[Celestia-developers] Cloud shadows patch

[Chris L. <cl...@gm...>]

This is a minor patch that fixes bug 2097546 by adding a new atmosphere
property to control whether cloud shadows should be rendered on a planet:

http://www.shatters.net/~claurel/celestia/files/patches/cloudshadows/

(As usual, there's a patch file and a zip file with all the changed source
files (all in src/celengine))

This new property allows add-on creators to disable shadows for a planet.
The default value of CloudShadows is false, so that the ugly appearance of
certain existing cloud add-ons for gas giant planets is fixed. It is also
desirable to leave cloud shadows disabled for bodies with global
nearly-opaque cloud layers like Venus and Titan. While some attenuation of
light from clouds is realistic, rendering clouded planet surfaces as nearly
black is a bad idea (for the same reason that it's bad to drastically reduce
the lighting for Pluto and other bodies far from their sun.) Cloud shadows
can look good on Earth and Mars. There are also some Voyager 2 images
showing obvious cloud shadows on Neptune.

A sample usage:

    Atmosphere {
        CloudHeight 7
        CloudSpeed 65
        CloudMap "earth-clouds.*"
        CloudShadows true

        Mie 0.001
        MieAsymmetry -0.25
        Rayleigh [ 0.001 0.0025 0.006 ]
        MieScaleHeight 12
    }

--Chris