// Filename: pnmReader.cxx
// Created by:  drose (14Jun00)
//
////////////////////////////////////////////////////////////////////
//
// PANDA 3D SOFTWARE
// Copyright (c) 2001 - 2004, Disney Enterprises, Inc.  All rights reserved
//
// All use of this software is subject to the terms of the Panda 3d
// Software license.  You should have received a copy of this license
// along with this source code; you will also find a current copy of
// the license at http://etc.cmu.edu/panda3d/docs/license/ .
//
// To contact the maintainers of this program write to
// panda3d-general@lists.sourceforge.net .
//
////////////////////////////////////////////////////////////////////

#include "pnmReader.h"
#include "virtualFileSystem.h"
#include "thread.h"

////////////////////////////////////////////////////////////////////
//     Function: PNMReader::Destructor
//       Access: Public, Virtual
//  Description:
////////////////////////////////////////////////////////////////////
PNMReader::
~PNMReader() {
  if (_owns_file) {
    VirtualFileSystem *vfs = VirtualFileSystem::get_global_ptr();

    // We're assuming here that the file was opened via VFS.  That
    // may not necessarily be the case, but we don't make that
    // distinction.  However, at the moment at least, that
    // distinction doesn't matter, since vfs->close_read_file()
    // just deletes the file pointer anyway.
    vfs->close_read_file(_file);
  }
  _file = (istream *)NULL;
}

////////////////////////////////////////////////////////////////////
//     Function: PNMReader::prepare_read
//       Access: Public, Virtual
//  Description: This method will be called before read_data() or
//               read_row() is called.  It instructs the reader to
//               initialize its data structures as necessary to
//               actually perform the read operation.  
//
//               After this call, _x_size and _y_size should reflect
//               the actual size that will be filled by read_data()
//               (as possibly modified by set_read_size()).
////////////////////////////////////////////////////////////////////
void PNMReader::
prepare_read() {
  if (!_is_valid) {
    return;
  }

  _x_shift = 0;
  _y_shift = 0;
  _orig_x_size = _x_size;
  _orig_y_size = _y_size;

  if (supports_read_row()) {
    // Maybe we can quick-filter each row down as we go.
    if (_has_read_size) {
      _x_shift = get_reduction_shift(_x_size, _read_x_size);
      _x_size = _x_size / (1 << _x_shift);
      _y_shift = get_reduction_shift(_y_size, _read_y_size);
      _y_size = _y_size / (1 << _y_shift);
    }
  }
}

////////////////////////////////////////////////////////////////////
//     Function: PNMReader::read_data
//       Access: Public, Virtual
//  Description: Reads in an entire image all at once, storing it in
//               the pre-allocated _x_size * _y_size array and alpha
//               pointers.  (If the image type has no alpha channel,
//               alpha is ignored.)  Returns the number of rows
//               correctly read.
//
//               Derived classes need not override this if they
//               instead provide supports_read_row() and read_row(),
//               below.
////////////////////////////////////////////////////////////////////
int PNMReader::
read_data(xel *array, xelval *alpha) {
  if (!is_valid()) {
    return 0;
  }

  if (_x_shift == 0 && _y_shift == 0) {
    // Read with no reduction.
    int y;
    for (y = 0; y < _y_size; ++y) {
      if (!read_row(array + y * _x_size, alpha + y * _x_size, _x_size, _y_size)) {
        Thread::consider_yield();
        return y;
      }
    }

  } else {
    int x_reduction = (1 << _x_shift);
    int y_reduction = (1 << _y_shift);
    
    int shift = _x_shift + _y_shift;

    // We need a temporary buffer, at least one row wide, with
    // full-width integers, for accumulating pixel data.
    int *accum_row_array = (int *)alloca(_orig_x_size * sizeof(int) * 3);
    int *accum_row_alpha = (int *)alloca(_orig_x_size * sizeof(int));

    // Each time we read a row, we will actually read the full row
    // here, before we filter it down into the above.
    xel *orig_row_array = (xel *)alloca(_orig_x_size * sizeof(xel));
    xelval *orig_row_alpha = (xelval *)alloca(_orig_x_size * sizeof(xelval));
    
    int y;
    for (y = 0; y < _y_size; ++y) {
      // Zero out the accumulation data, in preparation for
      // holding the results of the below.
      memset(accum_row_array, 0, _x_size * sizeof(int) * 3);
      if (has_alpha()) {
        memset(accum_row_alpha, 0, _x_size * sizeof(int));
      }

      for (int yi = 0; yi < y_reduction; ++yi) {
        // OK, read a row.  This reads the original, full-size row.
        if (!read_row(orig_row_array, orig_row_alpha, _orig_x_size, _orig_y_size)) {
          Thread::consider_yield();
          return y;
        }

        // Boil that row down to its proper, reduced size, and
        // accumulate it into the target row.
        xel *p = orig_row_array;
        int *q = accum_row_array;
        int *qstop = q + _x_size * 3;
        while (q < qstop) {
          for (int xi = 0; xi < x_reduction; ++xi) {
            q[0] += (*p).r;
            q[1] += (*p).g;
            q[2] += (*p).b;
            ++p;
          }
          q += 3;
        }
        if (has_alpha()) {
          // Now do it again for the alpha channel.
          xelval *p = orig_row_alpha;
          int *q = accum_row_alpha;
          int *qstop = q + _x_size;
          while (q < qstop) {
            for (int xi = 0; xi < x_reduction; ++xi) {
              (*q) += (*p);
              ++p;
            }
            ++q;
          }
        }
      }

      // OK, now copy the accumulated pixel data into the final
      // result.
      xel *target_row_array = array + y * _x_size;
      xelval *target_row_alpha = alpha + y * _x_size;

      int *p = accum_row_array;
      xel *q = target_row_array;
      xel *qstop = q + _x_size;
      while (q < qstop) {
        (*q).r = (*p++) >> shift;
        (*q).g = (*p++) >> shift;
        (*q).b = (*p++) >> shift;
        ++q;
      }

      if (has_alpha()) {
        int *p = accum_row_alpha;
        xelval *q = target_row_alpha;
        xelval *qstop = q + _x_size;
        while (q < qstop) {
          (*q) = (*p++) >> shift;
          ++q;
        }
      }
    }
  }
    

  return _y_size;
}


////////////////////////////////////////////////////////////////////
//     Function: PNMReader::supports_read_row
//       Access: Public, Virtual
//  Description: Returns true if this particular PNMReader is capable
//               of returning the data one row at a time, via repeated
//               calls to read_row().  Returns false if the only way
//               to read from this file is all at once, via
//               read_data().
////////////////////////////////////////////////////////////////////
bool PNMReader::
supports_read_row() const {
  return false;
}

////////////////////////////////////////////////////////////////////
//     Function: PNMReader::read_row
//       Access: Public, Virtual
//  Description: If supports_read_row(), above, returns true, this
//               function may be called repeatedly to read the image,
//               one horizontal row at a time, beginning from the top.
//               Returns true if the row is successfully read, false
//               if there is an error or end of file.
//
//               The x_size and y_size parameters are the value of
//               _x_size and _y_size as originally filled in by the
//               constructor; it is the actual number of pixels in the
//               image.  (The _x_size and _y_size members may have
//               been automatically modified by the time this method
//               is called if we are scaling on load, so should not be
//               used.)
////////////////////////////////////////////////////////////////////
bool PNMReader::
read_row(xel *, xelval *, int, int) {
  return false;
}


////////////////////////////////////////////////////////////////////
//     Function: PNMReader::supports_stream_read
//       Access: Public, Virtual
//  Description: Returns true if this particular PNMReader can read
//               from a general stream (including pipes, etc.), or
//               false if the reader must occasionally fseek() on its
//               input stream, and thus only disk streams are
//               supported.
////////////////////////////////////////////////////////////////////
bool PNMReader::
supports_stream_read() const {
  return false;
}

////////////////////////////////////////////////////////////////////
//     Function: PNMReader::get_reduction_shift
//       Access: Private
//  Description: Determines the reduction factor between the original
//               size and the requested size, returned as an exponent
//               of power of 2 (that is, a bit shift).  
//
//               Only power-of-two reductions are supported, since
//               those are common, easy, and fast.  Other reductions
//               will be handled in the higher level code.
////////////////////////////////////////////////////////////////////
int PNMReader::
get_reduction_shift(int orig_size, int new_size) {
  if (new_size == 0) {
    return 0;
  }

  int reduction = max(orig_size / new_size, 1);

  int shift = 0;

  int r = 2;
  while (r <= reduction) {
    shift += 1;
    r <<= 1;
  }

  if ((orig_size % r) != 0) {
    // If the reduction isn't even, never mind.
    shift = 0;
  }

  return shift;
}
