glEvalMesh(3G)		       OpenGL Reference			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 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.






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glEvalMesh(3G)		       OpenGL Reference			glEvalMesh(3G)



     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.Wu	+ u )
	  glEnd();		   1

	  where

	  Wu = (u -u )/n
		 2  1
     and n, u ,	and u  are the arguments to the	most recent glMapGrid1
     command.1 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.Wu +	u  is exactly u	.
				 1	       2
     In	the two-dimensional case, glEvalMesh2, let

				   Wu=(u -u )/n
					2  1
				   Wv=(v -v )/m,
					2  1
     where n, u	, u , m, v , and v  are	the arguments to the most recent
     glMapGrid21command.  Then,	if2mode	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.Wu + u	, j.Wv + v );
		  glEvalCoord2(i.Wu + u1, (j+1).Wv1+ v );
	      }			       1	      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.Wu + u	, j.Wv + v );
	      glEnd();		       1	  1
	  }
	  for (i = i1;	i <= i2; i += 1) {
	      glBegin(GL_LINE_STRIP);
	      for (j = j1; j <=	j1; j += 1)
		  glEvalCoord2(i.Wu + u	, j.Wv + v );
	      glEnd();		       1	  1
	  }




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glEvalMesh(3G)		       OpenGL Reference			glEvalMesh(3G)



     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.Wu + u	, j.Wv + v );
	      }			       1	  1
	  }
	  glEnd();


     In	all three cases, the only absolute numeric requirements	are that if
     i = n, then the value computed from i.Wu +	u  is exactly u	, and if
     j = m, then the value computed from j.Wv +	v1 is exactly v2.
						 1	       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


MACHINE	DEPENDENCIES
     RealityEngine, RealityEngine2, and	VTX systems do not handle 1D maps for
     colors correctly.


SEE ALSO
     glBegin, glEvalCoord, glEvalPoint,	glMap1,	glMap2,	glMapGrid



















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