Pl_PNGFilter.hh
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#ifndef PL_PNGFILTER_HH
#define PL_PNGFILTER_HH
// This pipeline applies or reverses the application of a PNG filter as described in the PNG
// specification.
// NOTE: In its current implementation, this filter always encodes using the "up" filter, but it
// decodes all the filters.
#include <qpdf/Pipeline.hh>
class Pl_PNGFilter: public Pipeline
{
public:
// Encoding is only partially supported
enum action_e { a_encode, a_decode };
Pl_PNGFilter(
char const* identifier,
Pipeline* next,
action_e action,
unsigned int columns,
unsigned int samples_per_pixel = 1,
unsigned int bits_per_sample = 8);
~Pl_PNGFilter() override = default;
void write(unsigned char const* data, size_t len) override;
void finish() override;
private:
void decodeSub();
void decodeUp();
void decodeAverage();
void decodePaeth();
void processRow();
void encodeRow();
void decodeRow();
int PaethPredictor(int a, int b, int c);
action_e action;
unsigned int bytes_per_row;
unsigned int bytes_per_pixel;
unsigned char* cur_row; // points to buf1 or buf2
unsigned char* prev_row; // points to buf1 or buf2
std::shared_ptr<unsigned char> buf1;
std::shared_ptr<unsigned char> buf2;
size_t pos;
size_t incoming;
};
#endif // PL_PNGFILTER_HH