/*
Copyright (C) 2013 by Brendan G Bohannon
Email: cr88192@gmail.com
Copying: http://pastebin.com/iJxtZHm6
 */

void BGBBTJ_BCn_EncodeBlockDXT1F(byte *block,
	byte *rgba, int xstride, int ystride, int nclr)
{
	byte clr0[4], clr1[4];
	byte pxy[16];
	int p0, p1, p2, p3;
	int mcr, mcg, mcb, mcy;
	int ncr, ncg, ncb, ncy;
	int acr, acg, acb;
	int cr, cg, cb, cy, acy;
	int i, j, k;
	
	mcr=255; mcg=255; mcb=255; mcy=255;
	ncr=  0; ncg=  0; ncb=  0; ncy=  0;
	acr=  0; acg=  0; acb=  0;

	for(i=0; i<4; i++)
		for(j=0; j<4; j++)
	{
		k=(i*ystride)+(j*xstride);
		cr=rgba[k+0];
		cg=rgba[k+1];
		cb=rgba[k+2];
		cy=(cr+2*cg+cb)>>2;
		pxy[i*4+j]=cy;

		if(cy<mcy) { mcr=cr; mcg=cg; mcb=cb; mcy=cy; }
		if(cy>ncy) { ncr=cr; ncg=cg; ncb=cb; ncy=cy; }
		acr+=cr;
		acg+=cg;
		acb+=cb;
	}
	
	acr=acr>>4;
	acg=acg>>4;
	acb=acb>>4;

	clr0[0]=(mcr*11+acr*5)>>4;
	clr0[1]=(mcg*11+acg*5)>>4;
	clr0[2]=(mcb*11+acb*5)>>4;
	clr1[0]=(ncr*11+acr*5)>>4;
	clr1[1]=(ncg*11+acg*5)>>4;
	clr1[2]=(ncb*11+acb*5)>>4;

	block[0]=((clr0[1]<<3)&0xE0) | (clr0[2]>>3);
	block[1]=(clr0[0]&0xF8) | (clr0[1]>>5);
	block[2]=((clr1[1]<<3)&0xE0) | (clr1[2]>>3);
	block[3]=(clr1[0]&0xF8) | (clr1[1]>>5);
	
	clr0[3]=(clr0[0]+2*clr0[1]+clr0[2])>>2;
	clr1[3]=(clr1[0]+2*clr1[1]+clr1[2])>>2;

	acy=(clr0[3]+clr1[3])>>1;

	p0=-((acy-pxy[ 0])>>16);
	p1=-((acy-pxy[ 1])>>16);
	p2=-((acy-pxy[ 2])>>16);
	p3=-((acy-pxy[ 3])>>16);
	block[4]=(p3<<6)|(p2<<4)|(p1<<2)|p0;
	p0=-((acy-pxy[ 4])>>16);
	p1=-((acy-pxy[ 5])>>16);
	p2=-((acy-pxy[ 6])>>16);
	p3=-((acy-pxy[ 7])>>16);
	block[5]=(p3<<6)|(p2<<4)|(p1<<2)|p0;
	p0=-((acy-pxy[ 8])>>16);
	p1=-((acy-pxy[ 9])>>16);
	p2=-((acy-pxy[10])>>16);
	p3=-((acy-pxy[11])>>16);
	block[6]=(p3<<6)|(p2<<4)|(p1<<2)|p0;
	p0=-((acy-pxy[12])>>16);
	p1=-((acy-pxy[13])>>16);
	p2=-((acy-pxy[14])>>16);
	p3=-((acy-pxy[15])>>16);
	block[7]=(p3<<6)|(p2<<4)|(p1<<2)|p0;
}

BGBBTJ_API void BGBBTJ_BCn_EncodeImageDXT1F(byte *block,
	byte *rgba, int xs, int ys, int stride)
{
	int xs1, ys1;
	int i, j;
	
	xs1=xs>>2; ys1=ys>>2;
	for(i=0; i<ys1; i++)
		for(j=0; j<xs1; j++)
	{
		BGBBTJ_BCn_EncodeBlockDXT1F(
			block+(i*xs1+j)*8,
			rgba+(i*4*xs+j*4)*stride,
			stride, xs*stride, 3);
	}
}