Invert: A program to flip a DOOM level upside-down.

Author:	Rand Phares

Syntax: flip <filename>

	where <filename> is the name of the wad file, including the ".wad"
	extension

	flip requires that go32.exe be in your PATH (flip was built
	using djgpp).

Output:	Creates a new wad file called "tmp.wad", which can be used as is
	or retouched to take care of missing or incorrect elements

What this program does:

	- flips sectors upside-down, rotated about a point that is
	  midway between the highest ceiling and lowest floor in the level,
	  then adjusted to be a multiple of 8

	- exchanges floor and ceiling textures for all sectors

	- exchanges upper and lower textures for all linedefs that have
	  them

	- horizontally rotates all vertices about a midpoint between the
	  leftmost and rightmost vertices, after it's been adjusted to
	  be a multiple of 8

	- horizontally rotates all things about the same midpoint and
	  corrects their orientation

	- exchanges the vertices for all linedefs, thus changing their
	  "left/right" nature

What this program doesn't do:

	- turn lifts into doors and doors into lifts

	- worry about upper/lower texture pegging

	- worry about objects ("things") that make sense rightside-up,
	  but can't be flipped upside-down (i.e. torches)

	- make waterfalls flow up

	- turn textures upside-down

	- correct X- or Y-alignment that worked in the rightside-up version

	- make things that were standing on the floor stick to the
	  ceiling

	- worry about impassable 2-sided lines that no longer make sense
	  in the upside-down version (i.e. balcony railing)

	- the nukage is on the ceiling now, but you're walking underneath
	  it--on a nice safe ceiling texture--and still getting zapped

Tips on making a flipped wad look good:

	1. Well, you can always flip the level, then do all your texture
	   work in the flipped version.  Some textures make no sense 
	   upside-down (i.e. those with writing on them).  Otherwise
	   the rightside-up version should be designed with textures
	   that are vertically symmetrical, and which will still look
	   appropriate when painted on an upside-down wall.

	2. Try not to rely too much on X- and Y-alignment.  This may
	   affect your choice of textures.

	3. Objects that have to be stuck to the ceiling could be 
	   supported by invisible pillars.

	4. You should be able to get through doors, even though they're
	   upside-down now.  Or, provide an alternate way through the
	   wall where the door is.

	5. Railing that was marked impassable rightside-up might not need
	   to be impassable upside-down.  Hey, it's up there on the
	   ceiling now, right?  And you can walk under it.