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defilter.h
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defilter.h
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#pragma once
#include <cstdint>
#include "misc/structs.h"
namespace png_decoder::defilter {
// Refer to: http://www.libpng.org/pub/png/spec/1.2/PNG-Filters.html
class Defilter {
public:
virtual bool applicable(const Scanline& scanline) const = 0;
/* bpp - number of bytes per complete pixel */
virtual void apply(Scanline& scanline, const Scanline& previousDefilteredScanline, uint32_t bpp) const = 0;
virtual ~Defilter() = default;
protected:
enum class FilterTypes : uint8_t {
None = 0,
Sub,
Up,
Average,
Paeth,
};
static uint32_t mod(uint32_t value);
static uint32_t prev(const Scanline& scanline, uint32_t pos, uint32_t bpp);
private:
static constexpr uint32_t MOD = 256;
};
// defilters
class Sub : public Defilter {
public:
bool applicable(const Scanline& scanline) const override;
void apply(Scanline& scanline, const Scanline& previousDefilteredScanline, uint32_t bpp) const override;
};
class Up : public Defilter {
public:
bool applicable(const Scanline& scanline) const override;
void apply(Scanline& scanline, const Scanline& previousDefilteredScanline, uint32_t bpp) const override;
};
class Average : public Defilter {
public:
bool applicable(const Scanline& scanline) const override;
void apply(Scanline& scanline, const Scanline& previousDefilteredScanline, uint32_t bpp) const override;
};
class Paeth : public Defilter {
public:
bool applicable(const Scanline& scanline) const override;
void apply(Scanline& scanline, const Scanline& previousDefilteredScanline, uint32_t bpp) const override;
private:
static int32_t predictor(int32_t a, int32_t b, int32_t c);
};
} // namespace png_decoder::defilter