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This commit is contained in:
Ryan Oldenburg 2022-06-15 12:22:01 -05:00
parent ad303de223
commit ff45edf131
1 changed files with 26 additions and 14 deletions
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40
src/pixie/fileformats/png.nim
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@ -114,39 +114,51 @@ proc unfilter(
rowBytes
)
of 1: # Sub
let
uncompressedStartIdx = uncompressedIdx(1, y)
unfilteredStartIx = unfiteredIdx(0, y)
for x in 0 ..< rowBytes:
var value = uncompressed.readUint8(uncompressedIdx(x + 1, y))
var value = uncompressed.readUint8(uncompressedStartIdx + x)
if x - bpp >= 0:
value += result.readUint8(unfiteredIdx(x - bpp, y))
result[unfiteredIdx(x, y)] = value.char
value += result.readUint8(unfilteredStartIx + x - bpp)
result[unfilteredStartIx + x] = value.char
of 2: # Up
let
uncompressedStartIdx = uncompressedIdx(1, y)
unfilteredStartIx = unfiteredIdx(0, y)
for x in 0 ..< rowBytes:
var value = uncompressed.readUint8(uncompressedIdx(x + 1, y))
var value = uncompressed.readUint8(uncompressedStartIdx + x)
if y - 1 >= 0:
value += result.readUint8(unfiteredIdx(x, y - 1))
result[unfiteredIdx(x, y)] = value.char
result[unfilteredStartIx + x] = value.char
of 3: # Average
let
uncompressedStartIdx = uncompressedIdx(1, y)
unfilteredStartIx = unfiteredIdx(0, y)
for x in 0 ..< rowBytes:
var
value = uncompressed.readUint8(uncompressedIdx(x + 1, y))
value = uncompressed.readUint8(uncompressedStartIdx + x)
left, up: int
if x - bpp >= 0:
left = result[unfiteredIdx(x - bpp, y)].int
left = result[unfilteredStartIx + x - bpp].int
if y - 1 >= 0:
up = result[unfiteredIdx(x, y - 1)].int
up = result[unfilteredStartIx + x - rowBytes].int
value += ((left + up) div 2).uint8
result[unfiteredIdx(x, y)] = value.char
result[unfilteredStartIx + x] = value.char
of 4: # Paeth
let
uncompressedStartIdx = uncompressedIdx(1, y)
unfilteredStartIx = unfiteredIdx(0, y)
for x in 0 ..< rowBytes:
var
value = uncompressed.readUint8(uncompressedIdx(x + 1, y))
value = uncompressed.readUint8(uncompressedStartIdx + x)
left, up, upLeft: int
if x - bpp >= 0:
left = result[unfiteredIdx(x - bpp, y)].int
left = result[unfilteredStartIx + x - bpp].int
if y - 1 >= 0:
up = result[unfiteredIdx(x, y - 1)].int
up = result[unfilteredStartIx + x - rowBytes].int
if x - bpp >= 0 and y - 1 >= 0:
upLeft = result[unfiteredIdx(x - bpp, y - 1)].int
upLeft = result[unfilteredStartIx + x - rowBytes - bpp].int
template paethPredictor(a, b, c: int): int =
let
p = a + b - c
@ -160,7 +172,7 @@ proc unfilter(
else:
c
value += paethPredictor(up, left, upLeft).uint8
result[unfiteredIdx(x, y)] = value.char
result[unfilteredStartIx + x] = value.char
else:
discard # Not possible, parseHeader validates