image/lib/src/formats/png_encoder.dart - third_party/dart-pkg - Git at Google

 import 'dart:typed_data';

 import 'package:archive/archive.dart';

 import '../animation.dart';
 import '../color.dart';
 import '../icc_profile_data.dart';
 import '../image.dart';
 import '../util/output_buffer.dart';
 import 'encoder.dart';

 /// Encode an image to the PNG format.
 class PngEncoder extends Encoder {
   PngEncoder({this.filter = FILTER_PAETH, this.level});

   void addFrame(Image image) {
     xOffset = image.xOffset;
     yOffset = image.xOffset;
     delay = image.duration;
     disposeMethod = image.disposeMethod;
     blendMethod = image.blendMethod;

     if (output == null) {
       output = OutputBuffer(bigEndian: true);

       channels = image.channels;
       _width = image.width;
       _height = image.height;

       _writeHeader(_width, _height);

       _writeICCPChunk(output, image.iccProfile);

       if (isAnimated) {
         _writeAnimationControlChunk();
       }
     }

     // Include room for the filter bytes (1 byte per row).
     final filteredImage = Uint8List(
         (image.width * image.height * image.numberOfChannels) + image.height);

     _filter(image, filteredImage);

     final compressed = ZLibEncoder().encode(filteredImage, level: level);

     if (isAnimated) {
       _writeFrameControlChunk();
       sequenceNumber++;
     }

     if (sequenceNumber <= 1) {
       _writeChunk(output!, 'IDAT', compressed);
     } else {
       // fdAT chunk
       final fdat = OutputBuffer(bigEndian: true);
       fdat.writeUint32(sequenceNumber);
       fdat.writeBytes(compressed);
       _writeChunk(output!, 'fdAT', fdat.getBytes());

       sequenceNumber++;
     }
   }

   List<int>? finish() {
     List<int>? bytes;

     if (output == null) {
       return bytes;
     }

     _writeChunk(output!, 'IEND', []);

     sequenceNumber = 0;

     bytes = output!.getBytes();
     output = null;
     return bytes;
   }

   /// Does this encoder support animation?
   @override
   bool get supportsAnimation => true;

   /// Encode an animation.
   @override
   List<int>? encodeAnimation(Animation anim) {
     isAnimated = true;
     _frames = anim.frames.length;
     repeat = anim.loopCount;

     for (var f in anim) {
       addFrame(f);
     }
     return finish();
   }

   /// Encode a single frame image.
   @override
   List<int> encodeImage(Image image) {
     isAnimated = false;
     addFrame(image);
     return finish()!;
   }

   void _writeHeader(int width, int height) {
     // PNG file signature
     output!.writeBytes([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]);

     // IHDR chunk
     final chunk = OutputBuffer(bigEndian: true);
     chunk.writeUint32(width);
     chunk.writeUint32(height);
     chunk.writeByte(8);
     chunk.writeByte(channels == Channels.rgb ? 2 : 6);
     chunk.writeByte(0); // compression method
     chunk.writeByte(0); // filter method
     chunk.writeByte(0); // interlace method
     _writeChunk(output!, 'IHDR', chunk.getBytes());
   }

   void _writeAnimationControlChunk() {
     final chunk = OutputBuffer(bigEndian: true);
     chunk.writeUint32(_frames); // number of frames
     chunk.writeUint32(repeat); // loop count
     _writeChunk(output!, 'acTL', chunk.getBytes());
   }

   void _writeFrameControlChunk() {
     final chunk = OutputBuffer(bigEndian: true);
     chunk.writeUint32(sequenceNumber);
     chunk.writeUint32(_width);
     chunk.writeUint32(_height);
     chunk.writeUint32(xOffset);
     chunk.writeUint32(yOffset);
     chunk.writeUint16(delay!);
     chunk.writeUint16(1000); // delay denominator
     chunk.writeByte(disposeMethod.index);
     chunk.writeByte(blendMethod.index);
     _writeChunk(output!, 'fcTL', chunk.getBytes());
   }

   void _writeICCPChunk(OutputBuffer? out, ICCProfileData? iccp) {
     if (iccp == null) {
       return;
     }

     final chunk = OutputBuffer(bigEndian: true);

     // name
     chunk.writeBytes(iccp.name.codeUnits);
     chunk.writeByte(0);

     // compression
     chunk.writeByte(0); // 0 - deflate

     // profile data
     chunk.writeBytes(iccp.compressed());

     _writeChunk(output!, 'iCCP', chunk.getBytes());
   }

   void _writeChunk(OutputBuffer out, String type, List<int> chunk) {
     out.writeUint32(chunk.length);
     out.writeBytes(type.codeUnits);
     out.writeBytes(chunk);
     final crc = _crc(type, chunk);
     out.writeUint32(crc);
   }

   void _filter(Image image, List<int> out) {
     var oi = 0;
     for (var y = 0; y < image.height; ++y) {
       switch (filter) {
         case FILTER_SUB:
           oi = _filterSub(image, oi, y, out);
           break;
         case FILTER_UP:
           oi = _filterUp(image, oi, y, out);
           break;
         case FILTER_AVERAGE:
           oi = _filterAverage(image, oi, y, out);
           break;
         case FILTER_PAETH:
           oi = _filterPaeth(image, oi, y, out);
           break;
         case FILTER_AGRESSIVE:
           // TODO Apply all five filters and select the filter that produces
           // the smallest sum of absolute values per row.
           oi = _filterPaeth(image, oi, y, out);
           break;
         default:
           oi = _filterNone(image, oi, y, out);
           break;
       }
     }
   }

   int _filterNone(Image image, int oi, int row, List<int> out) {
     out[oi++] = FILTER_NONE;
     for (var x = 0; x < image.width; ++x) {
       final c = image.getPixel(x, row);
       out[oi++] = getRed(c);
       out[oi++] = getGreen(c);
       out[oi++] = getBlue(c);
       if (image.channels == Channels.rgba) {
         out[oi++] = getAlpha(image.getPixel(x, row));
       }
     }
     return oi;
   }

   int _filterSub(Image image, int oi, int row, List<int> out) {
     out[oi++] = FILTER_SUB;

     out[oi++] = getRed(image.getPixel(0, row));
     out[oi++] = getGreen(image.getPixel(0, row));
     out[oi++] = getBlue(image.getPixel(0, row));
     if (image.channels == Channels.rgba) {
       out[oi++] = getAlpha(image.getPixel(0, row));
     }

     for (var x = 1; x < image.width; ++x) {
       final ar = getRed(image.getPixel(x - 1, row));
       final ag = getGreen(image.getPixel(x - 1, row));
       final ab = getBlue(image.getPixel(x - 1, row));

       final r = getRed(image.getPixel(x, row));
       final g = getGreen(image.getPixel(x, row));
       final b = getBlue(image.getPixel(x, row));

       out[oi++] = ((r - ar)) & 0xff;
       out[oi++] = ((g - ag)) & 0xff;
       out[oi++] = ((b - ab)) & 0xff;
       if (image.channels == Channels.rgba) {
         final aa = getAlpha(image.getPixel(x - 1, row));
         final a = getAlpha(image.getPixel(x, row));
         out[oi++] = ((a - aa)) & 0xff;
       }
     }

     return oi;
   }

   int _filterUp(Image image, int oi, int row, List<int> out) {
     out[oi++] = FILTER_UP;

     for (var x = 0; x < image.width; ++x) {
       final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
       final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
       final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

       final xr = getRed(image.getPixel(x, row));
       final xg = getGreen(image.getPixel(x, row));
       final xb = getBlue(image.getPixel(x, row));

       out[oi++] = (xr - br) & 0xff;
       out[oi++] = (xg - bg) & 0xff;
       out[oi++] = (xb - bb) & 0xff;
       if (image.channels == Channels.rgba) {
         final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
         final xa = getAlpha(image.getPixel(x, row));
         out[oi++] = (xa - ba) & 0xff;
       }
     }

     return oi;
   }

   int _filterAverage(Image image, int oi, int row, List<int> out) {
     out[oi++] = FILTER_AVERAGE;

     for (var x = 0; x < image.width; ++x) {
       final ar = (x == 0) ? 0 : getRed(image.getPixel(x - 1, row));
       final ag = (x == 0) ? 0 : getGreen(image.getPixel(x - 1, row));
       final ab = (x == 0) ? 0 : getBlue(image.getPixel(x - 1, row));

       final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
       final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
       final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

       final xr = getRed(image.getPixel(x, row));
       final xg = getGreen(image.getPixel(x, row));
       final xb = getBlue(image.getPixel(x, row));

       out[oi++] = (xr - ((ar + br) >> 1)) & 0xff;
       out[oi++] = (xg - ((ag + bg) >> 1)) & 0xff;
       out[oi++] = (xb - ((ab + bb) >> 1)) & 0xff;
       if (image.channels == Channels.rgba) {
         final aa = (x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row));
         final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
         final xa = getAlpha(image.getPixel(x, row));
         out[oi++] = (xa - ((aa + ba) >> 1)) & 0xff;
       }
     }

     return oi;
   }

   int _paethPredictor(int a, int b, int c) {
     final p = a + b - c;
     final pa = (p > a) ? p - a : a - p;
     final pb = (p > b) ? p - b : b - p;
     final pc = (p > c) ? p - c : c - p;
     if (pa <= pb && pa <= pc) {
       return a;
     } else if (pb <= pc) {
       return b;
     }
     return c;
   }

   int _filterPaeth(Image image, int oi, int row, List<int> out) {
     out[oi++] = FILTER_PAETH;

     for (var x = 0; x < image.width; ++x) {
       final ar = (x == 0) ? 0 : getRed(image.getPixel(x - 1, row));
       final ag = (x == 0) ? 0 : getGreen(image.getPixel(x - 1, row));
       final ab = (x == 0) ? 0 : getBlue(image.getPixel(x - 1, row));

       final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
       final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
       final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

       final cr =
           (row == 0 || x == 0) ? 0 : getRed(image.getPixel(x - 1, row - 1));
       final cg =
           (row == 0 || x == 0) ? 0 : getGreen(image.getPixel(x - 1, row - 1));
       final cb =
           (row == 0 || x == 0) ? 0 : getBlue(image.getPixel(x - 1, row - 1));

       final xr = getRed(image.getPixel(x, row));
       final xg = getGreen(image.getPixel(x, row));
       final xb = getBlue(image.getPixel(x, row));

       final pr = _paethPredictor(ar, br, cr);
       final pg = _paethPredictor(ag, bg, cg);
       final pb = _paethPredictor(ab, bb, cb);

       out[oi++] = (xr - pr) & 0xff;
       out[oi++] = (xg - pg) & 0xff;
       out[oi++] = (xb - pb) & 0xff;
       if (image.channels == Channels.rgba) {
         final aa = (x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row));
         final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
         final ca =
             (row == 0 || x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row - 1));
         final xa = getAlpha(image.getPixel(x, row));
         final pa = _paethPredictor(aa, ba, ca);
         out[oi++] = (xa - pa) & 0xff;
       }
     }

     return oi;
   }

   // Return the CRC of the bytes
   int _crc(String type, List<int> bytes) {
     final crc = getCrc32(type.codeUnits);
     return getCrc32(bytes, crc);
   }

   Channels? channels;
   int filter;
   int repeat = 0;
   int? level;
   late int xOffset;
   late int yOffset;
   int? delay;
   late DisposeMode disposeMethod;
   late BlendMode blendMethod;
   late int _width;
   late int _height;
   late int _frames;
   int sequenceNumber = 0;
   bool isAnimated = false;
   OutputBuffer? output;

   static const FILTER_NONE = 0;
   static const FILTER_SUB = 1;
   static const FILTER_UP = 2;
   static const FILTER_AVERAGE = 3;
   static const FILTER_PAETH = 4;
   static const FILTER_AGRESSIVE = 5;

 // Table of CRCs of all 8-bit messages.
 //final List<int> _crcTable = List<int>(256);
 }
	import 'dart:typed_data';

	import 'package:archive/archive.dart';

	import '../animation.dart';
	import '../color.dart';
	import '../icc_profile_data.dart';
	import '../image.dart';
	import '../util/output_buffer.dart';
	import 'encoder.dart';

	/// Encode an image to the PNG format.
	class PngEncoder extends Encoder {
	PngEncoder({this.filter = FILTER_PAETH, this.level});

	void addFrame(Image image) {
	xOffset = image.xOffset;
	yOffset = image.xOffset;
	delay = image.duration;
	disposeMethod = image.disposeMethod;
	blendMethod = image.blendMethod;

	if (output == null) {
	output = OutputBuffer(bigEndian: true);

	channels = image.channels;
	_width = image.width;
	_height = image.height;

	_writeHeader(_width, _height);

	_writeICCPChunk(output, image.iccProfile);

	if (isAnimated) {
	_writeAnimationControlChunk();
	}
	}

	// Include room for the filter bytes (1 byte per row).
	final filteredImage = Uint8List(
	(image.width * image.height * image.numberOfChannels) + image.height);

	_filter(image, filteredImage);

	final compressed = ZLibEncoder().encode(filteredImage, level: level);

	if (isAnimated) {
	_writeFrameControlChunk();
	sequenceNumber++;
	}

	if (sequenceNumber <= 1) {
	_writeChunk(output!, 'IDAT', compressed);
	} else {
	// fdAT chunk
	final fdat = OutputBuffer(bigEndian: true);
	fdat.writeUint32(sequenceNumber);
	fdat.writeBytes(compressed);
	_writeChunk(output!, 'fdAT', fdat.getBytes());

	sequenceNumber++;
	}
	}

	List<int>? finish() {
	List<int>? bytes;

	if (output == null) {
	return bytes;
	}

	_writeChunk(output!, 'IEND', []);

	sequenceNumber = 0;

	bytes = output!.getBytes();
	output = null;
	return bytes;
	}

	/// Does this encoder support animation?
	@override
	bool get supportsAnimation => true;

	/// Encode an animation.
	@override
	List<int>? encodeAnimation(Animation anim) {
	isAnimated = true;
	_frames = anim.frames.length;
	repeat = anim.loopCount;

	for (var f in anim) {
	addFrame(f);
	}
	return finish();
	}

	/// Encode a single frame image.
	@override
	List<int> encodeImage(Image image) {
	isAnimated = false;
	addFrame(image);
	return finish()!;
	}

	void _writeHeader(int width, int height) {
	// PNG file signature
	output!.writeBytes([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]);

	// IHDR chunk
	final chunk = OutputBuffer(bigEndian: true);
	chunk.writeUint32(width);
	chunk.writeUint32(height);
	chunk.writeByte(8);
	chunk.writeByte(channels == Channels.rgb ? 2 : 6);
	chunk.writeByte(0); // compression method
	chunk.writeByte(0); // filter method
	chunk.writeByte(0); // interlace method
	_writeChunk(output!, 'IHDR', chunk.getBytes());
	}

	void _writeAnimationControlChunk() {
	final chunk = OutputBuffer(bigEndian: true);
	chunk.writeUint32(_frames); // number of frames
	chunk.writeUint32(repeat); // loop count
	_writeChunk(output!, 'acTL', chunk.getBytes());
	}

	void _writeFrameControlChunk() {
	final chunk = OutputBuffer(bigEndian: true);
	chunk.writeUint32(sequenceNumber);
	chunk.writeUint32(_width);
	chunk.writeUint32(_height);
	chunk.writeUint32(xOffset);
	chunk.writeUint32(yOffset);
	chunk.writeUint16(delay!);
	chunk.writeUint16(1000); // delay denominator
	chunk.writeByte(disposeMethod.index);
	chunk.writeByte(blendMethod.index);
	_writeChunk(output!, 'fcTL', chunk.getBytes());
	}

	void _writeICCPChunk(OutputBuffer? out, ICCProfileData? iccp) {
	if (iccp == null) {
	return;
	}

	final chunk = OutputBuffer(bigEndian: true);

	// name
	chunk.writeBytes(iccp.name.codeUnits);
	chunk.writeByte(0);

	// compression
	chunk.writeByte(0); // 0 - deflate

	// profile data
	chunk.writeBytes(iccp.compressed());

	_writeChunk(output!, 'iCCP', chunk.getBytes());
	}

	void _writeChunk(OutputBuffer out, String type, List<int> chunk) {
	out.writeUint32(chunk.length);
	out.writeBytes(type.codeUnits);
	out.writeBytes(chunk);
	final crc = _crc(type, chunk);
	out.writeUint32(crc);
	}

	void _filter(Image image, List<int> out) {
	var oi = 0;
	for (var y = 0; y < image.height; ++y) {
	switch (filter) {
	case FILTER_SUB:
	oi = _filterSub(image, oi, y, out);
	break;
	case FILTER_UP:
	oi = _filterUp(image, oi, y, out);
	break;
	case FILTER_AVERAGE:
	oi = _filterAverage(image, oi, y, out);
	break;
	case FILTER_PAETH:
	oi = _filterPaeth(image, oi, y, out);
	break;
	case FILTER_AGRESSIVE:
	// TODO Apply all five filters and select the filter that produces
	// the smallest sum of absolute values per row.
	oi = _filterPaeth(image, oi, y, out);
	break;
	default:
	oi = _filterNone(image, oi, y, out);
	break;
	}
	}
	}

	int _filterNone(Image image, int oi, int row, List<int> out) {
	out[oi++] = FILTER_NONE;
	for (var x = 0; x < image.width; ++x) {
	final c = image.getPixel(x, row);
	out[oi++] = getRed(c);
	out[oi++] = getGreen(c);
	out[oi++] = getBlue(c);
	if (image.channels == Channels.rgba) {
	out[oi++] = getAlpha(image.getPixel(x, row));
	}
	}
	return oi;
	}

	int _filterSub(Image image, int oi, int row, List<int> out) {
	out[oi++] = FILTER_SUB;

	out[oi++] = getRed(image.getPixel(0, row));
	out[oi++] = getGreen(image.getPixel(0, row));
	out[oi++] = getBlue(image.getPixel(0, row));
	if (image.channels == Channels.rgba) {
	out[oi++] = getAlpha(image.getPixel(0, row));
	}

	for (var x = 1; x < image.width; ++x) {
	final ar = getRed(image.getPixel(x - 1, row));
	final ag = getGreen(image.getPixel(x - 1, row));
	final ab = getBlue(image.getPixel(x - 1, row));

	final r = getRed(image.getPixel(x, row));
	final g = getGreen(image.getPixel(x, row));
	final b = getBlue(image.getPixel(x, row));

	out[oi++] = ((r - ar)) & 0xff;
	out[oi++] = ((g - ag)) & 0xff;
	out[oi++] = ((b - ab)) & 0xff;
	if (image.channels == Channels.rgba) {
	final aa = getAlpha(image.getPixel(x - 1, row));
	final a = getAlpha(image.getPixel(x, row));
	out[oi++] = ((a - aa)) & 0xff;
	}
	}

	return oi;
	}

	int _filterUp(Image image, int oi, int row, List<int> out) {
	out[oi++] = FILTER_UP;

	for (var x = 0; x < image.width; ++x) {
	final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
	final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
	final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

	final xr = getRed(image.getPixel(x, row));
	final xg = getGreen(image.getPixel(x, row));
	final xb = getBlue(image.getPixel(x, row));

	out[oi++] = (xr - br) & 0xff;
	out[oi++] = (xg - bg) & 0xff;
	out[oi++] = (xb - bb) & 0xff;
	if (image.channels == Channels.rgba) {
	final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
	final xa = getAlpha(image.getPixel(x, row));
	out[oi++] = (xa - ba) & 0xff;
	}
	}

	return oi;
	}

	int _filterAverage(Image image, int oi, int row, List<int> out) {
	out[oi++] = FILTER_AVERAGE;

	for (var x = 0; x < image.width; ++x) {
	final ar = (x == 0) ? 0 : getRed(image.getPixel(x - 1, row));
	final ag = (x == 0) ? 0 : getGreen(image.getPixel(x - 1, row));
	final ab = (x == 0) ? 0 : getBlue(image.getPixel(x - 1, row));

	final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
	final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
	final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

	final xr = getRed(image.getPixel(x, row));
	final xg = getGreen(image.getPixel(x, row));
	final xb = getBlue(image.getPixel(x, row));

	out[oi++] = (xr - ((ar + br) >> 1)) & 0xff;
	out[oi++] = (xg - ((ag + bg) >> 1)) & 0xff;
	out[oi++] = (xb - ((ab + bb) >> 1)) & 0xff;
	if (image.channels == Channels.rgba) {
	final aa = (x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row));
	final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
	final xa = getAlpha(image.getPixel(x, row));
	out[oi++] = (xa - ((aa + ba) >> 1)) & 0xff;
	}
	}

	return oi;
	}

	int _paethPredictor(int a, int b, int c) {
	final p = a + b - c;
	final pa = (p > a) ? p - a : a - p;
	final pb = (p > b) ? p - b : b - p;
	final pc = (p > c) ? p - c : c - p;
	if (pa <= pb && pa <= pc) {
	return a;
	} else if (pb <= pc) {
	return b;
	}
	return c;
	}

	int _filterPaeth(Image image, int oi, int row, List<int> out) {
	out[oi++] = FILTER_PAETH;

	for (var x = 0; x < image.width; ++x) {
	final ar = (x == 0) ? 0 : getRed(image.getPixel(x - 1, row));
	final ag = (x == 0) ? 0 : getGreen(image.getPixel(x - 1, row));
	final ab = (x == 0) ? 0 : getBlue(image.getPixel(x - 1, row));

	final br = (row == 0) ? 0 : getRed(image.getPixel(x, row - 1));
	final bg = (row == 0) ? 0 : getGreen(image.getPixel(x, row - 1));
	final bb = (row == 0) ? 0 : getBlue(image.getPixel(x, row - 1));

	final cr =
	(row == 0 \|\| x == 0) ? 0 : getRed(image.getPixel(x - 1, row - 1));
	final cg =
	(row == 0 \|\| x == 0) ? 0 : getGreen(image.getPixel(x - 1, row - 1));
	final cb =
	(row == 0 \|\| x == 0) ? 0 : getBlue(image.getPixel(x - 1, row - 1));

	final xr = getRed(image.getPixel(x, row));
	final xg = getGreen(image.getPixel(x, row));
	final xb = getBlue(image.getPixel(x, row));

	final pr = _paethPredictor(ar, br, cr);
	final pg = _paethPredictor(ag, bg, cg);
	final pb = _paethPredictor(ab, bb, cb);

	out[oi++] = (xr - pr) & 0xff;
	out[oi++] = (xg - pg) & 0xff;
	out[oi++] = (xb - pb) & 0xff;
	if (image.channels == Channels.rgba) {
	final aa = (x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row));
	final ba = (row == 0) ? 0 : getAlpha(image.getPixel(x, row - 1));
	final ca =
	(row == 0 \|\| x == 0) ? 0 : getAlpha(image.getPixel(x - 1, row - 1));
	final xa = getAlpha(image.getPixel(x, row));
	final pa = _paethPredictor(aa, ba, ca);
	out[oi++] = (xa - pa) & 0xff;
	}
	}

	return oi;
	}

	// Return the CRC of the bytes
	int _crc(String type, List<int> bytes) {
	final crc = getCrc32(type.codeUnits);
	return getCrc32(bytes, crc);
	}

	Channels? channels;
	int filter;
	int repeat = 0;
	int? level;
	late int xOffset;
	late int yOffset;
	int? delay;
	late DisposeMode disposeMethod;
	late BlendMode blendMethod;
	late int _width;
	late int _height;
	late int _frames;
	int sequenceNumber = 0;
	bool isAnimated = false;
	OutputBuffer? output;

	static const FILTER_NONE = 0;
	static const FILTER_SUB = 1;
	static const FILTER_UP = 2;
	static const FILTER_AVERAGE = 3;
	static const FILTER_PAETH = 4;
	static const FILTER_AGRESSIVE = 5;

	// Table of CRCs of all 8-bit messages.
	//final List<int> _crcTable = List<int>(256);
	}