Add gif encoding parameters to export gif

lib/src/exporter.dart

@@ -2,6 +2,7 @@ import 'dart:ui' as ui show ImageByteFormat;
 
 import 'package:flutter/foundation.dart';
 import 'package:image/image.dart' as image;
+
 import 'frame.dart';
 
 class Exporter {
@@ -30,8 +31,7 @@ class Exporter {
     }
     final bytesImages = <RawFrame>[];
     for (final frame in _frames) {
-      final bytesImage =
-          await frame.image.toByteData(format: ui.ImageByteFormat.png);
+      final bytesImage = await frame.image.toByteData(format: ui.ImageByteFormat.png);
 
       if (frame.image.width >= _maxWidthFrame) {
         _maxWidthFrame = frame.image.width;
@@ -50,31 +50,46 @@ class Exporter {
     return bytesImages;
   }
 
-  Future<List<int>?> exportGif() async {
+  Future<List<int>?> exportGif({
+    bool singleFrame = false,
+    int repeat = 0,
+    int samplingFactor = 10,
+    image.DitherKernel dither = image.DitherKernel.floydSteinberg,
+    bool ditherSerpentine = false,
+  }) async {
     final frames = await exportFrames();
     if (frames == null) {
       return null;
     }
     return compute(
-        _exportGif, DataHolder(frames, _maxWidthFrame, _maxHeightFrame));
+      _exportGif,
+      DataHolder(
+        frames,
+        _maxWidthFrame,
+        _maxHeightFrame,
+        singleFrame: singleFrame,
+        repeat: repeat,
+        samplingFactor: samplingFactor,
+        dither: dither,
+        ditherSerpentine: ditherSerpentine,
+      ),
+    );
   }
 
   static Future<List<int>?> _exportGif(DataHolder data) async {
-    List<RawFrame> frames = data.frames;
-    int width = data.width;
-    int height = data.height;
+    final frames = data.frames;
+    final width = data.width;
+    final height = data.height;
 
     image.Image mainImage = image.Image.empty();
 
     for (final frame in frames) {
-      final iAsBytes = frame.image.buffer.asUint8List();
-      final decodedImage = image.decodePng(iAsBytes);
+      final decodedImage = image.decodePng(frame.image.buffer.asUint8List());
+
+      if (decodedImage == null) continue;
 
-      if (decodedImage == null) {
-        debugPrint('Skipped frame while enconding');
-        continue;
-      }
       decodedImage.frameDuration = frame.durationInMillis;
+
       mainImage.frames.add(
         _encodeGifWIthTransparency(
           image.copyExpandCanvas(
@@ -92,20 +107,25 @@ class Exporter {
       );
     }
 
-    return image.encodeGif(mainImage);
+    return image.encodeGif(
+      mainImage,
+      singleFrame: data.singleFrame,
+      repeat: data.repeat,
+      samplingFactor: data.samplingFactor,
+      dither: data.dither,
+      ditherSerpentine: data.ditherSerpentine,
+    );
   }
 
   static image.PaletteUint8 _convertPalette(image.Palette palette) {
     final newPalette = image.PaletteUint8(palette.numColors, 4);
     for (var i = 0; i < palette.numColors; i++) {
-      newPalette.setRgba(
-          i, palette.getRed(i), palette.getGreen(i), palette.getBlue(i), 255);
+      newPalette.setRgba(i, palette.getRed(i), palette.getGreen(i), palette.getBlue(i), 255);
     }
     return newPalette;
   }
 
-  static image.Image _encodeGifWIthTransparency(image.Image srcImage,
-      {int transparencyThreshold = 1}) {
+  static image.Image _encodeGifWIthTransparency(image.Image srcImage, {int transparencyThreshold = 1}) {
     final newImage = image.quantize(srcImage);
 
     // GifEncoder will use palette colors with a 0 alpha as transparent. Look at the pixels
@@ -121,8 +141,7 @@ class Exporter {
       for (final srcPixel in srcFrame) {
         if (srcPixel.a < transparencyThreshold) {
           final newPixel = newFrame.getPixel(srcPixel.x, srcPixel.y);
-          palette.setAlpha(
-              newPixel.index.toInt(), 0); // Set the palette color alpha to 0
+          palette.setAlpha(newPixel.index.toInt(), 0); // Set the palette color alpha to 0
         }
       }
 
@@ -141,10 +160,24 @@ class RawFrame {
 }
 
 class DataHolder {
-  DataHolder(this.frames, this.width, this.height);
-
-  List<RawFrame> frames;
-
-  int width;
-  int height;
+  DataHolder(
+    this.frames,
+    this.width,
+    this.height, {
+    this.singleFrame = false,
+    this.repeat = 0,
+    this.samplingFactor = 10,
+    this.dither = image.DitherKernel.floydSteinberg,
+    this.ditherSerpentine = false,
+  });
+
+  final List<RawFrame> frames;
+  final int width;
+  final int height;
+
+  final bool singleFrame;
+  final int repeat;
+  final int samplingFactor;
+  final image.DitherKernel dither;
+  final bool ditherSerpentine;
 }