Sprites Format

This document describes the sprites format used by the Wasteland 1 files IC0_9.WLF and MASKS.WLF.

It covers:

• the top-level file layout
• the relationship between the image file and the mask file
• the per-sprite record layout
• the planar pixel encoding
• the transparency mask encoding

Scope

Sprites are stored in two separate files:

• IC0_9.WLF contains the 4-bit sprite image data
• MASKS.WLF contains the 1-bit transparency masks

Each sprite is:

• width: 16 pixels
• height: 16 pixels

There is no header, no compression wrapper, and no per-sprite metadata in either file.

File Layout

Both files are simple concatenations of fixed-size sprite records until EOF.

IC0_9.WLF

IC0_9.WLF stores one image record per sprite:

• bytes per sprite image: 128
• sprite count: fileSize / 128

MASKS.WLF

MASKS.WLF stores one transparency-mask record per sprite:

• bytes per sprite mask: 32
• sprite count: fileSize / 32

For a valid sprite set, both files must contain the same number of sprite records.

In the shipped Wasteland 1 data:

• IC0_9.WLF is 1280 bytes, so it contains 10 sprite images
• MASKS.WLF is 320 bytes, so it contains 10 sprite masks

Sprite Pairing

Sprite n is formed by combining:

• image record n from IC0_9.WLF
• mask record n from MASKS.WLF

The record offsets are:

imageOffset = n * 128
maskOffset  = n * 32
Copy

Image Record Layout

Each sprite image record is 128 bytes long and consists of four 1-bit planes of 32 bytes each:

Offset	Size	Meaning
+0x00	32	Bitplane 0: blue bit
+0x20	32	Bitplane 1: green bit
+0x40	32	Bitplane 2: red bit
+0x60	32	Bitplane 3: intensity bit

Each plane stores a 16x16 bitmap:

• 16 rows
• 2 bytes per row
• 8 pixels per byte
• bits are read most-significant-bit first within each byte

So one plane uses:

16 rows * 2 bytes = 32 bytes
Copy

Mask Record Layout

Each sprite mask record is 32 bytes long and consists of a single 1-bit plane with the same geometry:

• 16 rows
• 2 bytes per row
• 8 pixels per byte
• bits are read most-significant-bit first within each byte

Mask bit meaning:

• 1 = transparent pixel
• 0 = visible pixel

Pixel Addressing

For a pixel at coordinates (x, y):

byteIndex = y * 2 + floor(x / 8)
bitIndex  = 7 - (x % 8)
Copy

So each row is stored in two bytes:

• byte 0 covers pixels 0..7
• byte 1 covers pixels 8..15

Within each byte, the leftmost pixel is stored in bit 7 and the rightmost in bit 0.

Color Decoding

If the mask bit at (x, y) is 1, the pixel is transparent and the color planes are ignored.

Otherwise the 4-bit palette index is built from the four image bitplanes:

blue      = bit from plane 0
green     = bit from plane 1
red       = bit from plane 2
intensity = bit from plane 3
Copy

Combined as:

colorIndex =
    (blue      << 0) |
    (green     << 1) |
    (red       << 2) |
    (intensity << 3)
Copy

This yields a 4-bit color value in the range 0..15.

Decoding Summary

To decode sprite n:

1. Read 128 bytes from IC0_9.WLF at n * 128.
2. Read 32 bytes from MASKS.WLF at n * 32.
3. For each pixel (x, y), compute the byte and bit position within the row.
4. If the mask bit is 1, output transparency.
5. Otherwise read the corresponding bit from each of the four image planes.
6. Combine those bits into the 4-bit palette index.

Validation Notes

Useful consistency checks when implementing a reader:

• IC0_9.WLF size should be a multiple of 128
• MASKS.WLF size should be a multiple of 32
• both files must contain the same number of records
• each image record must be exactly 128 bytes
• each mask record must be exactly 32 bytes