Function glFogiv

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, ƒ. 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 𝐢𝑓, the fog color index. The initial fog index is 0.

• GL_FOG_COLOR params 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 initial fog color is (0, 0, 0, 0).

• GL_FOG_COORD_SRC params contains either of the following symbolic constants: GL_FOG_COORD or GL_FRAGMENT_DEPTH. GL_FOG_COORD specifies that the current fog coordinate should be used as distance value in the fog color computation. GL_FRAGMENT_DEPTH specifies that the current fragment depth should be used as distance value in the fog computation.

Fog blends a fog color with each rasterized pixel fragment's post-texturing color using a blending factor ƒ. Factor ƒ is computed in one of three ways, depending on the fog mode. Let 𝐂 be either the distance in eye coordinate from the origin (in the case that the GL_FOG_COORD_SRC is GL_FRAGMENT_DEPTH) or the current fog coordinate (in the case that GL_FOG_COORD_SRC is GL_FOG_COORD). The equation for GL_LINEAR fog is

ƒ = end − 𝐂 / end − start

The equation for GL_EXP fog is

ƒ = 𝐞 ^ −(density⋅𝐂)

The equation for GL_EXP2 fog is

ƒ = 𝐞 ^ −(density⋅𝐂)²

Regardless of the fog mode, ƒ 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′′ = ƒ × 𝐂ᵣ + (1 − ƒ) × 𝐂𝑓

Fog does not affect a fragment's alpha component.

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

𝐢ᵣ′′ = 𝐢ᵣ + (1 − ƒ) × 𝐢𝑓

Summary

specify fog parameters

See

glFog