Index for Section 3G

Alphabetical listing for G

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glFog(3G)
NAME
  glFog, glFogf, glFogi, glFogfv, glFogiv - specify fog parameters

SYNOPSIS
  void glFogf(
	  GLenum pname,
	  const GLfloat param );

  void glFogi(
	  GLenum pname,
	  const GLint param );

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

  param
      Specifies the value that pname will be set to.

SYNOPSIS
  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) over (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 red, green,
  and blue colors, represented by C[r], are replaced by

       (C[r]' = fC[r] + (1-f) C[f]

  Fog does not affect a fragment's alpha component.

  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(3)

Index for Section 3G

Alphabetical listing for G

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