glTexGenf(3g)

1GLTEXGEN(3G)                     OpenGL Manual                    GLTEXGEN(3G)
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NAME

6       glTexGen - control the generation of texture coordinates
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C SPECIFICATION

9       void glTexGeni(GLenum coord, GLenum pname, GLint param);
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11       void glTexGenf(GLenum coord, GLenum pname, GLfloat param);
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13       void glTexGend(GLenum coord, GLenum pname, GLdouble param);
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PARAMETERS

16       coord
17           Specifies a texture coordinate. Must be one of GL_S, GL_T, GL_R, or
18           GL_Q.
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20       pname
21           Specifies the symbolic name of the texture-coordinate generation
22           function. Must be GL_TEXTURE_GEN_MODE.
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24       param
25           Specifies a single-valued texture generation parameter, one of
26           GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP, GL_NORMAL_MAP, or
27           GL_REFLECTION_MAP.
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C SPECIFICATION

30       void glTexGeniv(GLenum coord, GLenum pname, const GLint * params);
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32       void glTexGenfv(GLenum coord, GLenum pname, const GLfloat * params);
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34       void glTexGendv(GLenum coord, GLenum pname, const GLdouble * params);
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PARAMETERS

37       coord
38           Specifies a texture coordinate. Must be one of GL_S, GL_T, GL_R, or
39           GL_Q.
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41       pname
42           Specifies the symbolic name of the texture-coordinate generation
43           function or function parameters. Must be GL_TEXTURE_GEN_MODE,
44           GL_OBJECT_PLANE, or GL_EYE_PLANE.
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46       params
47           Specifies a pointer to an array of texture generation parameters.
48           If pname is GL_TEXTURE_GEN_MODE, then the array must contain a
49           single symbolic constant, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR,
50           GL_SPHERE_MAP, GL_NORMAL_MAP, or GL_REFLECTION_MAP. Otherwise,
51           params holds the coefficients for the texture-coordinate generation
52           function specified by pname.
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DESCRIPTION

55       glTexGen selects a texture-coordinate generation function or supplies
56       coefficients for one of the functions.  coord names one of the (s, t,
57       r, q) texture coordinates; it must be one of the symbols GL_S, GL_T,
58       GL_R, or GL_Q.  pname must be one of three symbolic constants:
59       GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If pname is
60       GL_TEXTURE_GEN_MODE, then params chooses a mode, one of
61       GL_OBJECT_LINEAR, GL_EYE_LINEAR, GL_SPHERE_MAP, GL_NORMAL_MAP, or
62       GL_REFLECTION_MAP. If pname is either GL_OBJECT_PLANE or GL_EYE_PLANE,
63       params contains coefficients for the corresponding texture generation
64       function.
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66       If the texture generation function is GL_OBJECT_LINEAR, the function
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68       g = p 1 × x o + p 2 × y o + p 3 × z o + p 4 × w o
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70       is used, where g is the value computed for the coordinate named in
71       coord, p 1, p 2, p 3, and p 4 are the four values supplied in params,
72       and x o, y o, z o, and w o are the object coordinates of the vertex.
73       This function can be used, for example, to texture-map terrain using
74       sea level as a reference plane (defined by p 1, p 2, p 3, and p 4). The
75       altitude of a terrain vertex is computed by the GL_OBJECT_LINEAR
76       coordinate generation function as its distance from sea level; that
77       altitude can then be used to index the texture image to map white snow
78       onto peaks and green grass onto foothills.
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80       If the texture generation function is GL_EYE_LINEAR, the function
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82       g = p 1 ″ × x e + p 2 ″ × y e + p 3 ″ × z e + p 4 ″ × w e
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84       is used, where
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86       p 1 ″ ⁢ p 2 ″ ⁢ p 3 ″ ⁢ p 4 ″ = p 1 ⁢ p 2 ⁢ p 3 ⁢ p 4 ⁢ M -1
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88       and x e, y e, z e, and w e are the eye coordinates of the vertex, p 1,
89       p 2, p 3, and p 4 are the values supplied in params, and M is the
90       modelview matrix when glTexGen is invoked. If M is poorly conditioned
91       or singular, texture coordinates generated by the resulting function
92       may be inaccurate or undefined.
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94       Note that the values in params define a reference plane in eye
95       coordinates. The modelview matrix that is applied to them may not be
96       the same one in effect when the polygon vertices are transformed. This
97       function establishes a field of texture coordinates that can produce
98       dynamic contour lines on moving objects.
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100       If the texture generation function is GL_SPHERE_MAP and coord is either
101       GL_S or GL_T, s and t texture coordinates are generated as follows. Let
102       u be the unit vector pointing from the origin to the polygon vertex (in
103       eye coordinates). Let n sup prime be the current normal, after
104       transformation to eye coordinates. Let
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106       f = f x ⁢ f y ⁢ f z T be the reflection vector such that
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108       f = u - 2 ⁢ n ″ ⁢ n ″ T ⁢ u
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110       Finally, let m = 2 ⁢ f x 2 + f y 2 + f z + 1 2. Then the values
111       assigned to the s and t texture coordinates are
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113       s = f x m + 1 2
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115       t = f y m + 1 2
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117       To enable or disable a texture-coordinate generation function, call
118       glEnable() or glDisable() with one of the symbolic texture-coordinate
119       names (GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or
120       GL_TEXTURE_GEN_Q) as the argument. When enabled, the specified texture
121       coordinate is computed according to the generating function associated
122       with that coordinate. When disabled, subsequent vertices take the
123       specified texture coordinate from the current set of texture
124       coordinates. Initially, all texture generation functions are set to
125       GL_EYE_LINEAR and are disabled. Both s plane equations are (1, 0, 0,
126       0), both t plane equations are (0, 1, 0, 0), and all r and q plane
127       equations are (0, 0, 0, 0).
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129       When the ARB_multitexture extension is supported, glTexGen sets the
130       texture generation parameters for the currently active texture unit,
131       selected with glActiveTexture().
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ERRORS

134       GL_INVALID_ENUM is generated when coord or pname is not an accepted
135       defined value, or when pname is GL_TEXTURE_GEN_MODE and params is not
136       an accepted defined value.
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138       GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE, params
139       is GL_SPHERE_MAP, and coord is either GL_R or GL_Q.
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141       GL_INVALID_OPERATION is generated if glTexGen is executed between the
142       execution of glBegin() and the corresponding execution of glEnd().
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ASSOCIATED GETS

145       glGetTexGen()
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147       glIsEnabled() with argument GL_TEXTURE_GEN_S
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149       glIsEnabled() with argument GL_TEXTURE_GEN_T
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151       glIsEnabled() with argument GL_TEXTURE_GEN_R
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153       glIsEnabled() with argument GL_TEXTURE_GEN_Q
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COPYRIGHT

163       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
164       under the SGI Free Software B License. For details, see
165       http://oss.sgi.com/projects/FreeB/.
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AUTHORS

168       opengl.org
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172opengl.org                        07/13/2018                      GLTEXGEN(3G)