glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f, glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, glEvalCoord2fv - 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 )
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
an 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. Maps are defined with glMap1 and glMap2 and enabled and
disabled with 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 was 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.
The GL 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 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 rather 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 four-
component vertex map is enabled for the specified dimension, the
glEvalCoord command is ignored.
If automatic normal generation is enabled, 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
Dp Dp
m = -- · --
Du Dv
where D represents the partial differential operator.
Then the generated normal n is
m
n = -----
||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, glColor, glEnable, glEvalMesh, glEvalPoint, glIndex, glMap1, glMap2, glMapGrid, glNormal, glTexCoord, glVertex
Introduction | Alphabetic | Specification
Last Edited: Mon, May 22, 1995