1GLTEXGEN(3G) GLTEXGEN(3G)
2
6 glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGeniv -
7 control the generation of texture coordinates
8
11 void glTexGend( GLenum coord,
12 GLenum pname,
13 GLdouble param )
14 void glTexGenf( GLenum coord,
15 GLenum pname,
16 GLfloat param )
17 void glTexGeni( GLenum coord,
18 GLenum pname,
19 GLint param )
20
23 coord Specifies a texture coordinate. Must be one of GL_S, GL_T,
24 GL_R, or GL_Q.
25 pname Specifies the symbolic name of the texture-coordinate genera‐
27 tion function. Must be GL_TEXTURE_GEN_MODE.
28 param Specifies a single-valued texture generation parameter, one of
30 GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP.
31
33 void glTexGendv( GLenum coord,
34 GLenum pname,
35 const GLdouble *params )
36 void glTexGenfv( GLenum coord,
37 GLenum pname,
38 const GLfloat *params )
39 void glTexGeniv( GLenum coord,
40 GLenum pname,
41 const GLint *params )
42
45 coord Specifies a texture coordinate. Must be one of GL_S, GL_T,
46 GL_R, or GL_Q.
47 pname Specifies the symbolic name of the texture-coordinate generation
49 function or function parameters. Must be GL_TEXTURE_GEN_MODE,
50 GL_OBJECT_PLANE, or GL_EYE_PLANE.
51 params Specifies a pointer to an array of texture generation parame‐
53 ters. If pname is GL_TEXTURE_GEN_MODE, then the array must con‐
54 tain a single symbolic constant, one of GL_OBJECT_LINEAR,
55 GL_EYE_LINEAR, or GL_SPHERE_MAP. Otherwise, params holds the
56 coefficients for the texture-coordinate generation function
57 specified by pname.
58
60 glTexGen selects a texture-coordinate generation function or supplies
61 coefficients for one of the functions. coord names one of the (s, t,
62 r, q) texture coordinates; it must be one of the symbols GL_S, GL_T,
63 GL_R, or GL_Q. pname must be one of three symbolic constants:
64 GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE. If pname is
65 GL_TEXTURE_GEN_MODE, then params chooses a mode, one of
66 GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP. If pname is either
67 GL_OBJECT_PLANE or GL_EYE_PLANE, params contains coefficients for the
68 corresponding texture generation function.
69 If the texture generation function is GL_OBJECT_LINEAR, the function
71 g=p1xo+p2yo+p3zo+p4wo
73 is used, where g is the value computed for the coordinate named in
75 coord, p1, p2, p3, and p4 are the four values supplied in params, and
76 xo, yo, zo, and wo are the object coordinates of the vertex. This
77 function can be used, for example, to texture-map terrain using sea
78 level as a reference plane (defined by p1, p2, p3, and p4). The alti‐
79 tude of a terrain vertex is computed by the GL_OBJECT_LINEAR coordinate
80 generation function as its distance from sea level; that altitude can
81 then be used to index the texture image to map white snow onto peaks
82 and green grass onto foothills.
83 If the texture generation function is GL_EYE_LINEAR, the function
85 g=p′1xe+p′2ye+p′3ze+p′4we
87 is used, where
89 (p′1p′2p′3p′4)=(p1p2p3p4)M−1
91 and xe, ye, ze, and we are the eye coordinates of the vertex, p1, p2,
93 p3, and p4 are the values supplied in params, and M is the modelview
94 matrix when glTexGen is invoked. If M is poorly conditioned or singu‐
95 lar, texture coordinates generated by the resulting function may be
96 inaccurate or undefined.
97 Note that the values in params define a reference plane in eye coordi‐
99 nates. The modelview matrix that is applied to them may not be the
100 same one in effect when the polygon vertices are transformed. This
101 function establishes a field of texture coordinates that can produce
102 dynamic contour lines on moving objects.
103 If pname is GL_SPHERE_MAP and coord is either GL_S or GL_T, s and t
105 texture coordinates are generated as follows. Let u be the unit vector
106 pointing from the origin to the polygon vertex (in eye coordinates).
107 Let n sup prime be the current normal, after transformation to eye
108 coordinates. Let
109 f=(fxfyfz)T
111 be the reflection vector such that
112 f=u−2n′n′Tu
114 Finally, let m=2√f2x+f2y+(fz+1)2. Then the values assigned to the s and
116 t texture coordinates are
117 s=f_xm_+12_
119 t=f_ym_+12_
121 To enable or disable a texture-coordinate generation function, call
123 glEnable or glDisable with one of the symbolic texture-coordinate names
124 (GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or
125 GL_TEXTURE_GEN_Q) as the argument. When enabled, the specified texture
126 coordinate is computed according to the generating function associated
127 with that coordinate. When disabled, subsequent vertices take the
128 specified texture coordinate from the current set of texture coordi‐
129 nates. Initially, all texture generation functions are set to
130 GL_EYE_LINEAR and are disabled. Both s plane equations are (1, 0, 0,
131 0), both t plane equations are (0, 1, 0, 0), and all r and q plane
132 equations are (0, 0, 0, 0).
133 When the GL_ARB_multitexture extension is supported, glTexGen set the
135 texture generation parameters for the currently active texture unit,
136 selected with glActiveTextureARB.
137
139 GL_INVALID_ENUM is generated when coord or pname is not an accepted
140 defined value, or when pname is GL_TEXTURE_GEN_MODE and params is not
141 an accepted defined value.
142 GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE, params
144 is GL_SPHERE_MAP, and coord is either GL_R or GL_Q.
145 GL_INVALID_OPERATION is generated if glTexGen is executed between the
147 execution of glBegin and the corresponding execution of glEnd.
148
150 glGetTexGen
151 glIsEnabled with argument GL_TEXTURE_GEN_S
152 glIsEnabled with argument GL_TEXTURE_GEN_T
153 glIsEnabled with argument GL_TEXTURE_GEN_R
154 glIsEnabled with argument GL_TEXTURE_GEN_Q
155
157 glActiveTextureARB(3G), glCopyPixels(3G), glCopyTexImage2D(3G),
158 glCopyTexSubImage1D(3G), glCopyTexSubImage2D(3G),
159 glCopyTexSubImage3D(3G), glTexEnv(3G), glTexImage1D(3G),
160 glTexImage2D(3G), glTexImage3D(3G), glTexParameter(3G),
161 glTexSubImage1D(3G), glTexSubImage2D(3G), glTexSubImage3D(3G)
162 GLTEXGEN(3G)