Support lossless WebP (#38)

CaiJingLong · Apr 3, 2024 · 545d611 · 545d611
1 parent cbacd48
commit 545d611
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diff --git a/example/asset/demo_lossless.webp b/example/asset/demo_lossless.webp
diff --git a/library/lib/src/decoder/impl/webp_decoder.dart b/library/lib/src/decoder/impl/webp_decoder.dart
@@ -20,6 +20,9 @@ class WebpDecoder extends BaseDecoder {
       final widthList = input.getRange(0x18, 0x1b);
       final heightList = input.getRange(0x1b, 0x1d);
       return _createExtendedFormatSize(widthList, heightList);
+    } else if (_isLosslessFormat(chunkHeader)) {
+      final sizeList = input.getRange(0x15, 0x19);
+      return _createLosslessFormatSize(sizeList);
     } else {
       final widthList = input.getRange(0x1a, 0x1c);
       final heightList = input.getRange(0x1c, 0x1e);
@@ -39,17 +42,38 @@ class WebpDecoder extends BaseDecoder {
     return Size(width, height);
   }
 
+  Size _createLosslessFormatSize(List<int> sizeList) {
+    final bits = sizeList
+        .map(
+          (i) => i.toRadixString(2).split('').reversed.join().padRight(8, '0'),
+        )
+        .join()
+        .split('');
+    final width =
+        (int.tryParse(bits.sublist(0, 14).reversed.join(), radix: 2) ?? 0) + 1;
+    final height =
+        (int.tryParse(bits.sublist(14, 28).reversed.join(), radix: 2) ?? 0) + 1;
+    return Size(width, height);
+  }
+
   bool _isExtendedFormat(List<int> chunkHeader) {
     return ListEquality().equals(chunkHeader, "VP8X".codeUnits);
   }
 
+  bool _isLosslessFormat(List<int> chunkHeader) {
+    return ListEquality().equals(chunkHeader, "VP8L".codeUnits);
+  }
+
   @override
   Future<Size> getSizeAsync(AsyncImageInput input) async {
     final chunkHeader = await input.getRange(12, 16);
     if (_isExtendedFormat(chunkHeader)) {
       final widthList = await input.getRange(0x18, 0x1b);
       final heightList = await input.getRange(0x1b, 0x1d);
       return _createExtendedFormatSize(widthList, heightList);
+    } else if (_isLosslessFormat(chunkHeader)) {
+      final sizeList = await input.getRange(0x15, 0x19);
+      return _createLosslessFormatSize(sizeList);
     } else {
       final widthList = await input.getRange(0x1a, 0x1c);
       final heightList = await input.getRange(0x1c, 0x1e);

diff --git a/library/test/image_size_getter_test.dart b/library/test/image_size_getter_test.dart
@@ -89,6 +89,13 @@ void main() {
       await expectLater(size, Size(988, 466));
     });
 
+    test('Test webp lossless format size', () async {
+      final file = File('../example/asset/demo_lossless.webp');
+      final size = ImageSizeGetter.getSize(FileInput(file));
+      print('size = $size');
+      await expectLater(size, Size(988, 466));
+    });
+
     test('Test jpeg size', () async {
       final file = File('../example/asset/IMG_20180908_080245.jpg');
       final size = ImageSizeGetter.getSize(FileInput(file));