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| Todo 
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6/10/98 -  problem with view culling when not looking forward.  Need to 
           generate the correct matrix and work it into the calculations.

6/10/98 -  terrain generation - add an option to try to iteratively change
           the error tolerance to try to generate "close" to a certain
           number of vertices so that we can have consistent size, rendering
           speed etc. among various terrain tiles.

6/10/98 -  Generate and store the transform matrix when rendering by
           material property so we don't have to push, transform, pop
           continually.  See mesa code for gluLookAt()

5/26/98 -  Add version checking to scenery files

4/25/98 -  Roll all of Time/sunpos.cxx into Astro/sun.cxx

4/21/98 -  Tweak lighting parameter interpolation tables to better fit
           "perceived" reality

4/21/98 -  Make sure all .hxx files have #ifndef cplusplus #error
           Make sure all #ifdef _FILE_H or _FILE_HXX

4/14/98 -  Convert gl__() calls in Cockpit/ to xgl__() calls

1/5/98 -   Create a development "roadmap"

12/29/97 - Add a mechanism to parse command line options
    * (done) A simple clear-screen sky.
    * (done) No fog.
    * No astronomy.
    * Less detailed terrain.
    * Texture - but no MIP-mapping.
    * Texture - but no bilinear blending.
    * (done) No texture.

12/29/97 - sky tweaking
  Steve Baker writes:
    So, by building the sky in the flattened shape, we can have it be
    very foggy at the horizon and clear blue overhead.

    The other important feature of this model is the colours. We
    colour each vertex of the dish individually to allow for cute
    sunsets, a darker blue overhead than at the horizon in daylight, a
    gradual darkening of the sky as a function of altitude for very
    high altitude flight - into space. Also we tint the horizon more
    in the direction of the sun so that sunset starts where the sun
    goes down - and the sky remains blue on the opposite side of the
    sky - then as the sun gets lower, the colour spreads outwards all
    around the sky and the black of night creeps in slowly from the
    opposite side of the sky from the sunset.

    We also like to tint the bottom edge of the sky with white - even
    in broad daylight - so it looks fuzzy - even when there is very
    little fog to achieve that effect.

    We use a text file that contains a lookup table relating the sun
    angle relative to the horizon to:

    *  The colour at the top of the sky dome,
    *  The colour of the horizon nearest to the sun
    *  The colour of the horizon farthest from the sun
    *  The colour of the texture environment blend for the clouds.
    *  The fog colour.

    We can then tweak that file to set up all the conditions. The
    realtime system interpolates the horizon colours all around the edge
    of the sky.

12/29/97 - Ground collision detection

12/29/97 - glut windows or something for panel area - consider 3d
           panels, careful of texture memory problems.