glEvalCoord

glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f, glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, glEvalCoord2fv

These functions evaluate enabled one- and two-dimensional maps.

void glEvalCoord1d(
  GLdouble u   
);
 
void glEvalCoord1f(
  GLfloat u   
);
 
void glEvalCoord2d(
  GLdouble u,  
  GLdouble v   
);
 
void glEvalCoord2f(
  GLfloat u,  
  GLfloat v   
);
 

Parameters

u

In glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, and glEvalCoord2f, specifies a value that is the domain coordinate u to the basis function defined in a previous glMap1 or glMap2 function.

v

A value that is the domain coordinate v to the basis function defined in a previous glMap2 function. This argument is not present in a glEvalCoord1 function.

void glEvalCoord1dv(
  const GLdouble * u   
);
 
void glEvalCoord1fv(
  const GLfloat * u   
);
 
void glEvalCoord2dv(
  const GLdouble * u   
);
 
void glEvalCoord2fv(
  const GLfloat * u   
);
 

Parameters

u

In glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, and glEvalCoord2fv, specifies a pointer to an array containing either one or two domain coordinates. The first coordinate is u. The second coordinate is v, which is present only in glEvalCoord2 versions.

Remarks

The glEvalCoord1 function evaluates enabled one-dimensional maps at argument u. The glEvalCoord2 function does the same for two-dimensional maps using two domain values, u and v. Maps are defined with glMap1 and glMap2, and are enabled and disabled with glEnable and glDisable.

When one of the glEvalCoord functions is issued, all currently enabled maps of the indicated dimension are evaluated. Then, for each enabled map, it is as if the corresponding OpenGL function were issued with the computed value. That is, if GL_MAP1_INDEX or GL_MAP2_INDEX is enabled, a glIndex function is simulated. If GL_MAP1_COLOR_4 or GL_MAP2_COLOR_4 is enabled, a glColor function is simulated. If GL_MAP1_NORMAL or GL_MAP2_NORMAL is enabled, a normal vector is produced, and if any of GL_MAP1_TEXTURE_COORD_1, GL_MAP1_TEXTURE_COORD_2, GL_MAP1_TEXTURE_COORD_3, GL_MAP1_TEXTURE_COORD_4, GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2, GL_MAP2_TEXTURE_COORD_3, and GL_MAP2_TEXTURE_COORD_4 is enabled, then an appropriate glTexCoord function is simulated.

OpenGL uses evaluated values instead of current values for those evaluations that are enabled, and current values otherwise, for color, color index, normal, and texture coordinates. However, the evaluated values do not update the current values. Thus, if glVertex functions are interspersed with glEvalCoord functions, the color, normal, and texture coordinates associated with the glVertex functions are not affected by the values generated by the glEvalCoord functions, but only by the most recent glColor, glIndex, glNormal, and glTexCoord functions.

No functions are issued for maps that are not enabled. If more than one texture evaluation is enabled for a particular dimension (for example, GL_MAP2_TEXTURE_COORD_1 and GL_MAP2_TEXTURE_COORD_2), then only the evaluation of the map that produces the larger number of coordinates (in this case, GL_MAP2_TEXTURE_COORD_2) is carried out. GL_MAP1_VERTEX_4 overrides GL_MAP1_VERTEX_3, and GL_MAP2_VERTEX_4 overrides GL_MAP2_VERTEX_3, in the same manner. If neither a three- nor four-component vertex map is enabled for the specified dimension, glEvalCoord is ignored.

If automatic normal generation is enabled, glEvalCoord2 calls glEnable with argument GL_AUTO_NORMAL to generate surface normals analytically, regardless of the contents or enabling of the GL_MAP2_NORMAL map. Let

The generated normal n is

If automatic normal generation is disabled, the corresponding normal map GL_MAP2_NORMAL, if enabled, is used to produce a normal. If neither automatic normal generation nor a normal map is enabled, no normal is generated for glEvalCoord2 functions.

The following functions retrieve information related to the glEvalCoord functions:

glIsEnabled with argument GL_MAP1_VERTEX_3

glIsEnabled with argument GL_MAP1_VERTEX_4

glIsEnabled with argument GL_MAP1_INDEX

glIsEnabled with argument GL_MAP1_COLOR_4

glIsEnabled with argument GL_MAP1_NORMAL

glIsEnabled with argument GL_MAP1_TEXTURE_COORD_1

glIsEnabled with argument GL_MAP1_TEXTURE_COORD_2

glIsEnabled with argument GL_MAP1_TEXTURE_COORD_3

glIsEnabled with argument GL_MAP1_TEXTURE_COORD_4

glIsEnabled with argument GL_MAP2_VERTEX_3

glIsEnabled with argument GL_MAP2_VERTEX_4

glIsEnabled with argument GL_MAP2_INDEX

glIsEnabled with argument GL_MAP2_COLOR_4

glIsEnabled with argument GL_MAP2_NORMAL

glIsEnabled with argument GL_MAP2_TEXTURE_COORD_1

glIsEnabled with argument GL_MAP2_TEXTURE_COORD_2

glIsEnabled with argument GL_MAP2_TEXTURE_COORD_3

glIsEnabled with argument GL_MAP2_TEXTURE_COORD_4

glIsEnabled with argument GL_AUTO_NORMAL

glGetMap

See Also

glBegin, glColor, glDisable, glEnable, glEvalMesh, glEvalPoint, glGetMap, glIndex, glIsEnabled, glMap1, glMap2, glMapGrid, glNormal, glTexCoord, glVertex