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LibGfx: Put code to add AC coefficients to a macroblock in a function

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This commit is contained in:
Lucas CHOLLET 2023-02-21 00:46:49 -05:00 • committed by Andreas Kling
parent 48f7b93a23
commit 3a8c52cabc
1 changed files with 42 additions and 36 deletions
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78
Userland/Libraries/LibGfx/JPEGLoader.cpp
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@ -297,6 +297,47 @@ static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock,
return {};
}
static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock, ComponentSpec const& component, unsigned component_index)
{
auto& ac_table = context.ac_tables.find(component.ac_destination_id)->value;
auto* select_component = get_component(macroblock, component_index);
// Compute the AC coefficients.
for (int j = 1; j < 64;) {
// AC symbols encode 2 pieces of information, the high 4 bits represent
// number of zeroes to be stuffed before reading the coefficient. Low 4
// bits represent the magnitude of the coefficient.
auto ac_symbol = TRY(get_next_symbol(context.huffman_stream, ac_table));
if (ac_symbol == 0)
break;
// ac_symbol = 0xF0 means we need to skip 16 zeroes.
u8 run_length = ac_symbol == 0xF0 ? 16 : ac_symbol >> 4;
j += run_length;
if (j >= 64) {
dbgln_if(JPEG_DEBUG, "Run-length exceeded boundaries. Cursor: {}, Skipping: {}!", j, run_length);
return Error::from_string_literal("Run-length exceeded boundaries");
}
u8 coeff_length = ac_symbol & 0x0F;
if (coeff_length > 10) {
dbgln_if(JPEG_DEBUG, "AC coefficient too long: {}!", coeff_length);
return Error::from_string_literal("AC coefficient too long");
}
if (coeff_length != 0) {
i32 ac_coefficient = TRY(read_huffman_bits(context.huffman_stream, coeff_length));
if (ac_coefficient < (1 << (coeff_length - 1)))
ac_coefficient -= (1 << coeff_length) - 1;
select_component[zigzag_map[j++]] = ac_coefficient;
}
}
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
@ -328,42 +369,7 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
Macroblock& block = macroblocks[mb_index];
TRY(add_dc(context, block, component, component_i));
auto& ac_table = context.ac_tables.find(component.ac_destination_id)->value;
auto* select_component = get_component(block, component_i);
// Compute the AC coefficients.
for (int j = 1; j < 64;) {
// AC symbols encode 2 pieces of information, the high 4 bits represent
// number of zeroes to be stuffed before reading the coefficient. Low 4
// bits represent the magnitude of the coefficient.
auto ac_symbol = TRY(get_next_symbol(context.huffman_stream, ac_table));
if (ac_symbol == 0)
break;
// ac_symbol = 0xF0 means we need to skip 16 zeroes.
u8 run_length = ac_symbol == 0xF0 ? 16 : ac_symbol >> 4;
j += run_length;
if (j >= 64) {
dbgln_if(JPEG_DEBUG, "Run-length exceeded boundaries. Cursor: {}, Skipping: {}!", j, run_length);
return Error::from_string_literal("Run-length exceeded boundaries");
}
u8 coeff_length = ac_symbol & 0x0F;
if (coeff_length > 10) {
dbgln_if(JPEG_DEBUG, "AC coefficient too long: {}!", coeff_length);
return Error::from_string_literal("AC coefficient too long");
}
if (coeff_length != 0) {
i32 ac_coefficient = TRY(read_huffman_bits(context.huffman_stream, coeff_length));
if (ac_coefficient < (1 << (coeff_length - 1)))
ac_coefficient -= (1 << coeff_length) - 1;
select_component[zigzag_map[j++]] = ac_coefficient;
}
}
TRY(add_ac(context, block, component, component_i));
}
}
}