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

void glTexGend( GLenumcoord, GLenumpname, GLdoubleparam) void glTexGenf( GLenumcoord, GLenumpname, GLfloatparam) void glTexGeni( GLenumcoord, GLenumpname, GLintparam)

coordSpecifies a texture coordinate. Must be one of the following: GL_S, GL_T, GL_R, or GL_Q.pnameSpecifies the symbolic name of the texture-coordinate generation function. Must be GL_TEXTURE_GEN_MODE.paramSpecifies a single-valued texture generation parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP.

void glTexGendv( GLenumcoord, GLenumpname, const GLdouble *params) void glTexGenfv( GLenumcoord, GLenumpname, const GLfloat *params) void glTexGeniv( GLenumcoord, GLenumpname, const GLint *params)

coordSpecifies a texture coordinate. Must be one of the following: GL_S, GL_T, GL_R, or GL_Q.pnameSpecifies 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.paramsSpecifies a pointer to an array of texture generation parameters. Ifpnameis 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,paramsholds the coefficients for the texture-coordinate generation function specified bypname.

glTexGen selects a texture-coordinate generation function or supplies coefficients for one of the functions.coordnames one of the (s,t,r,q) texture coordinates, and it must be one of these symbols: GL_S, GL_T, GL_R, or GL_Q.pnamemust be one of three symbolic constants: GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. Ifpnameis GL_TEXTURE_GEN_MODE, thenparamschooses a mode, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP. Ifpnameis either GL_OBJECT_PLANE or GL_EYE_PLANE,paramscontains 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 incoord, p , p , p , and p are the four values supplied inparams, and x , y , z , 1 2 3 4 o o o and w are the object coordinates of the vertex. This function can be used o to texture-map terrain using sea level as a reference plane (defined by p , 1 p , p , and p ). The altitude of a terrain vertex is computed by the 2 3 4 GL_OBJECT_LINEAR coordinate generation function as its distance from sea level; that altitude is used to index the texture image to map white snow onto peaks and green grass onto foothills, for example. 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 inparams, and M is the modelview matrix 4 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 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. Ifpnameis GL_SPHERE_MAP andcoordis either GL_S or GL_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). Letn'be the current normal, after transformation to eye coordinates. Let Tf= (f f f ) be the reflection vector such that x y z Tf=u- 2n'n' u_____________ | 2 2 2 Finally, let m = 2\|f +f +(f +1) . Then the values assigned to the s and x y z t texture coordinates are f x 1 s = --- + - m 2 f y 1 t = --- + - m 2 A texture-coordinate generation function is enabled or disabled using 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).

GL_INVALID_ENUM is generated whencoordorpnameis not an accepted defined value, or whenpnameis GL_TEXTURE_GEN_MODE andparamsis not an accepted defined value. GL_INVALID_ENUM is generated whenpnameis GL_TEXTURE_GEN_MODE,paramsis GL_SPHERE_MAP, andcoordis 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.

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

glTexEnv, glTexImage1D, glTexImage2D, glTexParameter

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Fri Dec 6 11:18:03 EST 1996
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