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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