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GLMAP2(3G)				  OpenGL Manual 			       GLMAP2(3G)

NAME
       glMap2 - define a two-dimensional evaluator

C SPECIFICATION
       void glMap2f(GLenum target, GLfloat u1, GLfloat u2, GLint ustride, GLint uorder,
		    GLfloat v1, GLfloat v2, GLint vstride, GLint vorder, const GLfloat * points);

       void glMap2d(GLenum target, GLdouble u1, GLdouble u2, GLint ustride, GLint uorder,
		    GLdouble v1, GLdouble v2, GLint vstride, GLint vorder,
		    const GLdouble * points);

PARAMETERS
       target
	   Specifies the kind of values that are generated by the evaluator. Symbolic constants
	   GL_MAP2_VERTEX_3, GL_MAP2_VERTEX_4, GL_MAP2_INDEX, GL_MAP2_COLOR_4, GL_MAP2_NORMAL,
	   GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2, GL_MAP2_TEXTURE_COORD_3, and
	   GL_MAP2_TEXTURE_COORD_4 are accepted.

       u1, u2
	   Specify a linear mapping of u, as presented to glEvalCoord2(), to u^, one of the two
	   variables that are evaluated by the equations specified by this command. Initially, u1
	   is 0 and u2 is 1.

       ustride
	   Specifies the number of floats or doubles between the beginning of control point R ij
	   and the beginning of control point R i + 1  j, where i and j are the u and v control
	   point indices, respectively. This allows control points to be embedded in arbitrary
	   data structures. The only constraint is that the values for a particular control point
	   must occupy contiguous memory locations. The initial value of ustride is 0.

       uorder
	   Specifies the dimension of the control point array in the u axis. Must be positive.
	   The initial value is 1.

       v1, v2
	   Specify a linear mapping of v, as presented to glEvalCoord2(), to v^, one of the two
	   variables that are evaluated by the equations specified by this command. Initially, v1
	   is 0 and v2 is 1.

       vstride
	   Specifies the number of floats or doubles between the beginning of control point R ij
	   and the beginning of control point R i  j + 1, where i and j are the u and v control
	   point indices, respectively. This allows control points to be embedded in arbitrary
	   data structures. The only constraint is that the values for a particular control point
	   must occupy contiguous memory locations. The initial value of vstride is 0.

       vorder
	   Specifies the dimension of the control point array in the v axis. Must be positive.
	   The initial value is 1.

       points
	   Specifies a pointer to the array of control points.

DESCRIPTION
       Evaluators provide a way to use polynomial or rational polynomial mapping to produce
       vertices, normals, texture coordinates, and colors. The values produced by an evaluator
       are sent on to further stages of GL processing just as if they had been presented using
       glVertex(), glNormal(), glTexCoord(), and glColor() commands, except that the generated
       values do not update the current normal, texture coordinates, or color.

       All polynomial or rational polynomial splines of any degree (up to the maximum degree
       supported by the GL implementation) can be described using evaluators. These include
       almost all surfaces used in computer graphics, including B-spline surfaces, NURBS
       surfaces, Bezier surfaces, and so on.

       Evaluators define surfaces based on bivariate Bernstein polynomials. Define p  u^ v^ as
		  _	    _
       p  u^ v^ = > i = 0 n > j = 0 m B i n  u^  B j m	v^  R ij

       where R ij is a control point, B i n  u^ is the ith Bernstein polynomial of degree n
       (uorder = n + 1)

       B i n  u^ = n i	u^ i  1 - u^ n - i

       and B j m  v^ is the jth Bernstein polynomial of degree m (vorder = m + 1)

       B j m  v^ = m j	v^ j  1 - v^ m - j

       Recall that 0 0 == 1 and n 0 == 1

       glMap2 is used to define the basis and to specify what kind of values are produced. Once
       defined, a map can be enabled and disabled by calling glEnable() and glDisable() with the
       map name, one of the nine predefined values for target, described below. When
       glEvalCoord2() presents values u and v, the bivariate Bernstein polynomials are evaluated
       using u^ and v^, where

       u^ = u - u1 u2 - u1

       v^ = v - v1 v2 - v1

       target is a symbolic constant that indicates what kind of control points are provided in
       points, and what output is generated when the map is evaluated. It can assume one of nine
       predefined values:

       GL_MAP2_VERTEX_3
	   Each control point is three floating-point values representing x, y, and z. Internal
	   glVertex3() commands are generated when the map is evaluated.

       GL_MAP2_VERTEX_4
	   Each control point is four floating-point values representing x, y, z, and w. Internal
	   glVertex4() commands are generated when the map is evaluated.

       GL_MAP2_INDEX
	   Each control point is a single floating-point value representing a color index.
	   Internal glIndex() commands are generated when the map is evaluated but the current
	   index is not updated with the value of these glIndex() commands.

       GL_MAP2_COLOR_4
	   Each control point is four floating-point values representing red, green, blue, and
	   alpha. Internal glColor4() commands are generated when the map is evaluated but the
	   current color is not updated with the value of these glColor4() commands.

       GL_MAP2_NORMAL
	   Each control point is three floating-point values representing the x, y, and z
	   components of a normal vector. Internal glNormal() commands are generated when the map
	   is evaluated but the current normal is not updated with the value of these glNormal()
	   commands.

       GL_MAP2_TEXTURE_COORD_1
	   Each control point is a single floating-point value representing the s texture
	   coordinate. Internal glTexCoord1() commands are generated when the map is evaluated
	   but the current texture coordinates are not updated with the value of these
	   glTexCoord() commands.

       GL_MAP2_TEXTURE_COORD_2
	   Each control point is two floating-point values representing the s and t texture
	   coordinates. Internal glTexCoord2() commands are generated when the map is evaluated
	   but the current texture coordinates are not updated with the value of these
	   glTexCoord() commands.

       GL_MAP2_TEXTURE_COORD_3
	   Each control point is three floating-point values representing the s, t, and r texture
	   coordinates. Internal glTexCoord3() commands are generated when the map is evaluated
	   but the current texture coordinates are not updated with the value of these
	   glTexCoord() commands.

       GL_MAP2_TEXTURE_COORD_4
	   Each control point is four floating-point values representing the s, t, r, and q
	   texture coordinates. Internal glTexCoord4() commands are generated when the map is
	   evaluated but the current texture coordinates are not updated with the value of these
	   glTexCoord() commands.

       ustride, uorder, vstride, vorder, and points define the array addressing for accessing the
       control points.	points is the location of the first control point, which occupies one,
       two, three, or four contiguous memory locations, depending on which map is being defined.
       There are uorder x vorder control points in the array.  ustride specifies how many float
       or double locations are skipped to advance the internal memory pointer from control point
       R i  j to control point R i + 1	j.  vstride specifies how many float or double locations
       are skipped to advance the internal memory pointer from control point R i  j to control
       point R i  j + 1.

NOTES
       As is the case with all GL commands that accept pointers to data, it is as if the contents
       of points were copied by glMap2 before glMap2 returns. Changes to the contents of points
       have no effect after glMap2 is called.

       Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL is enabled, normal vectors are
       generated when either GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4 is used to generate vertices.

ERRORS
       GL_INVALID_ENUM is generated if target is not an accepted value.

       GL_INVALID_VALUE is generated if u1 is equal to u2, or if v1 is equal to v2.

       GL_INVALID_VALUE is generated if either ustride or vstride is less than the number of
       values in a control point.

       GL_INVALID_VALUE is generated if either uorder or vorder is less than 1 or greater than
       the return value of GL_MAX_EVAL_ORDER.

       GL_INVALID_OPERATION is generated if glMap2 is executed between the execution of glBegin()
       and the corresponding execution of glEnd().

       GL_INVALID_OPERATION is generated if glMap2 is called and the value of GL_ACTIVE_TEXTURE
       is not GL_TEXTURE0.

ASSOCIATED GETS
       glGetMap()

       glGet() with argument GL_MAX_EVAL_ORDER

       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

SEE ALSO
       glBegin(), glColor(), glEnable(), glEvalCoord(), glEvalMesh(), glEvalPoint(), glMap1(),
       glMapGrid(), glNormal(), glTexCoord(), glVertex()

COPYRIGHT
       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI
       Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014				       GLMAP2(3G)
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