glTexGeniv man page on OpenBSD

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GLTEXGEN(3G)							  GLTEXGEN(3G)

NAME
       glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGeniv -
       control the generation of texture coordinates

C SPECIFICATION
       void glTexGend( GLenum coord,
	    GLenum pname,
	    GLdouble param )
       void glTexGenf( GLenum coord,
	    GLenum pname,
	    GLfloat param )
       void glTexGeni( GLenum coord,
	    GLenum pname,
	    GLint param )

       delim $$

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.

C SPECIFICATION
       void glTexGendv( GLenum coord,
	    GLenum pname,
	    const GLdouble *params )
       void glTexGenfv( GLenum coord,
	    GLenum pname,
	    const GLfloat *params )
       void glTexGeniv( GLenum coord,
	    GLenum pname,
	    const GLint *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 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
       glTexGen 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

       $g ~=~ p sub 1^x sub o ~+~ p sub 2^y sub o ~+~ p sub 3^z sub o ~+~ p
       sub 4^w sub o$

       is used, where $g$ is the value computed for the coordinate named in
       coord, $p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$ are the four
       values supplied in params, and $x sub o$, $y sub o$, $z sub o$, and $w
       sub o$ are the object coordinates of the vertex.	 This function can be
       used, for example, to texture-map terrain using sea level as a
       reference plane (defined by $p sub 1$, $p sub 2$, $p sub 3$, and $p sub
       4$).  The altitude of a 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

       $g ~=~ p sub 1 sup prime ^x sub e ~+~ p sub 2 sup prime ^y sub e ~+~ p
       sub 3 sup prime ^z sub e ~+~ p sub 4 sup prime ^w sub e$

       is used, where

       $( p sub 1 sup prime ~~p sub 2 sup prime~~p sub 3 sup prime~~ { p sub 4
       sup prime}) ~=~ ( p sub 1~~ p sub 2~~ p sub 3~~ p sub 4 ) ~M sup -1$

       and $x sub e$, $y sub e$, $z sub e$, and $w sub e$ are the eye
       coordinates of the vertex, $p sub 1$, $p sub 2$, $p sub 3$, and $p sub
       4$ are the values supplied in params, and $M$ is the modelview matrix
       when glTexGen 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 n sup prime be the current normal, after transformation to eye
       coordinates.  Let

       $f ~=~ ( f sub x~~f sub y~~f sub z ) sup T$ be the reflection vector
       such that

       $f ~=~  u ~-~ 2 n sup prime n sup prime sup T u$

       Finally, let $ m ~=~ 2 sqrt { f sub x sup {~2} ~+~ f sub y sup {~2} ~+~
       (f sub z ~+~ 1 ) sup 2}$.  Then the values assigned to the $s$ and $t$
       texture coordinates are

       $s ~=~ f sub x over m ~+~ 1 over 2$

       $t ~=~ f sub y over m ~+~ 1 over 2$

       To enable or disable a texture-coordinate generation function, call
       glEnable or glDisable 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).

       When the GL_ARB_multitexture extension is supported, glTexGen set the
       texture generation parameters for the currently active texture unit,
       selected with glActiveTextureARB.

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 glTexGen is executed between the
       execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS
       glGetTexGen
       glIsEnabled with argument GL_TEXTURE_GEN_S
       glIsEnabled with argument GL_TEXTURE_GEN_T
       glIsEnabled with argument GL_TEXTURE_GEN_R
       glIsEnabled with argument GL_TEXTURE_GEN_Q

SEE ALSO
       glActiveTextureARB(3G), glCopyPixels(3G), glCopyTexImage2D(3G),
       glCopyTexSubImage1D(3G), glCopyTexSubImage2D(3G),
       glCopyTexSubImage3D(3G), glTexEnv(3G), glTexImage1D(3G),
       glTexImage2D(3G), glTexImage3D(3G), glTexParameter(3G),
       glTexSubImage1D(3G), glTexSubImage2D(3G), glTexSubImage3D(3G)

								 March 1, 2011
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