draw.hxx

/*
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 University of Utah.
 
 
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// File         : draw.hxx
// Author       : Pavel A. Koshevoy
// Created      : 2006/01/04 11:26
// Copyright    : (C) 2004-2008 University of Utah
// Description  : Functions for drawing anti-aliased lines using
//                Xiaolin Wu's line algorithm taken from the wikipedia article
//                http://en.wikipedia.org/wiki/Xiaolin_Wu's_line_algorithm

#ifndef DRAW_HXX_
#define DRAW_HXX_


// system includes:
#include <algorithm>

// ITK includes:
#include <itkImage.h>


namespace wu
{
  //----------------------------------------------------------------
  // ipart
  // 
  // return integer part of x
  inline double ipart(const double & x)
  {
    return (x == x) ? x - fmod(x, 1.0) : x;
  }
  
  //----------------------------------------------------------------
  // round
  // 
  inline double round(const double & x)
  {
    return ipart(x + 0.5);
  }
  
  //----------------------------------------------------------------
  // fpart
  // 
  // return fractional part of x
  inline double fpart(const double & x)
  {
    return x - ipart(x);
  }
  
  //----------------------------------------------------------------
  // rfpart
  // 
  inline double rfpart(const double & x)
  {
    return 1.0 - fpart(x);
  }
  
  //----------------------------------------------------------------
  // plot_pixel
  // 
  template <class image_t>
  void
  plot_pixel(typename image_t::Pointer & image,
       const unsigned int & width,
       const unsigned int & height,
       const typename image_t::IndexType & index,
       const double & w,
       const double & c)
  {
    if ((unsigned int)(index[0]) >= width ||
  (unsigned int)(index[1]) >= height)
    {
      return;
    }
    
    typedef typename image_t::PixelType color_t;
    double o = double(image->GetPixel(index));
    double n = (1.0 - w) * o + w * c;
    n = std::max(0.0, std::min(255.0, n));
    image->SetPixel(index, color_t(n));
  }
  
  //----------------------------------------------------------------
  // plot_normal
  // 
  template <class image_t>
  void
  plot_normal(typename image_t::Pointer & image,
        const unsigned int & width,
        const unsigned int & height,
        const double & x,
        const double & y,
        const double & w,
        const double & c)
  {
    typename image_t::IndexType index;
    index[0] = (unsigned int)(x);
    index[1] = (unsigned int)(y);
    plot_pixel<image_t>(image, width, height, index, w, c);
  }
  
  //----------------------------------------------------------------
  // plot_swapped
  // 
  template <class image_t>
  void
  plot_swapped(typename image_t::Pointer & image,
         const unsigned int & width,
         const unsigned int & height,
         const double & x,
         const double & y,
         const double & w,
         const double & c)
  {
    typename image_t::IndexType index;
    index[0] = (unsigned int)(y);
    index[1] = (unsigned int)(x);
    plot_pixel<image_t>(image, width, height, index, w, c);
  }
  
  //----------------------------------------------------------------
  // draw_nearly_horizontal_line
  // 
  // Xiaolin Wu's line algorithm taken from the wikipedia article
  // http://en.wikipedia.org/wiki/Xiaolin_Wu's_line_algorithm
  // 
  template <class image_t>
  void
  draw_nearly_horizontal_line
  (typename image_t::Pointer & image,
   const double & c,
   double x1,
   double y1,
   double x2,
   double y2,
   void(*draw_pixel)(typename image_t::Pointer &, // image
         const unsigned int &,    // width
         const unsigned int &,    // height
         const double &,      // x
         const double &,      // y
         const double &,      // weight
         const double &))     // paint color
  {
    typename image_t::SizeType sz =
      image->GetLargestPossibleRegion().GetSize();
    
    // check that x1 < x2
    if (x2 < x1)
    {
      std::swap(x1, x2);
      std::swap(y1, y2);
    }
    
    double dx = x2 - x1;
    double dy = y2 - y1;
    double gradient = dy / dx;
    
    // handle first endpoint
    double xend = round(x1);
    double yend = y1 + gradient * (xend - x1);
    double xgap = rfpart(x1 + 0.5);
    double xpxl1 = xend;  // this will be used in the main loop
    double ypxl1 = ipart(yend);
    draw_pixel(image, sz[0], sz[1], xpxl1, ypxl1, rfpart(yend) * xgap, c);
    draw_pixel(image, sz[0], sz[1], xpxl1, ypxl1 + 1, fpart(yend) * xgap, c);
    double intery = yend + gradient; // first y-intersection for the main loop
    
    // handle second endpoint
    xend = round(x2);
    yend = y2 + gradient * (xend - x2);
    xgap = rfpart(x2 - 0.5);
    double xpxl2 = xend;  // this will be used in the main loop
    double ypxl2 = ipart(yend);
    draw_pixel(image, sz[0], sz[1], xpxl2, ypxl2, rfpart(yend) * xgap, c);
    draw_pixel(image, sz[0], sz[1], xpxl2, ypxl2 + 1, fpart(yend) * xgap, c);
    
    // main loop
    for (double x = xpxl1 + 1.0; x <= xpxl2 - 1.0; x += 1.0)
    {
      draw_pixel(image, sz[0], sz[1], x, ipart(intery), rfpart(intery), c);
      draw_pixel(image, sz[0], sz[1], x, ipart(intery) + 1, fpart(intery), c);
      intery = intery + gradient;
    }
  }
}

//----------------------------------------------------------------
// draw_line
//
template <class image_t>
void
draw_line(typename image_t::Pointer & image,
    const typename image_t::PixelType color,
    double x1,
    double y1,
    double x2,
    double y2)
{
  if (false)
  {
    // MSVC++ will not instantiate plot_normal and plot_swapped
    // unless it sees them called explicitly:
    wu::plot_normal<image_t>(image, 0, 0, 0.0, 0.0, 0.0, 0.0);
    wu::plot_swapped<image_t>(image, 0, 0, 0.0, 0.0, 0.0, 0.0);
  }
  
  double dx = fabs(x2 - x1);
  double dy = fabs(y2 - y1);
  
  typename image_t::PointType origin = image->GetOrigin();
  typename image_t::SpacingType spacing = image->GetSpacing();
  
  x1 /= spacing[0];
  x2 /= spacing[0];
  
  y1 /= spacing[1];
  y2 /= spacing[1];
  
  if (dx > dy)
  {
    // horizontal line:
    wu::draw_nearly_horizontal_line<image_t>(image,
               double(color),
               x1, y1, x2, y2,
               wu::plot_normal<image_t>);
  }
  else if (dy != 0.0)
  {
    // vertical line:
    wu::draw_nearly_horizontal_line<image_t>(image,
               double(color),
               y1, x1, y2, x2,
               wu::plot_swapped<image_t>);
  }
}

//----------------------------------------------------------------
// draw_line_rotated
// 
template <class image_t>
void
draw_line_rotated(typename image_t::Pointer & image,
      const typename image_t::PixelType color,
      const double & x1,
      const double & y1,
      const double & x2,
      const double & y2,
      const double & radians,
      const double & ox = 0.0,
      const double & oy = 0.0)
{
  const double ct = ::cos(radians);
  const double st = ::sin(radians);
  
  const double u1 = ox + ct * (x1 - ox) - st * (y1 - oy);
  const double v1 = oy + ct * (y1 - oy) + st * (x1 - ox);
  
  const double u2 = ox + ct * (x2 - ox) - st * (y2 - oy);
  const double v2 = oy + ct * (y2 - oy) + st * (x2 - ox);
  
  draw_line<image_t>(image, color, u1, v1, u2, v2);
}


#endif // DRAW_HXX_