/*

 * 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. */

  }

  /* 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;

  }

}