line_iterator.h

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/*
 * Copyright (c) 2012, Willow Garage, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Willow Garage, Inc. nor the names of its
 *       contributors may be used to endorse or promote products derived from
 *       this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
#ifndef LINE_ITERATOR_H
#define LINE_ITERATOR_H

#include <stdlib.h>

namespace base_local_planner
{

class LineIterator
{
public:
  LineIterator( int x0, int y0, int x1, int y1 )
    : x0_( x0 )
    , y0_( y0 )
    , x1_( x1 )
    , y1_( y1 )
    , x_( x0 ) // X and Y start of at first endpoint.
    , y_( y0 )
    , deltax_( abs( x1 - x0 ))
    , deltay_( abs( y1 - y0 ))
    , curpixel_( 0 )
  {
    if( x1_ >= x0_ )                 // The x-values are increasing
    {
      xinc1_ = 1;
      xinc2_ = 1;
    }
    else                          // The x-values are decreasing
    {
      xinc1_ = -1;
      xinc2_ = -1;
    }

    if( y1_ >= y0_)                 // The y-values are increasing
    {
      yinc1_ = 1;
      yinc2_ = 1;
    }
    else                          // The y-values are decreasing
    {
      yinc1_ = -1;
      yinc2_ = -1;
    }

    if( deltax_ >= deltay_ )         // There is at least one x-value for every y-value
    {
      xinc1_ = 0;                  // Don't change the x when numerator >= denominator
      yinc2_ = 0;                  // Don't change the y for every iteration
      den_ = deltax_;
      num_ = deltax_ / 2;
      numadd_ = deltay_;
      numpixels_ = deltax_;         // There are more x-values than y-values
    }
    else                          // There is at least one y-value for every x-value
    {
      xinc2_ = 0;                  // Don't change the x for every iteration
      yinc1_ = 0;                  // Don't change the y when numerator >= denominator
      den_ = deltay_;
      num_ = deltay_ / 2;
      numadd_ = deltax_;
      numpixels_ = deltay_;         // There are more y-values than x-values
    }
  }
    
  bool isValid() const
  {
    return curpixel_ <= numpixels_;
  }

  void advance()
  {
    num_ += numadd_;              // Increase the numerator by the top of the fraction
    if( num_ >= den_ )            // Check if numerator >= denominator
    {
      num_ -= den_;               // Calculate the new numerator value
      x_ += xinc1_;               // Change the x as appropriate
      y_ += yinc1_;               // Change the y as appropriate
    }
    x_ += xinc2_;                 // Change the x as appropriate
    y_ += yinc2_;                 // Change the y as appropriate

    curpixel_++;
  }
  
  int getX() const { return x_; }
  int getY() const { return y_; }

  int getX0() const { return x0_; }
  int getY0() const { return y0_; }

  int getX1() const { return x1_; }
  int getY1() const { return y1_; }

private:
  int x0_; 
  int y0_; 
  int x1_; 
  int y1_; 

  int x_; 
  int y_; 

  int deltax_; 
  int deltay_; 

  int curpixel_; 

  int xinc1_, xinc2_, yinc1_, yinc2_;
  int den_, num_, numadd_, numpixels_;
};

} // end namespace base_local_planner

#endif // LINE_ITERATOR_H