DragonFly On-Line Manual Pages

GLFOG()                                                                GLFOG()

NAME
       glFogf, glFogi, glFogfv, glFogiv - specify fog parameters

C SPECIFICATION
       void glFogf( GLenum pname,
                    GLfloat param )
       void glFogi( GLenum pname,
                    GLint param )

PARAMETERS
       pname   Specifies a single-valued fog parameter.  GL_FOG_MODE,
               GL_FOG_DENSITY, GL_FOG_START, GL_FOG_END, and GL_FOG_INDEX are
               accepted.

       param   Specifies the value that pname will be set to.

C SPECIFICATION
       void glFogfv( GLenum pname,
                     const GLfloat *params )
       void glFogiv( GLenum pname,
                     const GLint *params )

PARAMETERS
       pname  Specifies a fog parameter.  GL_FOG_MODE, GL_FOG_DENSITY,
              GL_FOG_START, GL_FOG_END, GL_FOG_INDEX, and GL_FOG_COLOR are
              accepted.

       params Specifies the value or values to be assigned to pname.
              GL_FOG_COLOR requires an array of four values.  All other
              parameters accept an array containing only a single value.

DESCRIPTION
       Fog is initially disabled.  While enabled, fog affects rasterized
       geometry, bitmaps, and pixel blocks, but not buffer clear operations.
       To enable and disable fog, call glEnable and glDisable with argument
       GL_FOG.

       glFog assigns the value or values in params to the fog parameter
       specified by pname.  The following values are accepted for pname:

       GL_FOG_MODE         params is a single integer or floating-point value
                           that specifies the equation to be used to compute
                           the fog blend factor, f.  Three symbolic constants
                           are accepted: GL_LINEAR, GL_EXP, and GL_EXP2.  The
                           equations corresponding to these symbolic constants
                           are defined below.  The initial fog mode is GL_EXP.

       GL_FOG_DENSITY      params is a single integer or floating-point value
                           that specifies density, the fog density used in
                           both exponential fog equations.  Only nonnegative
                           densities are accepted.  The initial fog density is
                           1.

       GL_FOG_START        params is a single integer or floating-point value
                           that specifies start, the near distance used in the
                           linear fog equation.  The initial near distance is
                           0.

       GL_FOG_END          params is a single integer or floating-point value
                           that specifies end, the far distance used in the
                           linear fog equation.  The initial far distance is
                           1.

       GL_FOG_INDEX        params is a single integer or floating-point value
                           that specifies i_f, the fog color index.  The
                           initial fog index is 0.

       GL_FOG_COLOR        params contains four integer or floating-point
                           values that specify C_f, the fog color.  Integer
                           values are mapped linearly such that the most
                           positive representable value maps to 1.0, and the
                           most negative representable value maps to -1.0.
                           Floating-point values are mapped directly.  After
                           conversion, all color components are clamped to the
                           range [0,1].  The initial fog color is (0, 0, 0,
                           0).

       Fog blends a fog color with each rasterized pixel fragment's
       posttexturing color using a blending factor f.  Factor f is computed in
       one of three ways, depending on the fog mode.  Let z be the distance in
       eye coordinates from the origin to the fragment being fogged.  The
       equation for GL_LINEAR fog is

       f = (end - z)/(end - start)

       The equation for GL_EXP fog is

       f = e ** (-(density . z))

       The equation for GL_EXP2 fog is

       f = e ** (-(density . z) ** 2)

       Regardless of the fog mode, f is clamped to the range [0,1] after it is
       computed.  Then, if the GL is in RGBA color mode, the fragment's color
       C_r is replaced by

       (C_r) ' = f C_r + (1 - f) C_f

       In color index mode, the fragment's color index i_r is replaced by

       (i_r) ' = i_r + (1 - f) i_f

ERRORS
       GL_INVALID_ENUM is generated if pname is not an accepted value, or if
       pname is GL_FOG_MODE and params is not an accepted value.

       GL_INVALID_VALUE is generated if pname is GL_FOG_DENSITY, and params is
       negative.

       GL_INVALID_OPERATION is generated if glFog is executed between the
       execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS
       glIsEnabled with argument GL_FOG
       glGet with argument GL_FOG_COLOR
       glGet with argument GL_FOG_INDEX
       glGet with argument GL_FOG_DENSITY
       glGet with argument GL_FOG_START
       glGet with argument GL_FOG_END
       glGet with argument GL_FOG_MODE

SEE ALSO
       glEnable

                                                                       GLFOG()