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LibGfx/JBIG2: Pass in decoder and contexts to generic region decoder

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The symbol segment decoding procedure will read generic regions
that aren't at a byte boundary, and that share contexts across
several regions.

No behavior change.
This commit is contained in:
Nico Weber 2024-03-20 21:24:31 -04:00 committed by Tim Flynn
parent 376b1a2309
commit 2099ca48a1
Notes: sideshowbarker 2024-07-16 22:17:03 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/2099ca48a1
Pull-request: https://github.com/SerenityOS/serenity/pull/23661
Reviewed-by: https://github.com/trflynn89
1 changed files with 18 additions and 9 deletions
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27
Userland/Libraries/LibGfx/ImageFormats/JBIG2Loader.cpp
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@ -769,6 +769,7 @@ struct AdaptiveTemplatePixel {
};
// 6.2.2 Input parameters
// Table 2 – Parameters for the generic region decoding procedure
struct GenericRegionDecodingInputParameters {
bool is_modified_modified_read { false }; // "MMR" in spec.
u32 region_width { 0 }; // "GBW" in spec.
@ -780,10 +781,13 @@ struct GenericRegionDecodingInputParameters {
Array<AdaptiveTemplatePixel, 12> adaptive_template_pixels; // "GBATX" / "GBATY" in spec.
// FIXME: GBCOLS, GBCOMBOP, COLEXTFLAG
// If is_modified_modified_read is false, generic_region_decoding_procedure() reads data off this decoder.
JBIG2::ArithmeticDecoder* arithmetic_decoder { nullptr };
};
// 6.2 Generic region decoding procedure
static ErrorOr<NonnullOwnPtr<BitBuffer>> generic_region_decoding_procedure(GenericRegionDecodingInputParameters const& inputs, ReadonlyBytes data)
static ErrorOr<NonnullOwnPtr<BitBuffer>> generic_region_decoding_procedure(GenericRegionDecodingInputParameters const& inputs, ReadonlyBytes data, Vector<JBIG2::ArithmeticDecoder::Context>& contexts)
{
if (inputs.is_modified_modified_read) {
dbgln_if(JBIG2_DEBUG, "JBIG2ImageDecoderPlugin: MMR image data");
@ -823,7 +827,6 @@ static ErrorOr<NonnullOwnPtr<BitBuffer>> generic_region_decoding_procedure(Gener
auto result = TRY(BitBuffer::create(inputs.region_width, inputs.region_height));
auto decoder = MUST(JBIG2::ArithmeticDecoder::initialize(data));
auto get_pixel = [&inputs](NonnullOwnPtr<BitBuffer> const& buffer, int x, int y) -> bool {
if (x < 0 || x >= (int)inputs.region_width || y < 0)
return false;
@ -848,16 +851,13 @@ static ErrorOr<NonnullOwnPtr<BitBuffer>> generic_region_decoding_procedure(Gener
// concatenating the label "GB" and the 10-16 pixel values gathered in CONTEXT."
// Implementor's note: What this is supposed to mean is that we have a bunch of independent contexts, and we pick the
// context for the current pixel based on pixel values in the neighborhood. The "GB" part just means this context is
// independent from other contexts in the spec. At the moment, these are the only contexts we have, so we just
// create them on demand here.
// I can't find where the spec says this, but the contexts all start out zero-initialized.
Vector<JBIG2::ArithmeticDecoder::Context> contexts;
contexts.resize(1 << 16);
// independent from other contexts in the spec. They are passed in to this function.
// Figure 8 – Reused context for coding the SLTP value when GBTEMPLATE is 0
constexpr u16 sltp_context_for_template_0 = 0b10011'0110010'0101;
// 6.2.5.7 Decoding the bitmap
JBIG2::ArithmeticDecoder& decoder = *inputs.arithmetic_decoder;
bool ltp = false; // "LTP" in spec. "Line (uses) Typical Prediction" maybe?
for (size_t y = 0; y < inputs.region_height; ++y) {
if (inputs.is_typical_prediction_used) {
@ -973,7 +973,9 @@ static ErrorOr<void> decode_immediate_generic_region(JBIG2LoadingContext& contex
// "1) Interpret its header, as described in 7.4.6.1"
// Done above.
// "2) As described in E.3.7, reset all the arithmetic coding statistics to zero."
// FIXME: Implement this once we support arithmetic coding.
Vector<JBIG2::ArithmeticDecoder::Context> contexts;
contexts.resize(1 << 16);
// "3) Invoke the generic region decoding procedure described in 6.2, with the parameters to the generic region decoding procedure set as shown in Table 37."
GenericRegionDecodingInputParameters inputs;
inputs.is_modified_modified_read = uses_mmr;
@ -984,7 +986,14 @@ static ErrorOr<void> decode_immediate_generic_region(JBIG2LoadingContext& contex
inputs.is_extended_reference_template_used = uses_extended_reference_template;
inputs.skip_pattern = OptionalNone {};
inputs.adaptive_template_pixels = adaptive_template_pixels;
auto result = TRY(generic_region_decoding_procedure(inputs, data));
Optional<JBIG2::ArithmeticDecoder> decoder;
if (!uses_mmr) {
decoder = TRY(JBIG2::ArithmeticDecoder::initialize(data));
inputs.arithmetic_decoder = &decoder.value();
}
auto result = TRY(generic_region_decoding_procedure(inputs, data, contexts));
// 8.2 Page image composition step 5)
if (information_field.x_location + information_field.width > (u32)context.page.size.width()