#include <cmath>

// Exponential blur, Jani Huhtanen, 2006
//
template<int aprec, int zprec>
static inline void blurinner(unsigned char *bptr, int &zR, int &zG, int &zB, int &zA, int alpha);

template<int aprec,int zprec>
static inline void blurrow( QImage & im, int line, int alpha);

template<int aprec, int zprec>
static inline void blurcol( QImage & im, int col, int alpha);

/*
*  expblur(QImage &img, int radius)
*
*  In-place blur of image 'img' with kernel
*  of approximate radius 'radius'.
*
*  Blurs with two sided exponential impulse
*  response.
*
*  aprec = precision of alpha parameter 
*  in fixed-point format 0.aprec
*
*  zprec = precision of state parameters
*  zR,zG,zB and zA in fp format 8.zprec
*/
template<int aprec,int zprec>
void expblur( QImage &img, int radius )
{
  if(radius<1)
    return;

  /* Calculate the alpha such that 90% of 
     the kernel is within the radius.
     (Kernel extends to infinity) 
  */
  int alpha = (int)((1<<aprec)*(1.0f-expf(-2.3f/(radius+1.f))));

  for(int row=0;row<img.height();row++)
  {
    blurrow<aprec,zprec>(img,row,alpha);
  }

  for(int col=0;col<img.width();col++)
  {
    blurcol<aprec,zprec>(img,col,alpha);
  }
  return;
}

template<int aprec, int zprec>
static inline void blurinner(unsigned char *bptr, int &zR, int &zG, int &zB, int &zA, int alpha)
{
  int R,G,B,A;
  R = *bptr;
  G = *(bptr+1);
  B = *(bptr+2);
  A = *(bptr+3);

  zR += (alpha * ((R<<zprec)-zR))>>aprec;
  zG += (alpha * ((G<<zprec)-zG))>>aprec;
  zB += (alpha * ((B<<zprec)-zB))>>aprec;
  zA += (alpha * ((A<<zprec)-zA))>>aprec;

  *bptr =     zR>>zprec;
  *(bptr+1) = zG>>zprec;
  *(bptr+2) = zB>>zprec;
  *(bptr+3) = zA>>zprec;
}

template<int aprec,int zprec>
static inline void blurrow( QImage & im, int line, int alpha)
{
  int zR,zG,zB,zA;

  QRgb *ptr = (QRgb *)im.scanLine(line);

  zR = *((unsigned char *)ptr    )<<zprec;
  zG = *((unsigned char *)ptr + 1)<<zprec;
  zB = *((unsigned char *)ptr + 2)<<zprec;
  zA = *((unsigned char *)ptr + 3)<<zprec;

  for(int index=1; index<im.width(); index++)
  {
    blurinner<aprec,zprec>((unsigned char *)&ptr[index],zR,zG,zB,zA,alpha);
  }
  for(int index=im.width()-2; index>=0; index--)
  {
    blurinner<aprec,zprec>((unsigned char *)&ptr[index],zR,zG,zB,zA,alpha);
  }
 

}

template<int aprec, int zprec>
static inline void blurcol( QImage & im, int col, int alpha)
{
  int zR,zG,zB,zA;

  QRgb *ptr = (QRgb *)im.bits();
  ptr+=col;

  zR = *((unsigned char *)ptr    )<<zprec;
  zG = *((unsigned char *)ptr + 1)<<zprec;
  zB = *((unsigned char *)ptr + 2)<<zprec;
  zA = *((unsigned char *)ptr + 3)<<zprec;

  for(int index=im.width(); index<(im.height()-1)*im.width(); index+=im.width())
  {
    blurinner<aprec,zprec>((unsigned char *)&ptr[index],zR,zG,zB,zA,alpha);
  }

  for(int index=(im.height()-2)*im.width(); index>=0; index-=im.width())
  {
    blurinner<aprec,zprec>((unsigned char *)&ptr[index],zR,zG,zB,zA,alpha);
  }

}

template<class T>
inline const T& qClamp(const T &x, const T &low, const T &high)
{
    if      (x <  low) return low;
    else if (x > high) return high;
    else               return x;
}