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  1. /*
  2.  * jdtrans.c
  3.  *
  4.  * Copyright (C) 1995-1997, Thomas G. Lane.
  5.  * This file is part of the Independent JPEG Group's software.
  6.  * For conditions of distribution and use, see the accompanying README file.
  7.  *
  8.  * This file contains library routines for transcoding decompression,
  9.  * that is, reading raw DCT coefficient arrays from an input JPEG file.
  10.  * The routines in jdapimin.c will also be needed by a transcoder.
  11.  */
  12.  
  13. #define JPEG_INTERNALS
  14. #include "jinclude.h"
  15. #include "jpeglib.h"
  16.  
  17.  
  18. /* Forward declarations */
  19. LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
  20.  
  21.  
  22. /*
  23.  * Read the coefficient arrays from a JPEG file.
  24.  * jpeg_read_header must be completed before calling this.
  25.  *
  26.  * The entire image is read into a set of virtual coefficient-block arrays,
  27.  * one per component.  The return value is a pointer to the array of
  28.  * virtual-array descriptors.  These can be manipulated directly via the
  29.  * JPEG memory manager, or handed off to jpeg_write_coefficients().
  30.  * To release the memory occupied by the virtual arrays, call
  31.  * jpeg_finish_decompress() when done with the data.
  32.  *
  33.  * An alternative usage is to simply obtain access to the coefficient arrays
  34.  * during a buffered-image-mode decompression operation.  This is allowed
  35.  * after any jpeg_finish_output() call.  The arrays can be accessed until
  36.  * jpeg_finish_decompress() is called.  (Note that any call to the library
  37.  * may reposition the arrays, so don't rely on access_virt_barray() results
  38.  * to stay valid across library calls.)
  39.  *
  40.  * Returns NULL if suspended.  This case need be checked only if
  41.  * a suspending data source is used.
  42.  */
  43.  
  44. GLOBAL(jvirt_barray_ptr *)
  45. jpeg_read_coefficients (j_decompress_ptr cinfo)
  46. {
  47.   if (cinfo->global_state == DSTATE_READY) {
  48.     /* First call: initialize active modules */
  49.     transdecode_master_selection(cinfo);
  50.     cinfo->global_state = DSTATE_RDCOEFS;
  51.   }
  52.   if (cinfo->global_state == DSTATE_RDCOEFS) {
  53.     /* Absorb whole file into the coef buffer */
  54.     for (;;) {
  55.       int retcode;
  56.       /* Call progress monitor hook if present */
  57.       if (cinfo->progress != NULL)
  58.         (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
  59.       /* Absorb some more input */
  60.       retcode = (*cinfo->inputctl->consume_input) (cinfo);
  61.       if (retcode == JPEG_SUSPENDED)
  62.         return NULL;
  63.       if (retcode == JPEG_REACHED_EOI)
  64.         break;
  65.       /* Advance progress counter if appropriate */
  66.       if (cinfo->progress != NULL &&
  67.           (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
  68.         if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
  69.           /* startup underestimated number of scans; ratchet up one scan */
  70.           cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
  71.         }
  72.       }
  73.     }
  74.     /* Set state so that jpeg_finish_decompress does the right thing */
  75.     cinfo->global_state = DSTATE_STOPPING;
  76.   }
  77.   /* At this point we should be in state DSTATE_STOPPING if being used
  78.    * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
  79.    * to the coefficients during a full buffered-image-mode decompression.
  80.    */
  81.   if ((cinfo->global_state == DSTATE_STOPPING ||
  82.        cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
  83.     return cinfo->coef->coef_arrays;
  84.   }
  85.   /* Oops, improper usage */
  86.   ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  87.   return NULL;                  /* keep compiler happy */
  88. }
  89.  
  90.  
  91. /*
  92.  * Master selection of decompression modules for transcoding.
  93.  * This substitutes for jdmaster.c's initialization of the full decompressor.
  94.  */
  95.  
  96. LOCAL(void)
  97. transdecode_master_selection (j_decompress_ptr cinfo)
  98. {
  99.   /* This is effectively a buffered-image operation. */
  100.   cinfo->buffered_image = TRUE;
  101.  
  102.   /* Entropy decoding: either Huffman or arithmetic coding. */
  103.   if (cinfo->arith_code) {
  104.     ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
  105.   } else {
  106.     if (cinfo->progressive_mode) {
  107. #ifdef D_PROGRESSIVE_SUPPORTED
  108.       jinit_phuff_decoder(cinfo);
  109. #else
  110.       ERREXIT(cinfo, JERR_NOT_COMPILED);
  111. #endif
  112.     } else
  113.       jinit_huff_decoder(cinfo);
  114.   }
  115.  
  116.   /* Always get a full-image coefficient buffer. */
  117.   jinit_d_coef_controller(cinfo, TRUE);
  118.  
  119.   /* We can now tell the memory manager to allocate virtual arrays. */
  120.   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
  121.  
  122.   /* Initialize input side of decompressor to consume first scan. */
  123.   (*cinfo->inputctl->start_input_pass) (cinfo);
  124.  
  125.   /* Initialize progress monitoring. */
  126.   if (cinfo->progress != NULL) {
  127.     int nscans;
  128.     /* Estimate number of scans to set pass_limit. */
  129.     if (cinfo->progressive_mode) {
  130.       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
  131.       nscans = 2 + 3 * cinfo->num_components;
  132.     } else if (cinfo->inputctl->has_multiple_scans) {
  133.       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
  134.       nscans = cinfo->num_components;
  135.     } else {
  136.       nscans = 1;
  137.     }
  138.     cinfo->progress->pass_counter = 0L;
  139.     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
  140.     cinfo->progress->completed_passes = 0;
  141.     cinfo->progress->total_passes = 1;
  142.   }
  143. }
  144.