ref: bbf2f51a02b2544f1bef32a5868503b474ae2fef
dir: /home/uncompress.asm/
; bankswitches and runs _UncompressSpriteData
; bank is given in a, sprite input stream is pointed to in wSpriteInputPtr
UncompressSpriteData::
ld b, a
ldh a, [hLoadedROMBank]
push af
ld a, b
ldh [hLoadedROMBank], a
ld [MBC1RomBank], a
ld a, SRAM_ENABLE
ld [MBC1SRamEnable], a
xor a
ld [MBC1SRamBank], a
call _UncompressSpriteData
pop af
ldh [hLoadedROMBank], a
ld [MBC1RomBank], a
ret
; initializes necessary data to load a sprite and runs UncompressSpriteDataLoop
_UncompressSpriteData::
ld hl, sSpriteBuffer1
ld c, LOW(2 * SPRITEBUFFERSIZE)
ld b, HIGH(2 * SPRITEBUFFERSIZE)
xor a
call FillMemory ; clear sprite buffer 1 and 2
ld a, $1
ld [wSpriteInputBitCounter], a
ld a, $3
ld [wSpriteOutputBitOffset], a
xor a
ld [wSpriteCurPosX], a
ld [wSpriteCurPosY], a
ld [wSpriteLoadFlags], a
call ReadNextInputByte ; first byte of input determines sprite width (high nybble) and height (low nybble) in tiles (8x8 pixels)
ld b, a
and $f
add a
add a
add a
ld [wSpriteHeight], a
ld a, b
swap a
and $f
add a
add a
add a
ld [wSpriteWidth], a
call ReadNextInputBit
ld [wSpriteLoadFlags], a ; initialite bit1 to 0 and bit0 to the first input bit
; this will load two chunks of data to sSpriteBuffer1 and sSpriteBuffer2
; bit 0 decides in which one the first chunk is placed
; fall through
; uncompresses a chunk from the sprite input data stream (pointed to at wd0da) into sSpriteBuffer1 or sSpriteBuffer2
; each chunk is a 1bpp sprite. A 2bpp sprite consist of two chunks which are merged afterwards
; note that this is an endless loop which is terminated during a call to MoveToNextBufferPosition by manipulating the stack
UncompressSpriteDataLoop::
ld hl, sSpriteBuffer1
ld a, [wSpriteLoadFlags]
bit 0, a
jr z, .useSpriteBuffer1 ; check which buffer to use
ld hl, sSpriteBuffer2
.useSpriteBuffer1
call StoreSpriteOutputPointer
ld a, [wSpriteLoadFlags]
bit 1, a
jr z, .startDecompression ; check if last iteration
call ReadNextInputBit ; if last chunk, read 1-2 bit unpacking mode
and a
jr z, .unpackingMode0 ; 0 -> mode 0
call ReadNextInputBit ; 1 0 -> mode 1
inc a ; 1 1 -> mode 2
.unpackingMode0
ld [wSpriteUnpackMode], a
.startDecompression
call ReadNextInputBit
and a
jr z, .readRLEncodedZeros ; if first bit is 0, the input starts with zeroes, otherwise with (non-zero) input
.readNextInput
call ReadNextInputBit
ld c, a
call ReadNextInputBit
sla c
or c ; read next two bits into c
and a
jr z, .readRLEncodedZeros ; 00 -> RLEncoded zeroes following
call WriteSpriteBitsToBuffer ; otherwise write input to output and repeat
call MoveToNextBufferPosition
jr .readNextInput
.readRLEncodedZeros
ld c, $0 ; number of zeroes it length encoded, the number
.countConsecutiveOnesLoop ; of consecutive ones determines the number of bits the number has
call ReadNextInputBit
and a
jr z, .countConsecutiveOnesFinished
inc c
jr .countConsecutiveOnesLoop
.countConsecutiveOnesFinished
ld a, c
add a
ld hl, LengthEncodingOffsetList
add l
ld l, a
jr nc, .noCarry
inc h
.noCarry
ld a, [hli] ; read offset that is added to the number later on
ld e, a ; adding an offset of 2^length - 1 makes every integer uniquely
ld d, [hl] ; representable in the length encoding and saves bits
push de
inc c
ld e, $0
ld d, e
.readNumberOfZerosLoop ; reads the next c+1 bits of input
call ReadNextInputBit
or e
ld e, a
dec c
jr z, .readNumberOfZerosDone
sla e
rl d
jr .readNumberOfZerosLoop
.readNumberOfZerosDone
pop hl ; add the offset
add hl, de
ld e, l
ld d, h
.writeZerosLoop
ld b, e
xor a ; write 00 to buffer
call WriteSpriteBitsToBuffer
ld e, b
call MoveToNextBufferPosition
dec de
ld a, d
and a
jr nz, .continueLoop
ld a, e
and a
.continueLoop
jr nz, .writeZerosLoop
jr .readNextInput
; moves output pointer to next position
; also cancels the calling function if the all output is done (by removing the return pointer from stack)
; and calls postprocessing functions according to the unpack mode
MoveToNextBufferPosition::
ld a, [wSpriteHeight]
ld b, a
ld a, [wSpriteCurPosY]
inc a
cp b
jr z, .curColumnDone
ld [wSpriteCurPosY], a
ld a, [wSpriteOutputPtr]
inc a
ld [wSpriteOutputPtr], a
ret nz
ld a, [wSpriteOutputPtr+1]
inc a
ld [wSpriteOutputPtr+1], a
ret
.curColumnDone
xor a
ld [wSpriteCurPosY], a
ld a, [wSpriteOutputBitOffset]
and a
jr z, .bitOffsetsDone
dec a
ld [wSpriteOutputBitOffset], a
ld hl, wSpriteOutputPtrCached
ld a, [hli]
ld [wSpriteOutputPtr], a
ld a, [hl]
ld [wSpriteOutputPtr+1], a
ret
.bitOffsetsDone
ld a, $3
ld [wSpriteOutputBitOffset], a
ld a, [wSpriteCurPosX]
add $8
ld [wSpriteCurPosX], a
ld b, a
ld a, [wSpriteWidth]
cp b
jr z, .allColumnsDone
ld a, [wSpriteOutputPtr]
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
inc hl
jp StoreSpriteOutputPointer
.allColumnsDone
pop hl
xor a
ld [wSpriteCurPosX], a
ld a, [wSpriteLoadFlags]
bit 1, a
jr nz, .done ; test if there is one more sprite to go
xor $1
set 1, a
ld [wSpriteLoadFlags], a
jp UncompressSpriteDataLoop
.done
jp UnpackSprite
; writes 2 bits (from a) to the output buffer (pointed to from wSpriteOutputPtr)
WriteSpriteBitsToBuffer::
ld e, a
ld a, [wSpriteOutputBitOffset]
and a
jr z, .offset0
cp $2
jr c, .offset1
jr z, .offset2
rrc e ; offset 3
rrc e
jr .offset0
.offset1
sla e
sla e
jr .offset0
.offset2
swap e
.offset0
ld a, [wSpriteOutputPtr]
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
ld a, [hl]
or e
ld [hl], a
ret
; reads next bit from input stream and returns it in a
ReadNextInputBit::
ld a, [wSpriteInputBitCounter]
dec a
jr nz, .curByteHasMoreBitsToRead
call ReadNextInputByte
ld [wSpriteInputCurByte], a
ld a, $8
.curByteHasMoreBitsToRead
ld [wSpriteInputBitCounter], a
ld a, [wSpriteInputCurByte]
rlca
ld [wSpriteInputCurByte], a
and $1
ret
; reads next byte from input stream and returns it in a
ReadNextInputByte::
ld a, [wSpriteInputPtr]
ld l, a
ld a, [wSpriteInputPtr+1]
ld h, a
ld a, [hli]
ld b, a
ld a, l
ld [wSpriteInputPtr], a
ld a, h
ld [wSpriteInputPtr+1], a
ld a, b
ret
; the nth item is 2^n - 1
LengthEncodingOffsetList::
dw %0000000000000001
dw %0000000000000011
dw %0000000000000111
dw %0000000000001111
dw %0000000000011111
dw %0000000000111111
dw %0000000001111111
dw %0000000011111111
dw %0000000111111111
dw %0000001111111111
dw %0000011111111111
dw %0000111111111111
dw %0001111111111111
dw %0011111111111111
dw %0111111111111111
dw %1111111111111111
; unpacks the sprite data depending on the unpack mode
UnpackSprite::
ld a, [wSpriteUnpackMode]
cp $2
jp z, UnpackSpriteMode2
and a
jp nz, XorSpriteChunks
ld hl, sSpriteBuffer1
call SpriteDifferentialDecode
ld hl, sSpriteBuffer2
; fall through
; decodes differential encoded sprite data
; input bit value 0 preserves the current bit value and input bit value 1 toggles it (starting from initial value 0).
SpriteDifferentialDecode::
xor a
ld [wSpriteCurPosX], a
ld [wSpriteCurPosY], a
call StoreSpriteOutputPointer
ld a, [wSpriteFlipped]
and a
jr z, .notFlipped
ld hl, DecodeNybble0TableFlipped
ld de, DecodeNybble1TableFlipped
jr .storeDecodeTablesPointers
.notFlipped
ld hl, DecodeNybble0Table
ld de, DecodeNybble1Table
.storeDecodeTablesPointers
ld a, l
ld [wSpriteDecodeTable0Ptr], a
ld a, h
ld [wSpriteDecodeTable0Ptr+1], a
ld a, e
ld [wSpriteDecodeTable1Ptr], a
ld a, d
ld [wSpriteDecodeTable1Ptr+1], a
ld e, $0 ; last decoded nybble, initialized to 0
.decodeNextByteLoop
ld a, [wSpriteOutputPtr]
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
ld a, [hl]
ld b, a
swap a
and $f
call DifferentialDecodeNybble ; decode high nybble
swap a
ld d, a
ld a, b
and $f
call DifferentialDecodeNybble ; decode low nybble
or d
ld b, a
ld a, [wSpriteOutputPtr]
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
ld a, b
ld [hl], a ; write back decoded data
ld a, [wSpriteHeight]
add l ; move on to next column
jr nc, .noCarry
inc h
.noCarry
ld [wSpriteOutputPtr], a
ld a, h
ld [wSpriteOutputPtr+1], a
ld a, [wSpriteCurPosX]
add $8
ld [wSpriteCurPosX], a
ld b, a
ld a, [wSpriteWidth]
cp b
jr nz, .decodeNextByteLoop ; test if current row is done
xor a
ld e, a
ld [wSpriteCurPosX], a
ld a, [wSpriteCurPosY] ; move on to next row
inc a
ld [wSpriteCurPosY], a
ld b, a
ld a, [wSpriteHeight]
cp b
jr z, .done ; test if all rows finished
ld a, [wSpriteOutputPtrCached]
ld l, a
ld a, [wSpriteOutputPtrCached+1]
ld h, a
inc hl
call StoreSpriteOutputPointer
jr .decodeNextByteLoop
.done
xor a
ld [wSpriteCurPosY], a
ret
; decodes the nybble stored in a. Last decoded data is assumed to be in e (needed to determine if initial value is 0 or 1)
DifferentialDecodeNybble::
srl a ; c=a%2, a/=2
ld c, $0
jr nc, .evenNumber
ld c, $1
.evenNumber
ld l, a
ld a, [wSpriteFlipped]
and a
jr z, .notFlipped ; determine if initial value is 0 or one
bit 3, e ; if flipped, consider MSB of last data
jr .selectLookupTable
.notFlipped
bit 0, e ; else consider LSB
.selectLookupTable
ld e, l
jr nz, .initialValue1 ; load the appropriate table
ld a, [wSpriteDecodeTable0Ptr]
ld l, a
ld a, [wSpriteDecodeTable0Ptr+1]
jr .tableLookup
.initialValue1
ld a, [wSpriteDecodeTable1Ptr]
ld l, a
ld a, [wSpriteDecodeTable1Ptr+1]
.tableLookup
ld h, a
ld a, e
add l
ld l, a
jr nc, .noCarry
inc h
.noCarry
ld a, [hl]
bit 0, c
jr nz, .selectLowNybble
swap a ; select high nybble
.selectLowNybble
and $f
ld e, a ; update last decoded data
ret
DecodeNybble0Table::
dn $0, $1
dn $3, $2
dn $7, $6
dn $4, $5
dn $f, $e
dn $c, $d
dn $8, $9
dn $b, $a
DecodeNybble1Table::
dn $f, $e
dn $c, $d
dn $8, $9
dn $b, $a
dn $0, $1
dn $3, $2
dn $7, $6
dn $4, $5
DecodeNybble0TableFlipped::
dn $0, $8
dn $c, $4
dn $e, $6
dn $2, $a
dn $f, $7
dn $3, $b
dn $1, $9
dn $d, $5
DecodeNybble1TableFlipped::
dn $f, $7
dn $3, $b
dn $1, $9
dn $d, $5
dn $0, $8
dn $c, $4
dn $e, $6
dn $2, $a
; combines the two loaded chunks with xor (the chunk loaded second is the destination). The source chunk is differeintial decoded beforehand.
XorSpriteChunks::
xor a
ld [wSpriteCurPosX], a
ld [wSpriteCurPosY], a
call ResetSpriteBufferPointers
ld a, [wSpriteOutputPtr] ; points to buffer 1 or 2, depending on flags
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
call SpriteDifferentialDecode ; decode buffer 1 or 2, depending on flags
call ResetSpriteBufferPointers
ld a, [wSpriteOutputPtr] ; source buffer, points to buffer 1 or 2, depending on flags
ld l, a
ld a, [wSpriteOutputPtr+1]
ld h, a
ld a, [wSpriteOutputPtrCached] ; destination buffer, points to buffer 2 or 1, depending on flags
ld e, a
ld a, [wSpriteOutputPtrCached+1]
ld d, a
.xorChunksLoop
ld a, [wSpriteFlipped]
and a
jr z, .notFlipped
push de
ld a, [de]
ld b, a
swap a
and $f
call ReverseNybble ; if flipped reverse the nybbles in the destination buffer
swap a
ld c, a
ld a, b
and $f
call ReverseNybble
or c
pop de
ld [de], a
.notFlipped
ld a, [hli]
ld b, a
ld a, [de]
xor b
ld [de], a
inc de
ld a, [wSpriteCurPosY]
inc a
ld [wSpriteCurPosY], a ; go to next row
ld b, a
ld a, [wSpriteHeight]
cp b
jr nz, .xorChunksLoop ; test if column finished
xor a
ld [wSpriteCurPosY], a
ld a, [wSpriteCurPosX]
add $8
ld [wSpriteCurPosX], a ; go to next column
ld b, a
ld a, [wSpriteWidth]
cp b
jr nz, .xorChunksLoop ; test if all columns finished
xor a
ld [wSpriteCurPosX], a
ret
; reverses the bits in the nybble given in register a
ReverseNybble::
ld de, NybbleReverseTable
add e
ld e, a
jr nc, .noCarry
inc d
.noCarry
ld a, [de]
ret
; resets sprite buffer pointers to buffer 1 and 2, depending on wSpriteLoadFlags
ResetSpriteBufferPointers::
ld a, [wSpriteLoadFlags]
bit 0, a
jr nz, .buffer2Selected
ld de, sSpriteBuffer1
ld hl, sSpriteBuffer2
jr .storeBufferPointers
.buffer2Selected
ld de, sSpriteBuffer2
ld hl, sSpriteBuffer1
.storeBufferPointers
ld a, l
ld [wSpriteOutputPtr], a
ld a, h
ld [wSpriteOutputPtr+1], a
ld a, e
ld [wSpriteOutputPtrCached], a
ld a, d
ld [wSpriteOutputPtrCached+1], a
ret
; maps each nybble to its reverse
NybbleReverseTable::
db $0, $8, $4, $c, $2, $a, $6 ,$e, $1, $9, $5, $d, $3, $b, $7 ,$f
; combines the two loaded chunks with xor (the chunk loaded second is the destination). Both chunks are differeintial decoded beforehand.
UnpackSpriteMode2::
call ResetSpriteBufferPointers
ld a, [wSpriteFlipped]
push af
xor a
ld [wSpriteFlipped], a ; temporarily clear flipped flag for decoding the destination chunk
ld a, [wSpriteOutputPtrCached]
ld l, a
ld a, [wSpriteOutputPtrCached+1]
ld h, a
call SpriteDifferentialDecode
call ResetSpriteBufferPointers
pop af
ld [wSpriteFlipped], a
jp XorSpriteChunks
; stores hl into the output pointers
StoreSpriteOutputPointer::
ld a, l
ld [wSpriteOutputPtr], a
ld [wSpriteOutputPtrCached], a
ld a, h
ld [wSpriteOutputPtr+1], a
ld [wSpriteOutputPtrCached+1], a
ret