glEvalMesh2 function

Computes a two-dimensional grid of points or lines.

Syntax

void WINAPI glEvalMesh2(
   GLenum mode,
   GLint  i1,
   GLint  i2,
   GLint  j1,
   GLint  j2
);

Parameters

mode

A value that specifies whether to compute a two-dimensional mesh of points, lines, or polygons. The following symbolic constants are accepted: GL_POINT, GL_LINE, and GL_FILL.

i1

The first integer value for grid ___domain variable i.

i2

The last integer value for grid ___domain variable i.

j1

The first integer value for grid ___domain variable j.

j2

The last integer value for grid ___domain variable j.

Return value

This function does not return a value.

Error codes

The following error codes can be retrieved by the glGetError function.

Remarks

Use glMapGrid and glEvalMesh in tandem to efficiently generate and evaluate a series of evenly spaced map ___domain values. The glEvalMesh function 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. The mode parameter determines whether the resulting vertices are connected as points, lines, or filled polygons.

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 function. Then, if mode is GL_FILL, glEvalMesh2 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( );

}

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. The following functions retrieve information relating to glEvalMesh:

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

Requirements