Index for Section 3G

Alphabetical listing for G

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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
  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.

SYNOPSIS
  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 . 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 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 . 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 equivalent
  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)

Index for Section 3G

Alphabetical listing for G

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