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53 lines
1.5 KiB
C++
53 lines
1.5 KiB
C++
#ifndef __PL_PNGFILTER_HH__
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#define __PL_PNGFILTER_HH__
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// This pipeline applies or reverses the application of a PNG filter
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// as described in the PNG specification.
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// NOTE: In its initial implementation, it only encodes and decodes
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// filters "none" and "up". The primary motivation of this code is to
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// encode and decode PDF 1.5+ XRef streams which are often encoded
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// with Flate predictor 12, which corresponds to the PNG up filter.
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// At present, the bytes_per_pixel parameter is ignored, and an
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// exception is thrown if any row of the file has a filter of other
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// than 0 or 2. Finishing the implementation would not be difficult.
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// See chapter 6 of the PNG specification for a description of the
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// filter algorithms.
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#include <qpdf/Pipeline.hh>
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class Pl_PNGFilter: public Pipeline
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{
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public:
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// Encoding is not presently supported
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enum action_e { a_encode, a_decode };
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DLL_EXPORT
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Pl_PNGFilter(char const* identifier, Pipeline* next,
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action_e action, unsigned int columns,
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unsigned int bytes_per_pixel);
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DLL_EXPORT
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virtual ~Pl_PNGFilter();
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DLL_EXPORT
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virtual void write(unsigned char* data, int len);
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DLL_EXPORT
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virtual void finish();
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private:
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void processRow();
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void encodeRow();
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void decodeRow();
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action_e action;
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unsigned int columns;
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unsigned char* cur_row;
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unsigned char* prev_row;
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unsigned char* buf1;
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unsigned char* buf2;
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int pos;
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int incoming;
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};
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#endif // __PL_PNGFILTER_HH__
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