View source for Image Formats (Apocalypse)

{{tocright}}Image file formats used by [[Apocalypse|X-COM: Apocalypse]].

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=PCK=
An advancement on the version used by [[Image_Formats#PCK|the previous games]], which can now use a variety of different compression methods on different sprites within the same image archive.

Most images are about 48x64 (the bounds of a single tile), but the format leaves itself open to much larger dimensions (for example, the giant [[Megaspawn]]s aren't split up into multiple "tiles" like the large units in the previous games (such as the [[Cyberdisc]]s) - they nearly double the average sprite dimensions as a result).

As before, the image data indexes into an palette consisting of 256 colours. There is a unique palette stored for every terrain, but they're mostly similar (after all, your units need to look the same regardless of where you send them).

==TAB==
Each PCK file is again accompanied by a TAB file. The TAB file contains a 32bit integer (4 bytes, little endian) per image. This value needs to be multipled by 4 to get the file offset in the PCK of the image header.

==Image Header==
The first twelve bytes of each image in the PCK are a header:

{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0
!0x00
|Compression mode. If 0, stop reading, there's no image to load and even the header won't be complete.
|- valign="top"
!1-3
!0x01-0x03
|Unknown, usually blank (unless the compression mode is 128).
|- valign="top"
!4-5
!0x04-0x05
|Left-most pixel within the sprite. No data should be rendered further left of this point.
|- valign="top"
!6-7
!0x08-0x09
|Right-most pixel within the sprite. No data should be rendered at this point or further.
|- valign="top"
!8-9
!0x08-0x09
|Top-most pixel within the sprite. No data should be rendered higher above this point.
|- valign="top"
!10-11
!0x0A-0x0B
|Bottom-most pixel within the sprite. No data should be rendered at this point or lower.
|-
|}

Width = Right-Most pixel - Left-ost pixel
Height = Bottom-Most pixel - Top-Most pixel

The image data then proceeds according to the compression mode used by the sprite.


==Compression mode: 0==
No image, don't render anything.


==Compression mode: 1==
[http://en.wikipedia.org/wiki/Run-length_encoding RLE compression], but opaque pixels aren't compressed at all. The concept is fairly similar to that of the old PCK format (though it's been expanded out a bit). Keep reading & rendering records according to this pattern:

{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0-3
!0x00-0x03
|Amount of pixels to skip from co-ordinate (0, 0). If this is 0xFF FF FF FF, then stop rendering, you've hit the end of the sprite.
You can calculate the Y co-ordinate for your row by taking the integer value of this divided by 640 (rounding down).
To make the Y co-ordinate relative to the individual sprite, you can subtract the "Top-Most pixel" from the header.
|- valign="top"
!4
!0x04
|Quick access to the X co-ordinate (so you don't have to calculate the modulus of the pixels to skip).
To make the X co-ordinate relative to the individual sprite, you can subtract the "Left-Most pixel" from the header.
|- valign="top"
!5
!0x05
|The amount of pixels this record contains.
|- valign="top"
!6
!0x06
|Always 0 (Assuming "Left Padding")
|- valign="top"
!7
!0x07
|Right Padding. This is the number of pixels in the row you don't need to draw.
Pixels To Draw = (Amount Of Pixels) - (Right Padding)
|- valign="top"
!8 ...
!0x08 ...
|From this point, read the amount of pixels specified by index 5 and render then left to right on the display. Palette Index 0 is transparent
|-
|}


==Compression mode: 2==
Uncommon, not entirely certain it's used at all...


==Compression mode: 3==
I guess you could describe this as [http://en.wikipedia.org/wiki/LZ77_and_LZ78 LZ77 compression]. Start out by loading the contents of TacData\XCOM.BLK into RAM - this contains all the actual pixel data used by sprites via this mode. Keep reading & rendering records according to the below pattern.

If a given record starts with 0xFF FF FF FF, then stop rendering, you've hit the end of the sprite.

{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0
!0x00
|The amount of sub-records to render on this row.
|- valign="top"
!1
!0x01
|Usually, this is 128 minus the amount of pixels drawn by the ''first'' sub-record rendered on the ''previous'' row. I'm not strictly sure what this means or why it's there.
|- valign="top"
!2
!0x02
|''Unknown''
|- valign="top"
!3
!0x03
|The row this record is to be rendered on.
|- valign="top"
!4
!0x04
|Sub-records. Read & render however many index 0 specified, on the current row:
{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0
!0x00
|Column to start rendering, relative to where the last sub-record finished (or relative to column 0, if this is the first sub-record on the row).
|- valign="top"
!1
!0x01
|Amount of pixels to render.
|- valign="top"
!2-4
!0x02-0x04
|A three byte value that indexes into TacData\XCOM.BLK. Starting from this location, read however many bytes index 1 specified and render them left-to-right on the display.
|-
|}
|-
|}

==Shadow sprites==
These files contain a transparent 'dither' mask to render shadows etc.
NOTE - These files do not seem to have the same first two bytes so that cannot be used solely to decide which 'compression format' each file is encoded with - for example 'tacdata/aliens/alien/poppers.pck (popper shadows) is this format with the first two bytes as '0x00 0x6e'. Which files are in this format may be 'baked in' to the executable, or it's a 'none of the above' clause.

It starts with an 8 byte header
{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0
!0x00
|Compression format header (Always seems to be either '0x0' or '0x80')
|- valign="top"
!1
!0x01
|Unknown - multiple different values seen
|- valign="top"
!2-3
!0x02-0x03
|Unknown - always seems to be zero?
|- valign="top"
!4-5
!0x04-0x05
|Width of the sprite
|- valign="top"
!6-7
!0x06-0x07
|Height of the sprite
|- valign="top"
|}

Following this are a number of 2-byte pairs implementing a RLE-like encoding, encoding pixels as a lookup into a 4 pixel wide lookup table of if each pixel is occluded or not
{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0
!0x00
|Repeat count - the number of repeated 4-pixel units - if 0xFF (255) stop as you've reached the end of the image.
|- valign="top"
!1
!0x01
|Index into a 7-entry lookup table for 4-pixel values
|- valign="top"
|}

The stride of these images always seems to be 640 pixels (140 4-pixel units) - IE each row contains 640 total pixel values, but only the width specified in the header are actually drawn.

The lookup table looks like this:
{| class="wikitable"
|-
!Index<br>(Decimal)
!Pixel value (0 = transparent, 1 = opaque)
|- valign="top"
!0
|0 0 0 0 (All transparent)
|- valign="top"
!1
|1 0 1 0
|- valign="top"
!2
|0 1 0 1
|- valign="top"
!3
|1 0 0 0
|- valign="top"
!4
| 0 1 0 0
|- valign="top"
!5
|0 0 1 0
|- valign="top"
!6
|0 0 0 1
|- valign="top"
|}

I do not know where the colour for the pixel is selected, maybe always black?

==Strategic map tiles==
These images are always 8x8 pixel format, they used to draw strategic maps:

{| class="wikitable"
|-
!Offset<br>(Decimal)
!Offset<br>(Hex)
!Usage
|- valign="top"
!0-2
!0x00-0x02
|Coordinate y. If this is 0xFF FF, then stop rendering, you've hit the end of the sprite.You can calculate the Y coordinate for your row by taking value divided by 640.
|- valign="top"
!2-4
!0x02-0x04
|The number of visible pixels in a row (the others are transparent).
|- valign="top"

!5...
!0x05 ...
|From this point, read the amount of pixels specified by 3 and 4 byte of header and render then left to right on the display. Palette Index 0 is transparent.
|-
|}

=PCX=
There are a number of images in PCX format, these are standard and most graphic packages can read them

=MOUSE.DAT=
This file contains 9 images with a resolution of 24 x 24 pixels, using 8bpp with a palette index

[[Category:Game Files]]
[[Category:Apocalypse]]