glEvalPoint

glEvalPoint1, glEvalPoint2: generate and evaluate a single point in a mesh.

C Specification | Parameters | Description | Associated Gets | See Also

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).

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·u + u₁);

where

DELTA u = (u₂ u₁) / n

and n, u₁, and u₂ 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· DELTA u + u₁ is exactly u₂.

In the two-dimensional case, glEvalPoint2, let

DELTA u = (u₂ u₁) / n
DELTA v = (v₂ v₁) / m

where n, u₁, u₂, m, v₁, and v₂ are the arguments to the most recent glMapGrid2 command. Then the glEvalPoint2 command is equivalent to calling

  glEvalCoord2(i·u + u₁, j·v + v₁);

The only absolute numeric requirements are that if i=n, then the value computed from i· DELTA

u + u₁ is exactly u₂, and if j=m, then the value computed from j· DELTA

v + v₁ is exactly v₂.

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