MirOS Manual: glLight(3), glLightf(3), glLightfv(3), glLighti(3), glLightiv(3)


GLLIGHT(3G)         UNIX Programmer's Manual          GLLIGHT(3G)

NAME

     glLightf, glLighti, glLightfv, glLightiv - set light source
     parameters

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 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 depends on the
          implementation, but at least eight lights are sup-
          ported. 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_CUTOFF, GL_SPOT_DIRECTION, GL_SPOT_EXPONENT,
          GL_CONSTANT_ATTENUATION, GL_LINEAR_ATTENUATION, and
          GL_QUADRATIC_ATTENUATION are accepted.

     params

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

DESCRIPTION

     glLight sets the values of individual light source parame-
     ters. light names the light and is a symbolic name of the
     form GL_LIGHTi, where 0 ≤ i < GL_MAX_LIGHTS. pname specifies
     one of ten light source parameters, again by symbolic name.
     params is either a single value or a pointer to an array
     that contains the new values.

     To enable and disable lighting calculation, call glEnable
     and glDisable with argument GL_LIGHTING. Lighting is ini-
     tially disabled. When it 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 initial
                         ambient light intensity is (0, 0, 0, 1).

     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 initial
                         value for GL_LIGHT0 is (1, 1, 1, 1); for
                         other lights, the initial value is (0,
                         0, 0, 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

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                         representable value maps to -1.0.
                         Floating-point values are mapped
                         directly. Neither integer nor floating-
                         point values are clamped. The initial
                         value for GL_LIGHT0 is (1, 1, 1, 1); for
                         other lights, the initial value is (0,
                         0, 0, 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 com-
                         ponent of the position is 0, the light
                         is treated as a directional source. Dif-
                         fuse and specular lighting calculations
                         take the light's direction, but not its
                         actual position, into account, and
                         attenuation is disabled. Otherwise, dif-
                         fuse and specular lighting calculations
                         are based on the actual location of the
                         light in eye coordinates, and attenua-
                         tion is enabled. The initial position is
                         (0, 0, 1, 0); thus, the initial 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 if it were a
                         normal), and it is stored in eye coordi-
                         nates. It is significant only when
                         GL_SPOT_CUTOFF is not 180, which it is
                         initially. The initial direction is (0,
                         0, -1).

     GL_SPOT_EXPONENT    params is a single integer or floating-

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                         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
                         GL_SPOT_CUTOFF, next paragraph). The
                         initial 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 initial 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 initial

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                         attenuation factors are (1, 0, 0),
                         resulting in no attenuation.

NOTES

     It is always the case that GL_LIGHTi = GL_LIGHT0 + i.

ERRORS

     GL_INVALID_ENUM is generated if either light or pname is not
     an accepted value.

     GL_INVALID_VALUE is generated if a spot exponent value is
     specified outside the range [0,128], or if spot cutoff is
     specified outside the range [0,90] (except for the special
     value 180), or if a negative attenuation factor is speci-
     fied.

     GL_INVALID_OPERATION is generated if glLight is executed
     between the execution of glBegin and the corresponding exe-
     cution of glEnd.

ASSOCIATED GETS

     glGetLight
     glIsEnabled with argument GL_LIGHTING

SEE ALSO

     glColorMaterial(3G), glLightModel(3G), glMaterial(3G)

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