glEvalMesh man page on MacOSX

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GLEVALMESH(3G)							GLEVALMESH(3G)

NAME
       glEvalMesh1,  glEvalMesh2  -  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	 vari‐
	     able 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 vari‐
	      able i.

       j1, j2 Specify the first and last integer values for grid domain	 vari‐
	      able 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 dot DELTA u + u1 );
	      glEnd();
where

	      DELTA(u) = (u2 - u1 ) / n

and  n,	 u1,  and  u2 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 dot DELTA(u) + u1 is exactly u2.

In the two-dimensional case, glEvalMesh2, let

       DELTA(u) = ( u2 - u1 ) / n

       DELTA(v) = ( v2 - v1 ) / m,

where n, u1, u2, m, v1, and v2 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 dot DELTA(u) + u1, j dot DELTA(v) + v1 );
	     glEvalCoord2( i dot DELTA(u) + u1, (j+1) dot DELTA(v) + v1 );
	  }
	  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 dot DELTA(u) + u1, j dot DELTA(v) + v1 );
	  glEnd();
       }

       for ( i = i1;  i <= i2; i += 1 ) {
	  glBegin( GL_LINE_STRIP );
	  for ( j = j1; j <= j1; j += 1 )
	     glEvalCoord2( i dot DELTA(u) + u1, j dot v + v1 );
	  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 dot u + u1, j dot DELTA(v) + v1 );
       glEnd();

In all three cases, the only absolute numeric requirements are that if i =  n,
then  the value computed from i dot DELTA(u) + u1 is exactly u2, and if j = m,
then the value computed from j dot DELTA(v) + v1 is exactly v2.

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

								GLEVALMESH(3G)
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