LibGfx/GIF: Correctly write frames with a non-null position

Tests/LibGfx/TestImageWriter.cpp

@@ -129,19 +129,23 @@ TEST_CASE(test_gif_animated)
 {
  auto bitmap_1 = TRY_OR_FAIL(TRY_OR_FAIL(create_test_rgb_bitmap())->cropped({ 0, 0, 16, 16 }));
  auto bitmap_2 = TRY_OR_FAIL(TRY_OR_FAIL(create_test_rgb_bitmap())->cropped({ 16, 16, 16, 16 }));
+ auto bitmap_3 = TRY_OR_FAIL(bitmap_2->clone());
+
+ bitmap_3->scanline(3)[3] = Color(Color::NamedColor::Red).value();
 
  auto stream_buffer = TRY_OR_FAIL(ByteBuffer::create_uninitialized(3072));
  FixedMemoryStream stream { Bytes { stream_buffer } };
  auto animation_writer = TRY_OR_FAIL(Gfx::GIFWriter::start_encoding_animation(stream, bitmap_1->size(), 0));
  TRY_OR_FAIL(animation_writer->add_frame(*bitmap_1, 100));
  TRY_OR_FAIL(animation_writer->add_frame(*bitmap_2, 200));
+ TRY_OR_FAIL(animation_writer->add_frame_relative_to_last_frame(*bitmap_3, 200, *bitmap_2));
 
  auto encoded_animation = ReadonlyBytes { stream_buffer.data(), stream.offset() };
 
  auto decoder = TRY_OR_FAIL(Gfx::GIFImageDecoderPlugin::create(encoded_animation));
 
  EXPECT_EQ(decoder->size(), bitmap_1->size());
- EXPECT_EQ(decoder->frame_count(), 2u);
+ EXPECT_EQ(decoder->frame_count(), 3u);
  EXPECT_EQ(decoder->loop_count(), 0u);
  EXPECT(decoder->is_animated());
 
@@ -152,6 +156,10 @@ TEST_CASE(test_gif_animated)
  auto const frame_2 = TRY_OR_FAIL(decoder->frame(1));
  EXPECT_EQ(frame_2.duration, 200);
  expect_bitmaps_equal(*frame_2.image, bitmap_2);
+
+ auto const frame_3 = TRY_OR_FAIL(decoder->frame(2));
+ EXPECT_EQ(frame_3.duration, 200);
+ expect_bitmaps_equal(*frame_3.image, bitmap_3);
 }
 
 TEST_CASE(test_jpeg)

Userland/Libraries/LibGfx/ImageFormats/GIFWriter.cpp

@@ -93,16 +93,16 @@ ErrorOr<void> write_image_data(Stream& stream, Bitmap const& bitmap, ColorPalett
  return {};
 }
 
-ErrorOr<void> write_image_descriptor(BigEndianOutputBitStream& stream, Bitmap const& bitmap)
+ErrorOr<void> write_image_descriptor(BigEndianOutputBitStream& stream, Bitmap const& bitmap, IntPoint at = {})
 {
  // 20. Image Descriptor
 
  // Image Separator
  TRY(stream.write_value<u8>(0x2c));
  // Image Left Position
- TRY(stream.write_value<u16>(0));
+ TRY(stream.write_value<u16>(at.x()));
  // Image Top Position
- TRY(stream.write_value<u16>(0));
+ TRY(stream.write_value<u16>(at.y()));
  // Image Width
  TRY(stream.write_value<u16>(bitmap.width()));
  // Image Height
@@ -177,9 +177,6 @@ class GIFAnimationWriter : public AnimationWriter {
 
 ErrorOr<void> GIFAnimationWriter::add_frame(Bitmap& bitmap, int duration_ms, IntPoint at = {})
 {
- // FIXME: Consider frame's position
- (void)at;
-
  // Let's get rid of the previously written trailer
  if (!m_is_first_frame)
  TRY(m_stream.seek(-1, SeekMode::FromCurrentPosition));
@@ -189,7 +186,7 @@ ErrorOr<void> GIFAnimationWriter::add_frame(Bitmap& bitmap, int duration_ms, Int
  // Write a Table-Based Image
  BigEndianOutputBitStream bit_stream { MaybeOwned { m_stream } };
  TRY(write_graphic_control_extension(bit_stream, duration_ms));
- TRY(write_image_descriptor(bit_stream, bitmap));
+ TRY(write_image_descriptor(bit_stream, bitmap, at));
 
  auto const palette = TRY(median_cut(bitmap, 256));
  TRY(write_color_table(m_stream, palette));