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);

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

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(iΔu + u₁);

where

Δu = (u₂ u₁) / n

and n, u₁, and u₂ are the arguments to the most recent glMapGrid1 function. The one absolute numeric requirement is that if i = n, then the value computed from iΔ u + u₁ is exactly u₂.

In the two-dimensional case, glEvalPoint2, let

Δu = (u₂ u₁)/n

Δv = (v₂ v₁)/m

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

glEvalCoord2(iΔu + u₁, jΔv + v₁);

The only absolute numeric requirements are that if i = n, then the value computed from iΔu + u₁ is exactly u₂, and if j = m, then the value computed from jΔv + v₁ is exactly v₂.

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

**  Windows NT/2000:** Requires Windows NT 3.5 or later.
**  Windows 95/98:** Requires Windows 95 or later. Available as a redistributable for Windows 95.
**  Header:** Declared in Gl.h.
**  Library:** Use Opengl32.lib.

glEvalCoord, glEvalMesh, glGet, glMap1, glMap2, glMapGrid