Dark Reign File Formats

This page documents the binary file formats used by the Dark Reign plugin (plugins/DarkReign/). These formats originate from the original 1997 Auran game and are documented here to help developers understand the loader code.

All multi-byte integers in these formats are little-endian.

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SPR Sprite Format (DRSprFormat.c)

SPR files contain palette-indexed, RLE-compressed sprite animation data. They come in two variants:

Magic	Type
"RSPR"	Normal (opaque) sprite
"SSPR"	Shadow sprite

Header (32 bytes)

Field	Type	Description
magic	char[4]	"RSPR" or "SSPR"
version	int32_t	Must be 0x0210
nanims	int32_t	Number of animation frames per rotation
nrots	int32_t	Number of rotations
szx	int32_t	Frame width (all frames share this size)
szy	int32_t	Frame height (all frames share this size)
npics	int32_t	Total number of compressed pictures
nsects	int32_t	Number of animation sections

Computed Offsets

No offsets are stored in the header — all are derived:

off_sections = 32 + 4 * nanims * nrots
off_anims    = off_sections + 16 * nsects
off_picoffs  = off_anims   + 4  * nanims
off_bits     = off_picoffs + 8  * npics + 4

Anim-Index Table (off = 32)

Immediately after the header: int32_t picnr[nanims * nrots]

Look up which compressed picture to display for animation frame a and rotation r:

picture_index = picnr[a * nrots + r]

Section Table (off = off_sections, 16 bytes × nsects)

Field	Type	Description
firstanim	int32_t	First animation index in this section
lastanim	int32_t	Last animation index (inclusive)
framerate	int32_t	Playback rate (stored but unused by the loader)
numhotspots	int32_t	Number of hotspot channels

Picture-Offset Table (off = off_picoffs)

npics + 1 entries of two int32_t values each:

Field	Description
picoff	Byte offset of compressed data from off_bits
hotoff	Hotspot table offset (ignored when numhotspots == 0)

The last entry is a sentinel, so the size of picture i is picoff[i+1] - picoff[i].

RLE Pixel Compression (off = off_bits)

Each picture is independently compressed, one scanline at a time. For each scanline:

1. Start with step = 0, currx = 0.
2. Read cnt = next_byte.
3. If step is odd: cnt &= 0x7F (clear the high bit).
4. Even step (0, 2, 4, …): transparent run — skip cnt pixels.
5. Odd step (1, 3, 5, …): opaque run of cnt pixels.
6. Normal sprite: copy cnt literal palette-index bytes from the stream.
7. Shadow sprite: fill cnt pixels with palette index 47 (shadow colour).
8. currx += cnt; step++.
9. Repeat until currx == szx.

Gotcha — sprite shadow index: Shadow sprites use palette index 47 for all opaque pixels. This index must map to a semi-transparent dark colour in the game palette; index 0 is always transparent.

Rotation Convention

Sprites face right at rotation 0 on disk. To align them with the conventional up direction, the loader shifts rotations by nrots / 4:

disk_rot = (display_rot + nrots / 4) % nrots   /* only applied when nrots >= 4 */

Texture Atlas Layout

All frames are packed into a horizontal strip in rotation-major, anim-minor order:

for each section:
  for r in [0, nrots):
    for a in [firstanim, lastanim]:
      place frame at x_cursor; x_cursor += szx

• atlas_width = total_frame_count × szx
• atlas_height = szy

Because all frames share the same szx × szy size, UV rectangles are uniform and computed without per-frame inspection.

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FTG Package Format (DRFtgPackage.c)

FTG is the archive format used by Dark Reign to bundle game assets. The format is documented in the drExplorer reference.

Header (12 bytes)

Field	Type	Description
identifier	uint32_t	Magic identifier bytes
directoryOffset	int32_t	Byte offset of the file directory
fileCount	int32_t	Number of files in the archive

Directory (at directoryOffset, 36 bytes × fileCount)

Field	Type	Description
name	char[28]	Null-terminated filename (up to 27 characters)
offset	int32_t	Byte offset of the file data
size	int32_t	Size of the file data in bytes

File data is stored uncompressed at the given offsets.

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FTG-bundled SPR Format (DRFtgPackage.c)

SPR files inside FTG archives use a simpler, uncompressed format than the standalone RSPR/SSPR sprites described above.

Header (8 bytes)

Field	Type	Description
num_frames	uint16_t	Total number of animation frames
max_width	uint16_t	Maximum frame width (informational, may be 0)
max_height	uint16_t	Maximum frame height (informational, may be 0)
reserved	uint16_t	Unused / padding

Per-Frame Descriptors (8 bytes × num_frames)

Field	Type	Description
width	uint16_t	Pixel width of this frame
height	uint16_t	Pixel height of this frame
offset_x	int16_t	Hotspot X — sprite origin is this many pixels to the right of top-left
offset_y	int16_t	Hotspot Y — sprite origin is this many pixels below top-left

Pixel Data

Immediately follows the descriptors: width × height bytes per frame (rows top-to-bottom), one byte per pixel (palette index). No compression.

Pixels are uploaded to the GPU as a GL_RED / kTextureFormatAlpha8 texture. The active palette (set via ViewEntity.palette) maps each index to a colour at render time.

FTG Texture Atlas Layout

Frames are packed into a horizontal strip:

• atlas_width = sum of all frame widths
• atlas_height = maximum frame height
• Frame i starts at x = sum of widths[0..i-1], y = 0.

Short frames are not padded; their UV rect height is set proportionally.