glLight

NAME

C SPECIFICATION

void glLightf(GLenum light,
              GLenum pname,
              GLfloat param)
void glLighti(GLenum light,
              GLenum pname,
              GLint param)

PARAMETERS

light

Specifies a light. The number of lights is depends on the implementation, but at least eight lights are supported. They are identified by symbolic names of the form GL_LIGHTi where 0 <= i < GL_MAX_LIGHTS.

pname

Specifies a single-valued light source parameter for light. GL_SPOT_EXPONENT, GL_SPOT_CUTOFF, GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, and GL_QUADRATIC_ATTENUATION are accepted.

param

Specifies the value that parameter pname of light source light will be set to.

C SPECIFICATION

void glLightfv(GLenum light,
               GLenum pname,
               const GLfloat *params)
void glLightiv(GLenum light,
               GLenum pname,
               const GLint *params)

PARAMETERS

light

Specifies a light. The number of lights is depends on the implementation, but at least eight lights are supported. They are identified by symbolic names of the form GL_LIGHTi where 0 <= i < GL_MAX_LIGHTS.

pname

Specifies a light source parameter for light. GL_AMBIENT, GL_DIFFUSE, GL_SPECULAR, GL_POSITION, GL_SPOT_DIRECTION, GL_SPOT_EXPONENT, GL_SPOT_CUTOFF, GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, and GL_QUADRATIC_ATTENUATION are accepted.

params

Specifies a pointer to the value or values that parameter pname of light source light will be set to.

DESCRIPTION

Lighting calculation is enabled and disabled using glEnable and glDisable with argument GL_LIGHTING. When lighting is enabled, light sources that are enabled contribute to the lighting calculation. Light source i is enabled and disabled using glEnable and glDisable with argument GL_LIGHTi.

The ten light parameters are as follows:

GL_AMBIENT

params contains four integer or floating-point values that specify the ambient RGBA intensity of the light. 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. Neither integer nor floating-point values are clamped. The default ambient light intensity is (0.0, 0.0, 0.0, 1.0).

GL_DIFFUSE

params contains four integer or floating-point values that specify the diffuse RGBA intensity of the light. 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. Neither integer nor floating-point values are clamped. The default diffuse intensity is (0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default diffuse intensity of light zero is (1.0, 1.0, 1.0, 1.0).

GL_SPECULAR

params contains four integer or floating-point values that specify the specular RGBA intensity of the light. 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. Neither integer nor floating-point values are clamped. The default specular intensity is (0.0, 0.0, 0.0, 1.0) for all lights other than light zero. The default specular intensity of light zero is (1.0, 1.0, 1.0, 1.0).

GL_POSITION

params contains four integer or floating-point values that specify the position of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped.

The position is transformed by the modelview matrix when glLight is called (just as if it were a point), and it is stored in eye coordinates. If the w component of the position is 0.0, the light is treated as a directional source. Diffuse and specular lighting calculations take the light's direction, but not its actual position, into account, and attenuation is disabled. Otherwise, diffuse and specular lighting calculations are based on the actual location of the light in eye coordinates, and attenuation is enabled. The default position is (0,0,1,0); thus, the default light source is directional, parallel to, and in the direction of the -z axis.

GL_SPOT_DIRECTION

params contains three integer or floating-point values that specify the direction of the light in homogeneous object coordinates. Both integer and floating-point values are mapped directly. Neither integer nor floating-point values are clamped.

The spot direction is transformed by the inverse of the modelview matrix when glLight is called (just as it it were a normal), and it is stored in eye coordinates. It is significant only when GL_SPOT_CUTOFF is not 180, which it is by default. The default direction is (0,0,-1).

GL_SPOT_EXPONENT

params is a single integer or floating-point value that specifies the intensity distribution of the light. Integer and floating-point values are mapped directly. Only values in the range [0, 128] are accepted.

Effective light intensity is attenuated by the cosine of the angle between the direction of the light and the direction from the light to the vertex being lighted, raised to the power of the spot exponent. Thus, higher spot exponents result in a more focused light source, regardless of the spot cutoff angle (see next paragraph). The default spot exponent is 0, resulting in uniform light distribution.

GL_SPOT_CUTOFF

params is a single integer or floating-point value that specifies the maximum spread angle of a light source. Integer and floating-point values are mapped directly. Only values in the range [0, 90], and the special value 180, are accepted. If the angle between the direction of the light and the direction from the light to the vertex being lighted is greater than the spot cutoff angle, the light is completely masked. Otherwise, its intensity is controlled by the spot exponent and the attenuation factors. The default spot cutoff is 180, resulting in uniform light distribution.

GL_CONSTANT_ATTENUATION

GL_LINEAR_ATTENUATION

GL_QUADRATIC_ATTENUATION

params is a single integer or floating-point value that specifies one of the three light attenuation factors. Integer and floating-point values are mapped directly. Only nonnegative values are accepted. If the light is positional, rather than directional, its intensity is attenuated by the reciprocal of the sum of: the constant factor, the linear factor times the distance between the light and the vertex being lighted, and the quadratic factor times the square of the same distance. The default attenuation factors are (1,0,0), resulting in no attenuation.

NOTES

ERRORS

GL_INVALID_VALUE is generated if a spot exponent value is specified outside the range [0, 180], or if spot cutoff is specified outside the range [0, 90] (except for the special value 180), or if a negative attenuation factor is specified.

GL_INVALID_OPERATION is generated if glLight is called between a call to glBegin and the corresponding call to glEnd.

ASSOCIATED GETS

SEE ALSO

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© 1995 Uwe Behrens. All rights reserved.