GLEVALPOINT(3G)

NAME¶

glEvalPoint1, glEvalPoint2 - 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
 $\cdot Δ u + u_{1}$ 
 );

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 $i \cdot Δ u + u_{1}$ is exactly $u_{2}$ .

In the two-dimensional case, glEvalPoint2, let

 $Δ u = (u_{2} - u_{1}) / n$ 

 $Δ v = (v_{2} - v_{1}) / m,$

where $n$ , $u_{1}$ , $u_{2}$ , $m$ , $v_{1}$ , and $v_{2}$ are the arguments to the most recent glMapGrid2 command. Then the glEvalPoint2 command is equivalent to calling

glEvalCoord2( i
 $\cdot Δ u + u_{1}$ 
, j
 $\cdot Δ v + v_{1}$ 
 );

The only absolute numeric requirements are that if

i = n

, then the value computed from

i \cdot Δ u + u_{1}

is exactly

u_{2}

, and if

j = m