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LibGfx/GIF: Write a Graphic Control Extension block

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This allows us to write the duration of each frame.
This commit is contained in:
Lucas CHOLLET 2024-05-18 19:36:33 -04:00 • committed by Tim Flynn
commit 3c4b8749f0
Notes: sideshowbarker 2024-07-16 17:12:03 +09:00
1 changed files with 37 additions and 3 deletions
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40
Userland/Libraries/LibGfx/ImageFormats/GIFWriter.cpp
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@ -17,7 +17,7 @@ namespace {
ErrorOr<void> write_header(Stream& stream)
{
// 17. Header
TRY(stream.write_until_depleted("GIF87a"sv));
TRY(stream.write_until_depleted("GIF89a"sv));
return {};
}
@ -121,6 +121,40 @@ ErrorOr<void> write_image_descriptor(BigEndianOutputBitStream& stream, Bitmap co
return {};
}
ErrorOr<void> write_graphic_control_extension(BigEndianOutputBitStream& stream, int duration_ms)
{
// 23. Graphic Control Extension
// Extension Introducer
TRY(stream.write_value<u8>(0x21));
// Graphic Control Label
TRY(stream.write_value<u8>(0xF9));
// Block Size
TRY(stream.write_value<u8>(4));
// Packed Field
// Reserved
TRY(stream.write_bits(0u, 3));
// Disposal Method
TRY(stream.write_bits(0u, 3));
// User Input Flag
TRY(stream.write_bits(false, 1));
// Transparency Flag
TRY(stream.write_bits(false, 1));
// Delay Time
TRY(stream.write_value<u16>(duration_ms / 10));
// Transparent Color Index
TRY(stream.write_value<u8>(0));
// Block Terminator
TRY(stream.write_value<u8>(0));
return {};
}
ErrorOr<void> write_trailer(Stream& stream)
{
TRY(stream.write_value<u8>(0x3B));
@ -143,8 +177,7 @@ private:
ErrorOr<void> GIFAnimationWriter::add_frame(Bitmap& bitmap, int duration_ms, IntPoint at = {})
{
// FIXME: Consider frame's duration and position
(void)duration_ms;
// FIXME: Consider frame's position
(void)at;
// Let's get rid of the previously written trailer
@ -155,6 +188,7 @@ 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));
auto const palette = TRY(median_cut(bitmap, 256));