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VGexp.cxx

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/*
 * @(#)src/VGexp.cxx  1.0  2002-09-07 09:52
 *
 * Copyright (C)  2002  Daniel Léonard
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#include <utility>
#include "Image.h"
#include "SFCPath.h"
#include "SFCPathFactory.h"
#include "VGexp.h"
#include "VGexpSpec.h"

namespace halftoner
{

//---------------------------
// Constructor
//---------------------------

   VGexp::VGexp() throw()
   {
   // nothing
   }


//---------------------------
// Destructor
//---------------------------

   VGexp::~VGexp()
   {
   // nothing
   }


//---------------------------
// Implemented method from Halftoner
//---------------------------

   Image* VGexp::halftone(const Image& source, const HalftonerSpec* spec) throw (std::invalid_argument)
   {
   // dimensions
      const int width = source.getWidth();
      const int height = source.getHeight();
   // square check
      if (width != height)
      {
         string s("image is not square");
         throw std::invalid_argument(s);
      }

   // error diffusion parameters
      const VGexpSpec* vgspec = dynamic_cast<const VGexpSpec*>(spec);
      const int cluster = vgspec->getClusterSize();
      const float err1 = vgspec->getErr1();
      const float err2 = vgspec->getErr2();
      const float err3 = vgspec->getErr3();
      float acc[] = {0.0f, 0.0f, 0.0f};

   // getting the curve (can throw std::invalid_argument)
      const SFCPathFactory::SizeMnemonic& mnemonic = vgspec->getMnemonic();
      SFCPath* curve = SFCPathFactory::getInstance(mnemonic);
   // destination image
      Image* out = new Image(width, height);
   // needed variables
      int len = width * height;
      std::pair<int, int> maxblack; maxblack.first = 0; maxblack.second = 255;
      int grey;
      float accumulator = 0.0;
      std::pair<int, int> p;
      int black;
      int step;
   // here we go
      for (int i = 0; i < len; i += cluster)
      {
      // accumulator
         accumulator = acc[0];
         for (int n = 0; n < cluster; n++)
         {
            if (i + n < len)
            {
            // coordinates
               p = (*curve)[i + n];
            // colour
               grey = source.getColorAt(p.first, p.second);
            // accumulation
               accumulator += grey;
            // index
               if (maxblack.second > grey)
               {
                  maxblack.first = i + n;
                  maxblack.second = grey;
               }
            // all cluster pixels to white
               out->setColorAt(p.first, p.second, 1);
            }
         }
      // finding how many black pixels
         black = cluster;
         step = len - i;
         if (black > step) black = step;
         while (accumulator >= 255)
         {
            black--;
            accumulator -= 255;
         }
      // distributing error
         acc[0] = acc[1] + accumulator * err1;
         acc[1] = acc[2] + accumulator * err2;
         acc[2] = accumulator * err3;
      // distributing black pixels
         if (black > 0)
         {
            p = (*curve)[maxblack.first];
            out->setColorAt(p.first, p.second, 0);
            black--;
         }
         int pos;
         for (int n = 1; i + n < len; n++)
         {
         // checking invariants
            if (black == 0) break;
         // to the left
            pos = static_cast<int>(maxblack.first - n);
            if (pos >= static_cast<int>(i))
            {
               p = (*curve)[pos];
               out->setColorAt(p.first, p.second, 0);
               black--;
            }
            // we hit the edge of the cluster
            else
            {
               while (black > 0)
               {
                  pos = maxblack.first + n; n++;
                  p = (*curve)[pos];
                  out->setColorAt(p.first, p.second, 0);
                  black--;
               }
               break;
            }
         // checking invariants
            if (black == 0) break;
         // to the right
            pos = maxblack.first + n;
            if (pos < static_cast<int>(i + cluster))
            {
               p = (*curve)[pos];
               out->setColorAt(p.first, p.second, 0);
               black--;
            }
            // we hit the edge of the cluster
            else
            {
               while (black > 0)
               {
                  n++; pos = maxblack.first - n;
                  p = (*curve)[pos];
                  out->setColorAt(p.first, p.second, 0);
                  black--;
               }
               break;
            }
         }
      // reset index
         maxblack.first = 0; maxblack.second = 255;
      }
      delete curve;
      return out;
   }

}

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