core/vil1/vil1_skip_image_impl.cxx

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// This is core/vil1/vil1_skip_image_impl.cxx
#ifdef VCL_NEEDS_PRAGMA_INTERFACE
#pragma implementation
#endif
//:
// \file
// \author fsm

#include "vil1_skip_image_impl.h"

#include <vcl_climits.h> // CHAR_BIT
#include <vcl_iostream.h>
#include <vcl_cassert.h>
#include <vcl_vector.h>

vil1_skip_image_impl::vil1_skip_image_impl(vil1_image const &underlying, unsigned sx, unsigned sy)
  : base(underlying)
  , skipx(sx)
  , skipy(sy)
{
  assert(base);
  assert(skipx>0);
  assert(skipy>0);
}

//--------------------------------------------------------------------------------

vil1_image vil1_skip_image_impl::get_plane(unsigned int p) const
{
  vil1_image_impl *i = new vil1_skip_image_impl(base.get_plane(p), skipx, skipy);
  return i;
}

bool vil1_skip_image_impl::put_section(void const * , int, int, int, int)
{
  return false;
}

bool vil1_skip_image_impl::get_property(char const *, void *) const
{
  return false;
}

//--------------------------------------------------------------------------------

bool vil1_skip_image_impl::get_section(void * buf, int x0, int y0, int w, int h) const
{
  if (base.bits_per_component() % CHAR_BIT) {
    vcl_cerr << __FILE__ " : urgh!\n";
    return false; // FIXME
  }

  // make a buffer for (skipx*w) x 1 sections of base :
  unsigned cell_size = base.planes() * base.components() * base.bits_per_component();
  cell_size /= CHAR_BIT;
  unsigned buffer_size = (skipx*w * cell_size);
  vcl_vector<unsigned char> buffer(buffer_size);

  // destination, as a unsigned char*
  unsigned char *dst = static_cast<unsigned char*>(buf);

  // for each raster
  for (int j=0; j<h; ++j) {
    // get from underlying :
    bool v = base.get_section(/* xxx */&buffer[0], skipx*x0, skipy*(y0+j), skipx*w, 1);
    if (!v)
      return false; // failed

    //
    for (int i=0; i<w; ++i)
      // copy the cell :
      for (unsigned k=0; k<cell_size; ++k)
        dst[cell_size*(j*w + i) + k] = buffer[cell_size*skipx*i + k];
  }

  return true;
}

---