Index for Section 3G

Alphabetical listing for G

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glMap(3G)
NAME
  glMap2, glMap2d, glMap2f - define a two-dimensional evaluator

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

  void glMap2f(
	  GLenum target,
	  GLfloat u1,
	  GLfloat u2,
	  GLint ustride,
	  GLint uorder,
	  GLfloat v1,
	  GLfloat v2,
	  GLint vstride,
	  GLint vorder,
	  const GLfloat *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
      hat, 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[i][j] and the beginning of control point R sub [(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
      hat, 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[i]j and the beginning of control point R sub [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 hat , v hat )  as

			      n	  m
       p ( u hat , v hat ) = sum sum B[i]^n(u hat) B[j]^m(v hat) R[ij]
			     i=0 j=0

  where R[i]j is a control point, B[i] sup n ( u hat ) is the ith Bernstein
  polynomial of degree n (uorder = n + 1)

       B[i]^n(u hat) = n above i u hat^i(1 - u hat)^n-i

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

       B[j]^m(v hat) = m above j v hat^j(1 - v hat)^m-j

  Recall that

       0^0 = 1 and n above = 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 hat and v
  hat, where

       u hat = {u - u1} over {u2 - u1}
       v hat = {v - v1} over {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"
  times "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 sub [i][ j]  to control point R sub [(i+1)[
  j]] .	 vstride specifies how many float or double locations are skipped to
  advance the internal memory pointer from control point R sub [i][ j]	to
  control point R sub [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().

  When the GL_ARB_multitexture extension is supported, GL_INVALID_OPERATION
  is generated if glMap2() is called and the value of GL_ACTIVE_TEXTURE_ARB
  is not GL_TEXTURE0_ARB.

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(3), glColor(3), glEnable(3), glEvalCoord(3), glEvalMesh(3),
  glEvalPoint(3), glMap1(3), glMapGrid(3), glNormal(3), glTexCoord(3),
  glVertex(3)

Index for Section 3G

Alphabetical listing for G

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