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<HTML><BODY><PRE>     <STRONG>NAME</STRONG>	  <STRONG>glEvalMesh1,</STRONG> <STRONG>glEvalMesh2</STRONG> - compute a one- or two-dimensional	  grid of points or lines     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>	  void <STRONG>glEvalMesh1</STRONG>( GLenum <EM>mode</EM>,			    GLint <EM>i1</EM>,			    GLint <EM>i2</EM> )     <STRONG>PARAMETERS</STRONG>	  <EM>mode</EM>	In <STRONG>glEvalMesh1</STRONG>,	specifies whether to compute a one-		dimensional mesh of points or lines.  Symbolic		constants <STRONG>GL_POINT</STRONG> and <STRONG>GL_LINE</STRONG> are accepted.	  <EM>i1</EM>, <EM>i2</EM>		Specify	the first and last integer values for grid		domain variable	i.     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>	  void <STRONG>glEvalMesh2</STRONG>( GLenum <EM>mode</EM>,			    GLint <EM>i1</EM>,			    GLint <EM>i2</EM>,			    GLint <EM>j1</EM>,			    GLint <EM>j2</EM> )     <STRONG>PARAMETERS</STRONG>	  <EM>mode</EM> In <STRONG>glEvalMesh2</STRONG>, specifies whether to compute a two-	       dimensional mesh	of points, lines, or polygons.	       Symbolic	constants <STRONG>GL_POINT</STRONG>, <STRONG>GL_LINE</STRONG>, and <STRONG>GL_FILL</STRONG> are	       accepted.	  <EM>i1</EM>, <EM>i2</EM>	       Specify the first and last integer values for grid	       domain variable i.	  <EM>j1</EM>, <EM>j2</EM>	       Specify the first and last integer values for grid	       domain variable j.     <STRONG>DESCRIPTION</STRONG>	  <STRONG>glMapGrid</STRONG> and	<STRONG>glEvalMesh</STRONG> are used in tandem to efficiently	  generate and evaluate	a series of evenly-spaced map domain	  values.  <STRONG>glEvalMesh</STRONG> steps through the	integer	domain of a	  one- or two-dimensional grid,	whose range is the domain of	  the evaluation maps specified	by <STRONG>glMap1</STRONG> and <STRONG>glMap2</STRONG>.  <EM>mode</EM>	  determines whether the resulting vertices are	connected as	  points, lines, or filled polygons.	  In the one-dimensional case, <STRONG>glEvalMesh1</STRONG>, the	mesh is	  generated as if the following	code fragment were executed:	  glBegin (<EM>type</EM>);	  for (i = <EM>i1</EM>; i &lt;= <EM>i2</EM>;	i += 1)	       glEvalCoord1(i .	DELTA u	+ u sub	1)	  glEnd();	  where	  DELTA	u = (u	- u ) /	1		      2	   1	  and n, u, and	u  are the arguments to	the most recent		  1	 2	  <STRONG>glMapGrid1</STRONG> command.  <EM>type</EM> is <STRONG>GL_POINTS</STRONG> if <EM>mode</EM> is <STRONG>GL_POINT</STRONG>,	  or <STRONG>GL_LINES</STRONG> if <EM>mode</EM> is <STRONG>GL_LINE</STRONG>.	  The one absolute numeric requirement is that if i = n, then	  the value computed from	  i . DELTA u +	u	  is exactly u.	  In the two-dimensional case, <STRONG>glEvalMesh2</STRONG>, let	  DELTA	u = (u	- u )/n		      2	   1	  DELTA	v = (v - v )/m,		      2	  1	  where	n, u , u , m, v	, and v		    1	2      1       2	  are the arguments to the most	recent <STRONG>glMapGrid2</STRONG> command.	  Then,	if <EM>mode</EM>	is <STRONG>GL_FILL</STRONG>, the	<STRONG>glEvalMesh2</STRONG> command is	  equivalent to:	  for (j = <EM>j1</EM>;	j &lt; <EM>j2</EM>;	j += 1)	{	      glBegin (GL_QUAD_STRIP);	      for (i = <EM>i1</EM>; i &lt;=	<EM>i2</EM>; i += 1) {		  glEvalCoord2(i . DELTA u + u , j . DELTA v + v );					      1			1		  glEvalCoord2(i . DELTA u + u , (j+1) . DELTA v + v );					      1			    1	      }	      glEnd();	  }	  If <EM>mode</EM> is <STRONG>GL_LINE</STRONG>, then a call to <STRONG>glEvalMesh2</STRONG> is equivalent	  to:	  for (j = <EM>j1</EM>;	j &lt;= <EM>j2</EM>; j += 1) {	      glBegin(GL_LINE_STRIP);	      for (i = <EM>i1</EM>; i &lt;=	<EM>i2</EM>; i += 1)		  glEvalCoord2(i . DELTA u + u , j . DELTA v + v );					      1			1	      glEnd();	  }	  for (i = <EM>i1</EM>;	i &lt;= <EM>i2</EM>; i += 1) {	      glBegin(GL_LINE_STRIP);	      for (j = <EM>j1</EM>; j &lt;=	<EM>j1</EM>; j += 1)		  glEvalCoord2)(i . DELTA u + u	, j . DELTA v +	v );					       1		 1	      glEnd();	  }	  And finally, if <EM>mode</EM> is <STRONG>GL_POINT</STRONG>, then a call	to <STRONG>glEvalMesh2</STRONG>	  is equivalent	to:	  glBegin (GL_POINTS);	  for (j = <EM>j1</EM>;	j &lt;= <EM>j2</EM>; j += 1) {	      for (i = <EM>i1</EM>; i &lt;=	<EM>i2</EM>; i += 1) {		  glEvalCoord2(i . DELTA u + u , j . DELTA v + v );					      1			1	      }	  }	  glEnd();	  In all three cases, the only absolute	numeric	requirements	  are that if i	= n, then the value computed from	  i . DELTA u +	u is exactly u ,			 1	      2	  and if j = m,	  then the value computed from	  j . DELTA v +	v is exactly v .			 1	      2     <STRONG>ERRORS</STRONG>	  <STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>mode</EM> is not an accepted	  value.	  <STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glEvalMesh</STRONG> is executed	  between the execution	of <STRONG>glBegin</STRONG> and the corresponding	  execution of <STRONG>glEnd</STRONG>.     <STRONG>ASSOCIATED</STRONG>	<STRONG>GETS</STRONG>	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_MAP1_GRID_DOMAIN</STRONG>	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_MAP2_GRID_DOMAIN</STRONG>	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_MAP1_GRID_SEGMENTS</STRONG>	  <STRONG>glGet</STRONG>	with argument <STRONG>GL_MAP2_GRID_SEGMENTS</STRONG>     <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>	  <STRONG>glBegin</STRONG>, <STRONG>glEvalCoord</STRONG>,	<STRONG>glEvalPoint</STRONG>, <STRONG>glMap1</STRONG>, <STRONG>glMap2</STRONG>, <STRONG>glMapGrid</STRONG></PRE></BODY></HTML>
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