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LibGfx/WebP: Move some to-be-shared code to WebPSharedLossless.h

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No behavior change. No measurable performance different either.

(I tried `hyperfine 'Build/lagom/bin/image --no-output foo.webp'`
for a few input images before and after this change, and I didn't
see a difference. I also tried if moving both
Gfx::CanonicalCode::read_symbol() and
Compress::CanonicalCode::read_symbol() inline, and that didn't
help either.)
This commit is contained in:
Nico Weber
2024-05-08 07:57:53 -04:00
committed by Tim Flynn
parent 86b0a56899
commit ed2658d72c
5 changed files with 94 additions and 71 deletions
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72
Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossless.cpp
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@@ -12,6 +12,7 @@
#include <AK/Vector.h>
#include <LibCompress/Deflate.h>
#include <LibGfx/ImageFormats/WebPLoaderLossless.h>
#include <LibGfx/ImageFormats/WebPSharedLossless.h>
// Lossless format: https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification
@@ -49,77 +50,6 @@ ErrorOr<VP8LHeader> decode_webp_chunk_VP8L_header(ReadonlyBytes vp8l_data)
return VP8LHeader { width, height, is_alpha_used, vp8l_data.slice(5) };
}
namespace {
// WebP-lossless's CanonicalCodes are almost identical to deflate's.
// One difference is that codes with a single element in webp-lossless consume 0 bits to produce that single element,
// while they consume 1 bit in Compress::CanonicalCode. This class wraps Compress::CanonicalCode to handle the case
// where the codes contain just a single element, and dispatches to Compress::CanonicalCode else.
class CanonicalCode {
public:
CanonicalCode()
: m_code(0)
{
}
static ErrorOr<CanonicalCode> from_bytes(ReadonlyBytes);
ErrorOr<u32> read_symbol(LittleEndianInputBitStream&) const;
private:
explicit CanonicalCode(u32 single_symbol)
: m_code(single_symbol)
{
}
explicit CanonicalCode(Compress::CanonicalCode code)
: m_code(move(code))
{
}
Variant<u32, Compress::CanonicalCode> m_code;
};
ErrorOr<CanonicalCode> CanonicalCode::from_bytes(ReadonlyBytes bytes)
{
auto non_zero_symbol_count = 0;
auto last_non_zero_symbol = -1;
for (size_t i = 0; i < bytes.size(); i++) {
if (bytes[i] != 0) {
non_zero_symbol_count++;
last_non_zero_symbol = i;
}
}
if (non_zero_symbol_count == 1)
return CanonicalCode(last_non_zero_symbol);
return CanonicalCode(TRY(Compress::CanonicalCode::from_bytes(bytes)));
}
ErrorOr<u32> CanonicalCode::read_symbol(LittleEndianInputBitStream& bit_stream) const
{
return TRY(m_code.visit(
[](u32 single_code) -> ErrorOr<u32> { return single_code; },
[&bit_stream](Compress::CanonicalCode const& code) { return code.read_symbol(bit_stream); }));
}
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#61_overview
// "From here on, we refer to this set as a prefix code group."
class PrefixCodeGroup {
public:
PrefixCodeGroup() = default;
PrefixCodeGroup(PrefixCodeGroup&&) = default;
PrefixCodeGroup(PrefixCodeGroup const&) = delete;
CanonicalCode& operator[](int i) { return m_codes[i]; }
CanonicalCode const& operator[](int i) const { return m_codes[i]; }
private:
Array<CanonicalCode, 5> m_codes;
};
}
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#621_decoding_and_building_the_prefix_codes
static ErrorOr<CanonicalCode> decode_webp_chunk_VP8L_prefix_code(LittleEndianInputBitStream& bit_stream, size_t alphabet_size)
{