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 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 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)