1 /* -----------------------------------------------------------------------------
2
3 Copyright (c) 2006 Simon Brown si@sjbrown.co.uk
4
5 Permission is hereby granted, free of charge, to any person obtaining
6 a copy of this software and associated documentation files (the
7 "Software"), to deal in the Software without restriction, including
8 without limitation the rights to use, copy, modify, merge, publish,
9 distribute, sublicense, and/or sell copies of the Software, and to
10 permit persons to whom the Software is furnished to do so, subject to
11 the following conditions:
12
13 The above copyright notice and this permission notice shall be included
14 in all copies or substantial portions of the Software.
15
16 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
17 OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
18 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
19 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
20 CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
21 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
22 SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23
24 -------------------------------------------------------------------------- */
25
26 #include "alpha.h"
27 #include <algorithm>
28
29 namespace squish {
30
FloatToInt(float a,int limit)31 static int FloatToInt( float a, int limit )
32 {
33 // use ANSI round-to-zero behaviour to get round-to-nearest
34 int i = ( int )( a + 0.5f );
35
36 // clamp to the limit
37 if( i < 0 )
38 i = 0;
39 else if( i > limit )
40 i = limit;
41
42 // done
43 return i;
44 }
45
CompressAlphaDxt3(u8 const * rgba,int mask,void * block)46 void CompressAlphaDxt3( u8 const* rgba, int mask, void* block )
47 {
48 u8* bytes = reinterpret_cast< u8* >( block );
49
50 // quantise and pack the alpha values pairwise
51 for( int i = 0; i < 8; ++i )
52 {
53 // quantise down to 4 bits
54 float alpha1 = ( float )rgba[8*i + 3] * ( 15.0f/255.0f );
55 float alpha2 = ( float )rgba[8*i + 7] * ( 15.0f/255.0f );
56 int quant1 = FloatToInt( alpha1, 15 );
57 int quant2 = FloatToInt( alpha2, 15 );
58
59 // set alpha to zero where masked
60 int bit1 = 1 << ( 2*i );
61 int bit2 = 1 << ( 2*i + 1 );
62 if( ( mask & bit1 ) == 0 )
63 quant1 = 0;
64 if( ( mask & bit2 ) == 0 )
65 quant2 = 0;
66
67 // pack into the byte
68 bytes[i] = ( u8 )( quant1 | ( quant2 << 4 ) );
69 }
70 }
71
DecompressAlphaDxt3(u8 * rgba,void const * block)72 void DecompressAlphaDxt3( u8* rgba, void const* block )
73 {
74 u8 const* bytes = reinterpret_cast< u8 const* >( block );
75
76 // unpack the alpha values pairwise
77 for( int i = 0; i < 8; ++i )
78 {
79 // quantise down to 4 bits
80 u8 quant = bytes[i];
81
82 // unpack the values
83 u8 lo = quant & 0x0f;
84 u8 hi = quant & 0xf0;
85
86 // convert back up to bytes
87 rgba[8*i + 3] = lo | ( lo << 4 );
88 rgba[8*i + 7] = hi | ( hi >> 4 );
89 }
90 }
91
FixRange(int & min,int & max,int steps)92 static void FixRange( int& min, int& max, int steps )
93 {
94 if( max - min < steps )
95 max = std::min( min + steps, 255 );
96 if( max - min < steps )
97 min = std::max( 0, max - steps );
98 }
99
FitCodes(u8 const * rgba,int mask,u8 const * codes,u8 * indices)100 static int FitCodes( u8 const* rgba, int mask, u8 const* codes, u8* indices )
101 {
102 // fit each alpha value to the codebook
103 int err = 0;
104 for( int i = 0; i < 16; ++i )
105 {
106 // check this pixel is valid
107 int bit = 1 << i;
108 if( ( mask & bit ) == 0 )
109 {
110 // use the first code
111 indices[i] = 0;
112 continue;
113 }
114
115 // find the least error and corresponding index
116 int value = rgba[4*i + 3];
117 int least = INT_MAX;
118 int index = 0;
119 for( int j = 0; j < 8; ++j )
120 {
121 // get the squared error from this code
122 int dist = ( int )value - ( int )codes[j];
123 dist *= dist;
124
125 // compare with the best so far
126 if( dist < least )
127 {
128 least = dist;
129 index = j;
130 }
131 }
132
133 // save this index and accumulate the error
134 indices[i] = ( u8 )index;
135 err += least;
136 }
137
138 // return the total error
139 return err;
140 }
141
WriteAlphaBlock(int alpha0,int alpha1,u8 const * indices,void * block)142 static void WriteAlphaBlock( int alpha0, int alpha1, u8 const* indices, void* block )
143 {
144 u8* bytes = reinterpret_cast< u8* >( block );
145
146 // write the first two bytes
147 bytes[0] = ( u8 )alpha0;
148 bytes[1] = ( u8 )alpha1;
149
150 // pack the indices with 3 bits each
151 u8* dest = bytes + 2;
152 u8 const* src = indices;
153 for( int i = 0; i < 2; ++i )
154 {
155 // pack 8 3-bit values
156 int value = 0;
157 for( int j = 0; j < 8; ++j )
158 {
159 int index = *src++;
160 value |= ( index << 3*j );
161 }
162
163 // store in 3 bytes
164 for( int j = 0; j < 3; ++j )
165 {
166 int byte = ( value >> 8*j ) & 0xff;
167 *dest++ = ( u8 )byte;
168 }
169 }
170 }
171
WriteAlphaBlock5(int alpha0,int alpha1,u8 const * indices,void * block)172 static void WriteAlphaBlock5( int alpha0, int alpha1, u8 const* indices, void* block )
173 {
174 // check the relative values of the endpoints
175 if( alpha0 > alpha1 )
176 {
177 // swap the indices
178 u8 swapped[16];
179 for( int i = 0; i < 16; ++i )
180 {
181 u8 index = indices[i];
182 if( index == 0 )
183 swapped[i] = 1;
184 else if( index == 1 )
185 swapped[i] = 0;
186 else if( index <= 5 )
187 swapped[i] = 7 - index;
188 else
189 swapped[i] = index;
190 }
191
192 // write the block
193 WriteAlphaBlock( alpha1, alpha0, swapped, block );
194 }
195 else
196 {
197 // write the block
198 WriteAlphaBlock( alpha0, alpha1, indices, block );
199 }
200 }
201
WriteAlphaBlock7(int alpha0,int alpha1,u8 const * indices,void * block)202 static void WriteAlphaBlock7( int alpha0, int alpha1, u8 const* indices, void* block )
203 {
204 // check the relative values of the endpoints
205 if( alpha0 < alpha1 )
206 {
207 // swap the indices
208 u8 swapped[16];
209 for( int i = 0; i < 16; ++i )
210 {
211 u8 index = indices[i];
212 if( index == 0 )
213 swapped[i] = 1;
214 else if( index == 1 )
215 swapped[i] = 0;
216 else
217 swapped[i] = 9 - index;
218 }
219
220 // write the block
221 WriteAlphaBlock( alpha1, alpha0, swapped, block );
222 }
223 else
224 {
225 // write the block
226 WriteAlphaBlock( alpha0, alpha1, indices, block );
227 }
228 }
229
CompressAlphaDxt5(u8 const * rgba,int mask,void * block)230 void CompressAlphaDxt5( u8 const* rgba, int mask, void* block )
231 {
232 // get the range for 5-alpha and 7-alpha interpolation
233 int min5 = 255;
234 int max5 = 0;
235 int min7 = 255;
236 int max7 = 0;
237 for( int i = 0; i < 16; ++i )
238 {
239 // check this pixel is valid
240 int bit = 1 << i;
241 if( ( mask & bit ) == 0 )
242 continue;
243
244 // incorporate into the min/max
245 int value = rgba[4*i + 3];
246 if( value < min7 )
247 min7 = value;
248 if( value > max7 )
249 max7 = value;
250 if( value != 0 && value < min5 )
251 min5 = value;
252 if( value != 255 && value > max5 )
253 max5 = value;
254 }
255
256 // handle the case that no valid range was found
257 if( min5 > max5 )
258 min5 = max5;
259 if( min7 > max7 )
260 min7 = max7;
261
262 // fix the range to be the minimum in each case
263 FixRange( min5, max5, 5 );
264 FixRange( min7, max7, 7 );
265
266 // set up the 5-alpha code book
267 u8 codes5[8];
268 codes5[0] = ( u8 )min5;
269 codes5[1] = ( u8 )max5;
270 for( int i = 1; i < 5; ++i )
271 codes5[1 + i] = ( u8 )( ( ( 5 - i )*min5 + i*max5 )/5 );
272 codes5[6] = 0;
273 codes5[7] = 255;
274
275 // set up the 7-alpha code book
276 u8 codes7[8];
277 codes7[0] = ( u8 )min7;
278 codes7[1] = ( u8 )max7;
279 for( int i = 1; i < 7; ++i )
280 codes7[1 + i] = ( u8 )( ( ( 7 - i )*min7 + i*max7 )/7 );
281
282 // fit the data to both code books
283 u8 indices5[16];
284 u8 indices7[16];
285 int err5 = FitCodes( rgba, mask, codes5, indices5 );
286 int err7 = FitCodes( rgba, mask, codes7, indices7 );
287
288 // save the block with least error
289 if( err5 <= err7 )
290 WriteAlphaBlock5( min5, max5, indices5, block );
291 else
292 WriteAlphaBlock7( min7, max7, indices7, block );
293 }
294
DecompressAlphaDxt5(u8 * rgba,void const * block)295 void DecompressAlphaDxt5( u8* rgba, void const* block )
296 {
297 // get the two alpha values
298 u8 const* bytes = reinterpret_cast< u8 const* >( block );
299 int alpha0 = bytes[0];
300 int alpha1 = bytes[1];
301
302 // compare the values to build the codebook
303 u8 codes[8];
304 codes[0] = ( u8 )alpha0;
305 codes[1] = ( u8 )alpha1;
306 if( alpha0 <= alpha1 )
307 {
308 // use 5-alpha codebook
309 for( int i = 1; i < 5; ++i )
310 codes[1 + i] = ( u8 )( ( ( 5 - i )*alpha0 + i*alpha1 )/5 );
311 codes[6] = 0;
312 codes[7] = 255;
313 }
314 else
315 {
316 // use 7-alpha codebook
317 for( int i = 1; i < 7; ++i )
318 codes[1 + i] = ( u8 )( ( ( 7 - i )*alpha0 + i*alpha1 )/7 );
319 }
320
321 // decode the indices
322 u8 indices[16];
323 u8 const* src = bytes + 2;
324 u8* dest = indices;
325 for( int i = 0; i < 2; ++i )
326 {
327 // grab 3 bytes
328 int value = 0;
329 for( int j = 0; j < 3; ++j )
330 {
331 int byte = *src++;
332 value |= ( byte << 8*j );
333 }
334
335 // unpack 8 3-bit values from it
336 for( int j = 0; j < 8; ++j )
337 {
338 int index = ( value >> 3*j ) & 0x7;
339 *dest++ = ( u8 )index;
340 }
341 }
342
343 // write out the indexed codebook values
344 for( int i = 0; i < 16; ++i )
345 rgba[4*i + 3] = codes[indices[i]];
346 }
347
348 } // namespace squish
349