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LibGfx/WebP: Move lossy decoder to its own file

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Pure code move (except of removing `static` on the two public functions
in the new header), not behavior change.

There isn't a lot of lossy decoder yet, but it'll make implementing it
more convenient.

No behavior change.
This commit is contained in:
Nico Weber 2023-05-08 00:48:23 -04:00 • committed by Andreas Kling
parent 83da7ad875
commit bc207fd0a0
4 changed files with 120 additions and 81 deletions
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82
Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp
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@ -11,11 +11,11 @@
#include <AK/Vector.h>
#include <LibGfx/ImageFormats/WebPLoader.h>
#include <LibGfx/ImageFormats/WebPLoaderLossless.h>
#include <LibGfx/ImageFormats/WebPLoaderLossy.h>
#include <LibGfx/Painter.h>
// Overview: https://developers.google.com/speed/webp/docs/compression
// Container: https://developers.google.com/speed/webp/docs/riff_container
// Lossy format: https://datatracker.ietf.org/doc/html/rfc6386
namespace Gfx {
@ -55,17 +55,6 @@ struct Chunk {
ReadonlyBytes data;
};
struct VP8Header {
u8 version;
bool show_frame;
u32 size_of_first_partition;
u32 width;
u8 horizontal_scale;
u32 height;
u8 vertical_scale;
ReadonlyBytes lossy_data;
};
struct VP8XHeader {
bool has_icc;
bool has_alpha;
@ -228,75 +217,6 @@ static ErrorOr<Chunk> decode_webp_advance_chunk(ReadonlyBytes& chunks)
return chunk;
}
// https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossy
// https://datatracker.ietf.org/doc/html/rfc6386#section-19 "Annex A: Bitstream Syntax"
static ErrorOr<VP8Header> decode_webp_chunk_VP8_header(ReadonlyBytes vp8_data)
{
if (vp8_data.size() < 10)
return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk too small");
// FIXME: Eventually, this should probably call into LibVideo/VP8,
// and image decoders should move into LibImageDecoders which depends on both LibGfx and LibVideo.
// (LibVideo depends on LibGfx, so LibGfx can't depend on LibVideo itself.)
// https://datatracker.ietf.org/doc/html/rfc6386#section-4 "Overview of Compressed Data Format"
// "The decoder is simply presented with a sequence of compressed frames [...]
// The first frame presented to the decompressor is [...] a key frame. [...]
// [E]very compressed frame has three or more pieces. It begins with an uncompressed data chunk comprising 10 bytes in the case of key frames
u8 const* data = vp8_data.data();
// https://datatracker.ietf.org/doc/html/rfc6386#section-9.1 "Uncompressed Data Chunk"
u32 frame_tag = data[0] | (data[1] << 8) | (data[2] << 16);
bool is_key_frame = (frame_tag & 1) == 0; // https://www.rfc-editor.org/errata/eid5534
u8 version = (frame_tag & 0xe) >> 1;
bool show_frame = (frame_tag & 0x10) != 0;
u32 size_of_first_partition = frame_tag >> 5;
if (!is_key_frame)
return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk not a key frame");
// FIXME: !show_frame does not make sense in a webp file either, probably?
u32 start_code = data[3] | (data[4] << 8) | (data[5] << 16);
if (start_code != 0x2a019d) // https://www.rfc-editor.org/errata/eid7370
return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk invalid start_code");
// "The scaling specifications for each dimension are encoded as follows.
// 0 | No upscaling (the most common case).
// 1 | Upscale by 5/4.
// 2 | Upscale by 5/3.
// 3 | Upscale by 2."
// This is a display-time operation and doesn't affect decoding.
u16 width_and_horizontal_scale = data[6] | (data[7] << 8);
u16 width = width_and_horizontal_scale & 0x3fff;
u8 horizontal_scale = width_and_horizontal_scale >> 14;
u16 heigth_and_vertical_scale = data[8] | (data[9] << 8);
u16 height = heigth_and_vertical_scale & 0x3fff;
u8 vertical_scale = heigth_and_vertical_scale >> 14;
dbgln_if(WEBP_DEBUG, "version {}, show_frame {}, size_of_first_partition {}, width {}, horizontal_scale {}, height {}, vertical_scale {}",
version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale);
return VP8Header { version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale, vp8_data.slice(10) };
}
static ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8_contents(VP8Header const& vp8_header, bool include_alpha_channel)
{
auto bitmap_format = include_alpha_channel ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888;
// Uncomment this to test ALPH decoding for WebP-lossy-with-alpha images while lossy decoding isn't implemented yet.
#if 0
return Bitmap::create(bitmap_format, { vp8_header.width, vp8_header.height });
#else
// FIXME: Implement webp lossy decoding.
(void)vp8_header;
(void)bitmap_format;
return Error::from_string_literal("WebPImageDecoderPlugin: decoding lossy webps not yet implemented");
#endif
}
// https://developers.google.com/speed/webp/docs/riff_container#alpha
static ErrorOr<void> decode_webp_chunk_ALPH(Chunk const& alph_chunk, Bitmap& bitmap)
{