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fglTexGen(3G)		       OpenGL Reference			 fglTexGen(3G)

NAME
     fglTexGend, fglTexGenf, fglTexGeni, fglTexGendv, fglTexGenfv, fglTexGeniv
     - control the generation of texture coordinates

FORTRAN SPECIFICATION
     SUBROUTINE fglTexGend( INTEGER*4 coord,
			    INTEGER*4 pname,
			    REAL*4 param )
     SUBROUTINE fglTexGenf( INTEGER*4 coord,
			    INTEGER*4 pname,
			    REAL*4 param )
     SUBROUTINE fglTexGeni( INTEGER*4 coord,
			    INTEGER*4 pname,
			    INTEGER*4 param )

PARAMETERS
     coord   Specifies a texture coordinate.  Must be one of GL_S, GL_T, GL_R,
	     or GL_Q.

     pname   Specifies the symbolic name of the texture-coordinate generation
	     function.	Must be GL_TEXTURE_GEN_MODE.

     param   Specifies a single-valued texture generation parameter, one of
	     GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP.

FORTRAN SPECIFICATION
     SUBROUTINE fglTexGendv( INTEGER*4 coord,
			     INTEGER*4 pname,
			     CHARACTER*8 params )
     SUBROUTINE fglTexGenfv( INTEGER*4 coord,
			     INTEGER*4 pname,
			     CHARACTER*8 params )
     SUBROUTINE fglTexGeniv( INTEGER*4 coord,
			     INTEGER*4 pname,
			     CHARACTER*8 params )

PARAMETERS
     coord
	  Specifies a texture coordinate.  Must be one of GL_S, GL_T, GL_R, or
	  GL_Q.

     pname
	  Specifies the symbolic name of the texture-coordinate generation
	  function or function parameters.  Must be GL_TEXTURE_GEN_MODE,
	  GL_OBJECT_PLANE, or GL_EYE_PLANE.

     params
	  Specifies a pointer to an array of texture generation parameters.
	  If pname is GL_TEXTURE_GEN_MODE, then the array must contain a

									Page 1

fglTexGen(3G)		       OpenGL Reference			 fglTexGen(3G)

	  single symbolic constant, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or
	  GL_SPHERE_MAP. Otherwise, params holds the coefficients for the
	  texture-coordinate generation function specified by pname.

DESCRIPTION
     fglTexGen selects a texture-coordinate generation function or supplies
     coefficients for one of the functions.  coord names one of the (s, t, r,
     q) texture coordinates; it must be one of the symbols GL_S, GL_T, GL_R,
     or GL_Q.  pname must be one of three symbolic constants:
     GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If pname is
     GL_TEXTURE_GEN_MODE, then params chooses a mode, one of GL_OBJECT_LINEAR,
     GL_EYE_LINEAR, or GL_SPHERE_MAP. If pname is either GL_OBJECT_PLANE or
     GL_EYE_PLANE, params contains coefficients for the corresponding texture
     generation function.

     If the texture generation function is GL_OBJECT_LINEAR, the function

			   g = p x  + p y  + p z  + p w
				1 o    2 o    3 o    4 o

     is used, where g is the value computed for the coordinate named in coord,
     p , p , p , and p	are the four values supplied in params, and x , y ,
      1	  2   3	      4						     o	 o
     z , and w	are the object coordinates of the vertex.  This function can
      o	      o
     be used, for example, to texture-map terrain using sea level as a
     reference plane (defined by p , p , p , and p ). The altitude of a
				  1   2	  3	  4
     terrain vertex is computed by the GL_OBJECT_LINEAR coordinate generation
     function as its distance from sea level; that altitude can then be used
     to index the texture image to map white snow onto peaks and green grass
     onto foothills.

     If the texture generation function is GL_EYE_LINEAR, the function

				'      '      '	     '
			   g = p x  + p y  + p z  + p w
				1 e    2 e    3 e    4 e

     is used, where

			'   '	'   '			   -1
		      (p   p   p   p ) = (p   p	  p   p ) M
			1   2	3   4	   1   2   3   4

     and x , y , z , and w  are the eye coordinates of the vertex, p , p , p ,
	  e   e	  e	  e					    1	2   3
     and p  are the values supplied in params, and M is the modelview matrix
	  4
     when fglTexGen is invoked.	 If M is poorly conditioned or singular,
     texture coordinates generated by the resulting function may be inaccurate
     or undefined.

     Note that the values in params define a reference plane in eye
     coordinates. The modelview matrix that is applied to them may not be the
     same one in effect when the polygon vertices are transformed. This
     function establishes a field of texture coordinates that can produce
     dynamic contour lines on moving objects.

     If pname is GL_SPHERE_MAP and coord is either GL_S or GL_T, s and t
     texture coordinates are generated as follows. Let u be the unit vector
     pointing from the origin to the polygon vertex (in eye coordinates). Let

									Page 2

fglTexGen(3G)		       OpenGL Reference			 fglTexGen(3G)

     n sup prime be the current normal, after transformation to eye
     coordinates. Let

						 T
				 f = (f	  f   f )
				       x   y   z

     be the reflection vector such that

					       T
					    ' '
				  f = u - 2n n	u

			 _____________________

			|  2	 2	     2
     Finally, let m = 2	 f   + f   + (f	 + 1) . Then the values assigned to
		       \| x	y      z
     the s and t texture coordinates are

					f
					__   _
				    s =	   +
					m    2

					f
					__   _
				    t =	   +
					m    2

     To enable or disable a texture-coordinate generation function, call
     fglEnable or fglDisable with one of the symbolic texture-coordinate names
     (GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or
     GL_TEXTURE_GEN_Q) as the argument. When enabled, the specified texture
     coordinate is computed according to the generating function associated
     with that coordinate. When disabled, subsequent vertices take the
     specified texture coordinate from the current set of texture coordinates.
     Initially, all texture generation functions are set to GL_EYE_LINEAR and
     are disabled.  Both s plane equations are (1, 0, 0, 0), both t plane
     equations are (0, 1, 0, 0), and all r and q plane equations are (0, 0, 0,
     0).

ERRORS
     GL_INVALID_ENUM is generated when coord or pname is not an accepted
     defined value, or when pname is GL_TEXTURE_GEN_MODE and params is not an
     accepted defined value.

     GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE, params is
     GL_SPHERE_MAP, and coord is either GL_R or GL_Q.

     GL_INVALID_OPERATION is generated if fglTexGen is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGetTexGen
     fglIsEnabled with argument GL_TEXTURE_GEN_S
     fglIsEnabled with argument GL_TEXTURE_GEN_T
     fglIsEnabled with argument GL_TEXTURE_GEN_R
     fglIsEnabled with argument GL_TEXTURE_GEN_Q

SEE ALSO
     fglCopyPixels, fglCopyTexImage2D, fglCopyTexSubImage1D,
     fglCopyTexSubImage2D, fglCopyTexSubImage3D, fglTexEnv, fglTexImage1D,
     fglTexImage2D, fglTexImage3D, fglTexParameter, fglTexSubImage1D,

									Page 3

fglTexGen(3G)		       OpenGL Reference			 fglTexGen(3G)

     fglTexSubImage2D, fglTexSubImage3D

									Page 4

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