MirOS Manual: glEvalMesh(3), glEvalMesh1(3), glEvalMesh2(3)


GLEVALMESH(3G)      UNIX Programmer's Manual       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 con-
           stants 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. Sym-
          bolic 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)      UNIX Programmer's Manual       GLEVALMESH(3G)

     In the one-dimensional case, glEvalMesh1, the mesh is gen-
     erated as if the following code fragment were executed:

          glBegin( type );
          for ( i = i1; i <= i2; i += 1 )
             glEvalCoord1( i._\_u + u1 );
          glEnd();

     where

          _\_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._\_u + u1 is exactly u2.

     In the two-dimensional case, glEvalMesh2, let

          _\_u = (u2 - u1)/n

          _\_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._\_u + u1, j._\_v + v1 );
                glEvalCoord2( i._\_u + u1, (j+1)._\_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._\_u + u1, j._\_v + v1 );
             glEnd();
          }

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GLEVALMESH(3G)      UNIX Programmer's Manual       GLEVALMESH(3G)

          for ( i = i1;  i <= i2; i += 1 ) {
             glBegin( GL_LINE_STRIP );
             for ( j = j1; j <= j1; j += 1 )
                glEvalCoord2( i._\_u + u1, j._\_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._\_u + u1, j._\_v + v1 );
          glEnd();

     In all three cases, the only absolute numeric requirements
     are that if i = n, then the value computed from i._\_u + u1
     is exactly u2, and if j = m, then the value computed from
     j._\_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 exe-
     cution 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(3G), glEvalCoord(3G), glEvalPoint(3G), glMap1(3G),
     glMap2(3G), glMapGrid(3G)

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