glEvalMesh man page on DigitalUNIX

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glEvalMesh(3G)							glEvalMesh(3G)

NAME
       glEvalMesh,  glEvalMesh2	 -  compute  a one- or two-dimensional grid of
       points or lines

SYNOPSIS
       void glEvalMesh1(
	       GLenum mode,
	       GLint i1,
	       GLint i2 );

PARAMETERS
       In glEvalMesh1(), specifies whether to compute a	 one-dimensional  mesh
       of  points  or  lines.  Symbolic	 constants  GL_POINT  and  GL_LINE are
       accepted.  Specify the first and last integer values  for  grid	domain
       variable i.

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

PARAMETERS
       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.  Specify the first and last integer values
       for grid domain variable i.  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 con‐
       nected 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 . DELTA u + u[1] ); glEnd();

       where DELTA u = (u[ 2] - u[1] ) / n

       and  n,	u[  1],	 and  u[2] are the arguments to the most recent glMap‐
       Grid1() 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 . DELTA u + u[1] is exactly u[2].

       In the two-dimensional case, glEvalMesh2(), let DELTA u = ( u[2] - u[1]
       ) / n DELTA 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.DELTA u + u[1], j.DELTA v + v[1] );
	      glEvalCoord2( i.DELTA u + u[1], (j+1)cdotDELTA 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( icdotDELTA u + u[1], jcdotDELTA v + v[1] );
	   }
	   glEnd(); }

       for ( i = i1; i <= i2; i += 1 ) {
	   glBegin( GL_LINE_STRIP );
	   for ( j = j1; j <= i2; j += 1 ) {
	      glEvalCoord2( icdotDELTA u + u[1], jcdotDELTA v + v[1] );
	   }
	   glEnd(); }

       And finally, if mode is GL_POINT, then a call toglEvalMesh2() is equiv‐
       alent to:

       glBegin( GL_POINTS ); for ( j = j1; j <= j2; j += 1 )
	   for ( i = i1; i <= i2; i += 1 )
	      glEvalCoord2( i^cdot^DELTA u + u[1], j^cdot^DELTA v  +  v[1]  );
       glEnd();

       In  all three cases, the only absolute numeric requirements are that if
       i=n, then the value computed from icdotDELTA u + u[1] is exactly	 u[2],
       and  if	j=m,  then  the	 value	computed from j cdot DELTA 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(3),   glEvalCoord(3),   glEvalPoint(3),	glMap1(3),  glMap2(3),
       glMapGrid(3)

								glEvalMesh(3G)
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