Bump version

.gitignore

@@ -2,3 +2,4 @@
 *.ez
 /build
 erl_crash.dump
+*.png

gleam.toml

@@ -1,5 +1,5 @@
 name = "pngleam"
-version = "1.0.2"
+version = "1.1.0"
 
 description = "PNG image library for Gleam"
 licences = ["AGPL-3.0-only"]
@@ -10,7 +10,8 @@ links = [
 
 [dependencies]
 gleam_stdlib = ">= 0.34.0 and < 2.0.0"
-gzlib = ">= 1.0.0 and < 2.0.0"
+gzlib = ">= 1.0.1 and < 2.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.0.0 and < 2.0.0"
+simplifile = ">= 2.0.0 and < 3.0.0"

manifest.toml

@@ -2,12 +2,15 @@
 # You typically do not need to edit this file
 
 packages = [
+  { name = "filepath", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "EFB6FF65C98B2A16378ABC3EE2B14124168C0CE5201553DE652E2644DCFDB594" },
   { name = "gleam_stdlib", version = "0.38.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "663CF11861179AF415A625307447775C09404E752FF99A24E2057C835319F1BE" },
   { name = "gleeunit", version = "1.1.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "72CDC3D3F719478F26C4E2C5FED3E657AC81EC14A47D2D2DEBB8693CA3220C3B" },
-  { name = "gzlib", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gzlib", source = "hex", outer_checksum = "EC6A3FAF20B8A707B5A550E1B622785685759991C9D13CFC4AAE8FE34FDDF3B8" },
+  { name = "gzlib", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gzlib", source = "hex", outer_checksum = "5E71EF6C973CB61CDF25D1C5CDBD129C481CE432D6FD089FBB4E30B95CCCE935" },
+  { name = "simplifile", version = "2.0.0", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "95219227A43FCFE62C6E494F413A1D56FF953B68FE420698612E3D89A1EFE029" },
 ]
 
 [requirements]
 gleam_stdlib = { version = ">= 0.34.0 and < 2.0.0" }
 gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
-gzlib = { version = ">= 1.0.0 and < 2.0.0" }
+gzlib = { version = ">= 1.0.1 and < 2.0.0"}
+simplifile = { version = ">= 2.0.0 and < 3.0.0" }

src/pngleam.gleam

@@ -1,5 +1,10 @@
 import gleam/bit_array
+import gleam/bool
+import gleam/float
+import gleam/int
 import gleam/list
+import gleam/option
+import gleam/result
 import gzlib
 
 pub const no_compression = gzlib.no_compression
@@ -33,6 +38,17 @@ fn color_type_to_int(color_type: ColorType) -> Int {
   }
 }
 
+fn int_to_color_type(color_type: Int) -> Result(ColorType, Nil) {
+  case color_type {
+    0b000 -> Ok(Greyscale)
+    0b010 -> Ok(Color)
+    0b011 -> Ok(Indexed)
+    0b100 -> Ok(GreyscaleWithAlpha)
+    0b110 -> Ok(ColorWithAlpha)
+    _ -> Error(Nil)
+  }
+}
+
 pub opaque type ColorInfo {
   ColorInfo(color_type: ColorType, bit_depth: Int)
 }
@@ -63,36 +79,63 @@ pub fn color_info(
   }
 }
 
+pub fn color_info_bits(color_info: ColorInfo) -> Int {
+  case color_info.color_type {
+    Greyscale -> color_info.bit_depth
+    Color -> 3 * color_info.bit_depth
+    Indexed -> color_info.bit_depth
+    GreyscaleWithAlpha -> 2 * color_info.bit_depth
+    ColorWithAlpha -> 4 * color_info.bit_depth
+  }
+}
+
+fn partition_bit_array(
+  data: BitArray,
+  at bytes: Int,
+) -> Result(#(BitArray, BitArray), Nil) {
+  use left <- result.try(bit_array.slice(data, 0, bytes))
+  use right <- result.try(bit_array.slice(
+    data,
+    bytes,
+    bit_array.byte_size(data) - bytes,
+  ))
+  Ok(#(left, right))
+}
+
+const chunk_size = 8192
+
+fn do_chunk_bit_array(data: BitArray, chunks: List(BitArray)) -> List(BitArray) {
+  case partition_bit_array(data, chunk_size) {
+    Ok(#(chunk, rest)) -> do_chunk_bit_array(rest, [chunk, ..chunks])
+    _ -> [data, ..chunks]
+  }
+}
+
 fn chunk_bit_array(data: BitArray) -> List(BitArray) {
   do_chunk_bit_array(data, []) |> list.reverse
 }
 
-fn do_chunk_bit_array(data: BitArray, chunks: List(BitArray)) -> List(BitArray) {
+fn create_chunk(tag: String, data: BitArray) -> BitArray {
-  case data {
-    <<chunk:bytes-size(8192), rest:bytes>> ->
-      do_chunk_bit_array(rest, [chunk, ..chunks])
-    chunk -> [chunk, ..chunks]
-  }
-}
-
-fn get_chunk(tag: String, data: BitArray) -> BitArray {
   let data_size = bit_array.byte_size(data)
-  let tag_bits = <<tag:utf8>>
+  let tag_bits = bit_array.from_string(tag)
   let checksum = gzlib.continue_crc32(gzlib.crc32(tag_bits), data)
   <<data_size:size(32), tag_bits:bits, data:bits, checksum:size(32)>>
 }
 
-const signature = <<137, "PNG":utf8, "\r\n":utf8, 26, "\n":utf8>>
+const signature = <<137, 80, 78, 71, 13, 10, 26, 10>>
+
+pub type BinaryRowData =
+  List(BitArray)
 
 pub fn from_packed(
-  row_data row_data: List(BitArray),
+  row_data row_data: BinaryRowData,
   width width: Int,
   height height: Int,
   color_info color_info: ColorInfo,
   compression_level compression_level: gzlib.CompressionLevel,
 ) -> BitArray {
   let ihdr =
-    get_chunk("IHDR", <<
+    create_chunk("IHDR", <<
       width:size(32),
       height:size(32),
       color_info.bit_depth:size(8),
@@ -101,14 +144,409 @@ pub fn from_packed(
       0:size(8),
       0:size(8),
     >>)
+  let no_filter_int = filter_type_to_int(None)
   let idats =
     row_data
-    |> list.map(fn(d) { <<0, d:bits>> })
+    |> list.map(fn(d) { <<no_filter_int:size(8), d:bits>> })
     |> bit_array.concat
     |> gzlib.compress_with_level(compression_level)
     |> chunk_bit_array
-    |> list.map(get_chunk("IDAT", _))
+    |> list.map(create_chunk("IDAT", _))
     |> bit_array.concat
-  let iend = get_chunk("IEND", <<>>)
+  let iend = create_chunk("IEND", <<>>)
   <<signature:bits, ihdr:bits, idats:bits, iend:bits>>
 }
+
+pub type ParseError {
+  InvalidSignature
+  InvalidChunkTag
+  ChecksumMismatch
+  InvalidChunkOrder
+  MissingHeaderChunk
+  InvalidChunkData
+  InvalidColorType
+  InvalidBitDepth
+  InvalidCompressionType
+  InvalidFilterMethod
+  InvalidInterlaceMethod
+  UnsupportedInterlaceMethod
+  InvalidRowFilterType
+  InvalidRowData
+}
+
+fn parse_chunk(
+  data: BitArray,
+) -> Result(#(String, BitArray, BitArray), ParseError) {
+  case data {
+    <<data_size:size(32), tag_bits:bytes-size(4), rest:bytes>> -> {
+      use tag <- result.try(
+        bit_array.to_string(tag_bits)
+        |> result.replace_error(InvalidChunkTag),
+      )
+      case partition_bit_array(rest, data_size) {
+        Ok(#(data, <<checksum:size(32), rest:bytes>>)) -> {
+          let computed_checksum =
+            gzlib.continue_crc32(gzlib.crc32(tag_bits), data)
+          use <- bool.guard(
+            computed_checksum != checksum,
+            Error(ChecksumMismatch),
+          )
+          Ok(#(tag, data, rest))
+        }
+        _ -> Error(InvalidChunkData)
+      }
+    }
+    _ -> Error(InvalidChunkData)
+  }
+}
+
+fn parse_signature(data: BitArray) -> Result(BitArray, ParseError) {
+  case data {
+    <<137, 80, 78, 71, 13, 10, 26, 10, rest:bytes>> -> Ok(rest)
+    _ -> Error(InvalidSignature)
+  }
+}
+
+pub type PngMetadata {
+  PngMetadata(width: Int, height: Int, color_info: ColorInfo)
+}
+
+fn parse_header(header_data: BitArray) -> Result(PngMetadata, ParseError) {
+  case header_data {
+    <<
+      width:size(32),
+      height:size(32),
+      bit_depth:size(8),
+      color_type:size(8),
+      compression_method:size(8),
+      filter_method:size(8),
+      interlace_method:size(8),
+    >> -> {
+      use col_type <- result.try(
+        int_to_color_type(color_type)
+        |> result.replace_error(InvalidColorType),
+      )
+      use col_info <- result.try(
+        color_info(col_type, bit_depth)
+        |> result.replace_error(InvalidBitDepth),
+      )
+      use <- bool.guard(compression_method != 0, Error(InvalidCompressionType))
+      use <- bool.guard(filter_method != 0, Error(InvalidFilterMethod))
+      use <- bool.guard(
+        interlace_method != 0 && interlace_method != 1,
+        Error(InvalidInterlaceMethod),
+      )
+      use <- bool.guard(
+        interlace_method == 1,
+        Error(UnsupportedInterlaceMethod),
+      )
+      Ok(PngMetadata(width, height, col_info))
+    }
+    _ -> Error(InvalidChunkData)
+  }
+}
+
+pub fn parse_metadata(data: BitArray) -> Result(PngMetadata, ParseError) {
+  use chunk_data <- result.try(parse_signature(data))
+  use #(tag, chunk_data, _) <- result.try(parse_chunk(chunk_data))
+  use <- bool.guard(tag != "IHDR", Error(MissingHeaderChunk))
+  parse_header(chunk_data)
+}
+
+pub type RawPalette =
+  BitArray
+
+type PngDataState {
+  PngDataState(palette: option.Option(RawPalette), image_parts: BinaryRowData)
+}
+
+fn do_parse_image_data(
+  data: BitArray,
+  state: PngDataState,
+) -> Result(PngDataState, ParseError) {
+  use #(tag, chunk_data, rest) <- result.try(parse_chunk(data))
+  case tag, state.image_parts {
+    "PLTE", [] ->
+      do_parse_image_data(
+        rest,
+        PngDataState(..state, palette: option.Some(chunk_data)),
+      )
+    "PLTE", _ -> Error(InvalidChunkOrder)
+    "IDAT", parts ->
+      do_parse_image_data(
+        rest,
+        PngDataState(..state, image_parts: [chunk_data, ..parts]),
+      )
+    "IEND", _ -> Ok(state)
+    _, [] -> do_parse_image_data(rest, state)
+    _, _ -> Ok(state)
+  }
+}
+
+fn parse_image_data(data: BitArray) -> Result(PngDataState, ParseError) {
+  do_parse_image_data(data, PngDataState(option.None, []))
+}
+
+pub type FilterType {
+  None
+  Sub
+  Up
+  Average
+  Paeth
+}
+
+pub fn int_to_filter_type(filter_type: Int) -> Result(FilterType, Nil) {
+  case filter_type {
+    0 -> Ok(None)
+    1 -> Ok(Sub)
+    2 -> Ok(Up)
+    3 -> Ok(Average)
+    4 -> Ok(Paeth)
+    _ -> Error(Nil)
+  }
+}
+
+pub fn filter_type_to_int(filter_type: FilterType) -> Int {
+  case filter_type {
+    None -> 0
+    Sub -> 1
+    Up -> 2
+    Average -> 3
+    Paeth -> 4
+  }
+}
+
+@external(erlang, "pngleam_erl", "subUnfilter")
+@external(javascript, "./pngleam_js.mjs", "subUnfilter")
+fn sub_unfilter(row: BitArray, bytes_per_pixel: Int) -> BitArray
+
+@external(erlang, "pngleam_erl", "upUnfilter")
+@external(javascript, "./pngleam_js.mjs", "upUnfilter")
+fn up_unfilter(row: BitArray, row_above: BitArray) -> BitArray
+
+@external(erlang, "pngleam_erl", "avgUnfilter")
+@external(javascript, "./pngleam_js.mjs", "avgUnfilter")
+fn avg_unfilter(
+  row: BitArray,
+  row_above: BitArray,
+  bytes_per_pixel: Int,
+) -> BitArray
+
+@external(erlang, "pngleam_erl", "paethUnfilter")
+@external(javascript, "./pngleam_js.mjs", "paethUnfilter")
+fn paeth_unfilter(
+  row: BitArray,
+  row_above: BitArray,
+  bytes_per_pixel: Int,
+) -> BitArray
+
+fn do_parse_image_rows(
+  data: BitArray,
+  bytes_per_row: Int,
+  bytes_per_pixel: Int,
+  rows: BinaryRowData,
+) -> Result(BinaryRowData, ParseError) {
+  let bits_per_row = bytes_per_row * 8
+  case data {
+    <<>> -> Ok(rows)
+    <<filter_type:size(8), rest:bytes>> -> {
+      use filter_type <- result.try(
+        int_to_filter_type(filter_type)
+        |> result.replace_error(InvalidRowFilterType),
+      )
+      use #(row, rest) <- result.try(
+        partition_bit_array(rest, bytes_per_row)
+        |> result.replace_error(InvalidRowData),
+      )
+      let row = case filter_type {
+        None -> row
+        Sub -> sub_unfilter(row, bytes_per_pixel)
+        Up ->
+          up_unfilter(
+            row,
+            result.unwrap(list.first(rows), <<0:size(bits_per_row)>>),
+          )
+        Average ->
+          avg_unfilter(
+            row,
+            result.unwrap(list.first(rows), <<0:size(bits_per_row)>>),
+            bytes_per_pixel,
+          )
+        Paeth ->
+          paeth_unfilter(
+            row,
+            result.unwrap(list.first(rows), <<0:size(bits_per_row)>>),
+            bytes_per_pixel,
+          )
+      }
+      do_parse_image_rows(rest, bytes_per_row, bytes_per_pixel, [row, ..rows])
+    }
+    _ -> Error(InvalidRowData)
+  }
+}
+
+fn parse_image_rows(
+  data: BitArray,
+  bytes_per_row: Int,
+  bytes_per_pixel: Int,
+) -> Result(BinaryRowData, ParseError) {
+  do_parse_image_rows(data, bytes_per_row, bytes_per_pixel, [])
+  |> result.map(list.reverse)
+}
+
+fn bits_to_bytes(bits: Int) -> Int {
+  bits
+  |> int.to_float
+  |> fn(x) { x /. 8.0 }
+  |> float.ceiling
+  |> float.round
+}
+
+pub type PngData(p, i) {
+  PngData(metadata: PngMetadata, palette: option.Option(p), image_data: i)
+}
+
+pub type PngBitArrayData =
+  PngData(RawPalette, BinaryRowData)
+
+pub fn parse_to_bit_arrays(
+  data: BitArray,
+) -> Result(PngBitArrayData, ParseError) {
+  use rest <- result.try(parse_signature(data))
+  use #(tag, chunk_data, rest) <- result.try(parse_chunk(rest))
+  use <- bool.guard(tag != "IHDR", Error(MissingHeaderChunk))
+  use metadata <- result.try(parse_header(chunk_data))
+  use PngDataState(palette, image_parts) <- result.try(parse_image_data(rest))
+  let image_data =
+    image_parts
+    |> list.reverse
+    |> bit_array.concat
+    |> gzlib.uncompress
+  let bits_per_pixel = color_info_bits(metadata.color_info)
+  let bytes_per_row = bits_to_bytes(metadata.width * bits_per_pixel)
+  let bytes_per_pixel = bits_to_bytes(bits_per_pixel)
+  use idat_rows <- result.try(parse_image_rows(
+    image_data,
+    bytes_per_row,
+    bytes_per_pixel,
+  ))
+  Ok(PngData(metadata, palette, idat_rows))
+}
+
+@external(erlang, "pngleam_erl", "bitArrayToInts")
+@external(javascript, "./pngleam_js.mjs", "bitArrayToInts")
+fn bit_array_to_ints(data: BitArray, int_size: Int) -> List(Int)
+
+fn do_chunk2(
+  values: List(a),
+  chunks: List(#(a, a)),
+) -> Result(List(#(a, a)), Nil) {
+  case values {
+    [] -> Ok(chunks)
+    [a, b, ..rest] -> do_chunk2(rest, [#(a, b), ..chunks])
+    _ -> Error(Nil)
+  }
+}
+
+fn chunk2(values: List(a)) -> Result(List(#(a, a)), Nil) {
+  do_chunk2(values, []) |> result.map(list.reverse)
+}
+
+fn do_chunk3(
+  values: List(a),
+  chunks: List(#(a, a, a)),
+) -> Result(List(#(a, a, a)), Nil) {
+  case values {
+    [] -> Ok(chunks)
+    [a, b, c, ..rest] -> do_chunk3(rest, [#(a, b, c), ..chunks])
+    _ -> Error(Nil)
+  }
+}
+
+fn chunk3(values: List(a)) -> Result(List(#(a, a, a)), Nil) {
+  do_chunk3(values, []) |> result.map(list.reverse)
+}
+
+fn do_chunk4(
+  values: List(a),
+  chunks: List(#(a, a, a, a)),
+) -> Result(List(#(a, a, a, a)), Nil) {
+  case values {
+    [] -> Ok(chunks)
+    [a, b, c, d, ..rest] -> do_chunk4(rest, [#(a, b, c, d), ..chunks])
+    _ -> Error(Nil)
+  }
+}
+
+fn chunk4(values: List(a)) -> Result(List(#(a, a, a, a)), Nil) {
+  do_chunk4(values, []) |> result.map(list.reverse)
+}
+
+pub type GreyscaleValue =
+  Int
+
+pub type ColorValue =
+  #(Int, Int, Int)
+
+pub type PalleteIndex =
+  Int
+
+pub type GreyscaleWithAlphaValue =
+  #(Int, Int)
+
+pub type ColorWithAlphaValue =
+  #(Int, Int, Int, Int)
+
+pub type Grid(a) =
+  List(List(a))
+
+pub type PixelData {
+  GreyscaleData(Grid(GreyscaleValue))
+  ColorData(Grid(ColorValue))
+  IndexedData(Grid(PalleteIndex))
+  GreyscaleWithAlphaData(Grid(GreyscaleWithAlphaValue))
+  ColorWithAlphaData(Grid(ColorWithAlphaValue))
+}
+
+pub type PaletteColor =
+  #(Int, Int, Int)
+
+pub type PaletteColors =
+  List(PaletteColor)
+
+pub type PngPixelData =
+  PngData(PaletteColors, PixelData)
+
+pub fn parse_to_pixel_data(data: BitArray) -> Result(PngPixelData, ParseError) {
+  use PngData(metadata, palette, row_data) <- result.try(parse_to_bit_arrays(
+    data,
+  ))
+  use palette <- result.try(case palette {
+    option.Some(p) ->
+      case bit_array_to_ints(p, 8) |> chunk3 {
+        Ok(p) -> Ok(option.Some(p))
+        Error(_) -> Error(InvalidChunkData)
+      }
+    option.None -> Ok(option.None)
+  })
+  let bit_depth = metadata.color_info.bit_depth
+  let num_values =
+    metadata.width * color_info_bits(metadata.color_info) / bit_depth
+  let values =
+    list.map(row_data, fn(row) {
+      bit_array_to_ints(row, bit_depth) |> list.take(num_values)
+    })
+  use image_data <- result.try(
+    case metadata.color_info.color_type {
+      Greyscale -> Ok(GreyscaleData(values))
+      Color -> list.try_map(values, chunk3) |> result.map(ColorData)
+      Indexed -> Ok(IndexedData(values))
+      GreyscaleWithAlpha ->
+        list.try_map(values, chunk2) |> result.map(GreyscaleWithAlphaData)
+      ColorWithAlpha ->
+        list.try_map(values, chunk4) |> result.map(ColorWithAlphaData)
+    }
+    |> result.replace_error(InvalidRowData),
+  )
+  Ok(PngData(metadata, palette, image_data))
+}

src/pngleam_erl.erl

@@ -0,0 +1,72 @@
+-module(pngleam_erl).
+
+-export([subUnfilter/2, upUnfilter/2, avgUnfilter/3, paethUnfilter/3, bitArrayToInts/1, bitArrayToInts/2]).
+
+addBytewise(As, Bs) ->
+    list_to_binary(lists:zipwith(fun(A, B) -> (A + B) rem 256 end, binary_to_list(As), binary_to_list(Bs), trim)).
+
+avgBytewise(As, Bs) ->
+    list_to_binary(lists:zipwith(fun(A, B) -> ((A + B) div 2) rem 256 end, binary_to_list(As), binary_to_list(Bs), trim)).
+
+paethBytewise(As, Bs, Cs) ->
+    list_to_binary(lists:zipwith3(fun(A, B, C) ->
+        P = A + B - C, % initial estimate
+        PA = abs(P - A), % distances to a, b, c
+        PB = abs(P - B),
+        PC = abs(P - C),
+        % return nearest of a,b,c,
+        % breaking ties in order a,b,c.
+        case (PA =< PB) and (PA =< PC) of
+            true -> A;
+            false -> case (PB =< PC) of
+                true -> B;
+                false -> C
+            end
+        end
+    end, binary_to_list(As), binary_to_list(Bs), binary_to_list(Cs), trim)).
+
+doSubUnfilter(Row, BytesPerPixel, Acc, Prev) ->
+    case Row of
+        <<>> -> Acc;
+        <<Curr:BytesPerPixel/binary, Rest/binary>> ->
+            New = addBytewise(Curr, Prev),
+            doSubUnfilter(Rest, BytesPerPixel, <<Acc/binary, New/binary>>, New)
+    end.
+
+subUnfilter(Row, BytesPerPixel) -> doSubUnfilter(Row, BytesPerPixel, <<>>, <<0:(BytesPerPixel * 8)>>).
+
+upUnfilter(Row, Above) -> addBytewise(Row, Above).
+
+doAvgUnfilter(Row, Above, BytesPerPixel, Acc, Prev) ->
+    case Row of
+        <<>> -> Acc;
+        <<Curr:BytesPerPixel/binary, Rest/binary>> ->
+            case Above of <<CurrAbove:BytesPerPixel/binary, RestAbove/binary>> ->
+                Avg = avgBytewise(Prev, CurrAbove),
+                New = addBytewise(Curr, Avg),
+                doAvgUnfilter(Rest, RestAbove, BytesPerPixel, <<Acc/binary, New/binary>>, New)
+            end
+    end.
+
+avgUnfilter(Row, Above, BytesPerPixel) -> doAvgUnfilter(Row, Above, BytesPerPixel, <<>>, <<0:(BytesPerPixel * 8)>>).
+
+doPaethUnfilter(Row, Above, BytesPerPixel, Acc, Prev, PrevAbove) ->
+    case Row of
+        <<>> -> Acc;
+        <<Curr:BytesPerPixel/binary, Rest/binary>> ->
+            case Above of <<CurrAbove:BytesPerPixel/binary, RestAbove/binary>> ->
+                Paeth = paethBytewise(Prev, CurrAbove, PrevAbove),
+                New = addBytewise(Curr, Paeth),
+                doPaethUnfilter(Rest, RestAbove, BytesPerPixel, <<Acc/binary, New/binary>>, New, CurrAbove)
+            end
+    end.
+
+paethUnfilter(Row, Above, BytesPerPixel) -> doPaethUnfilter(Row, Above, BytesPerPixel, <<>>, <<0:(BytesPerPixel * 8)>>, <<0:(BytesPerPixel * 8)>>).
+
+doBitArrayToInts(As, IntSize, Values) ->
+    case As of
+        <<V:IntSize, Rest/binary>> -> doBitArrayToInts(Rest, IntSize, [V | Values]);
+        _ -> Values
+    end.
+bitArrayToInts(As, IntSize) -> lists:reverse(doBitArrayToInts(As, IntSize, [])).
+bitArrayToInts(As) -> bitArrayToInts(As, 8).

src/pngleam_js.mjs

@@ -0,0 +1,82 @@
+import { BitArray, toList } from "./gleam.mjs"
+
+export const subUnfilter = (row, bpp) => {
+    const state = Buffer.alloc(bpp)
+    return new BitArray(new Uint8Array(row.buffer.map((x, i) => {
+        const j = i % bpp
+        const y = x + state[j]
+        state[j] = y
+        return y
+    })))
+}
+
+export const upUnfilter = (row, above) => new BitArray(new Uint8Array(row.buffer.map((x, i) => x + above[i])))
+
+const avg = (a, b) => Math.floor((a + b) / 2)
+
+export const avgUnfilter = (row, above, bpp) => {
+    const state = Buffer.alloc(bpp)
+    return new BitArray(new Uint8Array(row.buffer.map((x, i) => {
+        const j = i % bpp
+        const y = x + avg(state[j], above[i])
+        state[j] = y
+        return y
+    })))
+}
+
+const paeth = (a, b, c) => {
+    const p = a + b - c // initial estimate
+    const pa = Math.abs(p - a) // distances to a, b, c
+    const pb = Math.abs(p - b)
+    const pc = Math.abs(p - c)
+    // return nearest of a,b,c,
+    // breaking ties in order a,b,c.
+    if (pa <= pb && pa <= pc) return a
+    else if (pb <= pc) return b
+    else return c
+}
+
+export const paethUnfilter = (row, above, bpp) => {
+    const state = Buffer.alloc(bpp)
+    return new BitArray(new Uint8Array(row.buffer.map((x, i) => {
+        const j = i % bpp
+        const y = x + paeth(state[j], above[i], above[i - bpp] ?? 0)
+        state[j] = y
+        return y
+    })))
+}
+
+const doAddBytewise = (as, bs) => as.map((x, i) => x + bs[i])
+export const addBytewise = (as, bs) => new BitArray(new Uint8Array(doAddBytewise(as.buffer, bs.buffer)))
+
+const doSubBytewise = (as, bs) => as.map((a, i) => a - bs[i])
+export const subBytewise = (as, bs) => new BitArray(new Uint8Array(doSubBytewise(as.buffer, bs.buffer)))
+
+const doAvgBytewise = (as, bs) => as.map(a => Math.floor((a + bs[i]) / 2))
+export const avgBytewise = (as, bs) => new BitArray(new Uint8Array(doAvgBytewise(as.buffer, bs.buffer)))
+
+const doPaethBytewise = (as, bs, cs) => as.map((a, i) => {
+    const b = bs[i]
+    const c = cs[i]
+    const p = a + b - c // initial estimate
+    const pa = Math.abs(p - a) // distances to a, b, c
+    const pb = Math.abs(p - b)
+    const pc = Math.abs(p - c)
+    // return nearest of a,b,c,
+    // breaking ties in order a,b,c.
+    if (pa <= pb && pa <= pc) return a
+    else if (pb <= pc) return b
+    else return c
+})
+export const paethBytewise = (as, bs, cs) => new BitArray(new Uint8Array(doPaethBytewise(as.buffer, bs.buffer, cs.buffer)))
+
+const raise = message => { throw new Error(message) }
+
+export const bitArrayToInts = (as, intSize = 8) => toList(
+    intSize === 16 ? [...Array(as.buffer.length / 2)].map((_, i) => (as.buffer[i * 2] << 8) + as.buffer[i * 2 + 1]) :
+    intSize === 8 ? [...as.buffer] :
+    intSize === 4 ? [...as.buffer].flatMap(x => [x >> 4, x & 15]) :
+    intSize === 2 ? [...as.buffer].flatMap(x => [x >> 6, x >> 4 & 3, x >> 2 & 3, x & 3]) :
+    intSize === 1 ? [...as.buffer].flatMap(x => [x >> 7, x >> 6 & 1, x >> 5 & 1, x >> 4 & 1, x >> 3 & 1, x >> 2 & 1, x >> 1 & 1, x & 1]) :
+    raise("Invalid int size")
+)