lzss.h File Reference

LZSS (LZ77) Decompression for SNES. More...

#include <snes/types.h>

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Functions
void	LzssDecodeVram (u8 *source, u16 address)
	Decompress LZ77 data directly to VRAM.

Detailed Description

LZSS (LZ77) Decompression for SNES.

Provides LZ77 decompression directly to VRAM. Used for compressed tile/tilemap data generated by gfx4snes or external LZ77 tools.

LZ77 Format

• Tag byte: 0x10
• 3-byte little-endian uncompressed data length
• Flag bytes: 8 bits each (1=reference, 0=literal)
• References: 12-bit distance, 4-bit length (min 3 bytes)

Usage

extern u8 compressed_tiles[], compressed_tiles_end[];
 
// Decompress to VRAM during force blank
REG_INIDISP = 0x80;  // Force blank (required for VRAM writes)
LzssDecodeVram(compressed_tiles, 0x0000);
REG_INIDISP = 0x0F;  // Screen on, full brightness

Warning

VRAM writes must happen during VBlank or force blank. LzssDecodeVram disables interrupts internally, so call it during force blank for safety.

Author

OpenSNES Team (ported from PVSnesLib by Alekmaul)

Copyright

zlib License

Function Documentation

LzssDecodeVram()

void LzssDecodeVram	(	u8 *	source,
		u16	address
	)

Decompress LZ77 data directly to VRAM.

Reads LZ77-compressed data from ROM/RAM and writes decompressed output directly to VRAM via PPU registers. Disables interrupts during decompression to prevent NMI handler from interfering.

Parameters

source	Pointer to LZ77-compressed data (tag byte 0x10)
address	VRAM word address to write decompressed data

Note

The source data must start with the LZ77 tag byte (0x10). If the tag doesn't match, the function returns immediately.

Interrupts are disabled during decompression and restored after.