![[PukiWiki]](image/pukiwiki.png "[PukiWiki]")
[[Page006]] * Jpeg library の導入 [#j2a6640d] この節では、C の library を用いることを考察する。例として、前節の画像 document を jpeg 形式の画像も扱えるようにする。その際、古くから用いられている JFIF group の jpeg library を用いる。 この節の全 source file を固めたものを &ref("myapp07.tgz"); として置いておく。 この節で必要な全 source file 及び makefile を固めたものを &ref("myapp07.tgz"); として置いておく。 // mydjpeg.h #ifndef MYDJPEG_H_INCLUDED #define MYDJPEG_H_INCLUDED #include "myimage.h" #define XMD_H #include <stdio.h> #ifdef __cplusplus extern "C"{ #endif #include "jpeglib.h" #include "jerror.h" #ifdef __cplusplus } #endif namespace mylib { class CMyDjpeg : public CMyImage { public: CMyDjpeg(const TCHAR* szDocName); virtual ~CMyDjpeg(); protected: class my_source_mgr { // Expanded data source object for our io input public: struct jpeg_source_mgr pub; // public fields HANDLE hfile; /* source stream */ JOCTET * buffer; /* start of buffer */ bool start_of_file; /* have we gotten any data yet? */ }; typedef my_source_mgr* my_src_ptr; private: static void init_source(j_decompress_ptr cinfo); static boolean fill_input_buffer(j_decompress_ptr cinfo); static void skip_input_data(j_decompress_ptr cinfo, long num_bytes); static void term_source (j_decompress_ptr cinfo); static void set_srcio(j_decompress_ptr cinfo, HANDLE hfile); static const int INPUT_BUF_SIZE = 4096; private: bool ReadFile(const TCHAR* szFilename); bool Prepare(int width, int height, int numcomp); bool FillImage(int lineno, JOCTET* buffer, int nlen); protected: int m_width; int m_height; int m_numcomponents; int m_dispcomponents; size_t m_linelength; BITMAPINFO m_bmi; BYTE* m_lpFileData; }; } // namespace mylib #endif // MYDJPEG_H_INCLUDED 実装では、jpeg library の一部として一緒に配布されている例題を参考にする。 // mydjpeg.cpp #include "mydjpeg.h" namespace mylib { CMyDjpeg::CMyDjpeg(const TCHAR* lpFileName) { ::ZeroMemory(&m_bmi,sizeof(BITMAPINFO)); m_lpvBits = 0; m_lpbmi = &m_bmi; m_width = 0; m_height = 0; m_numcomponents = 0; m_dispcomponents = 3; m_linelength = 0; ReadFile(lpFileName); return; } CMyDjpeg::~CMyDjpeg() { delete [] m_lpvBits; } bool CMyDjpeg::Prepare(int width, int height, int numcomp) { ::ZeroMemory(&m_bmi,sizeof(BITMAPINFO)); delete [] m_lpvBits; m_lpvBits = 0; size_t n = ((width * m_dispcomponents + sizeof(LONG) - 1) / sizeof(LONG)) * sizeof(LONG); size_t nsize = n * height; if( nsize == 0 ) return false; m_lpvBits = new BYTE [nsize]; m_width = width; m_height = height; m_numcomponents = numcomp; m_linelength = n; m_bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); m_bmi.bmiHeader.biWidth = width; m_bmi.bmiHeader.biHeight = height; m_bmi.bmiHeader.biPlanes = 1; m_bmi.bmiHeader.biBitCount = m_dispcomponents * 8; m_bmi.bmiHeader.biCompression = BI_RGB; m_bmi.bmiHeader.biSizeImage = (DWORD)nsize; return true; } bool CMyDjpeg::FillImage(int lineno, JOCTET* buffer, int nlen) { if((m_lpvBits == 0) || (buffer == 0)) return false; if(m_numcomponents == 3) { int k = (int)m_linelength * lineno; for(int i = 0; i < m_width; i++) { int j = i * m_dispcomponents; m_lpvBits[k + j + 0] = (BYTE)buffer[j + 2]; m_lpvBits[k + j + 1] = (BYTE)buffer[j + 1]; m_lpvBits[k + j + 2] = (BYTE)buffer[j + 0]; } } else if(m_numcomponents == 1) { int k = (int)m_linelength * lineno; for(int i = 0; i < m_width; i++) { int j = i * m_dispcomponents; m_lpvBits[k + j + 0] = (BYTE)buffer[i]; m_lpvBits[k + j + 1] = (BYTE)buffer[i]; m_lpvBits[k + j + 2] = (BYTE)buffer[i]; } } else { for(int i = 0; i < nlen; i++) m_lpvBits[lineno * m_linelength + i] = (BYTE)buffer[i]; } return true; } /* * Initialize source --- called by jpeg_read_header * before any data is actually read. */ void CMyDjpeg::init_source(j_decompress_ptr cinfo) { my_src_ptr src = (my_src_ptr) cinfo->src; /* We reset the empty-input-file flag for each image, * but we don't clear the input buffer. * This is correct behavior for reading a series of images from one source. */ src->start_of_file = TRUE; } /* * Fill the input buffer --- called whenever buffer is emptied. * * In typical applications, this should read fresh data into the buffer * (ignoring the current state of next_input_byte & bytes_in_buffer), * reset the pointer & count to the start of the buffer, and return TRUE * indicating that the buffer has been reloaded. It is not necessary to * fill the buffer entirely, only to obtain at least one more byte. * * There is no such thing as an EOF return. If the end of the file has been * reached, the routine has a choice of ERREXIT() or inserting fake data into * the buffer. In most cases, generating a warning message and inserting a * fake EOI marker is the best course of action --- this will allow the * decompressor to output however much of the image is there. However, * the resulting error message is misleading if the real problem is an empty * input file, so we handle that case specially. * * In applications that need to be able to suspend compression due to input * not being available yet, a FALSE return indicates that no more data can be * obtained right now, but more may be forthcoming later. In this situation, * the decompressor will return to its caller (with an indication of the * number of scanlines it has read, if any). The application should resume * decompression after it has loaded more data into the input buffer. Note * that there are substantial restrictions on the use of suspension --- see * the documentation. * * When suspending, the decompressor will back up to a convenient restart point * (typically the start of the current MCU). next_input_byte & bytes_in_buffer * indicate where the restart point will be if the current call returns FALSE. * Data beyond this point must be rescanned after resumption, so move it to * the front of the buffer rather than discarding it. */ boolean CMyDjpeg::fill_input_buffer (j_decompress_ptr cinfo) { my_src_ptr src = (my_src_ptr) cinfo->src; size_t nbytes; // nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE); if(!::ReadFile(src->hfile, src->buffer, INPUT_BUF_SIZE, (DWORD*)&nbytes, 0)) return FALSE; if (nbytes <= 0) { //@ if (src->start_of_file) /* Treat empty input file as fatal error */ //@ ERREXIT(cinfo, JERR_INPUT_EMPTY); //@ WARNMS(cinfo, JWRN_JPEG_EOF); /* Insert a fake EOI marker */ src->buffer[0] = (JOCTET) 0xFF; src->buffer[1] = (JOCTET) JPEG_EOI; nbytes = 2; } src->pub.next_input_byte = src->buffer; src->pub.bytes_in_buffer = nbytes; src->start_of_file = FALSE; return TRUE; } /* * Skip data --- used to skip over a potentially large amount of * uninteresting data (such as an APPn marker). * * Writers of suspendable-input applications must note that skip_input_data * is not granted the right to give a suspension return. If the skip extends * beyond the data currently in the buffer, the buffer can be marked empty so * that the next read will cause a fill_input_buffer call that can suspend. * Arranging for additional bytes to be discarded before reloading the input * buffer is the application writer's problem. */ void CMyDjpeg::skip_input_data (j_decompress_ptr cinfo, long num_bytes) { my_src_ptr src = (my_src_ptr) cinfo->src; /* Just a dumb implementation for now. Could use fseek() except * it doesn't work on pipes. Not clear that being smart is worth * any trouble anyway --- large skips are infrequent. */ if (num_bytes > 0) { while (num_bytes > (long) src->pub.bytes_in_buffer) { num_bytes -= (long) src->pub.bytes_in_buffer; (void) fill_input_buffer(cinfo); /* note we assume that fill_input_buffer will never return FALSE, * so suspension need not be handled. */ } src->pub.next_input_byte += (size_t) num_bytes; src->pub.bytes_in_buffer -= (size_t) num_bytes; } } /* * An additional method that can be provided by data source modules is the * resync_to_restart method for error recovery in the presence of RST markers. * For the moment, this source module just uses the default resync method * provided by the JPEG library. That method assumes that no backtracking * is possible. */ /* * Terminate source --- called by jpeg_finish_decompress * after all data has been read. Often a no-op. * * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding * application must deal with any cleanup that should happen even * for error exit. */ void CMyDjpeg::term_source (j_decompress_ptr cinfo) { /* no work necessary here */ } void CMyDjpeg::set_srcio(j_decompress_ptr cinfo, HANDLE hfile) { my_src_ptr src; /* The source object and input buffer are made permanent so that a series * of JPEG images can be read from the same file by calling jpeg_stdio_src * only before the first one. (If we discarded the buffer at the end of * one image, we'd likely lose the start of the next one.) * This makes it unsafe to use this manager and a different source * manager serially with the same JPEG object. Caveat programmer. */ if (cinfo->src == NULL) { /* first time for this JPEG object? */ cinfo->src = (struct jpeg_source_mgr *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, sizeof(my_source_mgr)); src = (my_src_ptr) cinfo->src; src->buffer = (JOCTET *) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, INPUT_BUF_SIZE * sizeof(JOCTET)); } src = (my_src_ptr) cinfo->src; src->pub.init_source = init_source; src->pub.fill_input_buffer = fill_input_buffer; src->pub.skip_input_data = skip_input_data; src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */ src->pub.term_source = term_source; src->hfile = hfile; src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */ src->pub.next_input_byte = NULL; /* until buffer loaded */ } bool CMyDjpeg::ReadFile(const TCHAR* szFilename) { if(szFilename == 0) return false; struct jpeg_error_mgr jerr; struct jpeg_decompress_struct cinfo; HANDLE hfile; /* source file */ JSAMPARRAY buffer; /* Output row buffer */ int row_stride; /* physical row width in output buffer */ hfile = ::CreateFile(szFilename, GENERIC_READ, FILE_SHARE_READ, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0); // We set up the normal JPEG error routines, then override error_exit. */ cinfo.err = jpeg_std_error(&jerr); // Step 1: allocate and initialize JPEG decompression object // Now we can initialize the JPEG decompression object. jpeg_create_decompress(&cinfo); // Step 2: specify data source (eg, a file) set_srcio(&cinfo, hfile); // Step 3: read file parameters with jpeg_read_header() (void) jpeg_read_header(&cinfo, TRUE); // We can ignore the return value from jpeg_read_header since // (a) suspension is not possible with the stdio data source, and // (b) we passed TRUE to reject a tables-only JPEG file as an error. // See libjpeg.doc for more info. // Step 4: set parameters for decompression // In this example, we don't need to change any of the defaults set by // jpeg_read_header(), so we do nothing here. // Step 5: Start decompressor (void) jpeg_start_decompress(&cinfo); // We can ignore the return value since suspension is not possible // with the stdio data source. // We may need to do some setup of our own at this point before reading // the data. After jpeg_start_decompress() we have the correct scaled // output image dimensions available, as well as the output colormap // if we asked for color quantization. // In this example, we need to make an output work buffer of the right size. // JSAMPLEs per row in output buffer row_stride = cinfo.output_width * cinfo.output_components; // Make a one-row-high sample array that will go away when done with image buffer = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1); Prepare(cinfo.output_width, cinfo.output_height, cinfo.output_components); // Step 6: while (scan lines remain to be read) // jpeg_read_scanlines(...); // Here we use the library's state variable cinfo.output_scanline as the // loop counter, so that we don't have to keep track ourselves. while (cinfo.output_scanline < cinfo.output_height) { // jpeg_read_scanlines expects an array of pointers to scanlines. // Here the array is only one element long, but you could ask for // more than one scanline at a time if that's more convenient. (void) jpeg_read_scanlines(&cinfo, buffer, 1); // Assume put_scanline_someplace wants a pointer and sample count. // put_scanline_someplace(buffer[0], row_stride); int lineno = cinfo.output_height - cinfo.output_scanline; FillImage(lineno, buffer[0], row_stride); } // Step 7: Finish decompression (void) jpeg_finish_decompress(&cinfo); // We can ignore the return value since suspension is not possible // with the stdio data source. // Step 8: Release JPEG decompression object // This is an important step since it will release a good deal of memory. jpeg_destroy_decompress(&cinfo); // After finish_decompress, we can close the input file. // Here we postpone it until after no more JPEG errors are possible, // so as to simplify the setjmp error logic above. (Actually, I don't // think that jpeg_destroy can do an error exit, but why assume anything...) ::CloseHandle(hfile); return true; } } // namespace mylib
