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LibGfx: Don't assume that scans are always full when filling macroblocks
In other words: only consider coefficient of the current scan when adding coefficients to a macroblock. Information about which coefficients are present in the stream are passed through the spectral information in the context.
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1 changed files with 8 additions and 3 deletions
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@ -306,7 +306,11 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
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auto* select_component = get_component(macroblock, component_index);
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// Compute the AC coefficients.
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for (int j = 1; j < 64;) {
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// 0th coefficient is the dc, which is already handled
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auto first_coefficient = max(1, context.spectral_selection_start);
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for (int j = first_coefficient; j <= context.spectral_selection_end;) {
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// AC symbols encode 2 pieces of information, the high 4 bits represent
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// number of zeroes to be stuffed before reading the coefficient. Low 4
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// bits represent the magnitude of the coefficient.
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@ -318,7 +322,7 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
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u8 run_length = ac_symbol == 0xF0 ? 16 : ac_symbol >> 4;
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j += run_length;
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if (j >= 64) {
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if (j > context.spectral_selection_end) {
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dbgln_if(JPEG_DEBUG, "Run-length exceeded boundaries. Cursor: {}, Skipping: {}!", j, run_length);
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return Error::from_string_literal("Run-length exceeded boundaries");
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}
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@ -371,7 +375,8 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
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u32 mb_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hfactor_i + hcursor);
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Macroblock& block = macroblocks[mb_index];
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TRY(add_dc(context, block, component, component_i));
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if (context.spectral_selection_start == 0)
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TRY(add_dc(context, block, component, component_i));
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TRY(add_ac(context, block, component, component_i));
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}
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}
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