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stb_dxt: Initialize tables at compile time

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Also fix a "potentially uninitialized variable" warning.

This is a modified version of Alan's original PR that keeps the
table generator in the file (in case there's interest) and also
replaces the expand[] tables with math, since it's trivial.

Fixes issue #1117.
master
Alan Hickman ago%!(EXTRA string=4 years) committed by Fabian Giesen
parent 696cb038a3
commit 98623b9577
1 changed files with 191 additions and 76 deletions
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  1. 267
      stb_dxt.h

267
stb_dxt.h
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@ -29,6 +29,7 @@
// Kevin Schmidt (#defines for "freestanding" compilation)
// github:ppiastucki (BC4 support)
// Ignacio Castano - improve DXT endpoint quantization
// Alan Hickman - static table initialization
//
// LICENSE
//
@ -81,14 +82,10 @@ STBDDEF void stb_compress_bc5_block(unsigned char *dest, const unsigned char *sr
#include <stdlib.h>
#if !defined(STBD_ABS) || !defined(STBI_FABS)
#if !defined(STBI_FABS)
#include <math.h>
#endif
#ifndef STBD_ABS
#define STBD_ABS(i) abs(i)
#endif
#ifndef STBD_FABS
#define STBD_FABS(x) fabs(x)
#endif
@ -98,12 +95,112 @@ STBDDEF void stb_compress_bc5_block(unsigned char *dest, const unsigned char *sr
#define STBD_MEMSET memset
#endif
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 const unsigned char stb__QuantRBTab[256 + 16] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8,
8, 8, 8, 8, 8, 16, 16, 16, 16, 16, 16, 16, 16, 24, 24, 24,
24, 24, 24, 24, 24, 33, 33, 33, 33, 33, 33, 33, 33, 33, 41, 41,
41, 41, 41, 41, 41, 41, 49, 49, 49, 49, 49, 49, 49, 49, 57, 57,
57, 57, 57, 57, 57, 57, 66, 66, 66, 66, 66, 66, 66, 66, 74, 74,
74, 74, 74, 74, 74, 74, 74, 82, 82, 82, 82, 82, 82, 82, 82, 90,
90, 90, 90, 90, 90, 90, 90, 99, 99, 99, 99, 99, 99, 99, 99, 107,
107, 107, 107, 107, 107, 107, 107, 107, 115, 115, 115, 115, 115, 115, 115, 115,
123, 123, 123, 123, 123, 123, 123, 123, 132, 132, 132, 132, 132, 132, 132, 132,
140, 140, 140, 140, 140, 140, 140, 140, 148, 148, 148, 148, 148, 148, 148, 148,
148, 156, 156, 156, 156, 156, 156, 156, 156, 165, 165, 165, 165, 165, 165, 165,
165, 173, 173, 173, 173, 173, 173, 173, 173, 181, 181, 181, 181, 181, 181, 181,
181, 181, 189, 189, 189, 189, 189, 189, 189, 189, 198, 198, 198, 198, 198, 198,
198, 198, 206, 206, 206, 206, 206, 206, 206, 206, 214, 214, 214, 214, 214, 214,
214, 214, 222, 222, 222, 222, 222, 222, 222, 222, 222, 231, 231, 231, 231, 231,
231, 231, 231, 239, 239, 239, 239, 239, 239, 239, 239, 247, 247, 247, 247, 247,
247, 247, 247, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
};
static const unsigned char stb__QuantGTab[256 + 16] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 4, 4, 4, 8,
8, 8, 8, 12, 12, 12, 12, 16, 16, 16, 16, 20, 20, 20, 20, 24,
24, 24, 24, 28, 28, 28, 28, 32, 32, 32, 32, 36, 36, 36, 36, 40,
40, 40, 40, 44, 44, 44, 44, 48, 48, 48, 48, 52, 52, 52, 52, 56,
56, 56, 56, 60, 60, 60, 60, 65, 65, 65, 65, 69, 69, 69, 69, 73,
73, 73, 73, 77, 77, 77, 77, 81, 81, 81, 81, 85, 85, 85, 85, 85,
89, 89, 89, 89, 93, 93, 93, 93, 97, 97, 97, 97, 101, 101, 101, 101,
105, 105, 105, 105, 109, 109, 109, 109, 113, 113, 113, 113, 117, 117, 117, 117,
121, 121, 121, 121, 125, 125, 125, 125, 130, 130, 130, 130, 134, 134, 134, 134,
138, 138, 138, 138, 142, 142, 142, 142, 146, 146, 146, 146, 150, 150, 150, 150,
154, 154, 154, 154, 158, 158, 158, 158, 162, 162, 162, 162, 166, 166, 166, 166,
170, 170, 170, 170, 170, 174, 174, 174, 174, 178, 178, 178, 178, 182, 182, 182,
182, 186, 186, 186, 186, 190, 190, 190, 190, 195, 195, 195, 195, 199, 199, 199,
199, 203, 203, 203, 203, 207, 207, 207, 207, 211, 211, 211, 211, 215, 215, 215,
215, 219, 219, 219, 219, 223, 223, 223, 223, 227, 227, 227, 227, 231, 231, 231,
231, 235, 235, 235, 235, 239, 239, 239, 239, 243, 243, 243, 243, 247, 247, 247,
247, 251, 251, 251, 251, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
};
static const unsigned char stb__OMatch5[256][2] = {
{ 0, 0 }, { 0, 0 }, { 0, 1 }, { 0, 1 }, { 1, 0 }, { 1, 0 }, { 1, 0 }, { 1, 1 },
{ 1, 1 }, { 2, 0 }, { 2, 0 }, { 0, 4 }, { 2, 1 }, { 2, 1 }, { 2, 1 }, { 3, 0 },
{ 3, 0 }, { 3, 0 }, { 3, 1 }, { 1, 5 }, { 3, 2 }, { 3, 2 }, { 4, 0 }, { 4, 0 },
{ 4, 1 }, { 4, 1 }, { 4, 2 }, { 4, 2 }, { 4, 2 }, { 3, 5 }, { 5, 1 }, { 5, 1 },
{ 5, 2 }, { 4, 4 }, { 5, 3 }, { 5, 3 }, { 5, 3 }, { 6, 2 }, { 6, 2 }, { 6, 2 },
{ 6, 3 }, { 5, 5 }, { 6, 4 }, { 6, 4 }, { 4, 8 }, { 7, 3 }, { 7, 3 }, { 7, 3 },
{ 7, 4 }, { 7, 4 }, { 7, 4 }, { 7, 5 }, { 5, 9 }, { 7, 6 }, { 7, 6 }, { 8, 4 },
{ 8, 4 }, { 8, 5 }, { 8, 5 }, { 8, 6 }, { 8, 6 }, { 8, 6 }, { 7, 9 }, { 9, 5 },
{ 9, 5 }, { 9, 6 }, { 8, 8 }, { 9, 7 }, { 9, 7 }, { 9, 7 }, { 10, 6 }, { 10, 6 },
{ 10, 6 }, { 10, 7 }, { 9, 9 }, { 10, 8 }, { 10, 8 }, { 8, 12 }, { 11, 7 }, { 11, 7 },
{ 11, 7 }, { 11, 8 }, { 11, 8 }, { 11, 8 }, { 11, 9 }, { 9, 13 }, { 11, 10 }, { 11, 10 },
{ 12, 8 }, { 12, 8 }, { 12, 9 }, { 12, 9 }, { 12, 10 }, { 12, 10 }, { 12, 10 }, { 11, 13 },
{ 13, 9 }, { 13, 9 }, { 13, 10 }, { 12, 12 }, { 13, 11 }, { 13, 11 }, { 13, 11 }, { 14, 10 },
{ 14, 10 }, { 14, 10 }, { 14, 11 }, { 13, 13 }, { 14, 12 }, { 14, 12 }, { 12, 16 }, { 15, 11 },
{ 15, 11 }, { 15, 11 }, { 15, 12 }, { 15, 12 }, { 15, 12 }, { 15, 13 }, { 13, 17 }, { 15, 14 },
{ 15, 14 }, { 16, 12 }, { 16, 12 }, { 16, 13 }, { 16, 13 }, { 16, 14 }, { 16, 14 }, { 16, 14 },
{ 15, 17 }, { 17, 13 }, { 17, 13 }, { 17, 14 }, { 16, 16 }, { 17, 15 }, { 17, 15 }, { 17, 15 },
{ 18, 14 }, { 18, 14 }, { 18, 14 }, { 18, 15 }, { 17, 17 }, { 18, 16 }, { 18, 16 }, { 16, 20 },
{ 19, 15 }, { 19, 15 }, { 19, 15 }, { 19, 16 }, { 19, 16 }, { 19, 16 }, { 19, 17 }, { 17, 21 },
{ 19, 18 }, { 19, 18 }, { 20, 16 }, { 20, 16 }, { 20, 17 }, { 20, 17 }, { 20, 18 }, { 20, 18 },
{ 20, 18 }, { 19, 21 }, { 21, 17 }, { 21, 17 }, { 21, 18 }, { 20, 20 }, { 21, 19 }, { 21, 19 },
{ 21, 19 }, { 22, 18 }, { 22, 18 }, { 22, 18 }, { 22, 19 }, { 21, 21 }, { 22, 20 }, { 22, 20 },
{ 20, 24 }, { 23, 19 }, { 23, 19 }, { 23, 19 }, { 23, 20 }, { 23, 20 }, { 23, 20 }, { 23, 21 },
{ 21, 25 }, { 23, 22 }, { 23, 22 }, { 24, 20 }, { 24, 20 }, { 24, 21 }, { 24, 21 }, { 24, 22 },
{ 24, 22 }, { 24, 22 }, { 23, 25 }, { 25, 21 }, { 25, 21 }, { 25, 22 }, { 24, 24 }, { 25, 23 },
{ 25, 23 }, { 25, 23 }, { 26, 22 }, { 26, 22 }, { 26, 22 }, { 26, 23 }, { 25, 25 }, { 26, 24 },
{ 26, 24 }, { 24, 28 }, { 27, 23 }, { 27, 23 }, { 27, 23 }, { 27, 24 }, { 27, 24 }, { 27, 24 },
{ 27, 25 }, { 25, 29 }, { 27, 26 }, { 27, 26 }, { 28, 24 }, { 28, 24 }, { 28, 25 }, { 28, 25 },
{ 28, 26 }, { 28, 26 }, { 28, 26 }, { 27, 29 }, { 29, 25 }, { 29, 25 }, { 29, 26 }, { 28, 28 },
{ 29, 27 }, { 29, 27 }, { 29, 27 }, { 30, 26 }, { 30, 26 }, { 30, 26 }, { 30, 27 }, { 29, 29 },
{ 30, 28 }, { 30, 28 }, { 30, 28 }, { 31, 27 }, { 31, 27 }, { 31, 27 }, { 31, 28 }, { 31, 28 },
{ 31, 28 }, { 31, 29 }, { 31, 29 }, { 31, 30 }, { 31, 30 }, { 31, 30 }, { 31, 31 }, { 31, 31 },
};
static const unsigned char stb__OMatch6[256][2] = {
{ 0, 0 }, { 0, 1 }, { 1, 0 }, { 1, 0 }, { 1, 1 }, { 2, 0 }, { 2, 1 }, { 3, 0 },
{ 3, 0 }, { 3, 1 }, { 4, 0 }, { 4, 0 }, { 4, 1 }, { 5, 0 }, { 5, 1 }, { 6, 0 },
{ 6, 0 }, { 6, 1 }, { 7, 0 }, { 7, 0 }, { 7, 1 }, { 8, 0 }, { 8, 1 }, { 8, 1 },
{ 8, 2 }, { 9, 1 }, { 9, 2 }, { 9, 2 }, { 9, 3 }, { 10, 2 }, { 10, 3 }, { 10, 3 },
{ 10, 4 }, { 11, 3 }, { 11, 4 }, { 11, 4 }, { 11, 5 }, { 12, 4 }, { 12, 5 }, { 12, 5 },
{ 12, 6 }, { 13, 5 }, { 13, 6 }, { 8, 16 }, { 13, 7 }, { 14, 6 }, { 14, 7 }, { 9, 17 },
{ 14, 8 }, { 15, 7 }, { 15, 8 }, { 11, 16 }, { 15, 9 }, { 15, 10 }, { 16, 8 }, { 16, 9 },
{ 16, 10 }, { 15, 13 }, { 17, 9 }, { 17, 10 }, { 17, 11 }, { 15, 16 }, { 18, 10 }, { 18, 11 },
{ 18, 12 }, { 16, 16 }, { 19, 11 }, { 19, 12 }, { 19, 13 }, { 17, 17 }, { 20, 12 }, { 20, 13 },
{ 20, 14 }, { 19, 16 }, { 21, 13 }, { 21, 14 }, { 21, 15 }, { 20, 17 }, { 22, 14 }, { 22, 15 },
{ 25, 10 }, { 22, 16 }, { 23, 15 }, { 23, 16 }, { 26, 11 }, { 23, 17 }, { 24, 16 }, { 24, 17 },
{ 27, 12 }, { 24, 18 }, { 25, 17 }, { 25, 18 }, { 28, 13 }, { 25, 19 }, { 26, 18 }, { 26, 19 },
{ 29, 14 }, { 26, 20 }, { 27, 19 }, { 27, 20 }, { 30, 15 }, { 27, 21 }, { 28, 20 }, { 28, 21 },
{ 28, 21 }, { 28, 22 }, { 29, 21 }, { 29, 22 }, { 24, 32 }, { 29, 23 }, { 30, 22 }, { 30, 23 },
{ 25, 33 }, { 30, 24 }, { 31, 23 }, { 31, 24 }, { 27, 32 }, { 31, 25 }, { 31, 26 }, { 32, 24 },
{ 32, 25 }, { 32, 26 }, { 31, 29 }, { 33, 25 }, { 33, 26 }, { 33, 27 }, { 31, 32 }, { 34, 26 },
{ 34, 27 }, { 34, 28 }, { 32, 32 }, { 35, 27 }, { 35, 28 }, { 35, 29 }, { 33, 33 }, { 36, 28 },
{ 36, 29 }, { 36, 30 }, { 35, 32 }, { 37, 29 }, { 37, 30 }, { 37, 31 }, { 36, 33 }, { 38, 30 },
{ 38, 31 }, { 41, 26 }, { 38, 32 }, { 39, 31 }, { 39, 32 }, { 42, 27 }, { 39, 33 }, { 40, 32 },
{ 40, 33 }, { 43, 28 }, { 40, 34 }, { 41, 33 }, { 41, 34 }, { 44, 29 }, { 41, 35 }, { 42, 34 },
{ 42, 35 }, { 45, 30 }, { 42, 36 }, { 43, 35 }, { 43, 36 }, { 46, 31 }, { 43, 37 }, { 44, 36 },
{ 44, 37 }, { 44, 37 }, { 44, 38 }, { 45, 37 }, { 45, 38 }, { 40, 48 }, { 45, 39 }, { 46, 38 },
{ 46, 39 }, { 41, 49 }, { 46, 40 }, { 47, 39 }, { 47, 40 }, { 43, 48 }, { 47, 41 }, { 47, 42 },
{ 48, 40 }, { 48, 41 }, { 48, 42 }, { 47, 45 }, { 49, 41 }, { 49, 42 }, { 49, 43 }, { 47, 48 },
{ 50, 42 }, { 50, 43 }, { 50, 44 }, { 48, 48 }, { 51, 43 }, { 51, 44 }, { 51, 45 }, { 49, 49 },
{ 52, 44 }, { 52, 45 }, { 52, 46 }, { 51, 48 }, { 53, 45 }, { 53, 46 }, { 53, 47 }, { 52, 49 },
{ 54, 46 }, { 54, 47 }, { 57, 42 }, { 54, 48 }, { 55, 47 }, { 55, 48 }, { 58, 43 }, { 55, 49 },
{ 56, 48 }, { 56, 49 }, { 59, 44 }, { 56, 50 }, { 57, 49 }, { 57, 50 }, { 60, 45 }, { 57, 51 },
{ 58, 50 }, { 58, 51 }, { 61, 46 }, { 58, 52 }, { 59, 51 }, { 59, 52 }, { 62, 47 }, { 59, 53 },
{ 60, 52 }, { 60, 53 }, { 60, 53 }, { 60, 54 }, { 61, 53 }, { 61, 54 }, { 61, 54 }, { 61, 55 },
{ 62, 54 }, { 62, 55 }, { 62, 55 }, { 62, 56 }, { 63, 55 }, { 63, 56 }, { 63, 56 }, { 63, 57 },
{ 63, 58 }, { 63, 59 }, { 63, 59 }, { 63, 60 }, { 63, 61 }, { 63, 62 }, { 63, 62 }, { 63, 63 },
};
static int stb__Mul8Bit(int a, int b)
{
@ -117,9 +214,10 @@ static void stb__From16Bit(unsigned char *out, unsigned short v)
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];
// expand to 8 bits via bit replication
out[0] = (rv * 33) >> 2;
out[1] = (gv * 65) >> 4;
out[2] = (bv * 33) >> 2;
out[3] = 0;
}
@ -151,35 +249,6 @@ static void stb__Lerp13RGB(unsigned char *out, unsigned char *p1, unsigned char
/****************************************************************************/
// 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 = STBD_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 += STBD_ABS(maxe - mine) * 3 / 100;
if(err < bestErr)
{
Table[i*2+0] = (unsigned char)mx;
Table[i*2+1] = (unsigned char)mn;
bestErr = err;
}
}
}
}
}
static void stb__EvalColors(unsigned char *color,unsigned short c0,unsigned short c1)
{
stb__From16Bit(color+ 0, c0);
@ -198,7 +267,7 @@ static void stb__DitherBlock(unsigned char *dest, unsigned char *block)
// process channels separately
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;
const unsigned char *quant = (ch == 1) ? stb__QuantGTab+8 : stb__QuantRBTab+8;
STBD_MEMSET(err, 0, sizeof(err));
for(y=0; y<4; ++y) {
dp[ 0] = quant[bp[ 0] + ((3*ep2[1] + 5*ep2[0]) >> 4)];
@ -316,7 +385,7 @@ static unsigned int stb__MatchColorsBlock(unsigned char *block, unsigned char *c
// 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;
int mind,maxd;
unsigned char *minp, *maxp;
double magn;
int v_r,v_g,v_b;
@ -398,8 +467,10 @@ static void stb__OptimizeColorsBlock(unsigned char *block, unsigned short *pmax1
v_b = (int) (vfb * magn);
}
minp = maxp = block;
mind = maxd = block[0]*v_r + block[1]*v_g + block[2]*v_b;
// Pick colors at extreme points
for(i=0;i<16;i++)
for(i=1;i<16;i++)
{
int dot = block[i*4+0]*v_r + block[i*4+1]*v_g + block[i*4+2]*v_b;
@ -418,12 +489,12 @@ static void stb__OptimizeColorsBlock(unsigned char *block, unsigned short *pmax1
*pmin16 = stb__As16Bit(minp[0],minp[1],minp[2]);
}
static const float midpoints5[32] = {
static const float stb__midpoints5[32] = {
0.015686f, 0.047059f, 0.078431f, 0.111765f, 0.145098f, 0.176471f, 0.207843f, 0.241176f, 0.274510f, 0.305882f, 0.337255f, 0.370588f, 0.403922f, 0.435294f, 0.466667f, 0.5f,
0.533333f, 0.564706f, 0.596078f, 0.629412f, 0.662745f, 0.694118f, 0.725490f, 0.758824f, 0.792157f, 0.823529f, 0.854902f, 0.888235f, 0.921569f, 0.952941f, 0.984314f, 1.0f
};
static const float midpoints6[64] = {
static const float stb__midpoints6[64] = {
0.007843f, 0.023529f, 0.039216f, 0.054902f, 0.070588f, 0.086275f, 0.101961f, 0.117647f, 0.133333f, 0.149020f, 0.164706f, 0.180392f, 0.196078f, 0.211765f, 0.227451f, 0.245098f,
0.262745f, 0.278431f, 0.294118f, 0.309804f, 0.325490f, 0.341176f, 0.356863f, 0.372549f, 0.388235f, 0.403922f, 0.419608f, 0.435294f, 0.450980f, 0.466667f, 0.482353f, 0.500000f,
0.517647f, 0.533333f, 0.549020f, 0.564706f, 0.580392f, 0.596078f, 0.611765f, 0.627451f, 0.643137f, 0.658824f, 0.674510f, 0.690196f, 0.705882f, 0.721569f, 0.737255f, 0.754902f,
@ -435,7 +506,7 @@ static unsigned short stb__Quantize5(float x)
unsigned short q;
x = x < 0 ? 0 : x > 1 ? 1 : x; // saturate
q = (unsigned short)(x * 31);
q += (x > midpoints5[q]);
q += (x > stb__midpoints5[q]);
return q;
}
@ -444,7 +515,7 @@ static unsigned short stb__Quantize6(float x)
unsigned short q;
x = x < 0 ? 0 : x > 1 ? 1 : x; // saturate
q = (unsigned short)(x * 63);
q += (x > midpoints6[q]);
q += (x > stb__midpoints6[q]);
return q;
}
@ -654,35 +725,9 @@ static void stb__CompressAlphaBlock(unsigned char *dest,unsigned char *src, int
}
}
static void stb__InitDXT()
{
int i;
for(i=0;i<32;i++)
stb__Expand5[i] = (unsigned char)((i<<3)|(i>>2));
for(i=0;i<64;i++)
stb__Expand6[i] = (unsigned char)((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)
{
unsigned char data[16][4];
static int init=1;
if (init) {
stb__InitDXT();
init=0;
}
if (alpha) {
int i;
stb__CompressAlphaBlock(dest,(unsigned char*) src+3, 4);
@ -710,6 +755,76 @@ void stb_compress_bc5_block(unsigned char *dest, const unsigned char *src)
}
#endif // STB_DXT_IMPLEMENTATION
// Compile with STB_DXT_IMPLEMENTATION and STB_DXT_GENERATE_TABLES
// defined to generate the tables above.
#ifdef STB_DXT_GENERATE_TABLES
#include <stdio.h>
int main()
{
int i, j;
const char *quant_names[] = { "stb__QuantRBTab", "stb__QuantGTab" };
const char *omatch_names[] = { "stb__OMatch5", "stb__OMatch6" };
int dequant_mults[2] = { 33*4, 65 }; // .4 fixed-point dequant multipliers
// quant tables (for dither)
for (i=0; i < 2; ++i) {
int quant_mult = i ? 63 : 31;
printf("static const unsigned char %s[256 + 16] = {\n", quant_names[i]);
for (int j = 0; j < 256 + 16; ++j) {
int v = j - 8;
int q, dq;
v = (v < 0) ? 0 : (v > 255) ? 255 : v; // clamp
q = stb__Mul8Bit(v, quant_mult); // quantize
dq = (q * dequant_mults[i]) >> 4; // dequantize
if ((j % 16) == 0) printf(" "); // 2 spaces, third is done below
printf(" %3d,", dq);
if ((j % 16) == 15) printf("\n");
}
printf("};\n");
}
// optimal endpoint tables
for (i = 0; i < 2; ++i) {
int dequant = dequant_mults[i];
int size = i ? 64 : 32;
printf("static const unsigned char %s[256][2] = {\n", omatch_names[i]);
for (int j = 0; j < 256; ++j) {
int mn, mx;
int best_mn = 0, best_mx = 0;
int best_err = 256;
for (mn=0;mn<size;mn++) {
for (mx=0;mx<size;mx++) {
int mine = (mn * dequant) >> 4;
int maxe = (mx * dequant) >> 4;
int err = abs(stb__Lerp13(maxe, mine) - j);
// 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 < best_err) {
best_mn = mn;
best_mx = mx;
best_err = err;
}
}
}
if ((j % 8) == 0) printf(" "); // 2 spaces, third is done below
printf(" { %2d, %2d },", best_mx, best_mn);
if ((j % 8) == 7) printf("\n");
}
printf("};\n");
}
return 0;
}
#endif
/*
------------------------------------------------------------------------------
This software is available under 2 licenses -- choose whichever you prefer.

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