Simulation of the Sky
SilverLining™ also provides a visual simulation of the sky itself.
This is no simple gradient of blue drawn in the background - this
is based on a real-time physical simulation that starts with NASA
data of the solar spectrum, astronomical computations of the solar
position relative to the local horizon, and simulates the scattering
of this light through the Earth's atmosphere as it makes its way through
the molecules and particles of the air.
This
is done using a highly accurate clear-sky model developed by the National
Renewable Energy Laboratory adapted for real-time use, in conjuction
with previously published work on sky luminance distribution.
The
result: accurate skies for any time of day, for any location on the
planet. Sunsets and sunrises with red horizons. Illuminated full-moon
nights. Long shadows in the winter. It all adds up to increased realism
for your outdoor scenes.
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How do we do all this computation in real-time? Much of the calculation
is offloaded to your 3D graphics card using custom shaders written
to compute the sky color at any given direction in the sky. This allows
SilverLining™ to continue its calculations while the sky is
simulated in parallel using the processor on your video card.
There
are more things in the sky than just the sun. SilverLining™ also accurately
computes positions of visible stars and planets for nighttime scenes,
and renders them accurately according to their stellar magnitude.
The
moon also acts as a light source in SilverLining™ , and its position
and phase is simulated and affects your outdoor scenes as well. On
dark nights, especially bright planets or stars are also subjected
to a physically-based glare simulation, which is also offloaded to
your graphics card as a shader.
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