runtime/kioslave/thumbnail/jpegcreator.cpp

   1 /*  This file is part of the KDE libraries
   2     Copyright (C) 2008 Andre Gemünd <scroogie@gmail.com>
   3
   4     This library is free software; you can redistribute it and/or
   5     modify it under the terms of the GNU Library General Public
   6     License as published by the Free Software Foundation; either
   7     version 2 of the License, or (at your option) any later version.
   8
   9     This library is distributed in the hope that it will be useful,
  10     but WITHOUT ANY WARRANTY; without even the implied warranty of
  11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12     Library General Public License for more details.
  13
  14     You should have received a copy of the GNU Library General Public License
  15     along with this library; see the file COPYING.LIB.  If not, write to
  16     the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17     Boston, MA 02110-1301, USA.
  18 */
  19
  20 #include "jpegcreator.h"
  21
  22 #include <cstdio>
  23 #include <csetjmp>
  24 #include <QFile>
  25 #include <QImage>
  26 #include <kdemacros.h>
  27
  28 extern "C"
  29 {
  30     #include <jpeglib.h>
  31
  32     KDE_EXPORT ThumbCreator *new_creator()
  33     {
  34         return new JpegCreator;
  35     }
  36 }
  37
  38 struct jpeg_custom_error_mgr
  39 {
  40    struct jpeg_error_mgr builtin;
  41    jmp_buf setjmp_buffer;
  42 };
  43
  44 void jpeg_custom_error_callback(j_common_ptr jpegDecompress)
  45 {
  46    jpeg_custom_error_mgr *custom_err = (jpeg_custom_error_mgr *)jpegDecompress->err;
  47
  48    // jump to error recovery (fallback to old method)
  49    longjmp(custom_err->setjmp_buffer, 1);
  50 }
  51
  52 JpegCreator::JpegCreator()
  53 {
  54 }
  55
  56 /**
  57  * This is a faster thumbnail creation specifically for JPEG images, as it uses the libjpeg feature of
  58  * calculating the inverse dct for a part of coefficients for lower resolutions.
  59  * Interesting parameters are the quality settings of libjpeg
  60  *         jpegDecompress.do_fancy_upsampling (TRUE, FALSE)
  61  *         jpegDecompress.do_block_smoothing (TRUE, FALSE)
  62  *         jpegDecompress.dct_method (JDCT_IFAST, JDCT_ISLOW, JDCT_IFLOAT)
  63  * and the resampling parameter of QImage.
  64  *
  65  * Important: We do not need to scaled to exact dimesions, as thumbnail.cpp will check dimensions and
  66  * rescale anyway.
  67  */
  68 bool JpegCreator::create(const QString &path, int width, int height, QImage &img)
  69 {
  70     const QByteArray name = QFile::encodeName(path);
  71     FILE *jpegFile = fopen(name.constData(), "rb");
  72     if (jpegFile  == 0) {
  73        return false;
  74     }
  75
  76     // create jpeglib data structures and calculate scale denominator
  77     struct jpeg_decompress_struct jpegDecompress;
  78     struct jpeg_custom_error_mgr jpegError;
  79     jpegDecompress.err = jpeg_std_error(&jpegError.builtin);
  80     jpeg_create_decompress(&jpegDecompress);
  81     jpeg_stdio_src(&jpegDecompress, jpegFile);
  82     jpeg_read_header(&jpegDecompress, TRUE);
  83
  84     const double ratioWidth = jpegDecompress.image_width / (double)width;
  85     const double ratioHeight = jpegDecompress.image_height / (double)height;
  86     int scale = 1;
  87     if (ratioWidth > 7 || ratioHeight > 7) {
  88         scale = 8;
  89     } else if (ratioWidth > 3.5 || ratioHeight > 3.5) {
  90         scale = 4;
  91     } else if (ratioWidth > 1.75 || ratioHeight > 1.75) {
  92         scale = 2;
  93     }
  94
  95     // set jpeglib decompression parameters
  96     jpegDecompress.scale_num           = 1;
  97     jpegDecompress.scale_denom         = scale;
  98     jpegDecompress.do_fancy_upsampling = FALSE;
  99     jpegDecompress.do_block_smoothing  = FALSE;
 100     jpegDecompress.dct_method          = JDCT_IFAST;
 101     jpegDecompress.err->error_exit     = jpeg_custom_error_callback;
 102     jpegDecompress.out_color_space     = JCS_RGB;
 103
 104     jpeg_calc_output_dimensions(&jpegDecompress);
 105
 106     if (setjmp(jpegError.setjmp_buffer)) {
 107         jpeg_abort_decompress(&jpegDecompress);
 108         fclose(jpegFile);
 109         // libjpeg version failed, fall back to direct loading of QImage
 110         if (!img.load(path)) {
 111             return false;
 112         }
 113         if (img.depth() != 32) {
 114             img = img.convertToFormat(QImage::Format_RGB32);
 115         }
 116         return true;
 117     }
 118
 119     jpeg_start_decompress(&jpegDecompress);
 120     img = QImage(jpegDecompress.output_width, jpegDecompress.output_height, QImage::Format_RGB32);
 121     uchar *buffer = img.bits();
 122     const int bpl = img.bytesPerLine();
 123     while (jpegDecompress.output_scanline < jpegDecompress.output_height) {
 124         // advance line-pointer to next line
 125         uchar *line = buffer + jpegDecompress.output_scanline * bpl;
 126         jpeg_read_scanlines(&jpegDecompress, &line, 1);
 127     }
 128     jpeg_finish_decompress(&jpegDecompress);
 129
 130     // align correctly for QImage
 131     // code copied from Gwenview and digiKam
 132     for (int i = 0; i < jpegDecompress.output_height; ++i) {
 133         uchar *in = img.scanLine(i) + jpegDecompress.output_width * 3;
 134         QRgb *out = (QRgb*)img.scanLine(i);
 135         for (int j = jpegDecompress.output_width - 1; j >= 0; --j) {
 136             in -= 3;
 137             out[j] = qRgb(in[0], in[1], in[2]);
 138         }
 139     }
 140
 141     fclose(jpegFile);
 142     jpeg_destroy_decompress(&jpegDecompress);
 143     return true;
 144 }
 145
 146 ThumbCreator::Flags JpegCreator::flags() const
 147 {
 148     return None;
 149 }