The Last Express BG

BG

Format type: Image
Endianness: Little-endian

Format Specifications

uint32 {4} - position on screen?

uint32 {4}   - position on screen?
uint32 {4}   - image width
uint32 {4}   - image height
uint32 {4}   - red colour channel data size
uint32 {4}   - blue colour channel data size
uint32 {4}   - green colour channel data size
byte {x}     - red colour channel data
byte {x}     - green colour channel data

byte {x} - blue colour channel data

Notes and Comments

BG files usually contain the game's background images. The three single colour channels (red, green and blue; also note the switched order of the header size values) have been compressed separately by a custom scheme. To decompress such a channel, the following method may be used:

while InPos < InSize do
begin
  if InBuffer[InPos] < 0x80 then
  begin
    // direct decompression
    Len := InBuffer[InPos] shr 5 + 1;
    Data := InBuffer[InPos] shl 3;
    InPos++;
    Copy Data byte Len times into OutBuffer while increasing OutPos.
  end
  else
  begin
    // buffer back reference, 4096 byte window
    take InBuffer[InPos] and the following value as a big endian uint16 OfsLen
    while zeroing the first bit
    Len := OfsLen shr 12 + 3;
    HisPos := OutPos - 4096 + (OfsLen and 0x0fff);
    InPos += 2;
    copy Len many bytes from HisPos onwards to OutPos, increasing both
  end
end;