1 // stb_dxt.h - v1.10 - DXT1/DXT5 compressor - public domain
2 // original by fabian "ryg" giesen - ported to C by stb
3 // use '#define STB_DXT_IMPLEMENTATION' before including to create the implementation
6 // call stb_compress_dxt_block() for every block (you must pad)
7 // source should be a 4x4 block of RGBA data in row-major order;
8 // Alpha channel is not stored if you specify alpha=0 (but you
9 // must supply some constant alpha in the alpha channel).
10 // You can turn on dithering and "high quality" using mode.
13 // v1.10 - (i.c) various small quality improvements
14 // v1.09 - (stb) update documentation re: surprising alpha channel requirement
15 // v1.08 - (stb) fix bug in dxt-with-alpha block
16 // v1.07 - (stb) bc4; allow not using libc; add STB_DXT_STATIC
17 // v1.06 - (stb) fix to known-broken 1.05
18 // v1.05 - (stb) support bc5/3dc (Arvids Kokins), use extern "C" in C++ (Pavel Krajcevski)
19 // v1.04 - (ryg) default to no rounding bias for lerped colors (as per S3TC/DX10 spec);
20 // single color match fix (allow for inexact color interpolation);
21 // optimal DXT5 index finder; "high quality" mode that runs multiple refinement steps.
22 // v1.03 - (stb) endianness support
23 // v1.02 - (stb) fix alpha encoding bug
24 // v1.01 - (stb) fix bug converting to RGB that messed up quality, thanks ryg & cbloom
25 // v1.00 - (stb) first release
28 // Rich Geldreich (more accurate index selection)
29 // Kevin Schmidt (#defines for "freestanding" compilation)
30 // github:ppiastucki (BC4 support)
31 // Ignacio Castano - improve DXT endpoint quantization
35 // See end of file for license information.
37 #ifndef STB_INCLUDE_STB_DXT_H
38 #define STB_INCLUDE_STB_DXT_H
45 #define STBDDEF static
47 #define STBDDEF extern
50 // compression mode (bitflags)
51 #define STB_DXT_NORMAL 0
52 #define STB_DXT_DITHER 1 // use dithering. dubious win. never use for normal maps and the like!
53 #define STB_DXT_HIGHQUAL 2 // high quality mode, does two refinement steps instead of 1. ~30-40% slower.
55 STBDDEF
void stb_compress_dxt_block(unsigned char *dest
, const unsigned char *src_rgba_four_bytes_per_pixel
, int alpha
, int mode
);
56 STBDDEF
void stb_compress_bc4_block(unsigned char *dest
, const unsigned char *src_r_one_byte_per_pixel
);
57 STBDDEF
void stb_compress_bc5_block(unsigned char *dest
, const unsigned char *src_rg_two_byte_per_pixel
);
59 #define STB_COMPRESS_DXT_BLOCK
64 #endif // STB_INCLUDE_STB_DXT_H
66 #ifdef STB_DXT_IMPLEMENTATION
68 // configuration options for DXT encoder. set them in the project/makefile or just define
71 // STB_DXT_USE_ROUNDING_BIAS
72 // use a rounding bias during color interpolation. this is closer to what "ideal"
73 // interpolation would do but doesn't match the S3TC/DX10 spec. old versions (pre-1.03)
74 // implicitly had this turned on.
76 // in case you're targeting a specific type of hardware (e.g. console programmers):
77 // NVidia and Intel GPUs (as of 2010) as well as DX9 ref use DXT decoders that are closer
78 // to STB_DXT_USE_ROUNDING_BIAS. AMD/ATI, S3 and DX10 ref are closer to rounding with no bias.
79 // you also see "(a*5 + b*3) / 8" on some old GPU designs.
80 // #define STB_DXT_USE_ROUNDING_BIAS
84 #if !defined(STBD_ABS) || !defined(STBI_FABS)
89 #define STBD_ABS(i) abs(i)
93 #define STBD_FABS(x) fabs(x)
98 #define STBD_MEMSET memset
101 static unsigned char stb__Expand5
[32];
102 static unsigned char stb__Expand6
[64];
103 static unsigned char stb__OMatch5
[256][2];
104 static unsigned char stb__OMatch6
[256][2];
105 static unsigned char stb__QuantRBTab
[256+16];
106 static unsigned char stb__QuantGTab
[256+16];
108 static int stb__Mul8Bit(int a
, int b
)
111 return (t
+ (t
>> 8)) >> 8;
114 static void stb__From16Bit(unsigned char *out
, unsigned short v
)
116 int rv
= (v
& 0xf800) >> 11;
117 int gv
= (v
& 0x07e0) >> 5;
118 int bv
= (v
& 0x001f) >> 0;
120 out
[0] = stb__Expand5
[rv
];
121 out
[1] = stb__Expand6
[gv
];
122 out
[2] = stb__Expand5
[bv
];
126 static unsigned short stb__As16Bit(int r
, int g
, int b
)
128 return (unsigned short)((stb__Mul8Bit(r
,31) << 11) + (stb__Mul8Bit(g
,63) << 5) + stb__Mul8Bit(b
,31));
131 // linear interpolation at 1/3 point between a and b, using desired rounding type
132 static int stb__Lerp13(int a
, int b
)
134 #ifdef STB_DXT_USE_ROUNDING_BIAS
135 // with rounding bias
136 return a
+ stb__Mul8Bit(b
-a
, 0x55);
138 // without rounding bias
139 // replace "/ 3" by "* 0xaaab) >> 17" if your compiler sucks or you really need every ounce of speed.
140 return (2*a
+ b
) / 3;
145 static void stb__Lerp13RGB(unsigned char *out
, unsigned char *p1
, unsigned char *p2
)
147 out
[0] = (unsigned char)stb__Lerp13(p1
[0], p2
[0]);
148 out
[1] = (unsigned char)stb__Lerp13(p1
[1], p2
[1]);
149 out
[2] = (unsigned char)stb__Lerp13(p1
[2], p2
[2]);
152 /****************************************************************************/
154 // compute table to reproduce constant colors as accurately as possible
155 static void stb__PrepareOptTable(unsigned char *Table
,const unsigned char *expand
,int size
)
158 for (i
=0;i
<256;i
++) {
160 for (mn
=0;mn
<size
;mn
++) {
161 for (mx
=0;mx
<size
;mx
++) {
162 int mine
= expand
[mn
];
163 int maxe
= expand
[mx
];
164 int err
= STBD_ABS(stb__Lerp13(maxe
, mine
) - i
);
166 // DX10 spec says that interpolation must be within 3% of "correct" result,
167 // add this as error term. (normally we'd expect a random distribution of
168 // +-1.5% error, but nowhere in the spec does it say that the error has to be
169 // unbiased - better safe than sorry).
170 err
+= STBD_ABS(maxe
- mine
) * 3 / 100;
174 Table
[i
*2+0] = (unsigned char)mx
;
175 Table
[i
*2+1] = (unsigned char)mn
;
183 static void stb__EvalColors(unsigned char *color
,unsigned short c0
,unsigned short c1
)
185 stb__From16Bit(color
+ 0, c0
);
186 stb__From16Bit(color
+ 4, c1
);
187 stb__Lerp13RGB(color
+ 8, color
+0, color
+4);
188 stb__Lerp13RGB(color
+12, color
+4, color
+0);
191 // Block dithering function. Simply dithers a block to 565 RGB.
193 static void stb__DitherBlock(unsigned char *dest
, unsigned char *block
)
195 int err
[8],*ep1
= err
,*ep2
= err
+4, *et
;
198 // process channels separately
199 for (ch
=0; ch
<3; ++ch
) {
200 unsigned char *bp
= block
+ch
, *dp
= dest
+ch
;
201 unsigned char *quant
= (ch
== 1) ? stb__QuantGTab
+8 : stb__QuantRBTab
+8;
202 STBD_MEMSET(err
, 0, sizeof(err
));
204 dp
[ 0] = quant
[bp
[ 0] + ((3*ep2
[1] + 5*ep2
[0]) >> 4)];
205 ep1
[0] = bp
[ 0] - dp
[ 0];
206 dp
[ 4] = quant
[bp
[ 4] + ((7*ep1
[0] + 3*ep2
[2] + 5*ep2
[1] + ep2
[0]) >> 4)];
207 ep1
[1] = bp
[ 4] - dp
[ 4];
208 dp
[ 8] = quant
[bp
[ 8] + ((7*ep1
[1] + 3*ep2
[3] + 5*ep2
[2] + ep2
[1]) >> 4)];
209 ep1
[2] = bp
[ 8] - dp
[ 8];
210 dp
[12] = quant
[bp
[12] + ((7*ep1
[2] + 5*ep2
[3] + ep2
[2]) >> 4)];
211 ep1
[3] = bp
[12] - dp
[12];
214 et
= ep1
, ep1
= ep2
, ep2
= et
; // swap
219 // The color matching function
220 static unsigned int stb__MatchColorsBlock(unsigned char *block
, unsigned char *color
,int dither
)
222 unsigned int mask
= 0;
223 int dirr
= color
[0*4+0] - color
[1*4+0];
224 int dirg
= color
[0*4+1] - color
[1*4+1];
225 int dirb
= color
[0*4+2] - color
[1*4+2];
229 int c0Point
, halfPoint
, c3Point
;
232 dots
[i
] = block
[i
*4+0]*dirr
+ block
[i
*4+1]*dirg
+ block
[i
*4+2]*dirb
;
235 stops
[i
] = color
[i
*4+0]*dirr
+ color
[i
*4+1]*dirg
+ color
[i
*4+2]*dirb
;
237 // think of the colors as arranged on a line; project point onto that line, then choose
238 // next color out of available ones. we compute the crossover points for "best color in top
239 // half"/"best in bottom half" and then the same inside that subinterval.
241 // relying on this 1d approximation isn't always optimal in terms of euclidean distance,
242 // but it's very close and a lot faster.
243 // http://cbloomrants.blogspot.com/2008/12/12-08-08-dxtc-summary.html
245 c0Point
= (stops
[1] + stops
[3]);
246 halfPoint
= (stops
[3] + stops
[2]);
247 c3Point
= (stops
[2] + stops
[0]);
250 // the version without dithering is straightforward
251 for (i
=15;i
>=0;i
--) {
256 mask
|= (dot
< c0Point
) ? 1 : 3;
258 mask
|= (dot
< c3Point
) ? 2 : 0;
261 // with floyd-steinberg dithering
262 int err
[8],*ep1
= err
,*ep2
= err
+4;
275 dot
= (dp
[0] << 4) + (3*ep2
[1] + 5*ep2
[0]);
277 step
= (dot
< c0Point
) ? 1 : 3;
279 step
= (dot
< c3Point
) ? 2 : 0;
280 ep1
[0] = dp
[0] - stops
[step
];
283 dot
= (dp
[1] << 4) + (7*ep1
[0] + 3*ep2
[2] + 5*ep2
[1] + ep2
[0]);
285 step
= (dot
< c0Point
) ? 1 : 3;
287 step
= (dot
< c3Point
) ? 2 : 0;
288 ep1
[1] = dp
[1] - stops
[step
];
291 dot
= (dp
[2] << 4) + (7*ep1
[1] + 3*ep2
[3] + 5*ep2
[2] + ep2
[1]);
293 step
= (dot
< c0Point
) ? 1 : 3;
295 step
= (dot
< c3Point
) ? 2 : 0;
296 ep1
[2] = dp
[2] - stops
[step
];
299 dot
= (dp
[3] << 4) + (7*ep1
[2] + 5*ep2
[3] + ep2
[2]);
301 step
= (dot
< c0Point
) ? 1 : 3;
303 step
= (dot
< c3Point
) ? 2 : 0;
304 ep1
[3] = dp
[3] - stops
[step
];
308 mask
|= lmask
<< (y
*8);
309 { int *et
= ep1
; ep1
= ep2
; ep2
= et
; } // swap
316 // The color optimization function. (Clever code, part 1)
317 static void stb__OptimizeColorsBlock(unsigned char *block
, unsigned short *pmax16
, unsigned short *pmin16
)
319 int mind
= 0x7fffffff,maxd
= -0x7fffffff;
320 unsigned char *minp
, *maxp
;
323 static const int nIterPower
= 4;
324 float covf
[6],vfr
,vfg
,vfb
;
326 // determine color distribution
328 int mu
[3],min
[3],max
[3];
333 const unsigned char *bp
= ((const unsigned char *) block
) + ch
;
336 muv
= minv
= maxv
= bp
[0];
340 if (bp
[i
] < minv
) minv
= bp
[i
];
341 else if (bp
[i
] > maxv
) maxv
= bp
[i
];
344 mu
[ch
] = (muv
+ 8) >> 4;
349 // determine covariance matrix
355 int r
= block
[i
*4+0] - mu
[0];
356 int g
= block
[i
*4+1] - mu
[1];
357 int b
= block
[i
*4+2] - mu
[2];
367 // convert covariance matrix to float, find principal axis via power iter
369 covf
[i
] = cov
[i
] / 255.0f
;
371 vfr
= (float) (max
[0] - min
[0]);
372 vfg
= (float) (max
[1] - min
[1]);
373 vfb
= (float) (max
[2] - min
[2]);
375 for(iter
=0;iter
<nIterPower
;iter
++)
377 float r
= vfr
*covf
[0] + vfg
*covf
[1] + vfb
*covf
[2];
378 float g
= vfr
*covf
[1] + vfg
*covf
[3] + vfb
*covf
[4];
379 float b
= vfr
*covf
[2] + vfg
*covf
[4] + vfb
*covf
[5];
386 magn
= STBD_FABS(vfr
);
387 if (STBD_FABS(vfg
) > magn
) magn
= STBD_FABS(vfg
);
388 if (STBD_FABS(vfb
) > magn
) magn
= STBD_FABS(vfb
);
390 if(magn
< 4.0f
) { // too small, default to luminance
391 v_r
= 299; // JPEG YCbCr luma coefs, scaled by 1000.
396 v_r
= (int) (vfr
* magn
);
397 v_g
= (int) (vfg
* magn
);
398 v_b
= (int) (vfb
* magn
);
401 // Pick colors at extreme points
404 int dot
= block
[i
*4+0]*v_r
+ block
[i
*4+1]*v_g
+ block
[i
*4+2]*v_b
;
417 *pmax16
= stb__As16Bit(maxp
[0],maxp
[1],maxp
[2]);
418 *pmin16
= stb__As16Bit(minp
[0],minp
[1],minp
[2]);
421 static const float midpoints5
[32] = {
422 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
,
423 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
426 static const float midpoints6
[64] = {
427 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
,
428 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
,
429 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
,
430 0.772549f
, 0.788235f
, 0.803922f
, 0.819608f
, 0.835294f
, 0.850980f
, 0.866667f
, 0.882353f
, 0.898039f
, 0.913725f
, 0.929412f
, 0.945098f
, 0.960784f
, 0.976471f
, 0.992157f
, 1.0f
433 static unsigned short stb__Quantize5(float x
)
436 x
= x
< 0 ? 0 : x
> 1 ? 1 : x
; // saturate
437 q
= (unsigned short)(x
* 31);
438 q
+= (x
> midpoints5
[q
]);
442 static unsigned short stb__Quantize6(float x
)
445 x
= x
< 0 ? 0 : x
> 1 ? 1 : x
; // saturate
446 q
= (unsigned short)(x
* 63);
447 q
+= (x
> midpoints6
[q
]);
451 // The refinement function. (Clever code, part 2)
452 // Tries to optimize colors to suit block contents better.
453 // (By solving a least squares system via normal equations+Cramer's rule)
454 static int stb__RefineBlock(unsigned char *block
, unsigned short *pmax16
, unsigned short *pmin16
, unsigned int mask
)
456 static const int w1Tab
[4] = { 3,0,2,1 };
457 static const int prods
[4] = { 0x090000,0x000900,0x040102,0x010402 };
458 // ^some magic to save a lot of multiplies in the accumulating loop...
459 // (precomputed products of weights for least squares system, accumulated inside one 32-bit register)
462 unsigned short oldMin
, oldMax
, min16
, max16
;
463 int i
, akku
= 0, xx
,xy
,yy
;
464 int At1_r
,At1_g
,At1_b
;
465 int At2_r
,At2_g
,At2_b
;
466 unsigned int cm
= mask
;
471 if((mask
^ (mask
<<2)) < 4) // all pixels have the same index?
473 // yes, linear system would be singular; solve using optimal
474 // single-color match on average color
475 int r
= 8, g
= 8, b
= 8;
482 r
>>= 4; g
>>= 4; b
>>= 4;
484 max16
= (stb__OMatch5
[r
][0]<<11) | (stb__OMatch6
[g
][0]<<5) | stb__OMatch5
[b
][0];
485 min16
= (stb__OMatch5
[r
][1]<<11) | (stb__OMatch6
[g
][1]<<5) | stb__OMatch5
[b
][1];
487 At1_r
= At1_g
= At1_b
= 0;
488 At2_r
= At2_g
= At2_b
= 0;
489 for (i
=0;i
<16;++i
,cm
>>=2) {
491 int w1
= w1Tab
[step
];
492 int r
= block
[i
*4+0];
493 int g
= block
[i
*4+1];
494 int b
= block
[i
*4+2];
505 At2_r
= 3*At2_r
- At1_r
;
506 At2_g
= 3*At2_g
- At1_g
;
507 At2_b
= 3*At2_b
- At1_b
;
509 // extract solutions and decide solvability
511 yy
= (akku
>> 8) & 0xff;
512 xy
= (akku
>> 0) & 0xff;
514 f
= 3.0f
/ 255.0f
/ (xx
*yy
- xy
*xy
);
516 max16
= stb__Quantize5((At1_r
*yy
- At2_r
* xy
) * f
) << 11;
517 max16
|= stb__Quantize6((At1_g
*yy
- At2_g
* xy
) * f
) << 5;
518 max16
|= stb__Quantize5((At1_b
*yy
- At2_b
* xy
) * f
) << 0;
520 min16
= stb__Quantize5((At2_r
*xx
- At1_r
* xy
) * f
) << 11;
521 min16
|= stb__Quantize6((At2_g
*xx
- At1_g
* xy
) * f
) << 5;
522 min16
|= stb__Quantize5((At2_b
*xx
- At1_b
* xy
) * f
) << 0;
527 return oldMin
!= min16
|| oldMax
!= max16
;
530 // Color block compression
531 static void stb__CompressColorBlock(unsigned char *dest
, unsigned char *block
, int mode
)
537 unsigned short max16
, min16
;
538 unsigned char dblock
[16*4],color
[4*4];
540 dither
= mode
& STB_DXT_DITHER
;
541 refinecount
= (mode
& STB_DXT_HIGHQUAL
) ? 2 : 1;
543 // check if block is constant
545 if (((unsigned int *) block
)[i
] != ((unsigned int *) block
)[0])
548 if(i
== 16) { // constant color
549 int r
= block
[0], g
= block
[1], b
= block
[2];
551 max16
= (stb__OMatch5
[r
][0]<<11) | (stb__OMatch6
[g
][0]<<5) | stb__OMatch5
[b
][0];
552 min16
= (stb__OMatch5
[r
][1]<<11) | (stb__OMatch6
[g
][1]<<5) | stb__OMatch5
[b
][1];
554 // first step: compute dithered version for PCA if desired
556 stb__DitherBlock(dblock
,block
);
558 // second step: pca+map along principal axis
559 stb__OptimizeColorsBlock(dither
? dblock
: block
,&max16
,&min16
);
560 if (max16
!= min16
) {
561 stb__EvalColors(color
,max16
,min16
);
562 mask
= stb__MatchColorsBlock(block
,color
,dither
);
566 // third step: refine (multiple times if requested)
567 for (i
=0;i
<refinecount
;i
++) {
568 unsigned int lastmask
= mask
;
570 if (stb__RefineBlock(dither
? dblock
: block
,&max16
,&min16
,mask
)) {
571 if (max16
!= min16
) {
572 stb__EvalColors(color
,max16
,min16
);
573 mask
= stb__MatchColorsBlock(block
,color
,dither
);
585 // write the color block
588 unsigned short t
= min16
;
594 dest
[0] = (unsigned char) (max16
);
595 dest
[1] = (unsigned char) (max16
>> 8);
596 dest
[2] = (unsigned char) (min16
);
597 dest
[3] = (unsigned char) (min16
>> 8);
598 dest
[4] = (unsigned char) (mask
);
599 dest
[5] = (unsigned char) (mask
>> 8);
600 dest
[6] = (unsigned char) (mask
>> 16);
601 dest
[7] = (unsigned char) (mask
>> 24);
604 // Alpha block compression (this is easy for a change)
605 static void stb__CompressAlphaBlock(unsigned char *dest
,unsigned char *src
, int stride
)
607 int i
,dist
,bias
,dist4
,dist2
,bits
,mask
;
609 // find min/max color
615 if (src
[i
*stride
] < mn
) mn
= src
[i
*stride
];
616 else if (src
[i
*stride
] > mx
) mx
= src
[i
*stride
];
620 dest
[0] = (unsigned char)mx
;
621 dest
[1] = (unsigned char)mn
;
624 // determine bias and emit color indices
625 // given the choice of mx/mn, these indices are optimal:
626 // http://fgiesen.wordpress.com/2009/12/15/dxt5-alpha-block-index-determination/
630 bias
= (dist
< 8) ? (dist
- 1) : (dist
/2 + 2);
635 int a
= src
[i
*stride
]*7 + bias
;
638 // select index. this is a "linear scale" lerp factor between 0 (val=min) and 7 (val=max).
639 t
= (a
>= dist4
) ? -1 : 0; ind
= t
& 4; a
-= dist4
& t
;
640 t
= (a
>= dist2
) ? -1 : 0; ind
+= t
& 2; a
-= dist2
& t
;
643 // turn linear scale into DXT index (0/1 are extremal pts)
649 if((bits
+= 3) >= 8) {
650 *dest
++ = (unsigned char)mask
;
657 static void stb__InitDXT()
661 stb__Expand5
[i
] = (unsigned char)((i
<<3)|(i
>>2));
664 stb__Expand6
[i
] = (unsigned char)((i
<<2)|(i
>>4));
666 for(i
=0;i
<256+16;i
++)
668 int v
= i
-8 < 0 ? 0 : i
-8 > 255 ? 255 : i
-8;
669 stb__QuantRBTab
[i
] = stb__Expand5
[stb__Mul8Bit(v
,31)];
670 stb__QuantGTab
[i
] = stb__Expand6
[stb__Mul8Bit(v
,63)];
673 stb__PrepareOptTable(&stb__OMatch5
[0][0],stb__Expand5
,32);
674 stb__PrepareOptTable(&stb__OMatch6
[0][0],stb__Expand6
,64);
677 void stb_compress_dxt_block(unsigned char *dest
, const unsigned char *src
, int alpha
, int mode
)
679 unsigned char data
[16][4];
688 stb__CompressAlphaBlock(dest
,(unsigned char*) src
+3, 4);
690 // make a new copy of the data in which alpha is opaque,
691 // because code uses a fast test for color constancy
692 memcpy(data
, src
, 4*16);
693 for (i
=0; i
< 16; ++i
)
698 stb__CompressColorBlock(dest
,(unsigned char*) src
,mode
);
701 void stb_compress_bc4_block(unsigned char *dest
, const unsigned char *src
)
703 stb__CompressAlphaBlock(dest
,(unsigned char*) src
, 1);
706 void stb_compress_bc5_block(unsigned char *dest
, const unsigned char *src
)
708 stb__CompressAlphaBlock(dest
,(unsigned char*) src
,2);
709 stb__CompressAlphaBlock(dest
+ 8,(unsigned char*) src
+1,2);
711 #endif // STB_DXT_IMPLEMENTATION
714 ------------------------------------------------------------------------------
715 This software is available under 2 licenses -- choose whichever you prefer.
716 ------------------------------------------------------------------------------
717 ALTERNATIVE A - MIT License
718 Copyright (c) 2017 Sean Barrett
719 Permission is hereby granted, free of charge, to any person obtaining a copy of
720 this software and associated documentation files (the "Software"), to deal in
721 the Software without restriction, including without limitation the rights to
722 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
723 of the Software, and to permit persons to whom the Software is furnished to do
724 so, subject to the following conditions:
725 The above copyright notice and this permission notice shall be included in all
726 copies or substantial portions of the Software.
727 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
728 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
729 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
730 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
731 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
732 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
734 ------------------------------------------------------------------------------
735 ALTERNATIVE B - Public Domain (www.unlicense.org)
736 This is free and unencumbered software released into the public domain.
737 Anyone is free to copy, modify, publish, use, compile, sell, or distribute this
738 software, either in source code form or as a compiled binary, for any purpose,
739 commercial or non-commercial, and by any means.
740 In jurisdictions that recognize copyright laws, the author or authors of this
741 software dedicate any and all copyright interest in the software to the public
742 domain. We make this dedication for the benefit of the public at large and to
743 the detriment of our heirs and successors. We intend this dedication to be an
744 overt act of relinquishment in perpetuity of all present and future rights to
745 this software under copyright law.
746 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
747 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
748 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
749 AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
750 ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
751 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
752 ------------------------------------------------------------------------------