glEvalPoint1, glEvalPoint2

The glEvalPoint1 and glEvalPoint2 functions generate and evaluate a single point in a mesh.

void glEvalPoint1(
  GLint i   
);
 
void glEvalPoint2(
  GLint i,  
  GLint j   
);
 

Parameters

i

The integer value for grid domain variable i.

j

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

Remarks

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

glEvalCoord1(i·Δu + u (1) );

where

Δu = (u (2) – u (1) ) / n

and n, u (1) , and u (2) are the arguments to the most recent glMapGrid1 function. 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

Δu = (u (2) – u (1) )/n

Δv = (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 function. Then the glEvalPoint2 function is equivalent to calling

glEvalCoord2(i·Δu + u (1) , j·Δv + v (1) );

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

The following functions retrieve information relating to glEvalPoint1 and glEvalPoint2:

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

QuickInfo

  Windows NT: Use version 3.5 and later.
  Windows: Use Windows 95 and later.
  Windows CE: Unsupported.
  Header: Declared in gl.h.
  Import Library: Link with opengl32.lib.

See Also

glEvalCoord, glEvalMesh, glGet, glMap1, glMap2, glMapGrid