MirOS Manual: glTexGen(3), glTexGend(3), glTexGendv(3), glTexGenf(3), glTexGenfv(3), glTexGeni(3), glTexGeniv(3)


GLTEXGEN(3G)        UNIX Programmer's Manual         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 )

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 parame-
             ter, 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

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GLTEXGEN(3G)        UNIX Programmer's Manual         GLTEXGEN(3G)

          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. Oth-
          erwise, 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 func-
     tion.

     If the texture generation function is GL_OBJECT_LINEAR, the
     function

                    g = p1xo + p2yo + p3zo + p4wo

     is used, where g is the value computed for the coordinate
     named in coord, p1, p2, p3, and p4 are the four values sup-
     plied in params, and xo, yo, zo, and wo are the object coor-
     dinates of the vertex. This function can be used, for exam-
     ple, to texture-map terrain using sea level as a reference
     plane (defined by p1, p2, p3, and p4). The altitude of a
     terrain vertex is computed by the GL_OBJECT_LINEAR coordi-
     nate 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.
                             ') = (p1  p2  p3 'p4) M-1
     If the texture gener'tip4 function'ze G+L_pE4YE_LINEAR, the
     iasndusxeed,,ye,eze, andpwe are the eye3coordinates of the ver-
     tex, p1, p2,'p3,2and'p4 are2the values supplied in params,
     and M is the1modelview matrix when glTexGen is invoked. If M
     is poorly conditioned or singular, texture coordinates gen-
     erated by the resulting function may be inaccurate or unde-
     fined.

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     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 ver-
     tices 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 = (fx  fy  fz)T
     be the reflection vector such that
                                 2 + (fz + 1)2. Then the values
     assigned to the s and__t__te_xyt_ur_e_'c_o_11__r_dinates are
                        |fx       ____ + 2
     Tonenablelor disable a tetxt=urme-coordinate generation func-
     tion, 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.

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     GL_INVALID_OPERATION is generated if glTexGen is executed
     between the execution of glBegin and the corresponding exe-
     cution 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)

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