GLEVALPOINT(3G)

NAME
glEvalPoint - generate and evaluate a single point in a mesh

C SPECIFICATION

void glEvalPoint1(GLint i);

void glEvalPoint2(GLint i, GLint j);

PARAMETERS

i
    Specifies the integer value for grid domain variable i.

j
    Specifies the integer value for grid domain variable j (glEvalPoint2 only).

DESCRIPTION

glMapGrid() and glEvalMesh() are used in tandem to efficiently generate and evaluate a series of evenly spaced map domain values. glEvalPoint can be used to evaluate a single grid point in the same gridspace that is traversed by glEvalMesh(). Calling glEvalPoint1 is equivalent to calling

    glEvalCoord1(

         	                  i
         	                  ⋅
         	                  Δ
         	                  u

         	              +

         	                  u
         	                  1

                   );

where Δ u = u 2 - u 1 n

and n, u 1, and u 2 are the arguments to the most recent glMapGrid1() command. The one absolute numeric requirement is that if i = n, then the value computed from i ⋅ Δ u + u 1 is exactly u 2.

In the two-dimensional case, glEvalPoint2, let

Δ u = u 2 - u 1 n

where n, u 1, u 2, m, v 1, and v 2 are the arguments to the most recent glMapGrid2() command. Then the glEvalPoint2 command is equivalent to calling

    glEvalCoord2(

    			        i
    				⋅
    			        Δ
    		                u

    		            +

    		                u
    		                1

    			    ,

    			        j
    				⋅
    			        Δ
    		                v

    		            +

    		                v
    		                1

    		     );

The only absolute numeric requirements are that if i = n, then the value computed from i ⋅ Δ u + u 1 is exactly u 2, and if j = m, then the value computed from j ⋅ Δ v + v 1 is exactly v 2.

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

glEvalCoord(), glEvalMesh(), glMap1(), glMap2(), glMapGrid()

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.