GLTEXGEN(3gl) GLTEXGEN(3gl)[top]NAMEglTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGenivcontrol the generation of texture coordinates-C SPECIFICATIONvoid glTexGend( GLenum coord, GLenum pname, GLdouble param ) void glTexGenf( GLenum coord, GLenum pname, GLfloat param ) void glTexGeni( GLenum coord, GLenum pname, GLint param )PARAMETERScoord 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 genera‐ tion function. Must be GL_TEXTURE_GEN_MODE. param Specifies a single-valued texture generation parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP, GL_REFLEC‐ TION_MAP or GL_NORMAL_MAP.C SPECIFICATIONvoid 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 )PARAMETERScoord 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 parame‐ ters. If pname is GL_TEXTURE_GEN_MODE, then the array must con‐ tain a single symbolic constant, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP, GL_REFLECTION_MAP, or GL_NOR‐ MAL_MAP. Otherwise, params holds the coefficients for the tex‐ ture-coordinate generation function specified by pname.DESCRIPTIONglTexGen 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_TEX‐ TURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If pname is GL_TEX‐ TURE_GEN_MODE, then params chooses a mode, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP, GL_REFLECTION_MAP, or GL_NORMAL_MAP. If pname is either GL_OBJECT_PLANE or GL_EYE_PLANE, params contains coef‐ ficients for the corresponding texture generation function. 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 supplied in params, and xo, yo, zo, and wo 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 p1, p2, p3, and p4). The alti‐ tude 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=p1′xe+p2′ye+p3′ze+p4′we is used, where (p1′p2′p3′p4′)=(p1p2p3p4)M−1 and xe, ye, ze, and we are the eye coordinates of the vertex, p1, p2, p3, and p4 are the values supplied in params, and M is the modelview matrix when glTexGen is invoked. If M is poorly conditioned or singu‐ lar, texture coordinates generated by the resulting function may be inaccurate or undefined. Note that the values in params define a reference plane in eye coordi‐ nates. 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=(fxfyfz)T be the reflection vector such that f=u−2n′n′Tu Finally, let m=2√fx+fy+(fz+1)2 . Then the values assigned to the s and t texture coordinates are s=__+_ t=__+_ If pname is GL_REFLECTION_MAP, a reflection vector r is computed as described for the GL_SPHERE_MAP mode. Then the value assigned to s coordinate is s = rx; the value assigned to a t coordinate is t = ry; and the value assigned to the r coordinate is r = rz. If pname is GL_NORMAL_MAP, a normal vector nf is computed. Then the value assigned to s coordinate is s = nfx; the value assigned to t coordinate is t = nfy; and the value assigned to the r coordinate is r = nfz. (the values nfx,nfy,and nfz are the components of nf.) 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_TEX‐ TURE_GEN_Q) as the argument. When enabled, the specified texture coor‐ dinate 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. Ini‐ tially, 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).ERRORSGL_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. GL_INVALID_ENUM is generated when TexGen is called with a coord of GL_Q when pname indicates GL_REFLECTION_MAP, or GL_NORMAL_MAP.ASSOCIATED GETSglGetTexGen 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_QSEE ALSOglCopyPixels, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubIm‐ age2D, glTexEnv, glTexImage1D, glTexImage2D, glTexParameter, glTex‐ SubImage1D, glTexSubImage2D 15 Mar 97 GLTEXGEN(3gl)

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