@node Constants
@chapter Constants

@file{<libred.h>} defines a number of symbolic constants
suitable for using a @code{#if} preprocessing directives.

@table @code
@item LIBRED_SOLAR_APPARENT_RADIUS
The approximate apparent size of the Sun in degrees.
This value should be about 0.5(3).

@item LIBRED_SOLAR_ELEVATION_SUNSET_SUNRISE
The Sun's elevation at sunset and sunrise, measured in
degrees. This value will always be 0.0.

@item LIBRED_SOLAR_ELEVATION_CIVIL_DUSK_DAWN
The Sun's elevation at civil dusk and civil dawn, measured
in degrees. This value will always be @math{-6.0}.

@item LIBRED_SOLAR_ELEVATION_NAUTICAL_DUSK_DAWN
The Sun's elevation at nautical dusk and nautical dawn,
measured in degrees. This value will always be @math{-12.0}.

@item LIBRED_SOLAR_ELEVATION_ASTRONOMICAL_DUSK_DAWN
The Sun's elevation at astronomical dusk and astronomical
dawn, measured in degrees. This value will always be @math{-18.0}.

@item LIBRED_HIGHEST_TEMPERATURE
The highest temperature, in kelvins, for which there is a
colour temperature in the table of colour temperature. Any
temperature above this is automatically truncated by
@code{libred_get_colour}, as higher values shall be
unnoticeable. Currently, this value is 40@tie{}000.

@item LIBRED_LOWEST_TEMPERATURE
The lowest temperature, in kelvins, for which there is a
colour temperature in the table of colour temperature. Any
temperature below this results in @code{libred_get_colour}
failing and setting @code{errno} to @code{EDOM}. Currently
this value 1000, hypothetical changes will be very small.

@item LIBRED_DELTA_TEMPERATURE
The temperatures differences between sequential colour
temperatures in the colour temperatures look up table.
Currently this value is 100.
@end table