Png.png.unfilter: def of gralha-png-decode@0.1.0.1
Import: import gralha-png-decode@0.1.0.1/png.bend as Png
Lines 80-85 of gralha-png-decode@0.1.0.1/png.bend: https://jend.leeeet.dev/read.txt?path=gralha-png-decode@0.1.0.1/png.bend&start_line=80&end_line=85

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

def png.unfilter(n: Nat, +raw: Bin.Bytes, +at: U32, +stride: U32, +bpp: U32, +out: Bin.Bytes) -> Maybe<&2, Bin.Bytes>:
  match n:
    case 0n: Some{out}
    case 1n+d:
      +kind = Bin.bytes.get(raw, at)
      U.branch(Maybe<&2, Bin.Bytes>, U32.is_le(kind, 4), _ => png.unfilter(d, raw, (at + stride + 1 : U32), stride, bpp, png.unfilter.row(U32.to_nat(stride), raw, U32.inc(at), 0, stride, bpp, kind, out)), _ => None{})

Uses (11):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.add
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.inc
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.is_le
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.to_nat
  https://jend.leeeet.dev/definition.txt?path=gralha-bytes@0.1.0.1/bytes.bend&name=Bytes
  https://jend.leeeet.dev/definition.txt?path=gralha-bytes@0.1.0.1/bytes.bend&name=bytes.get
  https://jend.leeeet.dev/definition.txt?path=gralha-png-decode@0.1.0.1/png.bend&name=png.unfilter.row
  https://jend.leeeet.dev/definition.txt?path=gralha-text-scan@0.1.0.1/scan.bend&name=branch