www.pudn.com > imgport.rar > jdtrans.c, change:2008-11-05,size:5233b


/* 
 * jdtrans.c 
 * 
 * Copyright (C) 1995-1997, Thomas G. Lane. 
 * This file is part of the Independent JPEG Group's software. 
 * For conditions of distribution and use, see the accompanying README file. 
 * 
 * This file contains library routines for transcoding decompression, 
 * that is, reading raw DCT coefficient arrays from an input JPEG file. 
 * The routines in jdapimin.c will also be needed by a transcoder. 
 */ 
 
#define JPEG_INTERNALS 
#include "jinclude.h" 
#include "jpeglib.h" 
 
 
/* Forward declarations */ 
LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo)); 
 
 
/* 
 * Read the coefficient arrays from a JPEG file. 
 * jpeg_read_header must be completed before calling this. 
 * 
 * The entire image is read into a set of virtual coefficient-block arrays, 
 * one per component.  The return value is a pointer to the array of 
 * virtual-array descriptors.  These can be manipulated directly via the 
 * JPEG memory manager, or handed off to jpeg_write_coefficients(). 
 * To release the memory occupied by the virtual arrays, call 
 * jpeg_finish_decompress() when done with the data. 
 * 
 * An alternative usage is to simply obtain access to the coefficient arrays 
 * during a buffered-image-mode decompression operation.  This is allowed 
 * after any jpeg_finish_output() call.  The arrays can be accessed until 
 * jpeg_finish_decompress() is called.  (Note that any call to the library 
 * may reposition the arrays, so don't rely on access_virt_barray() results 
 * to stay valid across library calls.) 
 * 
 * Returns NULL if suspended.  This case need be checked only if 
 * a suspending data source is used. 
 */ 
 
GLOBAL(jvirt_barray_ptr *) 
jpeg_read_coefficients (j_decompress_ptr cinfo) 
{ 
  if (cinfo->global_state == DSTATE_READY) { 
    /* First call: initialize active modules */ 
    transdecode_master_selection(cinfo); 
    cinfo->global_state = DSTATE_RDCOEFS; 
  } 
  if (cinfo->global_state == DSTATE_RDCOEFS) { 
    /* Absorb whole file into the coef buffer */ 
    for (;;) { 
      int retcode; 
      /* Call progress monitor hook if present */ 
      if (cinfo->progress != NULL) 
	(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo); 
      /* Absorb some more input */ 
      retcode = (*cinfo->inputctl->consume_input) (cinfo); 
      if (retcode == JPEG_SUSPENDED) 
	return NULL; 
      if (retcode == JPEG_REACHED_EOI) 
	break; 
      /* Advance progress counter if appropriate */ 
      if (cinfo->progress != NULL && 
	  (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) { 
	if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) { 
	  /* startup underestimated number of scans; ratchet up one scan */ 
	  cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows; 
	} 
      } 
    } 
    /* Set state so that jpeg_finish_decompress does the right thing */ 
    cinfo->global_state = DSTATE_STOPPING; 
  } 
  /* At this point we should be in state DSTATE_STOPPING if being used 
   * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access 
   * to the coefficients during a full buffered-image-mode decompression. 
   */ 
  if ((cinfo->global_state == DSTATE_STOPPING || 
       cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) { 
    return cinfo->coef->coef_arrays; 
  } 
  /* Oops, improper usage */ 
  ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state); 
  return NULL;			/* keep compiler happy */ 
} 
 
 
/* 
 * Master selection of decompression modules for transcoding. 
 * This substitutes for jdmaster.c's initialization of the full decompressor. 
 */ 
 
LOCAL(void) 
transdecode_master_selection (j_decompress_ptr cinfo) 
{ 
  /* This is effectively a buffered-image operation. */ 
  cinfo->buffered_image = TRUE; 
 
  /* Entropy decoding: either Huffman or arithmetic coding. */ 
  if (cinfo->arith_code) { 
    ERREXIT(cinfo, JERR_ARITH_NOTIMPL); 
  } else { 
    if (cinfo->progressive_mode) { 
#ifdef D_PROGRESSIVE_SUPPORTED 
      jinit_phuff_decoder(cinfo); 
#else 
      ERREXIT(cinfo, JERR_NOT_COMPILED); 
#endif 
    } else 
      jinit_huff_decoder(cinfo); 
  } 
 
  /* Always get a full-image coefficient buffer. */ 
  jinit_d_coef_controller(cinfo, TRUE); 
 
  /* We can now tell the memory manager to allocate virtual arrays. */ 
  (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo); 
 
  /* Initialize input side of decompressor to consume first scan. */ 
  (*cinfo->inputctl->start_input_pass) (cinfo); 
  /* Initialize progress monitoring. */ 
  if (cinfo->progress != NULL) { 
    int nscans; 
    /* Estimate number of scans to set pass_limit. */ 
    if (cinfo->progressive_mode) { 
      /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */ 
      nscans = 2 + 3 * cinfo->num_components; 
    } else if (cinfo->inputctl->has_multiple_scans) { 
      /* For a nonprogressive multiscan file, estimate 1 scan per component. */ 
      nscans = cinfo->num_components; 
    } else { 
      nscans = 1; 
    } 
    cinfo->progress->pass_counter = 0L; 
    cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans; 
    cinfo->progress->completed_passes = 0; 
    cinfo->progress->total_passes = 1; 
  } 
}