188 lines
6.4 KiB
Plaintext
188 lines
6.4 KiB
Plaintext
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'\" te
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'\"! tbl|eqn | mmdoc
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'\"macro stdmacro
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.ds Vn Version 1.2
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.ds Dt 24 September 1999
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.ds Re Release 1.2.1
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.ds Dp Jan 14 18:30
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.ds Dm 01 getlight.
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.ds Xs 45912 8 getlight.gl
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.TH GLGETLIGHT 3G
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.SH NAME
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.B "glGetLightfv, glGetLightiv
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\- return light source parameter values
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.SH C SPECIFICATION
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void \f3glGetLightfv\fP(
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GLenum \fIlight\fP,
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.nf
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.ta \w'\f3void \fPglGetLightfv( 'u
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GLenum \fIpname\fP,
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GLfloat \fI*params\fP )
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.fi
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void \f3glGetLightiv\fP(
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GLenum \fIlight\fP,
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.nf
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.ta \w'\f3void \fPglGetLightiv( 'u
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GLenum \fIpname\fP,
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GLint \fI*params\fP )
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.fi
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.EQ
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delim $$
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.EN
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.SH PARAMETERS
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.TP \w'\fIparams\fP\ \ 'u
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\f2light\fP
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Specifies a light source.
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The number of possible lights depends on the implementation,
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but at least eight lights are supported.
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They are identified by symbolic names of the form \%\f3GL_LIGHT\fP$i$
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where 0 \(<= $ i $ < \%\f3GL_MAX_LIGHTS\fP.
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.TP
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\f2pname\fP
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Specifies a light source parameter for \f2light\fP.
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Accepted symbolic names are
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\%\f3GL_AMBIENT\fP,
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\%\f3GL_DIFFUSE\fP,
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\%\f3GL_SPECULAR\fP,
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\%\f3GL_POSITION\fP,
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\%\f3GL_SPOT_DIRECTION\fP,
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\%\f3GL_SPOT_EXPONENT\fP,
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\%\f3GL_SPOT_CUTOFF\fP,
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\%\f3GL_CONSTANT_ATTENUATION\fP,
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\%\f3GL_LINEAR_ATTENUATION\fP, and
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\%\f3GL_QUADRATIC_ATTENUATION\fP.
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.TP
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\f2params\fP
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Returns the requested data.
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.SH DESCRIPTION
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\%\f3glGetLight\fP returns in \f2params\fP the value or values of a light source parameter.
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\f2light\fP names the light and is a symbolic name of the form \%\f3GL_LIGHT\fP$i$
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for 0 \(<= $i$ < \%\f3GL_MAX_LIGHTS\fP,
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where \%\f3GL_MAX_LIGHTS\fP is an implementation dependent constant that is
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greater than or equal to eight.
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\f2pname\fP specifies one of ten light source parameters,
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again by symbolic name.
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.P
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The following parameters are defined:
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.TP 20
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\%\f3GL_AMBIENT\fP
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\f2params\fP returns four integer or floating-point values representing the
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ambient intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and \-1.0 maps to the most negative representable integer value.
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If the internal value is outside the range [\-1, 1],
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the corresponding integer return value is undefined. The initial value is
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(0, 0, 0, 1).
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.TP
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\%\f3GL_DIFFUSE\fP
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\f2params\fP returns four integer or floating-point values representing the
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diffuse intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and \-1.0 maps to the most negative representable integer value.
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If the internal value is outside the range [\-1, 1],
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the corresponding integer return value is undefined. The initial value
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for \%\f3GL_LIGHT0\fP is (1, 1, 1, 1); for other lights, the
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initial value is (0, 0, 0, 0).
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.TP
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\%\f3GL_SPECULAR\fP
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\f2params\fP returns four integer or floating-point values representing the
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specular intensity of the light source.
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Integer values,
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when requested,
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are linearly mapped from the internal floating-point representation
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such that 1.0 maps to the most positive representable integer value,
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and \-1.0 maps to the most negative representable integer value.
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If the internal value is outside the range [\-1, 1],
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the corresponding integer return value is undefined. The initial value
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for \%\f3GL_LIGHT0\fP is (1, 1, 1, 1); for other lights, the
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initial value is (0, 0, 0, 0).
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.TP
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\%\f3GL_POSITION\fP
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\f2params\fP returns four integer or floating-point values representing the
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position of the light source.
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Integer values,
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when requested,
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are computed by rounding the internal floating-point values to the
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nearest integer value.
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The returned values are those maintained in eye coordinates.
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They will not be equal to the values specified using \%\f3glLight\fP,
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unless the modelview matrix was identity at the time \%\f3glLight\fP was
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called. The initial value is (0, 0, 1, 0).
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.TP
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\%\f3GL_SPOT_DIRECTION\fP
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\f2params\fP returns three integer or floating-point values representing the
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direction of the light source.
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Integer values,
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when requested,
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are computed by rounding the internal floating-point values to the
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nearest integer value.
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The returned values are those maintained in eye coordinates.
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They will not be equal to the values specified using \%\f3glLight\fP,
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unless the modelview matrix was identity at the time \%\f3glLight\fP was called.
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Although spot direction is normalized before being used in the lighting
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equation,
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the returned values are the transformed versions of the specified values
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prior to normalization. The initial value is (0, 0, \-1).
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.TP
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\%\f3GL_SPOT_EXPONENT\fP
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\f2params\fP returns a single integer or floating-point value representing the
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spot exponent of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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.TP
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\%\f3GL_SPOT_CUTOFF\fP
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\f2params\fP returns a single integer or floating-point value representing the
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spot cutoff angle of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 180.
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.TP
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\%\f3GL_CONSTANT_ATTENUATION\fP
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\f2params\fP returns a single integer or floating-point value representing the
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constant (not distance-related) attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 1.
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.TP
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\%\f3GL_LINEAR_ATTENUATION \fP
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\f2params\fP returns a single integer or floating-point value representing the
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linear attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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.TP
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\%\f3GL_QUADRATIC_ATTENUATION\fP
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\f2params\fP returns a single integer or floating-point value representing the
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quadratic attenuation of the light.
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An integer value,
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when requested,
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is computed by rounding the internal floating-point representation to
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the nearest integer. The initial value is 0.
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.SH NOTES
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It is always the case that \%\f3GL_LIGHT\fP$i$ = \%\f3GL_LIGHT0\fP + $i$.
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.P
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If an error is generated,
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no change is made to the contents of \f2params\fP.
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.SH ERRORS
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\%\f3GL_INVALID_ENUM\fP is generated if \f2light\fP or \f2pname\fP is not an
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accepted value.
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.P
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\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glGetLight\fP
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is executed between the execution of \%\f3glBegin\fP
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and the corresponding execution of \%\f3glEnd\fP.
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.SH SEE ALSO
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\%\f3glLight(3G)\fP
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