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LibGfx: Only iterate components of the current scan

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A scan can have fewer components than what the final image contains.
This commit is contained in:
Lucas CHOLLET 2023-02-22 20:46:19 -05:00 • committed by Andreas Kling
parent 9fa375b844
commit f98668f8b2
1 changed files with 15 additions and 10 deletions
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25
Userland/Libraries/LibGfx/JPEGLoader.cpp
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@ -134,6 +134,12 @@ struct Component {
u8 hsample_factor { 1 }; // Hi, Horizontal sampling factor
u8 vsample_factor { 1 }; // Vi, Vertical sampling factor
u8 qtable_id { 0 }; // Tqi, Quantization table destination selector
// The JPEG specification does not specify which component correspond to
// Y, Cb or Cr. This field (actually the index in the parent Vector) will
// act as an authority to determine the *real* component.
// Please note that this is implementation specific.
u8 index { 0 };
};
struct ScanComponent {
@ -294,7 +300,7 @@ static inline i32* get_component(Macroblock& block, unsigned component)
}
}
static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component, unsigned component_index)
static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component)
{
auto& dc_table = context.dc_tables.find(scan_component.dc_destination_id)->value;
@ -312,17 +318,17 @@ static ErrorOr<void> add_dc(JPEGLoadingContext& context, Macroblock& macroblock,
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];
auto* select_component = get_component(macroblock, scan_component.component.index);
auto& previous_dc = context.previous_dc_values[scan_component.component.index];
select_component[0] = previous_dc += dc_diff;
return {};
}
static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component, unsigned component_index)
static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock, ScanComponent const& scan_component)
{
auto& ac_table = context.ac_tables.find(scan_component.ac_destination_id)->value;
auto* select_component = get_component(macroblock, component_index);
auto* select_component = get_component(macroblock, scan_component.component.index);
// Compute the AC coefficients.
@ -381,9 +387,7 @@ static ErrorOr<void> add_ac(JPEGLoadingContext& context, Macroblock& macroblock,
*/
static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macroblock>& macroblocks, u32 hcursor, u32 vcursor)
{
for (unsigned component_i = 0; component_i < context.current_scan.components.size(); component_i++) {
auto& scan_component = context.current_scan.components[component_i];
for (auto const& scan_component : context.current_scan.components) {
if (scan_component.dc_destination_id >= context.dc_tables.size())
return Error::from_string_literal("DC destination ID is greater than number of DC tables");
if (scan_component.ac_destination_id >= context.ac_tables.size())
@ -395,8 +399,8 @@ static ErrorOr<void> build_macroblocks(JPEGLoadingContext& context, Vector<Macro
Macroblock& block = macroblocks[mb_index];
if (context.current_scan.spectral_selection_start == 0)
TRY(add_dc(context, block, scan_component, component_i));
TRY(add_ac(context, block, scan_component, component_i));
TRY(add_dc(context, block, scan_component));
TRY(add_ac(context, block, scan_component));
}
}
}
@ -837,6 +841,7 @@ static ErrorOr<void> read_start_of_frame(AK::SeekableStream& stream, JPEGLoading
for (u8 i = 0; i < component_count; i++) {
Component component;
component.id = TRY(stream.read_value<u8>());
component.index = i;
u8 subsample_factors = TRY(stream.read_value<u8>());
component.hsample_factor = subsample_factors >> 4;