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GLMAP1(3gl)							   GLMAP1(3gl)

NAME
       glMap1d, glMap1f - define a one-dimensional evaluator

C SPECIFICATION
       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 evalua‐
	       tor.  Symbolic  constants  GL_MAP1_VERTEX_3,  GL_MAP1_VERTEX_4,
	       GL_MAP1_INDEX,  GL_MAP1_COLOR_4,	 GL_MAP1_NORMAL,  GL_MAP1_TEX‐
	       TURE_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, 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  map‐
       ping  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)
       as

				   p(u)=iΣ0Bi(u)Ri

       where  Ri  is a control point and Bi(u) is the ith Bernstein polynomial
       of degree n (order = n+1):
					n

				 Bi(u)=⎝ ⎠ui(1−u)n−i

					i

       Recall that
					     n

				   00≡1 and ⎝ ⎠≡1

					     0

       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 call‐
       ing glEnable and glDisable with the map name, one of  the  nine	prede‐
       fined  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, where

				       u=_____

       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 val‐
				ues  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 val‐
				ues 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  com‐
				mands  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 coor‐
				dinates	 are  not  updated  with  the value of
				these glTexCoord commands.

       GL_MAP1_TEXTURE_COORD_2	Each control point is two floating-point  val‐
				ues  representing  the s and t texture coordi‐
				nates.	Internal
				glTexCoord2 commands are  generated  when  the
				map is evaluated but the current texture coor‐
				dinates 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 val‐
				ues representing the s, t, r,  and  q  texture
				coordinates.  Internal
				glTexCoord4  commands  are  generated when the
				map is evaluated but the current texture coor‐
				dinates	 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 con‐
       trol points in the array.  stride specifies how many  float  or	double
       locations to advance the internal memory pointer to reach the next con‐
       trol 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 val‐
       ues 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.

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,	 glColor,  glEnable,  glEvalCoord,  glEvalMesh,	  glEvalPoint,
       glMap2, glMapGrid, glNormal, glTexCoord, glVertex

				   15 Mar 97			   GLMAP1(3gl)
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