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GLFOG() GLFOG() NAME glFogf, glFogi, glFogfv, glFogiv - specify fog parameters C SPECIFICATION void glFogf( GLenum pname, GLfloat param ) void glFogi( GLenum pname, GLint param ) delim $$ 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. C SPECIFICATION void glFogfv( GLenum pname, const GLfloat *params ) void glFogiv( GLenum pname, const GLint *params ) PARAMETERS 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 ac- cepted. params Specifies the value or values to be assigned to pname. GL_FOG_COLOR requires an array of four values. All other para- meters accept an array containing only a single value. DESCRIPTION Fog is initially disabled. While enabled, fog affects rasterized geom- etry, 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 speci- fied 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 con- stants are accepted: GL_LINEAR, GL_EXP, and GL_EXP2. The equations corresponding to these sym- bolic 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 $i sub f$, the fog color index. The initial fog index is 0. GL_FOG_COLOR params contains four integer or floating-point val- ues that specify $C sub f$, the fog color. Integer values are mapped linearly such that the most posi- tive representable value maps to 1.0, and the most negative representable value maps to -1.0. Float- ing-point values are mapped directly. After con- version, 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 posttex- turing 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 f ~=~ {end ~-~ z} over {end ~-~ start} The equation for GL_EXP fog is f ~=~ e ** (-(density ~cdot~ z)) The equation for GL_EXP2 fog is f ~=~ e ** (-(density ~cdot~ 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 $C sub r$ is replaced by {C sub r} prime ~=~ f C sub r + (1 - f) C sub f In color index mode, the fragment's color index $i sub r$ is replaced by {i sub r} prime ~=~ i sub r + (1 - f) i sub 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 exe- cution of glBegin and the corresponding execution of glEnd. ASSOCIATED GETS glIsEnabled with argument GL_FOG 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 SEE ALSO glEnable GLFOG()
NAME | C SPECIFICATION | PARAMETERS | C SPECIFICATION | PARAMETERS | DESCRIPTION | ERRORS | ASSOCIATED GETS | SEE ALSO
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