glFog

C Specification

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

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

param

Specifies the value that pname will be set to.

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

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).

f = (end z ) / (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 color C_r is replaced by

C_r' = f C_r + (1 f ) C_f

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

See Also