Name
gl.Fog -- specify fog parameters
Synopsis
gl.Fog(pname, param)
Function
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 gl.Enable() and gl.Disable() with argument #GL_FOG.

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

#GL_FOG_MODE
param 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 below. The initial fog mode is #GL_EXP.

#GL_FOG_DENSITY
param is a single 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
param is a single floating-point value that specifies start, the near distance used in the linear fog equation. The initial near distance is 0.

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

#GL_FOG_INDEX
param is a single floating-point value that specifies i f , the fog color index. The initial fog index is 0.

#GL_FOG_COLOR
param must be a table containing four floating-point values that specify Cf, the fog color. 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 post-texturing color using a blending factor f. Factor f is computed in one of three ways, depending on the fog mode. Let c be the distance in eye coordinates from the origin to the fragment being fogged. The equation for #GL_LINEAR fog is

 
f = (end - c) / (end - start)

The equation for #GL_EXP fog is

 
f = e^(-density*c)

The equation for #GL_EXP2 fog is

 
f = e^(-density*c)^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 Cr , are replaced by

 
Cr' = f*Cr+(1-f)*Cf

Fog does not affect a fragment's alpha component.

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

 
ir' = f*ir+(1-f)*if

Please consult an OpenGL reference manual for more information.

Inputs
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
Errors
#GL_INVALID_ENUM is generated if pname is not an accepted value, or if pname is #GL_FOG_MODE and param is not an accepted value.

#GL_INVALID_VALUE is generated if pname is #GL_FOG_DENSITY and param is negative.

#GL_INVALID_OPERATION is generated if gl.Fog() is executed between the execution of gl.Begin() and the corresponding execution of gl.End() .

Associated gets
gl.IsEnabled() with argument #GL_FOG

gl.Get() with argument #GL_FOG_COLOR

gl.Get() with argument #GL_FOG_INDEX

gl.Get() with argument #GL_FOG_DENSITY

gl.Get() with argument #GL_FOG_START

gl.Get() with argument #GL_FOG_END

gl.Get() with argument #GL_FOG_MODE

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