glFogi(3gl)

1GLFOG(3G)                                                            GLFOG(3G)
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NAME

6       glFogf, glFogi, glFogfv, glFogiv - specify fog parameters
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C SPECIFICATION

10       void glFogf( GLenum pname,
11                    GLfloat param )
12       void glFogi( GLenum pname,
13                    GLint param )
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PARAMETERS

17       pname   Specifies   a   single-valued   fog   parameter.   GL_FOG_MODE,
18               GL_FOG_DENSITY, GL_FOG_START, GL_FOG_END, and GL_FOG_INDEX  are
19               accepted.
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21       param   Specifies the value that pname will be set to.
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C SPECIFICATION

24       void glFogfv( GLenum pname,
25                     const GLfloat *params )
26       void glFogiv( GLenum pname,
27                     const GLint *params )
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PARAMETERS

31       pname  Specifies   a   fog   parameter.   GL_FOG_MODE,  GL_FOG_DENSITY,
32              GL_FOG_START, GL_FOG_END,  GL_FOG_INDEX,  and  GL_FOG_COLOR  are
33              accepted.
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35       params Specifies   the  value  or  values  to  be  assigned  to  pname.
36              GL_FOG_COLOR requires an array of four values.  All other param‐
37              eters accept an array containing only a single value.
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DESCRIPTION

40       Fog is initially disabled.  While enabled, fog affects rasterized geom‐
41       etry, bitmaps, and pixel blocks, but not buffer  clear  operations.  To
42       enable  and  disable  fog,  call  glEnable  and glDisable with argument
43       GL_FOG.
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45       glFog assigns the value or values in params to the fog parameter speci‐
46       fied by pname.  The following values are accepted for pname:
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48       GL_FOG_MODE         params  is a single integer or floating-point value
49                           that specifies the equation to be used  to  compute
50                           the  fog blend factor, f.  Three symbolic constants
51                           are accepted: GL_LINEAR, GL_EXP, and GL_EXP2.   The
52                           equations corresponding to these symbolic constants
53                           are defined below.  The initial fog mode is GL_EXP.
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55       GL_FOG_DENSITY      params is a single integer or floating-point  value
56                           that  specifies  density,  the  fog density used in
57                           both exponential fog equations.   Only  nonnegative
58                           densities are accepted.  The initial fog density is
59                           1.
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61       GL_FOG_START        params is a single integer or floating-point  value
62                           that specifies start, the near distance used in the
63                           linear fog equation.  The initial near distance  is
64                           0.
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66       GL_FOG_END          params  is a single integer or floating-point value
67                           that specifies end, the far distance  used  in  the
68                           linear  fog  equation.  The initial far distance is
69                           1.
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71       GL_FOG_INDEX        params is a single integer or floating-point  value
72                           that  specifies  if, the fog color index.  The ini‐
73                           tial fog index is 0.
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75       GL_FOG_COLOR        params contains four integer or floating-point val‐
76                           ues that specify Cf, the fog color.  Integer values
77                           are mapped linearly such  that  the  most  positive
78                           representable value maps to 1.0, and the most nega‐
79                           tive representable value maps to  -1.0.   Floating-
80                           point  values  are  mapped directly.  After conver‐
81                           sion, all color components are clamped to the range
82                           [0,1].  The initial fog color is (0, 0, 0, 0).
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84       Fog  blends  a fog color with each rasterized pixel fragment's posttex‐
85       turing color using a blending factor f.  Factor f is computed in one of
86       three  ways,  depending  on the fog mode.  Let z be the distance in eye
87       coordinates from the origin to the fragment being fogged.  The equation
88       for GL_LINEAR fog is
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90                                     f=e_n_ed_n−_ds_−t_za_r_t_
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93The equation for GL_EXP fog is
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95                               f=e−(density⋅z)
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98The equation for GL_EXP2 fog is
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100                               f=e−(density⋅z)2
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103Regardless  of the fog mode, f is clamped to the range [0, 1] after it is com‐
104puted.  Then, if the GL is in RGBA color mode, the fragment's red, green,  and
105blue colors, represented by Cr, are replaced by
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107                               Cr′=fCr+(1−f)Cf
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110Fog does not affect a fragment's alpha component.
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112In color index mode, the fragment's color index ir is replaced by
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114                                ir′=ir+(1−f)if
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ERRORS

117       GL_INVALID_ENUM  is  generated if pname is not an accepted value, or if
118       pname is GL_FOG_MODE and params is not an accepted value.
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120       GL_INVALID_VALUE is generated if pname is GL_FOG_DENSITY, and params is
121       negative.
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123       GL_INVALID_OPERATION is generated if glFog is executed between the exe‐
124       cution of glBegin and the corresponding execution of glEnd.
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ASSOCIATED GETS

127       glIsEnabled with argument GL_FOG
128       glGet with argument GL_FOG_COLOR
129       glGet with argument GL_FOG_INDEX
130       glGet with argument GL_FOG_DENSITY
131       glGet with argument GL_FOG_START
132       glGet with argument GL_FOG_END
133       glGet with argument GL_FOG_MODE
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