def png.unfilter.row

gralha-png-decode@0.1.0.1 · png.bend:70

import Base
import gralha-text-scan@0.1.0.1/scan.bend as U
import gralha-bytes@0.1.0.1/bytes.bend as Bin

70def png.unfilter.row(n: Nat, +raw: Bin.Bytes, +at: U32, +x: U32, +stride: U32, +bpp: U32, +kind: U32, +out: Bin.Bytes) -> Bin.Bytes:
71  match n:
72    case 0n: out
73    case 1n+d:
74      +pos = Bin.bytes.size(out)
75      +a = U.choose(U32, U32.is_ge(x, bpp), Bin.bytes.get(out, (pos - bpp : U32)), 0)
76      +b = U.choose(U32, U32.is_ge(pos, stride), Bin.bytes.get(out, (pos - stride : U32)), 0)
77      +c = U.choose(U32, U32.is_ge(x, bpp) && U32.is_ge(pos, stride), Bin.bytes.get(out, (pos - stride - bpp : U32)), 0)
78      png.unfilter.row(d, raw, U32.inc(at), U32.inc(x), stride, bpp, kind, Bin.bytes.push(out, ((Bin.bytes.get(raw, at) + png.predict(kind, a, b, c)) % 256 : U32)))