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LibGfx: Put code to add the DC coefficient to a macroblock in a function

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This commit is contained in:
Lucas CHOLLET 2023-02-21 00:45:09 -05:00 • committed by Andreas Kling
parent e38cd8eb4e
commit 48f7b93a23
1 changed files with 28 additions and 19 deletions
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47
Userland/Libraries/LibGfx/JPEGLoader.cpp
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@ -272,6 +272,31 @@ static inline i32* get_component(Macroblock& block, unsigned component)
}
}
static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock, ComponentSpec const& component, unsigned component_index)
{
auto& dc_table = context.dc_tables.find(component.dc_destination_id)->value;
// For DC coefficients, symbol encodes the length of the coefficient.
auto dc_length = TRY(get_next_symbol(context.huffman_stream, dc_table));
if (dc_length > 11) {
dbgln_if(JPEG_DEBUG, "DC coefficient too long: {}!", dc_length);
return Error::from_string_literal("DC coefficient too long");
}
// DC coefficients are encoded as the difference between previous and current DC values.
i32 dc_diff = TRY(read_huffman_bits(context.huffman_stream, dc_length));
// If MSB in diff is 0, the difference is -ve. Otherwise +ve.
if (dc_length != 0 && dc_diff < (1 << (dc_length - 1)))
dc_diff -= (1 << dc_length) - 1;
auto* select_component = get_component(macroblock, component_index);
auto& previous_dc = context.previous_dc_values[component_index];
select_component[0] = previous_dc += dc_diff;
return {};
}
/**
* Build the macroblocks possible by reading single (MCU) subsampled pair of CbCr.
* Depending on the sampling factors, we may not see triples of y, cb, cr in that
@ -302,26 +327,10 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
u32 mb_index = (vcursor + vfactor_i) * context.mblock_meta.hpadded_count + (hfactor_i + hcursor);
Macroblock& block = macroblocks[mb_index];
auto& dc_table = context.dc_tables.find(component.dc_destination_id)->value;
TRY(add_dc(context, block, component, component_i));
auto& ac_table = context.ac_tables.find(component.ac_destination_id)->value;
// For DC coefficients, symbol encodes the length of the coefficient.
auto dc_length = TRY(get_next_symbol(context.huffman_stream, dc_table));
if (dc_length > 11) {
dbgln_if(JPEG_DEBUG, "DC coefficient too long: {}!", dc_length);
return Error::from_string_literal("DC coefficient too long");
}
// DC coefficients are encoded as the difference between previous and current DC values.
i32 dc_diff = TRY(read_huffman_bits(context.huffman_stream, dc_length));
// If MSB in diff is 0, the difference is -ve. Otherwise +ve.
if (dc_length != 0 && dc_diff < (1 << (dc_length - 1)))
dc_diff -= (1 << dc_length) - 1;
auto select_component = get_component(block, component_i);
auto& previous_dc = context.previous_dc_values[component_i];
select_component[0] = previous_dc += dc_diff;
auto* select_component = get_component(block, component_i);
// Compute the AC coefficients.
for (int j = 1; j < 64;) {