GLEVALPOINT

Section: Misc. Reference Manual Pages (3G)
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NAME

glEvalPoint1, glEvalPoint2 - generate and evaluate a single point in a mesh

C SPECIFICATION

void glEvalPoint1( GLint i )

void glEvalPoint2( GLint i,


                     GLint j )

delim $$

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$^cdot^DELTA u ~+~ u sub 1$ );

where

$DELTA u ~=~ ( u sub 2 - u sub 1 ) ^/^ n$

and $n$, $u sub 1$, and $u sub 2$ are the arguments to the most recent glMapGrid1 command. The one absolute numeric requirement is that if $i~=~n$, then the value computed from $i ^cdot^ DELTA u ~+~ u sub 1$ is exactly $u sub 2$. In the two-dimensional case, glEvalPoint2, let


$DELTA u ~=~ mark ( u sub 2 - u sub 1 ) ^/^ n$

$DELTA v ~=~ mark ( v sub 2 - v sub 1 ) ^/^ m,$

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



glEvalCoord2( i$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA v ~+~ v sub 1$ );

The only absolute numeric requirements are that if $i~=~n$, then the value computed from $i ^cdot^DELTA u ~+~ u sub 1$ is exactly $u sub 2$, and if $j~=~m$, then the value computed from $i ^cdot^DELTA v ~+~ v sub 1$ is exactly $v sub 2$.

ASSOCIATED GETS