NAMEglTexGend,glTexGenf,glTexGeni,glTexGendv,glTexGenfv,glTexGeniv- control the generation of texture coordinatesCSPECIFICATIONvoidglTexGend( GLenumcoord, GLenumpname, GLdoubleparam) voidglTexGenf( GLenumcoord, GLenumpname, GLfloatparam) voidglTexGeni( GLenumcoord, GLenumpname, GLintparam)PARAMETERScoordSpecifies a texture coordinate. Must be one ofGL_S,GL_T,GL_R, orGL_Q.pnameSpecifies the symbolic name of the texture- coordinate generation function. Must beGL_TEXTURE_GEN_MODE.paramSpecifies a single-valued texture generation parameter, one ofGL_OBJECT_LINEAR,GL_EYE_LINEAR, orGL_SPHERE_MAP.CSPECIFICATIONvoidglTexGendv( GLenumcoord, GLenumpname, const GLdouble *params) voidglTexGenfv( GLenumcoord, GLenumpname, const GLfloat *params) voidglTexGeniv( GLenumcoord, GLenumpname, const GLint *params)PARAMETERScoordSpecifies a texture coordinate. Must be one ofGL_S,GL_T,GL_R, orGL_Q.pnameSpecifies the symbolic name of the texture-coordinate generation function or function parameters. Must beGL_TEXTURE_GEN_MODE,GL_OBJECT_PLANE, orGL_EYE_PLANE.paramsSpecifies a pointer to an array of texture generation parameters. IfpnameisGL_TEXTURE_GEN_MODE, then the array must contain a single symbolic constant, one ofGL_OBJECT_LINEAR,GL_EYE_LINEAR, orGL_SPHERE_MAP. Otherwise,paramsholds the coefficients for the texture-coordinate generation function specified bypname.DESCRIPTIONglTexGenselects a texture-coordinate generation function or supplies coefficients for one of the functions.coordnames one of the (s,t,r,q) texture coordinates; it must be one of the symbolsGL_S,GL_T,GL_R, orGL_Q.pnamemust be one of three symbolic constants:GL_TEXTURE_GEN_MODE,GL_OBJECT_PLANE, orGL_EYE_PLANE. IfpnameisGL_TEXTURE_GEN_MODE, thenparamschooses a mode, one ofGL_OBJECT_LINEAR,GL_EYE_LINEAR, orGL_SPHERE_MAP. Ifpnameis eitherGL_OBJECT_PLANEorGL_EYE_PLANE,paramscontains coefficients for the corresponding texture generation function. If the texture generation function isGL_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 incoord, p , p , p , and p are the four values supplied inparam<EM>s, and x3, y , z4, and w are the object coordinates of the vertex.Thisfunctionocan 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 terrain vertexis computed by theGL_OBJECT_LINEARcoordinate 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 isGL_EYE_LINEAR, the function g=p ' x +p ' y +p ' z +p ' w 1 e 2 e 3 e 4 e is used, where (p ' p ' p ' p ')=(p p p p ) M-1 1 2 3 4 1 2 3 4 and x , y , z , and w are the eye coordinates of the vertex, pe, pe, p , and p are the values supplied inparams, and M2isthe modelview matrix whenglTexGenis invoked. If M is poorly conditioned or singular, texture coordinates generated by the resulting function may be inaccurate or undefined. Note that the values inparamsdefine 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. IfpnameisGL_SPHERE_MAPandcoordis eitherGL_SorGL_T, s and t texture coordinates are generated as follows. Letube the unit vector pointing from the origin to the polygon vertex (in eye coordinates). Letnsup prime be the current normal, after transformation to eye coordinates. Let f = (f f f )T be the reflection vector such that z ' 'T f = u - 2n n u _______________ Finally, let m = 2 |f 2+f 2+(f +1)2. Then the values assigned to the sandxt texturecoordinates are___s = m + 2 f t = __+_m 2 To enable or disable a texture-coordinate generation function, callglEnableorglDisablewith one of the symbolic texture-coordinate names (GL_TEXTURE_GEN_S,GL_TEXTURE_GEN_T,GL_TEXTURE_GEN_R, orGL_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 toGL_EYE_LINEARand 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_ENUMis generated whencoordorpnameis not an accepted defined value, or whenpnameisGL_TEXTURE_GEN_MODEandparamsis not an accepted defined value.GL_INVALID_ENUMis generated whenpnameisGL_TEXTURE_GEN_MODE,paramsisGL_SPHERE_MAP, andcoordis eitherGL_RorGL_Q.GL_INVALID_OPERATIONis generated ifglTexGenis executed between the execution ofglBeginand the corresponding execution ofglEnd.ASSOCIATEDGETSglGetTexGenglIsEnabledwith argumentGL_TEXTURE_GEN_SglIsEnabledwith argumentGL_TEXTURE_GEN_TglIsEnabledwith argumentGL_TEXTURE_GEN_RglIsEnabledwith argumentGL_TEXTURE_GEN_QSEEALSOglCopyPixels,glCopyTexImage2D,glCopyTexSubImage1D,glCopyTexSubImage2D,glTexEnv,glTexImage1D,glTexImage2D,glTexParameter,glTexSubImage1D,glTexSubImage2D