glMap1 man page on YellowDog

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GLMAP1(3G)							    GLMAP1(3G)

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_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, 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.

       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(3G),	 glColor(3G),	   glEnable(3G),      glEvalCoord(3G),
       glEvalMesh(3G),	   glEvalPoint(3G),	glMap2(3G),	glMapGrid(3G),
       glNormal(3G), glTexCoord(3G), glVertex(3G)

								    GLMAP1(3G)
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