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Manual Reference Pages  - GLEVALCOORD (3G)

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glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f, glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, glEvalCoord2fv - evaluate enabled one- and two-dimensional maps

CONTENTS

C Specification
Parameters
C Specification
Parameters
Description
Associated Gets
See Also

void glEvalCoord1d( GLdouble u )

void glEvalCoord1f( GLfloat u )

void glEvalCoord2d( GLdouble u,

                  GLdouble v )

void glEvalCoord2f( GLfloat u,

                  GLfloat v )

u	Specifies a value that is the domain coordinate u to the basis function defined in a previous  glMap1 or  glMap2 command.
v	Specifies a value that is the domain coordinate v to the basis function defined in a previous  glMap2 command. This argument is not present in a  glEvalCoord1 command.

void glEvalCoord1dv( const GLdouble *u )

void glEvalCoord1fv( const GLfloat *u )

void glEvalCoord2dv( const GLdouble *u )

void glEvalCoord2fv( const GLfloat *u )

u	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.

 glEvalCoord1 evaluates enabled one-dimensional maps at argument u.  glEvalCoord2 does the same for two-dimensional maps using two domain values, u and v. To define a map, call  glMap1 and  glMap2; to enable and disable it, call  glEnable and  glDisable.

When one of the  glEvalCoord commands is issued, all currently enabled maps of the indicated dimension are evaluated. Then, for each enabled map, it is as if the corresponding GL command had been issued with the computed value. That is, if  GL_MAP1_INDEX or  GL_MAP2_INDEX is enabled, a  glIndex command is simulated. If  GL_MAP1_COLOR_4 or  GL_MAP2_COLOR_4 is enabled, a  glColor command 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, or  GL_MAP2_TEXTURE_COORD_4 is enabled, then an appropriate  glTexCoord command is simulated.

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

No commands 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 a four-component vertex map is enabled for the specified dimension, the  glEvalCoord command is ignored.

If you have enabled automatic normal generation, by calling  glEnable with argument  GL_AUTO_NORMAL,  glEvalCoord2 generates surface normals analytically, regardless of the contents or enabling of the  GL_MAP2_NORMAL map. Let

m = partialp / partialu times partialp / partialv

Then the generated normal n is
n = m / ||m||

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 commands.

 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

 glBegin(3G),  glColor(3G),  glEnable(3G),  glEvalMesh(3G),  glEvalPoint(3G),  glIndex(3G),  glMap1(3G),  glMap2(3G),  glMapGrid(3G),  glNormal(3G),  glTexCoord(3G),  glVertex(3G)

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