glFogf function

Article
02/04/2021

The glFogf and function specifies fog parameters.

Syntax

void WINAPI glFogf(
   GLenum  pname,
   GLfloat param
);

Parameters

pname

Specifies a single-valued fog parameter.

Accepts one of the following values.

Value	Meaning
GL_FOG_MODE	The params parameter is a single 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 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 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 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 floating-point value that specifies i_f , the fog color index. The default fog index is 0.0.

param

Specifies the value that pname will be set to.

Return value

This function does not return a value.

Error codes

The following error codes can be retrieved by the glGetError function.

Name	Meaning
GL_INVALID_ENUM	pname was not an accepted value.
GL_INVALID_OPERATION	The function was called between a call to glBegin and the corresponding call to glEnd.

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 glFogf 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:

Equation showing the value of GL_LINEAR fog.

The equation for GL_EXP fog is:

Equation showing the value of the blending factor in GL_EXP fog mode.

The equation for GL_EXP2 fog is:

Equation showing the value of the blending factor in GL_EXP2 fog mode.

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 C_r is replaced by

Equation showing the fogged fragment's color as a function of blending factor and fog color.

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

Equation showing the fogged fragment's color index as a function of blending factor and indexed color.

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

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Gl.h
Library	Opengl32.lib
DLL	Opengl32.dll

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