Index for Section 3G

Alphabetical listing for G

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glMap1(3G)
NAME
  glMap1, glMap1d, glMap1f - define a one-dimensional evaluator

SYNOPSIS
  void glMap1d(
	  GLenum target,
	  GLdouble u1,
	  GLdouble u2,
	  GLint stride,
	  GLint order,
	  const GLdouble *points );

  void glMap1f(
	  GLenum target,
	  GLfloat u1,
	  GLfloat u2,
	  GLint stride,
	  GLint order,
	  const GLfloat *points );

PARAMETERS
  target
      Specifies the kind of values that are generated by the evaluator.
      Symbolic constants GL_MAP1_VERTEX_3, GL_MAP1_VERTEX_4, GL_MAP1_INDEX,
      GL_MAP1_COLOR_4, GL_MAP1_NORMAL, GL_MAP1_TEXTURE_COORD_1,
      GL_MAP1_TEXTURE_COORD_2, GL_MAP1_TEXTURE_COORD_3, and
      GL_MAP1_TEXTURE_COORD_4 are accepted.

  u1, u2
      Specify a linear mapping of u, as presented to glEvalCoord1(), to u
      hat, the variable that is evaluated by the equations specified by this
      command.

  stride
      Specifies the number of floats or doubles between the beginning of one
      control point and the beginning of the next one in the data structure
      referenced in points. 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.

  order
      Specifies the number of control points. Must be positive.

  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 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 splines used in computer graphics: B-
  splines, Bezier curves, Hermite splines, and so on.

  Evaluators define curves based on Bernstein polynomials. Define

       p ( u hat )  as p ( u hat ) { sum from i=0 to n } B[i] sup n ( u hat ) R[i]

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

       B[i] sup n ( u hat ) { n above i }} u hat sup i ( 1 - u hat ) sup { n - i }

  Recall that

       0 sup 0 == 1 { n above 0 }}  right ) == 1

  glMap1() 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.  glEvalCoord1() evaluates the one-
  dimensional maps that are enabled. When glEvalCoord1() presents a value u,
  the Bernstein functions are evaluated using u hat, where

       u hat = {u - "u1"} over {"u2" - "u1"}

  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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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_MAP1_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.

  stride, order, 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.  order is the number of control points in the
  array.  stride specifies how many float or double locations to advance the
  internal memory pointer to reach the next control point.

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 glMap1() before glMap1() returns.
  Changes to the contents of points have no effect after glMap1() is called.

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

  GL_INVALID_VALUE is generated if u1 is equal to u2.

  GL_INVALID_VALUE is generated if stride is less than the number of values
  in a control point.

  GL_INVALID_VALUE is generated if order is less than 1 or greater than the
  return value of GL_MAX_EVAL_ORDER.

  GL_INVALID_OPERATION is generated if glMap1() 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 glMap1() 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_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

SEE ALSO
  glBegin(3), glColor(3), glEnable(3), glEvalCoord(3), glEvalMesh(3),
  glEvalPoint(3), glMap2(3), glMapGrid(3), glNormal(3), glTexCoord(3),
  glVertex(3)

Index for Section 3G

Alphabetical listing for G

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