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LibGfx/JPEG: Add a fast path for sequential JPEGs

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Decoding progressive JPEGs involves a much more complicated logic than
sequential JPEGs. Thanks to template specialization, this patch allow us
to skip the additional cost of progressive images when it's not needed.

It gives a nice 10% improvements on sequential JPEGs :^)
This commit is contained in:
Lucas CHOLLET 2023-07-01 18:30:12 -04:00 • committed by Jelle Raaijmakers
parent 510dfbb7e6
commit f52e3e540f
1 changed files with 58 additions and 20 deletions
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78
Userland/Libraries/LibGfx/ImageFormats/JPEGLoader.cpp
View file

@ -481,6 +481,12 @@ static ErrorOr<void> refine_coefficient(Scan& scan, auto& coefficient)
return {};
}
enum class JPEGDecodingMode {
Sequential,
Progressive
};
template<JPEGDecodingMode DecodingMode>
static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component)
{
auto maybe_table = context.dc_tables.get(scan_component.dc_destination_id);
@ -495,7 +501,7 @@ static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock,
auto* select_component = get_component(macroblock, scan_component.component.index);
auto& coefficient = select_component[0];
if (scan.successive_approximation_high > 0) {
if (DecodingMode == JPEGDecodingMode::Progressive && scan.successive_approximation_high > 0) {
TRY(refine_coefficient(scan, coefficient));
return {};
}
@ -525,8 +531,14 @@ static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock,
return {};
}
static ErrorOr<bool> read_eob(Scan& scan, u32 symbol)
template<JPEGDecodingMode DecodingMode>
static ALWAYS_INLINE ErrorOr<bool> read_eob(Scan& scan, u32 symbol)
{
// OPTIMIZATION: This is a fast path for sequential JPEGs, these
// only supports EOB with a value of one block.
if constexpr (DecodingMode == JPEGDecodingMode::Sequential)
return symbol == 0x00;
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
// Note: We also use it for non-progressive encoding as it supports both EOB and ZRL
@ -555,6 +567,7 @@ static bool is_progressive(StartOfFrame::FrameType frame_type)
|| frame_type == StartOfFrame::FrameType::Differential_Progressive_DCT_Arithmetic;
}
template<JPEGDecodingMode DecodingMode>
static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component)
{
auto maybe_table = context.ac_tables.get(scan_component.ac_destination_id);
@ -587,7 +600,7 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
if (!in_zrl && scan.end_of_bands_run_count == 0 && !saved_symbol.has_value()) {
saved_symbol = TRY(scan.huffman_stream.next_symbol(ac_table));
if (!TRY(read_eob(scan, *saved_symbol))) {
if (!TRY(read_eob<DecodingMode>(scan, *saved_symbol))) {
to_skip = *saved_symbol >> 4;
in_zrl = *saved_symbol == JPEG_ZRL;
@ -596,17 +609,30 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
saved_symbol.clear();
}
if (!in_zrl && is_progressive(context.frame.type) && scan.successive_approximation_high != 0) {
// G.1.2.3 - Coding model for subsequent scans of successive approximation
// Bit sign from rule a
saved_bit_for_rule_a = TRY(scan.huffman_stream.read_bits(1));
if constexpr (DecodingMode == JPEGDecodingMode::Sequential) {
j += to_skip - 1;
to_skip = 0;
in_zrl = false;
continue;
}
if constexpr (DecodingMode == JPEGDecodingMode::Progressive) {
if (!in_zrl && scan.successive_approximation_high != 0) {
// G.1.2.3 - Coding model for subsequent scans of successive approximation
// Bit sign from rule a
saved_bit_for_rule_a = TRY(scan.huffman_stream.read_bits(1));
}
}
} else if constexpr (DecodingMode == JPEGDecodingMode::Sequential) {
break;
}
}
if (coefficient != 0) {
TRY(refine_coefficient(scan, coefficient));
continue;
if constexpr (DecodingMode == JPEGDecodingMode::Progressive) {
if (coefficient != 0) {
TRY(refine_coefficient(scan, coefficient));
continue;
}
}
if (to_skip > 0) {
@ -619,7 +645,7 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
if (scan.end_of_bands_run_count > 0)
continue;
if (is_progressive(context.frame.type) && scan.successive_approximation_high != 0) {
if (DecodingMode == JPEGDecodingMode::Progressive && scan.successive_approximation_high != 0) {
// G.1.2.3 - Coding model for subsequent scans of successive approximation
if (auto const low_bits = *saved_symbol & 0x0F; low_bits != 1) {
dbgln_if(JPEG_DEBUG, "AC coefficient low bits isn't equal to 1: {}!", low_bits);
@ -675,6 +701,7 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
* macroblocks that share the chrominance data. Next two iterations (assuming that
* we are dealing with three components) will fill up the blocks with chroma data.
*/
template<JPEGDecodingMode DecodingMode>
static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macroblock>& macroblocks, u32 hcursor, u32 vcursor)
{
for (auto const& scan_component : context.current_scan->components) {
@ -699,15 +726,20 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
Macroblock& block = macroblocks[macroblock_index];
if (context.current_scan->spectral_selection_start == 0)
TRY(add_dc(context, block, scan_component));
if (context.current_scan->spectral_selection_end != 0)
TRY(add_ac(context, block, scan_component));
if constexpr (DecodingMode == JPEGDecodingMode::Sequential) {
TRY(add_dc<DecodingMode>(context, block, scan_component));
TRY(add_ac<DecodingMode>(context, block, scan_component));
} else {
if (context.current_scan->spectral_selection_start == 0)
TRY(add_dc<DecodingMode>(context, block, scan_component));
if (context.current_scan->spectral_selection_end != 0)
TRY(add_ac<DecodingMode>(context, block, scan_component));
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
if (context.current_scan->end_of_bands_run_count > 0) {
--context.current_scan->end_of_bands_run_count;
continue;
// G.1.2.2 - Progressive encoding of AC coefficients with Huffman coding
if (context.current_scan->end_of_bands_run_count > 0) {
--context.current_scan->end_of_bands_run_count;
continue;
}
}
}
}
@ -763,7 +795,13 @@ static ErrorOr<void> decode_huffman_stream(JPEGLoadingContext& context, Vector<M
}
}
if (auto result = build_macroblocks(context, macroblocks, hcursor, vcursor); result.is_error()) {
auto result = [&]() {
if (is_progressive(context.frame.type))
return build_macroblocks<JPEGDecodingMode::Progressive>(context, macroblocks, hcursor, vcursor);
return build_macroblocks<JPEGDecodingMode::Sequential>(context, macroblocks, hcursor, vcursor);
}();
if (result.is_error()) {
if constexpr (JPEG_DEBUG) {
dbgln("Failed to build Macroblock {}: {}", i, result.error());
dbgln("Huffman stream byte offset {}", context.stream.byte_offset());