GLTEXGEN() GLTEXGEN() NAME glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGeniv - con- trol 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 sin- gle 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 coef- ficients 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 ob- ject 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 tex- ture 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 val- ues 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 ef- fect 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 coor- dinates 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 glEn- able 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 com- puted 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 genera- tion 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). 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 exe- cution 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 glCopyPixels, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glTexEnv, glTexImage1D, glTexImage2D, glTexParameter, glTexSubImage1D, gl- TexSubImage2D GLTEXGEN()
NAME | C SPECIFICATION | PARAMETERS | C SPECIFICATION | PARAMETERS | DESCRIPTION | ERRORS | ASSOCIATED GETS | SEE ALSO
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