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nothings-stb/stb_dxt.h

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// stb_dxt.h - v1.04 - DXT1/DXT5 compressor - public domain
// original by fabian "ryg" giesen - ported to C by stb
// use '#define STB_DXT_IMPLEMENTATION' before including to create the implementation
//
// USAGE:
// call stb_compress_dxt_block() for every block (you must pad)
// source should be a 4x4 block of RGBA data in row-major order;
// A is ignored if you specify alpha=0; you can turn on dithering
// and "high quality" using mode.
//
// version history:
// v1.04 - (ryg) default to no rounding bias for lerped colors (as per S3TC/DX10 spec);
// single color match fix (allow for inexact color interpolation);
// optimal DXT5 index finder; "high quality" mode that runs multiple refinement steps.
// v1.03 - (stb) endianness support
// v1.02 - (stb) fix alpha encoding bug
// v1.01 - (stb) fix bug converting to RGB that messed up quality, thanks ryg & cbloom
// v1.00 - (stb) first release
#ifndef STB_INCLUDE_STB_DXT_H
#define STB_INCLUDE_STB_DXT_H
// compression mode (bitflags)
#define STB_DXT_NORMAL 0
#define STB_DXT_DITHER 1 // use dithering. dubious win. never use for normal maps and the like!
#define STB_DXT_HIGHQUAL 2 // high quality mode, does two refinement steps instead of 1. ~30-40% slower.
void stb_compress_dxt_block(unsigned char *dest, const unsigned char *src, int alpha, int mode);
#define STB_COMPRESS_DXT_BLOCK
#ifdef STB_DXT_IMPLEMENTATION
// configuration options for DXT encoder. set them in the project/makefile or just define
// them at the top.
// STB_DXT_USE_ROUNDING_BIAS
// use a rounding bias during color interpolation. this is closer to what "ideal"
// interpolation would do but doesn't match the S3TC/DX10 spec. old versions (pre-1.03)
// implicitly had this turned on.
//
// in case you're targeting a specific type of hardware (e.g. console programmers):
// NVidia and Intel GPUs (as of 2010) as well as DX9 ref use DXT decoders that are closer
// to STB_DXT_USE_ROUNDING_BIAS. AMD/ATI, S3 and DX10 ref are closer to rounding with no bias.
// you also see "(a*5 + b*3) / 8" on some old GPU designs.
// #define STB_DXT_USE_ROUNDING_BIAS
#include <stdlib.h>
#include <math.h>
#include <string.h> // memset
static unsigned char stb__Expand5[32];
static unsigned char stb__Expand6[64];
static unsigned char stb__OMatch5[256][2];
static unsigned char stb__OMatch6[256][2];
static unsigned char stb__QuantRBTab[256+16];
static unsigned char stb__QuantGTab[256+16];
static int stb__Mul8Bit(int a, int b)
{
int t = a*b + 128;
return (t + (t >> 8)) >> 8;
}
static void stb__From16Bit(unsigned char *out, unsigned short v)
{
int rv = (v & 0xf800) >> 11;
int gv = (v & 0x07e0) >> 5;
int bv = (v & 0x001f) >> 0;
out[0] = stb__Expand5[rv];
out[1] = stb__Expand6[gv];
out[2] = stb__Expand5[bv];
out[3] = 0;
}
static unsigned short stb__As16Bit(int r, int g, int b)
{
return (stb__Mul8Bit(r,31) << 11) + (stb__Mul8Bit(g,63) << 5) + stb__Mul8Bit(b,31);
}
// linear interpolation at 1/3 point between a and b, using desired rounding type
static int stb__Lerp13(int a, int b)
{
#ifdef STB_DXT_USE_ROUNDING_BIAS
// with rounding bias
return a + stb__Mul8Bit(b-a, 0x55);
#else
// without rounding bias
// replace "/ 3" by "* 0xaaab) >> 17" if your compiler sucks or you really need every ounce of speed.
return (2*a + b) / 3;
#endif
}
// lerp RGB color
static void stb__Lerp13RGB(unsigned char *out, unsigned char *p1, unsigned char *p2)
{
out[0] = stb__Lerp13(p1[0], p2[0]);
out[1] = stb__Lerp13(p1[1], p2[1]);
out[2] = stb__Lerp13(p1[2], p2[2]);
}
/****************************************************************************/
// compute table to reproduce constant colors as accurately as possible
static void stb__PrepareOptTable(unsigned char *Table,const unsigned char *expand,int size)
{
int i,mn,mx;
for (i=0;i<256;i++) {
int bestErr = 256;
for (mn=0;mn<size;mn++) {
for (mx=0;mx<size;mx++) {
int mine = expand[mn];
int maxe = expand[mx];
int err = abs(stb__Lerp13(maxe, mine) - i);
// DX10 spec says that interpolation must be within 3% of "correct" result,
// add this as error term. (normally we'd expect a random distribution of
// +-1.5% error, but nowhere in the spec does it say that the error has to be
// unbiased - better safe than sorry).
err += abs(maxe - mine) * 3 / 100;
if(err < bestErr)
{
Table[i*2+0] = mx;
Table[i*2+1] = mn;
bestErr = err;
}
}
}
}
}
static void stb__EvalColors(unsigned char *color,unsigned short c0,unsigned short c1)
{
stb__From16Bit(color+ 0, c0);
stb__From16Bit(color+ 4, c1);
stb__Lerp13RGB(color+ 8, color+0, color+4);
stb__Lerp13RGB(color+12, color+4, color+0);
}
// Block dithering function. Simply dithers a block to 565 RGB.
// (Floyd-Steinberg)
static void stb__DitherBlock(unsigned char *dest, unsigned char *block)
{
int err[8],*ep1 = err,*ep2 = err+4, *et;
int ch,y;
// process channels seperately
for (ch=0; ch<3; ++ch) {
unsigned char *bp = block+ch, *dp = dest+ch;
unsigned char *quant = (ch == 1) ? stb__QuantGTab+8 : stb__QuantRBTab+8;
memset(err, 0, sizeof(err));
for(y=0; y<4; ++y) {
dp[ 0] = quant[bp[ 0] + ((3*ep2[1] + 5*ep2[0]) >> 4)];
ep1[0] = bp[ 0] - dp[ 0];
dp[ 4] = quant[bp[ 4] + ((7*ep1[0] + 3*ep2[2] + 5*ep2[1] + ep2[0]) >> 4)];
ep1[1] = bp[ 4] - dp[ 4];
dp[ 8] = quant[bp[ 8] + ((7*ep1[1] + 3*ep2[3] + 5*ep2[2] + ep2[1]) >> 4)];
ep1[2] = bp[ 8] - dp[ 8];
dp[12] = quant[bp[12] + ((7*ep1[2] + 5*ep2[3] + ep2[2]) >> 4)];
ep1[3] = bp[12] - dp[12];
bp += 16;
dp += 16;
et = ep1, ep1 = ep2, ep2 = et; // swap
}
}
}
// The color matching function
static unsigned int stb__MatchColorsBlock(unsigned char *block, unsigned char *color,int dither)
{
unsigned int mask = 0;
int dirr = color[0*4+0] - color[1*4+0];
int dirg = color[0*4+1] - color[1*4+1];
int dirb = color[0*4+2] - color[1*4+2];
int dots[16];
int stops[4];
int i;
int c0Point, halfPoint, c3Point;
for(i=0;i<16;i++)
dots[i] = block[i*4+0]*dirr + block[i*4+1]*dirg + block[i*4+2]*dirb;
for(i=0;i<4;i++)
stops[i] = color[i*4+0]*dirr + color[i*4+1]*dirg + color[i*4+2]*dirb;
// think of the colors as arranged on a line; project point onto that line, then choose
// next color out of available ones. we compute the crossover points for "best color in top
// half"/"best in bottom half" and then the same inside that subinterval.
//
// relying on this 1d approximation isn't always optimal in terms of euclidean distance,
// but it's very close and a lot faster.
// http://cbloomrants.blogspot.com/2008/12/12-08-08-dxtc-summary.html
c0Point = (stops[1] + stops[3]) >> 1;
halfPoint = (stops[3] + stops[2]) >> 1;
c3Point = (stops[2] + stops[0]) >> 1;
if(!dither) {
// the version without dithering is straightforward
for (i=15;i>=0;i--) {
int dot = dots[i];
mask <<= 2;
if(dot < halfPoint)
mask |= (dot < c0Point) ? 1 : 3;
else
mask |= (dot < c3Point) ? 2 : 0;
}
} else {
// with floyd-steinberg dithering
int err[8],*ep1 = err,*ep2 = err+4;
int *dp = dots, y;
c0Point <<= 4;
halfPoint <<= 4;
c3Point <<= 4;
for(i=0;i<8;i++)
err[i] = 0;
for(y=0;y<4;y++)
{
int dot,lmask,step;
dot = (dp[0] << 4) + (3*ep2[1] + 5*ep2[0]);
if(dot < halfPoint)
step = (dot < c0Point) ? 1 : 3;
else
step = (dot < c3Point) ? 2 : 0;
ep1[0] = dp[0] - stops[step];
lmask = step;
dot = (dp[1] << 4) + (7*ep1[0] + 3*ep2[2] + 5*ep2[1] + ep2[0]);
if(dot < halfPoint)
step = (dot < c0Point) ? 1 : 3;
else
step = (dot < c3Point) ? 2 : 0;
ep1[1] = dp[1] - stops[step];
lmask |= step<<2;
dot = (dp[2] << 4) + (7*ep1[1] + 3*ep2[3] + 5*ep2[2] + ep2[1]);
if(dot < halfPoint)
step = (dot < c0Point) ? 1 : 3;
else
step = (dot < c3Point) ? 2 : 0;
ep1[2] = dp[2] - stops[step];
lmask |= step<<4;
dot = (dp[3] << 4) + (7*ep1[2] + 5*ep2[3] + ep2[2]);
if(dot < halfPoint)
step = (dot < c0Point) ? 1 : 3;
else
step = (dot < c3Point) ? 2 : 0;
ep1[3] = dp[3] - stops[step];
lmask |= step<<6;
dp += 4;
mask |= lmask << (y*8);
{ int *et = ep1; ep1 = ep2; ep2 = et; } // swap
}
}
return mask;
}
// The color optimization function. (Clever code, part 1)
static void stb__OptimizeColorsBlock(unsigned char *block, unsigned short *pmax16, unsigned short *pmin16)
{
int mind = 0x7fffffff,maxd = -0x7fffffff;
unsigned char *minp, *maxp;
double magn;
int v_r,v_g,v_b;
static const int nIterPower = 4;
float covf[6],vfr,vfg,vfb;
// determine color distribution
int cov[6];
int mu[3],min[3],max[3];
int ch,i,iter;
for(ch=0;ch<3;ch++)
{
const unsigned char *bp = ((const unsigned char *) block) + ch;
int muv,minv,maxv;
muv = minv = maxv = bp[0];
for(i=4;i<64;i+=4)
{
muv += bp[i];
if (bp[i] < minv) minv = bp[i];
else if (bp[i] > maxv) maxv = bp[i];
}
mu[ch] = (muv + 8) >> 4;
min[ch] = minv;
max[ch] = maxv;
}
// determine covariance matrix
for (i=0;i<6;i++)
cov[i] = 0;
for (i=0;i<16;i++)
{
int r = block[i*4+0] - mu[0];
int g = block[i*4+1] - mu[1];
int b = block[i*4+2] - mu[2];
cov[0] += r*r;
cov[1] += r*g;
cov[2] += r*b;
cov[3] += g*g;
cov[4] += g*b;
cov[5] += b*b;
}
// convert covariance matrix to float, find principal axis via power iter
for(i=0;i<6;i++)
covf[i] = cov[i] / 255.0f;
vfr = (float) (max[0] - min[0]);
vfg = (float) (max[1] - min[1]);
vfb = (float) (max[2] - min[2]);
for(iter=0;iter<nIterPower;iter++)
{
float r = vfr*covf[0] + vfg*covf[1] + vfb*covf[2];
float g = vfr*covf[1] + vfg*covf[3] + vfb*covf[4];
float b = vfr*covf[2] + vfg*covf[4] + vfb*covf[5];
vfr = r;
vfg = g;
vfb = b;
}
magn = fabs(vfr);
if (fabs(vfg) > magn) magn = fabs(vfg);
if (fabs(vfb) > magn) magn = fabs(vfb);
if(magn < 4.0f) { // too small, default to luminance
v_r = 299; // JPEG YCbCr luma coefs, scaled by 1000.
v_g = 587;
v_b = 114;
} else {
magn = 512.0 / magn;
v_r = (int) (vfr * magn);
v_g = (int) (vfg * magn);
v_b = (int) (vfb * magn);
}
// Pick colors at extreme points
for(i=0;i<16;i++)
{
int dot = block[i*4+0]*v_r + block[i*4+1]*v_g + block[i*4+2]*v_b;
if (dot < mind) {
mind = dot;
minp = block+i*4;
}
if (dot > maxd) {
maxd = dot;
maxp = block+i*4;
}
}
*pmax16 = stb__As16Bit(maxp[0],maxp[1],maxp[2]);
*pmin16 = stb__As16Bit(minp[0],minp[1],minp[2]);
}
static int stb__sclamp(float y, int p0, int p1)
{
int x = (int) y;
if (x < p0) return p0;
if (x > p1) return p1;
return x;
}
// The refinement function. (Clever code, part 2)
// Tries to optimize colors to suit block contents better.
// (By solving a least squares system via normal equations+Cramer's rule)
static int stb__RefineBlock(unsigned char *block, unsigned short *pmax16, unsigned short *pmin16, unsigned int mask)
{
static const int w1Tab[4] = { 3,0,2,1 };
static const int prods[4] = { 0x090000,0x000900,0x040102,0x010402 };
// ^some magic to save a lot of multiplies in the accumulating loop...
// (precomputed products of weights for least squares system, accumulated inside one 32-bit register)
float frb,fg;
unsigned short oldMin, oldMax, min16, max16;
int i, akku = 0, xx,xy,yy;
int At1_r,At1_g,At1_b;
int At2_r,At2_g,At2_b;
unsigned int cm = mask;
oldMin = *pmin16;
oldMax = *pmax16;
if((mask ^ (mask<<2)) < 4) // all pixels have the same index?
{
// yes, linear system would be singular; solve using optimal
// single-color match on average color
int r = 8, g = 8, b = 8;
for (i=0;i<16;++i) {
r += block[i*4+0];
g += block[i*4+1];
b += block[i*4+2];
}
r >>= 4; g >>= 4; b >>= 4;
max16 = (stb__OMatch5[r][0]<<11) | (stb__OMatch6[g][0]<<5) | stb__OMatch5[b][0];
min16 = (stb__OMatch5[r][1]<<11) | (stb__OMatch6[g][1]<<5) | stb__OMatch5[b][1];
} else {
At1_r = At1_g = At1_b = 0;
At2_r = At2_g = At2_b = 0;
for (i=0;i<16;++i,cm>>=2) {
int step = cm&3;
int w1 = w1Tab[step];
int r = block[i*4+0];
int g = block[i*4+1];
int b = block[i*4+2];
akku += prods[step];
At1_r += w1*r;
At1_g += w1*g;
At1_b += w1*b;
At2_r += r;
At2_g += g;
At2_b += b;
}
At2_r = 3*At2_r - At1_r;
At2_g = 3*At2_g - At1_g;
At2_b = 3*At2_b - At1_b;
// extract solutions and decide solvability
xx = akku >> 16;
yy = (akku >> 8) & 0xff;
xy = (akku >> 0) & 0xff;
frb = 3.0f * 31.0f / 255.0f / (xx*yy - xy*xy);
fg = frb * 63.0f / 31.0f;
// solve.
max16 = stb__sclamp((At1_r*yy - At2_r*xy)*frb+0.5f,0,31) << 11;
max16 |= stb__sclamp((At1_g*yy - At2_g*xy)*fg +0.5f,0,63) << 5;
max16 |= stb__sclamp((At1_b*yy - At2_b*xy)*frb+0.5f,0,31) << 0;
min16 = stb__sclamp((At2_r*xx - At1_r*xy)*frb+0.5f,0,31) << 11;
min16 |= stb__sclamp((At2_g*xx - At1_g*xy)*fg +0.5f,0,63) << 5;
min16 |= stb__sclamp((At2_b*xx - At1_b*xy)*frb+0.5f,0,31) << 0;
}
*pmin16 = min16;
*pmax16 = max16;
return oldMin != min16 || oldMax != max16;
}
// Color block compression
static void stb__CompressColorBlock(unsigned char *dest, unsigned char *block, int mode)
{
unsigned int mask;
int i;
int dither;
int refinecount;
unsigned short max16, min16;
unsigned char dblock[16*4],color[4*4];
dither = mode & STB_DXT_DITHER;
refinecount = (mode & STB_DXT_HIGHQUAL) ? 2 : 1;
// check if block is constant
for (i=1;i<16;i++)
if (((unsigned int *) block)[i] != ((unsigned int *) block)[0])
break;
if(i == 16) { // constant color
int r = block[0], g = block[1], b = block[2];
mask = 0xaaaaaaaa;
max16 = (stb__OMatch5[r][0]<<11) | (stb__OMatch6[g][0]<<5) | stb__OMatch5[b][0];
min16 = (stb__OMatch5[r][1]<<11) | (stb__OMatch6[g][1]<<5) | stb__OMatch5[b][1];
} else {
// first step: compute dithered version for PCA if desired
if(dither)
stb__DitherBlock(dblock,block);
// second step: pca+map along principal axis
stb__OptimizeColorsBlock(dither ? dblock : block,&max16,&min16);
if (max16 != min16) {
stb__EvalColors(color,max16,min16);
mask = stb__MatchColorsBlock(block,color,dither);
} else
mask = 0;
// third step: refine (multiple times if requested)
for (i=0;i<refinecount;i++) {
unsigned int lastmask = mask;
if (stb__RefineBlock(dither ? dblock : block,&max16,&min16,mask)) {
if (max16 != min16) {
stb__EvalColors(color,max16,min16);
mask = stb__MatchColorsBlock(block,color,dither);
} else {
mask = 0;
break;
}
}
if(mask == lastmask)
break;
}
}
// write the color block
if(max16 < min16)
{
unsigned short t = min16;
min16 = max16;
max16 = t;
mask ^= 0x55555555;
}
dest[0] = (unsigned char) (max16);
dest[1] = (unsigned char) (max16 >> 8);
dest[2] = (unsigned char) (min16);
dest[3] = (unsigned char) (min16 >> 8);
dest[4] = (unsigned char) (mask);
dest[5] = (unsigned char) (mask >> 8);
dest[6] = (unsigned char) (mask >> 16);
dest[7] = (unsigned char) (mask >> 24);
}
// Alpha block compression (this is easy for a change)
static void stb__CompressAlphaBlock(unsigned char *dest,unsigned char *src,int mode)
{
int i,dist,bias,dist4,dist2,bits,mask;
// find min/max color
int mn,mx;
mn = mx = src[3];
for (i=1;i<16;i++)
{
if (src[i*4+3] < mn) mn = src[i*4+3];
else if (src[i*4+3] > mx) mx = src[i*4+3];
}
// encode them
((unsigned char *)dest)[0] = mx;
((unsigned char *)dest)[1] = mn;
dest += 2;
// determine bias and emit color indices
// given the choice of mx/mn, these indices are optimal:
// http://fgiesen.wordpress.com/2009/12/15/dxt5-alpha-block-index-determination/
dist = mx-mn;
dist4 = dist*4;
dist2 = dist*2;
bias = (dist < 8) ? (dist - 1) : (dist/2 + 2);
bias -= mn * 7;
bits = 0,mask=0;
for (i=0;i<16;i++) {
int a = src[i*4+3]*7 + bias;
int ind,t;
// select index. this is a "linear scale" lerp factor between 0 (val=min) and 7 (val=max).
t = (a >= dist4) ? -1 : 0; ind = t & 4; a -= dist4 & t;
t = (a >= dist2) ? -1 : 0; ind += t & 2; a -= dist2 & t;
ind += (a >= dist);
// turn linear scale into DXT index (0/1 are extremal pts)
ind = -ind & 7;
ind ^= (2 > ind);
// write index
mask |= ind << bits;
if((bits += 3) >= 8) {
*dest++ = mask;
mask >>= 8;
bits -= 8;
}
}
}
static void stb__InitDXT()
{
int i;
for(i=0;i<32;i++)
stb__Expand5[i] = (i<<3)|(i>>2);
for(i=0;i<64;i++)
stb__Expand6[i] = (i<<2)|(i>>4);
for(i=0;i<256+16;i++)
{
int v = i-8 < 0 ? 0 : i-8 > 255 ? 255 : i-8;
stb__QuantRBTab[i] = stb__Expand5[stb__Mul8Bit(v,31)];
stb__QuantGTab[i] = stb__Expand6[stb__Mul8Bit(v,63)];
}
stb__PrepareOptTable(&stb__OMatch5[0][0],stb__Expand5,32);
stb__PrepareOptTable(&stb__OMatch6[0][0],stb__Expand6,64);
}
void stb_compress_dxt_block(unsigned char *dest, const unsigned char *src, int alpha, int mode)
{
static int init=1;
if (init) {
stb__InitDXT();
init=0;
}
if (alpha) {
stb__CompressAlphaBlock(dest,(unsigned char*) src,mode);
dest += 8;
}
stb__CompressColorBlock(dest,(unsigned char*) src,mode);
}
#endif // STB_DXT_IMPLEMENTATION
#endif // STB_INCLUDE_STB_DXT_H
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