/*
img_quant.c - image quantizer. based on Antony Dekker original code
Copyright (C) 2011 Uncle Mike

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
*/

#include "imagelib.h"


#define netsize		256			// number of colours used
#define prime1		499
#define prime2		491
#define prime3		487
#define prime4		503

#define minpicturebytes	(3*prime4)		// minimum size for input image

#define maxnetpos		(netsize-1)
#define netbiasshift	4			// bias for colour values
#define ncycles		100			// no. of learning cycles

// defs for freq and bias
#define intbiasshift	16			// bias for fractions
#define intbias		(1<<intbiasshift)
#define gammashift  	10			// gamma = 1024
#define gamma		(1<<gammashift)
#define betashift		10
#define beta		(intbias>>betashift)	// beta = 1 / 1024
#define betagamma		(intbias<<(gammashift - betashift))

// defs for decreasing radius factor
#define initrad		(netsize>>3)		// for 256 cols, radius starts
#define radiusbiasshift	6			// at 32.0 biased by 6 bits
#define radiusbias		(1<<radiusbiasshift)
#define initradius		(initrad * radiusbias)	// and decreases by a
#define radiusdec		30			// factor of 1/30 each cycle 

// defs for decreasing alpha factor
#define alphabiasshift	10			// alpha starts at 1.0
#define initalpha		(1<<alphabiasshift)
int			alphadec;			// biased by 10 bits

// radbias and alpharadbias used for radpower calculation
#define radbiasshift	8
#define radbias		(1<<radbiasshift)
#define alpharadbshift	(alphabiasshift+radbiasshift)
#define alpharadbias	(1<<alpharadbshift)

// types and global variables
static byte		*thepicture;		// the input image itself
static int		lengthcount;		// lengthcount = H*W*3
static int		samplefac;		// sampling factor 1..30
static int		network[netsize][4];	// the network itself
static int		netindex[256];		// for network lookup - really 256
static int		bias[netsize];		// bias and freq arrays for learning
static int		freq[netsize];
static int		radpower[initrad];		// radpower for precomputation

void initnet( byte *thepic, int len, int sample )	
{
	register int	i, *p;
	
	thepicture = thepic;
	lengthcount = len;
	samplefac = sample;
	
	for( i = 0; i < netsize; i++ )
	{
		p = network[i];
		p[0] = p[1] = p[2] = (i << (netbiasshift + 8)) / netsize;
		freq[i] = intbias / netsize;	// 1 / netsize
		bias[i] = 0;
	}
}
	
// Unbias network to give byte values 0..255 and record position i to prepare for sort
void unbiasnet( void )
{
	int	i, j, temp;

	for( i = 0; i < netsize; i++ )
	{
		for( j = 0; j < 3; j++ )
		{
			// OLD CODE: network[i][j] >>= netbiasshift;
			// Fix based on bug report by Juergen Weigert jw@suse.de
			temp = (network[i][j] + (1 << (netbiasshift - 1))) >> netbiasshift;
			if( temp > 255 ) temp = 255;
			network[i][j] = temp;
		}

		network[i][3] = i; // record colour num
	}
}

// Insertion sort of network and building of netindex[0..255] (to do after unbias)
void inxbuild( void )
{
	register int	*p, *q;
	register int	i, j, smallpos, smallval;
	int		previouscol, startpos;

	previouscol = 0;
	startpos = 0;

	for( i = 0; i < netsize; i++ )
	{
		p = network[i];
		smallpos = i;
		smallval = p[1];			// index on g

		// find smallest in i..netsize-1
		for( j = i + 1; j < netsize; j++ )
		{
			q = network[j];
			if( q[1] < smallval )
			{
				// index on g
				smallpos = j;
				smallval = q[1];	// index on g
			}
		}

		q = network[smallpos];

		// swap p (i) and q (smallpos) entries
		if( i != smallpos )
		{
			j = q[0];   q[0] = p[0];   p[0] = j;
			j = q[1];   q[1] = p[1];   p[1] = j;
			j = q[2];   q[2] = p[2];   p[2] = j;
			j = q[3];   q[3] = p[3];   p[3] = j;
		}

		// smallval entry is now in position i
		if( smallval != previouscol )
		{
			netindex[previouscol] = (startpos+i) >> 1;

			for( j = previouscol + 1; j < smallval; j++ )
				netindex[j] = i;

			previouscol = smallval;
			startpos = i;
		}
	}

	netindex[previouscol] = (startpos + maxnetpos)>>1;

	for( j = previouscol + 1; j < 256; j++ )
		netindex[j] = maxnetpos; // really 256
}


// Search for BGR values 0..255 (after net is unbiased) and return colour index
int inxsearch( int r, int g, int b )
{
	register int	i, j, dist, a, bestd;
	register int	*p;
	int		best;

	bestd = 1000;	// biggest possible dist is 256 * 3
	best = -1;
	i = netindex[g];	// index on g
	j = i - 1;	// start at netindex[g] and work outwards

	while(( i < netsize ) || ( j >= 0 ))
	{
		if( i < netsize )
		{
			p = network[i];
			dist = p[1] - g;		// inx key

			if( dist >= bestd )
			{
				i = netsize;	// stop iter
			}
			else
			{
				i++;
				if( dist < 0 ) dist = -dist;
				a = p[2] - b;
				if( a < 0 ) a = -a;
				dist += a;

				if( dist < bestd )
				{
					a = p[0] - r;
					if( a < 0 ) a = -a;
					dist += a;

					if( dist < bestd )
					{
						bestd = dist;
						best = p[3];
					}
				}
			}
		}

		if( j >= 0 )
		{
			p = network[j];
			dist = g - p[1]; // inx key - reverse dif

			if( dist >= bestd )
			{
				j = -1; // stop iter
			}
			else
			{
				j--;
				if( dist < 0 ) dist = -dist;
				a = p[2] - b;
				if( a < 0 ) a = -a;
				dist += a;

				if( dist < bestd )
				{
					a = p[0] - r;
					if( a < 0 ) a = -a;
					dist += a;
					if( dist < bestd )
					{
						bestd = dist;
						best = p[3];
					}
				}
			}
		}
	}

	return best;
}

// Search for biased BGR values
int contest( int r, int g, int b )
{
	// finds closest neuron (min dist) and updates freq
	// finds best neuron (min dist-bias) and returns position
	// for frequently chosen neurons, freq[i] is high and bias[i] is negative
	// bias[i] = gamma * ((1 / netsize) - freq[i])

	register int	*p, *f, *n;
	register int	i, dist, a, biasdist, betafreq;
	int		bestpos, bestbiaspos, bestd, bestbiasd;

	bestd = ~(1<<31);
	bestbiasd = bestd;
	bestpos = -1;
	bestbiaspos = bestpos;
	p = bias;
	f = freq;

	for( i = 0; i < netsize; i++ )
	{
		n = network[i];
		dist = n[2] - b;
		if( dist < 0 ) dist = -dist;
		a = n[1] - g;
		if( a < 0 ) a = -a;
		dist += a;
		a = n[0] - r;
		if( a < 0 ) a = -a;
		dist += a;

		if( dist < bestd )
		{
			bestd = dist;
			bestpos = i;
		}

		biasdist = dist - ((*p) >> (intbiasshift - netbiasshift));

		if( biasdist < bestbiasd )
		{
			bestbiasd = biasdist;
			bestbiaspos = i;
		}

		betafreq = (*f >> betashift);
		*f++ -= betafreq;
		*p++ += (betafreq << gammashift);
	}

	freq[bestpos] += beta;
	bias[bestpos] -= betagamma;

	return bestbiaspos;
}

// Move neuron i towards biased (b,g,r) by factor alpha
void altersingle( int alpha, int i, int r, int g, int b )
{
	register int	*n;

	n = network[i];	// alter hit neuron
	*n -= (alpha * (*n - r)) / initalpha;
	n++;
	*n -= (alpha * (*n - g)) / initalpha;
	n++;
	*n -= (alpha * (*n - b)) / initalpha;
}

// Move adjacent neurons by precomputed alpha*(1-((i-j)^2/[r]^2)) in radpower[|i-j|]
void alterneigh( int rad, int i, int r, int g, int b )
{
	register int	j, k, lo, hi, a;
	register int	*p, *q;

	lo = i - rad;
	if( lo < -1 ) lo = -1;
	hi = i + rad;
	if( hi > netsize ) hi = netsize;

	j = i + 1;
	k = i - 1;
	q = radpower;

	while(( j < hi ) || ( k > lo ))
	{
		a = (*(++q));

		if( j < hi )
		{
			p = network[j];
			*p -= (a * (*p - r)) / alpharadbias;
			p++;
			*p -= (a * (*p - g)) / alpharadbias;
			p++;
			*p -= (a * (*p - b)) / alpharadbias;
			j++;
		}

		if( k > lo )
		{
			p = network[k];
			*p -= (a * (*p - r)) / alpharadbias;
			p++;
			*p -= (a * (*p - g)) / alpharadbias;
			p++;
			*p -= (a * (*p - b)) / alpharadbias;
			k--;
		}
	}
}

// Main Learning Loop
void learn( void )
{
	register byte	*p;
	register int	i, j, r, g, b;
	int		radius, rad, alpha, step;
	int		delta, samplepixels;
	byte		*lim;

	alphadec = 30 + ((samplefac - 1) / 3);
	p = thepicture;
	lim = thepicture + lengthcount;
	samplepixels = lengthcount / (image.bpp * samplefac);
	delta = samplepixels / ncycles;
	alpha = initalpha;
	radius = initradius;
	
	rad = radius >> radiusbiasshift;
	if( rad <= 1 ) rad = 0;

	for( i = 0; i < rad; i++ ) 
		radpower[i] = alpha * ((( rad * rad - i * i ) * radbias ) / ( rad * rad ));	

	if( delta <= 0 ) return;

	if(( lengthcount % prime1 ) != 0 )
	{
		step = prime1 * image.bpp;
	}
	else if(( lengthcount % prime2 ) != 0 )
	{
		step = prime2 * image.bpp;
	}
	else if(( lengthcount % prime3 ) != 0 )
	{
		step = prime3 * image.bpp;
	}
	else
	{
		step = prime4 * image.bpp;
	}
	
	i = 0;

	while( i < samplepixels )
	{
		r = p[0] << netbiasshift;
		g = p[1] << netbiasshift;
		b = p[2] << netbiasshift;
		j = contest( r, g, b );

		altersingle( alpha, j, r, g, b );
		if( rad ) alterneigh( rad, j, r, g, b );   // alter neighbours

		p += step;
		if( p >= lim ) p -= lengthcount;
	
		i++;

		if( i % delta == 0 )
		{	
			alpha -= alpha / alphadec;
			radius -= radius / radiusdec;
			rad = radius >> radiusbiasshift;
			if( rad <= 1 ) rad = 0;

			for( j = 0; j < rad; j++ ) 
				radpower[j] = alpha * ((( rad * rad - j * j ) * radbias ) / ( rad * rad ));
		}
	}
}

// returns the actual number of palette entries.
rgbdata_t *Image_Quantize( rgbdata_t *pic )
{
	int	i;

	// quick case to reject unneeded conversions
	if( pic->type == PF_INDEXED_24 || pic->type ==  PF_INDEXED_32 )
		return pic;

	Image_CopyParms( pic );
	image.size = image.width * image.height;
	image.bpp = PFDesc[pic->type].bpp;
	image.ptr = 0;

	// allocate 8-bit buffer
	image.tempbuffer = Mem_Realloc( host.imagepool, image.tempbuffer, image.size );

	initnet( pic->buffer, pic->size, 10 );
	learn();
	unbiasnet();

	pic->palette = Mem_Alloc( host.imagepool, netsize * 3 );

	for( i = 0; i < netsize; i++ )
	{
		pic->palette[i*3+0] = network[i][0];	// red
		pic->palette[i*3+1] = network[i][1];	// green
		pic->palette[i*3+2] = network[i][2];	// blue 
	}

	inxbuild();

	for( i = 0; i < image.width * image.height; i++ )
	{
		image.tempbuffer[i] = inxsearch( pic->buffer[i*image.bpp+0], pic->buffer[i*image.bpp+1], pic->buffer[i*image.bpp+2] );
	}

	pic->buffer = Mem_Realloc( host.imagepool, pic->buffer, image.size );
	memcpy( pic->buffer, image.tempbuffer, image.size );
	pic->type = PF_INDEXED_24;
	pic->size = image.size;

	return pic;
}