PANL LFD Resource Type
Author: Jagged Fel (jaggedfel621@gmail.com)
Site: http://idmr.empirereborn.net
Updated: 2009.10.05
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The PANL resource is image data found primarily in cockpit LFD files. These
files do not contain RMAPs, although are comprised of a PANL, MASK and PLTT.
The PANL is an indexed image detailing the opaque areas of the cockpit and
instruments.

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PANL Structure

The following values are used through this and all of my file definitions
unless otherwise specified:
NAME	LENGTH	DESC
----	------	----
BYTE	1	unsigned 8-bit
CHAR	1	ASCII character
INT	4	signed Int32

--
Header
Row[]
BYTE	EndImage (0xFF)
--

struct Header (size 0x10)
{
	0x0	CHAR[4]	"PANL"
	0x4	CHAR[8]	Name
	0x8	INT	Length
}

struct Row
{
	OpCode[]
	BYTE	EndRow (0xFE)
}

strcut OpCode
{
	BYTE	Value
	#if (Value==0xFC) (Repeat2)
	BYTE	ColorIndex
	BYTE	NumRepeat
	#elseif (Value==0xFD) (Repeat)
	BYTE	NumRepeat
	BYTE	ColorIndex
	#else (Short)
	#endif
}

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PANL Details

Unlike most image resources found in the LFDs, PANL does not have a Width and
Height defined in the resource itself. Presumably the image sizes if explicitly
defined are in the executable, since there are two resolutions that can be
used. The sizes can be determined computationally, and is much more reliable
than MASK size derivations.

There are three types of OpCodes that are relevant to pixel data. The first is
the main Repeat code, FD. Following the Repeat op code, two bytes are required;
the NumRepeat of pixels (number of repeats, so 0B is 12px), and the ColorIndex
from the PLTT resource. Another OpCode immediately follows the Index value.

Now, in a certain form of brilliance that I have come to expect from LA/TG,
there is a second Repeat op code, FC. This works exactly the same as FD, but
instead the Index value comes before NumRepeat. There appears to be no special
reason for this, it's just an "ism" of the format.

The PLTTs of the cockpit LFDs use indexes 00-3F (b00111111), which allow for a
1-byte OP_CODE to be used for small (1-4) lengths of pixels. This Short code is
evaluated as ColorIndex << 2 + NumRepeat. Say you have 2px of Index 0x32. Then
the op code will be C9 (32<<2 = C8, + NumRepeat=1). 4px of Index 35 becomes D7
(35<<2 = D4, NumRepeat=3), and so on. There's never data loss in the shift
because the top two bits are never used for Index.

Note: because PANL uses FC-FF as OpCodes, it's advised to avoid using the
Short code for Index 3F. Affects of doing so are unknown.

At the end of every row is an EndRow op code, FE. After the final row, the
PANL is terminated with an EndImage op code, FF (stray bytes have been seen
after the EndImage code, but are ignored).

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