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glFogf, glFogi, glFogfv, glFogiv

These functions specify fog parameters.

void glFogf(
  GLenum pname,
  GLfloat param
);

void glFogi(
  GLenum pname,
  GLint param
);

void glFogfv(
  GLenum pname,
  const GLfloat *params
);

void glFogiv(
  GLenum pname,
  const GLint * params
);

Parameters

pname
In glFogf and glFogi, pname specifies a single-valued fog parameter.

In glFogfv and glFogiv, pname specifies a fog parameter.

The glFogf, glFogi, glFogfv, and glFogiv functions accept the following values.

Value Meaning
GL_FOG_MODE The params parameter 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 in the following Remarks section. The default fog mode is GL_EXP.
GL_FOG_DENSITY The params parameter 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 default fog density is 1.0.
GL_FOG_START The params parameter is a single integer or floating-point value that specifies start, the near distance used in the linear fog equation. The default near distance is 0.0.
GL_FOG_END The params parameter is a single integer or floating-point value that specifies end, the far distance used in the linear fog equation. The default far distance is 1.0.
GL_FOG_INDEX The params parameter is a single integer or floating-point value that specifies if, the fog color index. The default fog index is 0.0.
GL_FOG_COLOR The glFogfv and glFogiv functions also accept GL_FOG_COLOR:

The params parameter contains four integer or floating-point values that specify Cf, 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 default fog color is (0,0,0,0).


param
In glFogf and glFogi, specifies the value that pname will be set to.
params
In glFogfv and glFogiv, 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.

Remarks

You enable and disable fog with glEnable and glDisable, using the argument GL_FOG. While enabled, fog affects rasterized geometry, bitmaps, and pixel blocks, but not buffer-clear operations.

The glFog function assigns the value or values in params to the fog parameter specified by pname.

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:

The equation for GL_EXP fog is:

The equation for GL_EXP2 fog is:

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

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

The following functions retrieve information related to the glFog functions:

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

glIsEnabled with argument GL_FOG

Error Codes

The following are the error codes generated and their conditions.

Error code Condition
GL_INVALID_ENUM pname was not an accepted value.
GL_INVALID_OPERATION glFinish was called between a call to glBegin and the corresponding call to glEnd.

Requirements

  Windows NT/2000: Requires Windows NT 3.5 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in Gl.h.
  Library: Use Opengl32.lib.

See Also

glBegin, glDisable, glEnable, glEnd, glGet, glIsEnabled


  

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