1

			  );
	      glEnd();
	   }

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

				  i
			       ⋅
				  Δ
				     u

				 +

				     u
				     1

			      ,

				  j
			       ⋅
				  Δ
				     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
			       ⋅
				  Δ
				     u

				 +

				     u
				     1

			      ,

				  j
			       ⋅
				  Δ
				     v

				 +

				     v
				     1

			  );
	   glEnd();

       In all three cases, the only absolute numeric requirements are that if
       i = n, then the value computed from i ⋅ Δ u + u 1 is exactly u 2, and
       if j = m, then the value computed from j ⋅ Δ 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 © 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			  04/29/2014			GLEVALMESH(3G)

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