#include <cassert>
#include <Extctrls.hpp>

//Darken an image by fraction f
// * f = 0.0 denotes no bleaching  (image untouched)
// * f = 1.0 denotes max bleaching (image black)
//From http://www.richelbilderbeek.nl/CppDarken.htm
void Darken(
  const Extctrls::TImage * const source,
  const double f,                   
  Extctrls::TImage * const target)
{
  assert(f >=  0.0);
  assert(f <=  1.0);
  assert(source!=0 && "Image is NULL");
  assert(source->Picture->Bitmap!=0 && "Image bitmap is NULL");
  assert(source->Picture->Bitmap->PixelFormat == pf24bit && "Image bitmap must be 24 bit");
  assert(target!=0 && "Image is NULL");
  assert(target->Picture->Bitmap!=0 && "Image bitmap is NULL");
  assert(target->Picture->Bitmap->PixelFormat == pf24bit && "Image bitmap must be 24 bit");
  //Get the width and height from the source
  const int width  = source->Picture->Bitmap->Width;
  const int height = source->Picture->Bitmap->Height;
  //Set the target's width and height
  target->Picture->Bitmap->Width  = width;
  target->Picture->Bitmap->Height = height;

  for (int y=0; y!=height; ++y)
  {
    const unsigned char * lineSource
      = static_cast<const unsigned char *>(
        source->Picture->Bitmap->ScanLine[y]);
    unsigned char * lineTarget
      = static_cast<unsigned char *>(
        target->Picture->Bitmap->ScanLine[y]);
    for (int x=0; x!=width; ++x)
    {
      const int r = lineSource[x*3+2]; //Red;
      const int g = lineSource[x*3+1]; //Green;
      const int b = lineSource[x*3+0]; //Blue;
      const double dist_r = static_cast<double>(r) * (1.0-f);
      const double dist_g = static_cast<double>(g) * (1.0-f);
      const double dist_b = static_cast<double>(b) * (1.0-f);
      const int new_r = static_cast<int>(dist_r);
      const int new_g = static_cast<int>(dist_g);
      const int new_b = static_cast<int>(dist_b);
      assert(new_r >=   0);
      assert(new_r <  256);
      assert(new_g >=   0);
      assert(new_g <  256);
      assert(new_b >=   0);
      assert(new_b <  256);
      lineTarget[x*3+2] = new_r; //Red
      lineTarget[x*3+1] = new_g; //Green
      lineTarget[x*3+0] = new_b; //Blue
    }
  }

}