/*=============================================================================
  Unreal backdrops
  By: Tim Sweeney, Epic MegaGames, Inc.
=============================================================================*/

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Concept:
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Each Unreal level can have a unique backdrop, which includes the sky, sea,
sun, moon, and color scheme.  The backdrop appears through all polygons
in the level which are tagged "fake backdrop", which are usually ceilings
in areas which are meant to look like open areas.  

The properties of the backdrop are completely defined by the one LevelDescriptor
actor that exists in each level.  You can edit these properties by selecting
"Options" / "Level Properties" in UnrealEd.

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Backdrop composition:
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The backdrop consists of the following elements:

* A sky texture, a regular Unreal texture with palette that must ramp from
  0 (minimum brightness) to 255 (maximum brightness).  The palette will be altered
  on the fly, so it must conform to a simple ramp.

* A sky cloud overlay, a non-editable fractal field which scrolls independently,
  meant to look as if it exists beneath the sky texture.

* A sun or moon illumination object, which brightens the sky beneath it. 

* If specially scripted, lightning may affect the overall brightness of the sky.

* Polygons in the world tagged with "CloudCast" are shaded by the shadows of the
  clouds scrolling above.

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Temporal effects:
-----------------

As time passes:

* The sun and moon rise/fall according to the day/night cycle.
* The background palettes change continuously with time, to give the
  sky a different hue at different times.

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LevelDescriptor options:
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* Texture SkyTex: The sky texture, simple ramp palette.

* Texture SkyPal[4]:   Texture containing sky palette.
* Texture CloudPal[4]: Texture containing cloud palette.
  The index corresponds to: 0-day, 1-dusk, 2-night, 3-dawm

* SatelliteRadius[2]: Radius of satellite
* SatelliteBrightness[2]: Brightness of satellite
  Index corresponds to: 0-sun, 1-moon

* Lightning: Amount (0 - 255) to increase sky brightness by, animated
  under script control for lightning.

* SkySpeed:   Speed of sky scrolling (only X and Y matter)
* CloudSpeed: Speed of cloud scrolling

* Wavy: Wavyness of clouds and sky.
