HP b2600 Reference Manual page 252

L
glLight
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 coordinates. 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-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 attenuation factors
are (1, 0, 0), resulting in no attenuation.
Notes
It is always the case that GL_LIGHTi = GL_LIGHT0 + i.
Errors
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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 specified.
GL_INVALID_OPERATION is generated if glLight is executed between the
execution of glBegin and the corresponding execution of glEnd.
Chapter 10