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                    Daggerfall SKY File Format
                         February 23, 2004

This is the format for the SKY##.DAT files that come with TES: 
Daggerfall. They contain the backdrop images and palettes used in 
the outdoor game environment.
					

  OVERALL SKY FORMAT
=======================================
The overall file is divided into three sections:

	Bytes      1 -   24832	Main palettes.
	Bytes  24833 -  549120	Fade-in lookup tables.
	Bytes 549121 - 7758080	Sky images.


  MAIN PALETTE SECTION
=======================================
The palette section consists of 32 records with the following format:

	Bytes  1 -   4	INT32	Record size (always 776).
	Bytes  5 -   8	INT32	Unknown (always 45347).
	Bytes  9 - 776	BYTES	256-color, 24-bit RGB palette.

Which record is used depends on what time it is in the game.

Only the first 32 colors in the palette vary from record to record.
Surprisingly, the palette's color channels have values ranging from
0 to 255, rather than the usual 0 to 63 of ordinary VGA palettes.


  OBJECT FADE-IN LOOKUP TABLES
=======================================
These lookup tables are used when "fading in" objects from beyond 
the edge of the player's visibility range. There are 32 sets (one 
for each palette) of 64 tables of 256 bytes each.

Rather than explain it in plain English, I am going to throw some 
heavily-commented pseudocode at you:

	for each visible surface do
	  Z = SomeFunctionOf(SurfacePos, PlayerSightRange)
	  /* Z = surface's distance from the edge of the 
	   * player's visibility range. Z of 0 means the 
	   * surface is right at the edge. Z of 63 means 
	   * the surface is not faded at all. */
	  for each pixel do
	    PixelColor = Shifted(PaletteNumber, Z, PixelColor)
	    /* Shifted(Set, Table, Color) effectively returns 
	     * the value of the byte at (zero-based) offset
	     * (24832 + (Set * 16384) + (Table * 256) + Color)
	     * in the current SKY##.DAT file. */
	  loop
	loop


  SKY IMAGES
=======================================
There are 64 images in the file. Each image is 512 by 220 pixels 
in size, and is stored in uncompressed 8-bit-per-pixel format. 
The images are divided into two sets:

	Images  0 - 31	Series with no sun.
	Images 32 - 63	Series with sun.

The images in each set are assigned one of the 32 palette records 
in ascending order (i.e., the first image in each set uses the first 
palette record, the second one uses the second palette, and so on).

Each image is used for only half the sky; initially, images from the 
first series (0-31) are assigned to the western sky, and image from 
the second (32-63) are used for the eastern sky. At noon, the set 
assignment is switched, and the sets are played backwards; this 
allows the effect of the sun rising in the east and setting in the 
west, without the need to store large images of the whole sky.


  CREDITS
=======================================

	Corroded Coder (corrodedcoder@hotmail.com)

	Gavin Clayton (interkarma@yahoo.com.au)
		http://www.svatopluk.com/interkarma/

	Sean Weinmann (andux@bigfoot.com)
		http://meepo.dnsalias.org/

Some credit should also be given to Dave Humphrey, as this document 
blatantly rips off his documentation style.