/*
 * Based on gdImageCopyResampled from libgd.
 * Original copyright notice follow:

     Portions copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
		 Pierre-Alain Joye (pierre@libgd.org).

     Permission has been granted to copy, distribute and modify gd in
     any context without fee, including a commercial application,
     provided that this notice is present in user-accessible supporting
     documentation.

     This does not affect your ownership of the derived work itself, and 
     the intent is to assure proper credit for the authors of gd, not to
     interfere with your productive use of gd. If you have questions,
     ask. "Derived works" includes all programs that utilize the   
     library. Credit must be given in user-accessible documentation.

     This software is provided "AS IS." The copyright holders disclaim  
     all warranties, either express or implied, including but not
     limited to implied warranties of merchantability and fitness for a
     particular purpose, with respect to this code and accompanying  
     documentation.
 */

/*
 *
 * @todo Simplify: Offsets of images are 0,0 => no dstX, dstY, srcX, srcY;
 *             Screenshot has no alpha channel => no processing of alpha byte.
 */

#include <iprt/types.h>

/* 2.0.10: cast instead of floor() yields 35% performance improvement. 
	Thanks to John Buckman. */

#define floor2(exp) ((long) exp)
/*#define floor2(exp) floor(exp)*/

typedef uint8_t *gdImagePtr;

DECLINLINE(int) gdImageGetTrueColorPixel (gdImagePtr im, int x, int y, int w)
{
    return *(int32_t *)(im + y * w * 4 + x * 4);
}

DECLINLINE(void) gdImageSetPixel (gdImagePtr im, int x, int y, int color, int w)
{
    *(int32_t *)(im + y * w * 4 + x * 4) = color;
}

#define gdAlphaMax 127
#define gdAlphaOpaque 0
#define gdAlphaTransparent 127
#define gdRedMax 255
#define gdGreenMax 255
#define gdBlueMax 255
#define gdTrueColorGetAlpha(c) (((c) & 0x7F000000) >> 24)
#define gdTrueColorGetRed(c) (((c) & 0xFF0000) >> 16)
#define gdTrueColorGetGreen(c) (((c) & 0x00FF00) >> 8)
#define gdTrueColorGetBlue(c) ((c) & 0x0000FF)
#define gdTrueColorAlpha(r, g, b, a) (((a) << 24) + \
	((r) << 16) + \
	((g) << 8) + \
	(b))

void gdImageCopyResampled (uint8_t *dst,
		      uint8_t *src,
		      int dstX, int dstY,
		      int srcX, int srcY,
		      int dstW, int dstH, int srcW, int srcH)
{
  int x, y;
  double sy1, sy2, sx1, sx2;
  for (y = dstY; (y < dstY + dstH); y++)
    {
      sy1 = ((double) y - (double) dstY) * (double) srcH / (double) dstH;
      sy2 = ((double) (y + 1) - (double) dstY) * (double) srcH /
	(double) dstH;
      for (x = dstX; (x < dstX + dstW); x++)
	{
	  double sx, sy;
	  double spixels = 0;
	  double red = 0.0, green = 0.0, blue = 0.0, alpha = 0.0;
	  sx1 = ((double) x - (double) dstX) * (double) srcW / dstW;
	  sx2 = ((double) (x + 1) - (double) dstX) * (double) srcW / dstW;
	  sy = sy1;
	  do
	    {
	      double yportion;
	      if (floor2 (sy) == floor2 (sy1))
		{
		  yportion = 1.0 - (sy - floor2 (sy));
		  if (yportion > sy2 - sy1)
		    {
		      yportion = sy2 - sy1;
		    }
		  sy = floor2 (sy);
		}
	      else if (sy == floor2 (sy2))
		{
		  yportion = sy2 - floor2 (sy2);
		}
	      else
		{
		  yportion = 1.0;
		}
	      sx = sx1;
	      do
		{
		  double xportion;
		  double pcontribution;
		  int p;
		  if (floor2 (sx) == floor2 (sx1))
		    {
		      xportion = 1.0 - (sx - floor2 (sx));
		      if (xportion > sx2 - sx1)
			{
			  xportion = sx2 - sx1;
			}
		      sx = floor2 (sx);
		    }
		  else if (sx == floor2 (sx2))
		    {
		      xportion = sx2 - floor2 (sx2);
		    }
		  else
		    {
		      xportion = 1.0;
		    }
		  pcontribution = xportion * yportion;
		  /* 2.08: previously srcX and srcY were ignored. 
		     Andrew Pattison */
		  p = gdImageGetTrueColorPixel (src,
						(int) sx + srcX,
						(int) sy + srcY, srcW);
		  red += gdTrueColorGetRed (p) * pcontribution;
		  green += gdTrueColorGetGreen (p) * pcontribution;
		  blue += gdTrueColorGetBlue (p) * pcontribution;
		  alpha += gdTrueColorGetAlpha (p) * pcontribution;
		  spixels += xportion * yportion;
		  sx += 1.0;
		}
	      while (sx < sx2);
	      sy += 1.0;
	    }
	  while (sy < sy2);
	  if (spixels != 0.0)
	    {
	      red /= spixels;
	      green /= spixels;
	      blue /= spixels;
	      alpha /= spixels;
	    }
	  /* Clamping to allow for rounding errors above */
	  if (red > 255.0)
	    {
	      red = 255.0;
	    }
	  if (green > 255.0)
	    {
	      green = 255.0;
	    }
	  if (blue > 255.0)
	    {
	      blue = 255.0;
	    }
	  if (alpha > gdAlphaMax)
	    {
	      alpha = gdAlphaMax;
	    }
	  gdImageSetPixel (dst,
			   x, y,
			   gdTrueColorAlpha ((int) red,
					     (int) green,
					     (int) blue, (int) alpha), dstW);
	}
    }
}