glGetLight Subroutine

OpenGL 1.1 for AIX: Reference Manual

glGetLight Subroutine

Purpose

Returns light source parameter values.

Library

OpenGL C bindings library: libGL.a

C Syntax

void glGetLightfv(GLenum Light,
                GLenum ParameterName, 
                GLfloat *ParameterValues)

void glGetLightiv(GLenum Light,
                GLenum ParameterName, 
                GLint *ParameterValues)

Parameters

Light	Specifies a light source. The number of possible lights depends on the implementation; however, at least eight lights are supported. They are identified by symbolic names of the form GL_LIGHTi where 0 < i < GL_MAX_LIGHTS.
ParameterName	Specifies a light source parameter for Light. Accepted symbolic names are 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.
ParameterValues	Returns the requested data.

Description

The glGetLight subroutine returns in ParameterValues the value or values of a light source parameter. Light names the light and is a symbolic name of the form GL_LIGHTi for 0 < i < GL_MAX_LIGHTS, where GL_MAX_LIGHTS is an implementation-dependent constant that is greater than or equal to 8. ParameterName specifies one of 10 light source parameters, again by symbolic name.

The parameters are:

GL_AMBIENT	ParameterValues returns four integer or floating-point values representing the ambient intensity of the light source. Integer values, when requested, are linearly mapped from the internal floating-point representation such that 1.0 maps to the most positive representable integer value, and -1.0 maps to the most negative representable integer value. If the internal value is outside the range [-1,1], the corresponding integer return value is undefined.
GL_DIFFUSE	ParameterValues returns four integer or floating-point values representing the diffuse intensity of the light source. Integer values, when requested, are linearly mapped from the internal floating-point representation such that 1.0 maps to the most positive representable integer value, and -1.0 maps to the most negative representable integer value. If the internal value is outside the range [-1,1], the corresponding integer return value is undefined.
GL_SPECULAR	ParameterValues returns four integer or floating-point values representing the specular intensity of the light source. Integer values, when requested, are linearly mapped from the internal floating-point representation such that 1.0 maps to the most positive representable integer value, and -1.0 maps to the most negative representable integer value. If the internal value is outside the range [-1,1], the corresponding integer return value is undefined.
GL_POSITION	ParameterValues returns four integer or floating-point values representing the position of the light source. Integer values, when requested, are computed by rounding the internal floating-point values to the nearest integer value. The returned values are those maintained in eye coordinates. They will not be equal to the values specified using glLight, unless the modelview matrix was identified at the time glLight was called.
GL_SPOT_DIRECTION	ParameterValues returns three integer or floating-point values representing the direction of the light source. Integer values, when requested, are computed by rounding the internal floating-point values to the nearest integer value. The returned values are those maintained in eye coordinates. They will not be equal to the values specified using glLight, unless the modelview matrix was identity at the time glLight was called. Although spot direction is normalized before being used in the lighting equation, the returned values are the transformed versions of the specified values prior to normalization.
GL_SPOT_EXPONENT	ParameterValues returns a single integer or floating-point value representing the spot exponent of the light. An integer value, when requested, is computed by rounding the internal floating-point representation to the nearest integer.
GL_SPOT_CUTOFF	ParameterValues returns a single integer or floating-point value representing the spot cutoff angle of the light. An integer value, when requested, is computed by rounding the internal floating-point representation to the nearest integer.
GL_CONSTANT_ATTENUATION	ParameterValues returns a single integer or floating-point value representing the constant (not distance related) attenuation of the light. An integer value, when requested, is computed by rounding the internal floating point representation to the nearest integer.
GL_LINEAR_ATTENUATION	ParameterValues returns a single integer or floating-point value representing the linear attenuation of the light. An integer value, when requested, is computed by rounding the internal floating-point representation to the nearest integer.
GL_QUADRATIC_ATTENUATION	ParameterValues returns a single integer or floating-point value representing the quadratic attenuation of the light. An integer value, when requested, is computed by rounding the internal floating-point representation to the nearest integer.

Notes

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

If an error is generated, no change is made to the contents of ParameterValues.

Errors

GL_INVALID_ENUM	Either Light or ParameterName is not an accepted value.
GL_INVALID_OPERATION	The glGetLight subroutine is called between a call to glBegin and the corresponding call to glEnd.

Files

/usr/include/GL/gl.h

Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.

Related Information

The glBegin or glEnd subroutine, glLight subroutine.

OpenGL Overview.