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                 *** Tempest's BUILD Tutorial ***
                  Lesson 10 : Making sky windows
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Purpose:
   A Tutorial on making sky windows in Duke Nukem 3D using Build.
   What the hell are sky windows? A sky windows is a window where
   you can see a parallaxed sky texture outside. A sky window makes
   a level less claustrophobic and gives the player a feeling of 
   being 'somewhere'. The same effect can be used to construct low
   perimeter walls. That is, if you have a level with a sky texture
   and a huge building in the middle, then you also have perimeter
   walls as tall as the tallest 'building' in your level. This can
   sometimes look awful or less realistic. Using the sky window
   technique you can construct perimeter walls that look much shorter.
   But let's concentrate on making a sky window first.   

Step 1:
   Construct a base for your window. Please refer to the example map
   for a visual explanation. I have color coded the walls of the 
   window so that you can see things more clearer. The sector which
   represents the 'window sill' will be called the 'blue sector'
   because the walls of that sector have a blue texture (doh!).

Step 2:
   Split the base sector into three sectors, a blue, red and brown
   sector. The blue sector will be the window sill; the red and brown
   sectors are needed for the sky texture effect. Give the ceiling
   of the red and brown sector a parallax sky texture. You also need 
   to give the floor of the brown sector a parallax sky texture.

Step 3:
   Bring the ceiling of the brown sector all the way down to its
   floor. Look at the window. Cool eh? Notice the you can see the
   side walls of the red sector sticking out. We have to hide those
   protruding walls.

Step 4:
   Make the line separating the blue and the red sector blockable
   (hit 'B' in 2D-mode) and hittable (hit 'Ctrl-H' also in 2D-mode).
   What this does is stop the player from moving 'through' the window.
   Making the line hittable also means that bullets are stopped when 
   they hit the window, otherwise they'll go through into the red and 
   brown sectors and explode at the end of the brown sector.
   Effectively you have a window with 'unbreakable glass' even though
   there is no glass! I hope you still know what I mean :-) If you
   think this might look odd, try masking the wall (the one between 
   the blue and red sector) and giving it the forcefield texture 
   (sprite #663). We still have to hide the protruding red walls. Move
   the vertices of the red sector closer to the blue sector. Refer
   to the example map to see what I mean.

Step 5:
   You can move the line between the red and brown sector, and place
   it right on top the line between the blue and red sector, to hide
   the red walls. Look closely at the map and move the vertices around
   to see what I mean. What we have done is make the red sector thinner
   and thinner, until it is only as thick as a line! The red sector
   has 'disappeared'!!! We know have a window that looks out into 
   parallax sky. Now, wasn't that easy?

Step 6:
   Low perimeter walls are easy. Just make the ceiling of the blue
   sector as high as the inner sector, and give it a parallax sky
   texture. That's it!!!

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 Cho Yan Wong (aka Tempest)
 pwong@pobox.leidenuniv.nl
 http://www.wi.leidenuniv.nl/~cwong/myindex.html 
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