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; scales both uncompressed sprite chunks by two in every dimension (creating 2x2 output pixels per input pixel)
; assumes that input sprite chunks are 4x4 tiles, and the rightmost and bottommost 4 pixels will be ignored
; resulting in a 7*7 tile output sprite chunk
ScaleSpriteByTwo:
ld de, sSpriteBuffer1 + (4*4*8) - 5 ; last byte of input data, last 4 rows already skipped
ld hl, sSpriteBuffer0 + SPRITEBUFFERSIZE - 1 ; end of destination buffer
call ScaleLastSpriteColumnByTwo ; last tile column is special case
call ScaleFirstThreeSpriteColumnsByTwo ; scale first 3 tile columns
ld de, sSpriteBuffer2 + (4*4*8) - 5 ; last byte of input data, last 4 rows already skipped
ld hl, sSpriteBuffer1 + SPRITEBUFFERSIZE - 1 ; end of destination buffer
call ScaleLastSpriteColumnByTwo ; last tile column is special case
ScaleFirstThreeSpriteColumnsByTwo:
ld b, $3 ; 3 tile columns
.columnLoop
ld c, 4*8 - 4 ; $1c, 4 tiles minus 4 unused rows
.columnInnerLoop
push bc
ld a, [de]
ld bc, -(7*8)+1 ; -$37, scale lower nybble and seek to previous output column
call ScalePixelsByTwo
ld a, [de]
dec de
swap a
ld bc, 7*8+1-2 ; $37, scale upper nybble and seek back to current output column and to the next 2 rows
call ScalePixelsByTwo
pop bc
dec c
jr nz, .columnInnerLoop
dec de
dec de
dec de
dec de
ld a, b
ld bc, -7*8 ; -$38, skip one output column (which has already been written along with the current one)
add hl, bc
ld b, a
dec b
jr nz, .columnLoop
ret
ScaleLastSpriteColumnByTwo:
ld a, 4*8 - 4 ; $1c, 4 tiles minus 4 unused rows
ldh [hSpriteInterlaceCounter], a
ld bc, -1
.columnInnerLoop
ld a, [de]
dec de
swap a ; only high nybble contains information
call ScalePixelsByTwo
ldh a, [hSpriteInterlaceCounter]
dec a
ldh [hSpriteInterlaceCounter], a
jr nz, .columnInnerLoop
dec de ; skip last 4 rows of new column
dec de
dec de
dec de
ret
; scales the given 4 bits in a (4x1 pixels) to 2 output bytes (8x2 pixels)
; hl: destination pointer
; bc: destination pointer offset (added after the two bytes have been written)
ScalePixelsByTwo:
push hl
and $f
ld hl, DuplicateBitsTable
add l
ld l, a
jr nc, .noCarry
inc h
.noCarry
ld a, [hl]
pop hl
ld [hld], a ; write output byte twice to make it 2 pixels high
ld [hl], a
add hl, bc ; add offset
ret
; repeats each input bit twice
DuplicateBitsTable:
db %00000000
db %00000011
db %00001100
db %00001111
db %00110000
db %00110011
db %00111100
db %00111111
db %11000000
db %11000011
db %11001100
db %11001111
db %11110000
db %11110011
db %11111100
db %11111111
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