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LibGfx: correctly handle GIF frame disposal modes

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RestoreBackground disposal mode is now a transparent fill to allow
background to show through.

RestorePrevious disposal mode now restores the previous frame.
This commit is contained in:
Peter Nelson 2020-08-29 15:04:41 +01:00 • committed by Andreas Kling
parent 3ae55770c8
commit 1341025da7
1 changed files with 17 additions and 8 deletions
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25
Libraries/LibGfx/GIFLoader.cpp
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@ -260,6 +260,15 @@ private:
Vector<u8> m_output {};
};
static void copy_frame(Bitmap& destination, Bitmap& source)
{
for (int y = 0; y < source.height(); ++y) {
for (int x = 0; x < source.width(); ++x) {
destination.set_pixel(x, y, source.get_pixel(x, y));
}
}
}
static bool decode_frames_up_to_index(GIFLoadingContext& context, size_t frame_index)
{
if (frame_index >= context.images.size()) {
@ -285,18 +294,18 @@ static bool decode_frames_up_to_index(GIFLoadingContext& context, size_t frame_i
image.bitmap = Bitmap::create_purgeable(BitmapFormat::RGBA32, { context.logical_screen.width, context.logical_screen.height });
if (i == 0) {
image.bitmap->fill(background_color);
}
const auto previous_image_disposal_method = i > 0 ? context.images.at(i - 1).disposal_method : ImageDescriptor::DisposalMethod::None;
if (previous_image_disposal_method == ImageDescriptor::DisposalMethod::InPlace) {
for (int y = 0; y < image.bitmap->height(); ++y) {
for (int x = 0; x < image.bitmap->width(); ++x) {
image.bitmap->set_pixel(x, y, context.images.at(i - 1).bitmap->get_pixel(x, y));
}
}
if (i > 0 && (previous_image_disposal_method == ImageDescriptor::DisposalMethod::None || previous_image_disposal_method == ImageDescriptor::DisposalMethod::InPlace)) {
copy_frame(*image.bitmap, *context.images.at(i - 1).bitmap);
} else if (previous_image_disposal_method == ImageDescriptor::DisposalMethod::RestoreBackground) {
image.bitmap->fill(background_color);
} else if (previous_image_disposal_method == ImageDescriptor::DisposalMethod::RestorePrevious) {
image.bitmap->fill(Color(Color::NamedColor::Transparent));
} else if (i > 1 && previous_image_disposal_method == ImageDescriptor::DisposalMethod::RestorePrevious) {
copy_frame(*image.bitmap, *context.images.at(i - 2).bitmap);
}
int pixel_index = 0;