summaryrefslogtreecommitdiffstats
path: root/tools/aapt2/Png.cpp
blob: 4e9b68e8c95f062c5afb3c2c104f31cf90ca93aa (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "BigBuffer.h"
#include "Logger.h"
#include "Png.h"
#include "Source.h"
#include "Util.h"

#include <androidfw/ResourceTypes.h>
#include <iostream>
#include <png.h>
#include <sstream>
#include <string>
#include <vector>
#include <zlib.h>

namespace aapt {

constexpr bool kDebug = false;
constexpr size_t kPngSignatureSize = 8u;

struct PngInfo {
    ~PngInfo() {
        for (png_bytep row : rows) {
            if (row != nullptr) {
                delete[] row;
            }
        }

        delete[] xDivs;
        delete[] yDivs;
    }

    void* serialize9Patch() {
        void* serialized = android::Res_png_9patch::serialize(info9Patch, xDivs, yDivs,
                                                              colors.data());
        reinterpret_cast<android::Res_png_9patch*>(serialized)->deviceToFile();
        return serialized;
    }

    uint32_t width = 0;
    uint32_t height = 0;
    std::vector<png_bytep> rows;

    bool is9Patch = false;
    android::Res_png_9patch info9Patch;
    int32_t* xDivs = nullptr;
    int32_t* yDivs = nullptr;
    std::vector<uint32_t> colors;

    // Layout padding.
    bool haveLayoutBounds = false;
    int32_t layoutBoundsLeft;
    int32_t layoutBoundsTop;
    int32_t layoutBoundsRight;
    int32_t layoutBoundsBottom;

    // Round rect outline description.
    int32_t outlineInsetsLeft;
    int32_t outlineInsetsTop;
    int32_t outlineInsetsRight;
    int32_t outlineInsetsBottom;
    float outlineRadius;
    uint8_t outlineAlpha;
};

static void readDataFromStream(png_structp readPtr, png_bytep data, png_size_t length) {
    std::istream* input = reinterpret_cast<std::istream*>(png_get_io_ptr(readPtr));
    if (!input->read(reinterpret_cast<char*>(data), length)) {
        png_error(readPtr, strerror(errno));
    }
}

static void writeDataToStream(png_structp writePtr, png_bytep data, png_size_t length) {
    BigBuffer* outBuffer = reinterpret_cast<BigBuffer*>(png_get_io_ptr(writePtr));
    png_bytep buf = outBuffer->nextBlock<png_byte>(length);
    memcpy(buf, data, length);
}

static void flushDataToStream(png_structp /*writePtr*/) {
}

static void logWarning(png_structp readPtr, png_const_charp warningMessage) {
    SourceLogger* logger = reinterpret_cast<SourceLogger*>(png_get_error_ptr(readPtr));
    logger->warn() << warningMessage << "." << std::endl;
}


static bool readPng(png_structp readPtr, png_infop infoPtr, PngInfo* outInfo,
                    std::string* outError) {
    if (setjmp(png_jmpbuf(readPtr))) {
        *outError = "failed reading png";
        return false;
    }

    png_set_sig_bytes(readPtr, kPngSignatureSize);
    png_read_info(readPtr, infoPtr);

    int colorType, bitDepth, interlaceType, compressionType;
    png_get_IHDR(readPtr, infoPtr, &outInfo->width, &outInfo->height, &bitDepth, &colorType,
                 &interlaceType, &compressionType, nullptr);

    if (colorType == PNG_COLOR_TYPE_PALETTE) {
        png_set_palette_to_rgb(readPtr);
    }

    if (colorType == PNG_COLOR_TYPE_GRAY && bitDepth < 8) {
        png_set_expand_gray_1_2_4_to_8(readPtr);
    }

    if (png_get_valid(readPtr, infoPtr, PNG_INFO_tRNS)) {
        png_set_tRNS_to_alpha(readPtr);
    }

    if (bitDepth == 16) {
        png_set_strip_16(readPtr);
    }

    if (!(colorType & PNG_COLOR_MASK_ALPHA)) {
        png_set_add_alpha(readPtr, 0xFF, PNG_FILLER_AFTER);
    }

    if (colorType == PNG_COLOR_TYPE_GRAY || colorType == PNG_COLOR_TYPE_GRAY_ALPHA) {
        png_set_gray_to_rgb(readPtr);
    }

    png_set_interlace_handling(readPtr);
    png_read_update_info(readPtr, infoPtr);

    const uint32_t rowBytes = png_get_rowbytes(readPtr, infoPtr);
    outInfo->rows.resize(outInfo->height);
    for (size_t i = 0; i < outInfo->height; i++) {
        outInfo->rows[i] = new png_byte[rowBytes];
    }

    png_read_image(readPtr, outInfo->rows.data());
    png_read_end(readPtr, infoPtr);
    return true;
}

static void checkNinePatchSerialization(android::Res_png_9patch* inPatch,  void* data) {
    size_t patchSize = inPatch->serializedSize();
    void* newData = malloc(patchSize);
    memcpy(newData, data, patchSize);
    android::Res_png_9patch* outPatch = inPatch->deserialize(newData);
    outPatch->fileToDevice();
    // deserialization is done in place, so outPatch == newData
    assert(outPatch == newData);
    assert(outPatch->numXDivs == inPatch->numXDivs);
    assert(outPatch->numYDivs == inPatch->numYDivs);
    assert(outPatch->paddingLeft == inPatch->paddingLeft);
    assert(outPatch->paddingRight == inPatch->paddingRight);
    assert(outPatch->paddingTop == inPatch->paddingTop);
    assert(outPatch->paddingBottom == inPatch->paddingBottom);
/*    for (int i = 0; i < outPatch->numXDivs; i++) {
        assert(outPatch->getXDivs()[i] == inPatch->getXDivs()[i]);
    }
    for (int i = 0; i < outPatch->numYDivs; i++) {
        assert(outPatch->getYDivs()[i] == inPatch->getYDivs()[i]);
    }
    for (int i = 0; i < outPatch->numColors; i++) {
        assert(outPatch->getColors()[i] == inPatch->getColors()[i]);
    }*/
    free(newData);
}

/*static void dump_image(int w, int h, const png_byte* const* rows, int color_type) {
    int i, j, rr, gg, bb, aa;

    int bpp;
    if (color_type == PNG_COLOR_TYPE_PALETTE || color_type == PNG_COLOR_TYPE_GRAY) {
        bpp = 1;
    } else if (color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
        bpp = 2;
    } else if (color_type == PNG_COLOR_TYPE_RGB || color_type == PNG_COLOR_TYPE_RGB_ALPHA) {
        // We use a padding byte even when there is no alpha
        bpp = 4;
    } else {
        printf("Unknown color type %d.\n", color_type);
    }

    for (j = 0; j < h; j++) {
        const png_byte* row = rows[j];
        for (i = 0; i < w; i++) {
            rr = row[0];
            gg = row[1];
            bb = row[2];
            aa = row[3];
            row += bpp;

            if (i == 0) {
                printf("Row %d:", j);
            }
            switch (bpp) {
            case 1:
                printf(" (%d)", rr);
                break;
            case 2:
                printf(" (%d %d", rr, gg);
                break;
            case 3:
                printf(" (%d %d %d)", rr, gg, bb);
                break;
            case 4:
                printf(" (%d %d %d %d)", rr, gg, bb, aa);
                break;
            }
            if (i == (w - 1)) {
                printf("\n");
            }
        }
    }
}*/

#define MAX(a,b) ((a)>(b)?(a):(b))
#define ABS(a)   ((a)<0?-(a):(a))

static void analyze_image(SourceLogger* logger, const PngInfo& imageInfo, int grayscaleTolerance,
                          png_colorp rgbPalette, png_bytep alphaPalette,
                          int *paletteEntries, bool *hasTransparency, int *colorType,
                          png_bytepp outRows) {
    int w = imageInfo.width;
    int h = imageInfo.height;
    int i, j, rr, gg, bb, aa, idx;
    uint32_t colors[256], col;
    int num_colors = 0;
    int maxGrayDeviation = 0;

    bool isOpaque = true;
    bool isPalette = true;
    bool isGrayscale = true;

    // Scan the entire image and determine if:
    // 1. Every pixel has R == G == B (grayscale)
    // 2. Every pixel has A == 255 (opaque)
    // 3. There are no more than 256 distinct RGBA colors

    if (kDebug) {
        printf("Initial image data:\n");
        //dump_image(w, h, imageInfo.rows.data(), PNG_COLOR_TYPE_RGB_ALPHA);
    }

    for (j = 0; j < h; j++) {
        const png_byte* row = imageInfo.rows[j];
        png_bytep out = outRows[j];
        for (i = 0; i < w; i++) {
            rr = *row++;
            gg = *row++;
            bb = *row++;
            aa = *row++;

            int odev = maxGrayDeviation;
            maxGrayDeviation = MAX(ABS(rr - gg), maxGrayDeviation);
            maxGrayDeviation = MAX(ABS(gg - bb), maxGrayDeviation);
            maxGrayDeviation = MAX(ABS(bb - rr), maxGrayDeviation);
            if (maxGrayDeviation > odev) {
                if (kDebug) {
                    printf("New max dev. = %d at pixel (%d, %d) = (%d %d %d %d)\n",
                            maxGrayDeviation, i, j, rr, gg, bb, aa);
                }
            }

            // Check if image is really grayscale
            if (isGrayscale) {
                if (rr != gg || rr != bb) {
                    if (kDebug) {
                        printf("Found a non-gray pixel at %d, %d = (%d %d %d %d)\n",
                                i, j, rr, gg, bb, aa);
                    }
                    isGrayscale = false;
                }
            }

            // Check if image is really opaque
            if (isOpaque) {
                if (aa != 0xff) {
                    if (kDebug) {
                        printf("Found a non-opaque pixel at %d, %d = (%d %d %d %d)\n",
                                i, j, rr, gg, bb, aa);
                    }
                    isOpaque = false;
                }
            }

            // Check if image is really <= 256 colors
            if (isPalette) {
                col = (uint32_t) ((rr << 24) | (gg << 16) | (bb << 8) | aa);
                bool match = false;
                for (idx = 0; idx < num_colors; idx++) {
                    if (colors[idx] == col) {
                        match = true;
                        break;
                    }
                }

                // Write the palette index for the pixel to outRows optimistically
                // We might overwrite it later if we decide to encode as gray or
                // gray + alpha
                *out++ = idx;
                if (!match) {
                    if (num_colors == 256) {
                        if (kDebug) {
                            printf("Found 257th color at %d, %d\n", i, j);
                        }
                        isPalette = false;
                    } else {
                        colors[num_colors++] = col;
                    }
                }
            }
        }
    }

    *paletteEntries = 0;
    *hasTransparency = !isOpaque;
    int bpp = isOpaque ? 3 : 4;
    int paletteSize = w * h + bpp * num_colors;

    if (kDebug) {
        printf("isGrayscale = %s\n", isGrayscale ? "true" : "false");
        printf("isOpaque = %s\n", isOpaque ? "true" : "false");
        printf("isPalette = %s\n", isPalette ? "true" : "false");
        printf("Size w/ palette = %d, gray+alpha = %d, rgb(a) = %d\n",
                paletteSize, 2 * w * h, bpp * w * h);
        printf("Max gray deviation = %d, tolerance = %d\n", maxGrayDeviation, grayscaleTolerance);
    }

    // Choose the best color type for the image.
    // 1. Opaque gray - use COLOR_TYPE_GRAY at 1 byte/pixel
    // 2. Gray + alpha - use COLOR_TYPE_PALETTE if the number of distinct combinations
    //     is sufficiently small, otherwise use COLOR_TYPE_GRAY_ALPHA
    // 3. RGB(A) - use COLOR_TYPE_PALETTE if the number of distinct colors is sufficiently
    //     small, otherwise use COLOR_TYPE_RGB{_ALPHA}
    if (isGrayscale) {
        if (isOpaque) {
            *colorType = PNG_COLOR_TYPE_GRAY; // 1 byte/pixel
        } else {
            // Use a simple heuristic to determine whether using a palette will
            // save space versus using gray + alpha for each pixel.
            // This doesn't take into account chunk overhead, filtering, LZ
            // compression, etc.
            if (isPalette && (paletteSize < 2 * w * h)) {
                *colorType = PNG_COLOR_TYPE_PALETTE; // 1 byte/pixel + 4 bytes/color
            } else {
                *colorType = PNG_COLOR_TYPE_GRAY_ALPHA; // 2 bytes per pixel
            }
        }
    } else if (isPalette && (paletteSize < bpp * w * h)) {
        *colorType = PNG_COLOR_TYPE_PALETTE;
    } else {
        if (maxGrayDeviation <= grayscaleTolerance) {
            logger->note() << "forcing image to gray (max deviation = " << maxGrayDeviation
                           << ")."
                           << std::endl;
            *colorType = isOpaque ? PNG_COLOR_TYPE_GRAY : PNG_COLOR_TYPE_GRAY_ALPHA;
        } else {
            *colorType = isOpaque ? PNG_COLOR_TYPE_RGB : PNG_COLOR_TYPE_RGB_ALPHA;
        }
    }

    // Perform postprocessing of the image or palette data based on the final
    // color type chosen

    if (*colorType == PNG_COLOR_TYPE_PALETTE) {
        // Create separate RGB and Alpha palettes and set the number of colors
        *paletteEntries = num_colors;

        // Create the RGB and alpha palettes
        for (int idx = 0; idx < num_colors; idx++) {
            col = colors[idx];
            rgbPalette[idx].red   = (png_byte) ((col >> 24) & 0xff);
            rgbPalette[idx].green = (png_byte) ((col >> 16) & 0xff);
            rgbPalette[idx].blue  = (png_byte) ((col >>  8) & 0xff);
            alphaPalette[idx]     = (png_byte)  (col        & 0xff);
        }
    } else if (*colorType == PNG_COLOR_TYPE_GRAY || *colorType == PNG_COLOR_TYPE_GRAY_ALPHA) {
        // If the image is gray or gray + alpha, compact the pixels into outRows
        for (j = 0; j < h; j++) {
            const png_byte* row = imageInfo.rows[j];
            png_bytep out = outRows[j];
            for (i = 0; i < w; i++) {
                rr = *row++;
                gg = *row++;
                bb = *row++;
                aa = *row++;

                if (isGrayscale) {
                    *out++ = rr;
                } else {
                    *out++ = (png_byte) (rr * 0.2126f + gg * 0.7152f + bb * 0.0722f);
                }
                if (!isOpaque) {
                    *out++ = aa;
                }
           }
        }
    }
}

static bool writePng(png_structp writePtr, png_infop infoPtr, PngInfo* info,
                     int grayScaleTolerance, SourceLogger* logger, std::string* outError) {
    if (setjmp(png_jmpbuf(writePtr))) {
        *outError = "failed to write png";
        return false;
    }

    uint32_t width, height;
    int colorType, bitDepth, interlaceType, compressionType;

    png_unknown_chunk unknowns[3];
    unknowns[0].data = nullptr;
    unknowns[1].data = nullptr;
    unknowns[2].data = nullptr;

    png_bytepp outRows = (png_bytepp) malloc((int) info->height * sizeof(png_bytep));
    if (outRows == (png_bytepp) 0) {
        printf("Can't allocate output buffer!\n");
        exit(1);
    }
    for (uint32_t i = 0; i < info->height; i++) {
        outRows[i] = (png_bytep) malloc(2 * (int) info->width);
        if (outRows[i] == (png_bytep) 0) {
            printf("Can't allocate output buffer!\n");
            exit(1);
        }
    }

    png_set_compression_level(writePtr, Z_BEST_COMPRESSION);

    if (kDebug) {
        logger->note() << "writing image: w = " << info->width
                       << ", h = " << info->height
                       << std::endl;
    }

    png_color rgbPalette[256];
    png_byte alphaPalette[256];
    bool hasTransparency;
    int paletteEntries;

    analyze_image(logger, *info, grayScaleTolerance, rgbPalette, alphaPalette,
                  &paletteEntries, &hasTransparency, &colorType, outRows);

    // If the image is a 9-patch, we need to preserve it as a ARGB file to make
    // sure the pixels will not be pre-dithered/clamped until we decide they are
    if (info->is9Patch && (colorType == PNG_COLOR_TYPE_RGB ||
            colorType == PNG_COLOR_TYPE_GRAY || colorType == PNG_COLOR_TYPE_PALETTE)) {
        colorType = PNG_COLOR_TYPE_RGB_ALPHA;
    }

    if (kDebug) {
        switch (colorType) {
        case PNG_COLOR_TYPE_PALETTE:
            logger->note() << "has " << paletteEntries
                           << " colors" << (hasTransparency ? " (with alpha)" : "")
                           << ", using PNG_COLOR_TYPE_PALLETTE."
                           << std::endl;
            break;
        case PNG_COLOR_TYPE_GRAY:
            logger->note() << "is opaque gray, using PNG_COLOR_TYPE_GRAY." << std::endl;
            break;
        case PNG_COLOR_TYPE_GRAY_ALPHA:
            logger->note() << "is gray + alpha, using PNG_COLOR_TYPE_GRAY_ALPHA." << std::endl;
            break;
        case PNG_COLOR_TYPE_RGB:
            logger->note() << "is opaque RGB, using PNG_COLOR_TYPE_RGB." << std::endl;
            break;
        case PNG_COLOR_TYPE_RGB_ALPHA:
            logger->note() << "is RGB + alpha, using PNG_COLOR_TYPE_RGB_ALPHA." << std::endl;
            break;
        }
    }

    png_set_IHDR(writePtr, infoPtr, info->width, info->height, 8, colorType,
                 PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);

    if (colorType == PNG_COLOR_TYPE_PALETTE) {
        png_set_PLTE(writePtr, infoPtr, rgbPalette, paletteEntries);
        if (hasTransparency) {
            png_set_tRNS(writePtr, infoPtr, alphaPalette, paletteEntries, (png_color_16p) 0);
        }
        png_set_filter(writePtr, 0, PNG_NO_FILTERS);
    } else {
        png_set_filter(writePtr, 0, PNG_ALL_FILTERS);
    }

    if (info->is9Patch) {
        int chunkCount = 2 + (info->haveLayoutBounds ? 1 : 0);
        int pIndex = info->haveLayoutBounds ? 2 : 1;
        int bIndex = 1;
        int oIndex = 0;

        // Chunks ordered thusly because older platforms depend on the base 9 patch data being last
        png_bytep chunkNames = info->haveLayoutBounds
                ? (png_bytep)"npOl\0npLb\0npTc\0"
                : (png_bytep)"npOl\0npTc";

        // base 9 patch data
        if (kDebug) {
            logger->note() << "adding 9-patch info..." << std::endl;
        }
        strcpy((char*)unknowns[pIndex].name, "npTc");
        unknowns[pIndex].data = (png_byte*) info->serialize9Patch();
        unknowns[pIndex].size = info->info9Patch.serializedSize();
        // TODO: remove the check below when everything works
        checkNinePatchSerialization(&info->info9Patch, unknowns[pIndex].data);

        // automatically generated 9 patch outline data
        int chunkSize = sizeof(png_uint_32) * 6;
        strcpy((char*)unknowns[oIndex].name, "npOl");
        unknowns[oIndex].data = (png_byte*) calloc(chunkSize, 1);
        png_byte outputData[chunkSize];
        memcpy(&outputData, &info->outlineInsetsLeft, 4 * sizeof(png_uint_32));
        ((float*) outputData)[4] = info->outlineRadius;
        ((png_uint_32*) outputData)[5] = info->outlineAlpha;
        memcpy(unknowns[oIndex].data, &outputData, chunkSize);
        unknowns[oIndex].size = chunkSize;

        // optional optical inset / layout bounds data
        if (info->haveLayoutBounds) {
            int chunkSize = sizeof(png_uint_32) * 4;
            strcpy((char*)unknowns[bIndex].name, "npLb");
            unknowns[bIndex].data = (png_byte*) calloc(chunkSize, 1);
            memcpy(unknowns[bIndex].data, &info->layoutBoundsLeft, chunkSize);
            unknowns[bIndex].size = chunkSize;
        }

        for (int i = 0; i < chunkCount; i++) {
            unknowns[i].location = PNG_HAVE_PLTE;
        }
        png_set_keep_unknown_chunks(writePtr, PNG_HANDLE_CHUNK_ALWAYS,
                                    chunkNames, chunkCount);
        png_set_unknown_chunks(writePtr, infoPtr, unknowns, chunkCount);

#if PNG_LIBPNG_VER < 10600
        // Deal with unknown chunk location bug in 1.5.x and earlier.
        png_set_unknown_chunk_location(writePtr, infoPtr, 0, PNG_HAVE_PLTE);
        if (info->haveLayoutBounds) {
            png_set_unknown_chunk_location(writePtr, infoPtr, 1, PNG_HAVE_PLTE);
        }
#endif
    }

    png_write_info(writePtr, infoPtr);

    png_bytepp rows;
    if (colorType == PNG_COLOR_TYPE_RGB || colorType == PNG_COLOR_TYPE_RGB_ALPHA) {
        if (colorType == PNG_COLOR_TYPE_RGB) {
            png_set_filler(writePtr, 0, PNG_FILLER_AFTER);
        }
        rows = info->rows.data();
    } else {
        rows = outRows;
    }
    png_write_image(writePtr, rows);

    if (kDebug) {
        printf("Final image data:\n");
        //dump_image(info->width, info->height, rows, colorType);
    }

    png_write_end(writePtr, infoPtr);

    for (uint32_t i = 0; i < info->height; i++) {
        free(outRows[i]);
    }
    free(outRows);
    free(unknowns[0].data);
    free(unknowns[1].data);
    free(unknowns[2].data);

    png_get_IHDR(writePtr, infoPtr, &width, &height, &bitDepth, &colorType, &interlaceType,
                 &compressionType, nullptr);

    if (kDebug) {
        logger->note() << "image written: w = " << width << ", h = " << height
                       << ", d = " << bitDepth << ", colors = " << colorType
                       << ", inter = " << interlaceType << ", comp = " << compressionType
                       << std::endl;
    }
    return true;
}

constexpr uint32_t kColorWhite = 0xffffffffu;
constexpr uint32_t kColorTick = 0xff000000u;
constexpr uint32_t kColorLayoutBoundsTick = 0xff0000ffu;

enum class TickType {
    kNone,
    kTick,
    kLayoutBounds,
    kBoth
};

static TickType tickType(png_bytep p, bool transparent, const char** outError) {
    png_uint_32 color = p[0] | (p[1] << 8) | (p[2] << 16) | (p[3] << 24);

    if (transparent) {
        if (p[3] == 0) {
            return TickType::kNone;
        }
        if (color == kColorLayoutBoundsTick) {
            return TickType::kLayoutBounds;
        }
        if (color == kColorTick) {
            return TickType::kTick;
        }

        // Error cases
        if (p[3] != 0xff) {
            *outError = "Frame pixels must be either solid or transparent "
                        "(not intermediate alphas)";
            return TickType::kNone;
        }

        if (p[0] != 0 || p[1] != 0 || p[2] != 0) {
            *outError = "Ticks in transparent frame must be black or red";
        }
        return TickType::kTick;
    }

    if (p[3] != 0xFF) {
        *outError = "White frame must be a solid color (no alpha)";
    }
    if (color == kColorWhite) {
        return TickType::kNone;
    }
    if (color == kColorTick) {
        return TickType::kTick;
    }
    if (color == kColorLayoutBoundsTick) {
        return TickType::kLayoutBounds;
    }

    if (p[0] != 0 || p[1] != 0 || p[2] != 0) {
        *outError = "Ticks in white frame must be black or red";
        return TickType::kNone;
    }
    return TickType::kTick;
}

enum class TickState {
    kStart,
    kInside1,
    kOutside1
};

static bool getHorizontalTicks(png_bytep row, int width, bool transparent, bool required,
                               int32_t* outLeft, int32_t* outRight, const char** outError,
                               uint8_t* outDivs, bool multipleAllowed) {
    *outLeft = *outRight = -1;
    TickState state = TickState::kStart;
    bool found = false;

    for (int i = 1; i < width - 1; i++) {
        if (tickType(row+i*4, transparent, outError) == TickType::kTick) {
            if (state == TickState::kStart ||
                (state == TickState::kOutside1 && multipleAllowed)) {
                *outLeft = i-1;
                *outRight = width-2;
                found = true;
                if (outDivs != NULL) {
                    *outDivs += 2;
                }
                state = TickState::kInside1;
            } else if (state == TickState::kOutside1) {
                *outError = "Can't have more than one marked region along edge";
                *outLeft = i;
                return false;
            }
        } else if (!*outError) {
            if (state == TickState::kInside1) {
                // We're done with this div.  Move on to the next.
                *outRight = i-1;
                outRight += 2;
                outLeft += 2;
                state = TickState::kOutside1;
            }
        } else {
            *outLeft = i;
            return false;
        }
    }

    if (required && !found) {
        *outError = "No marked region found along edge";
        *outLeft = -1;
        return false;
    }
    return true;
}

static bool getVerticalTicks(png_bytepp rows, int offset, int height, bool transparent,
                             bool required, int32_t* outTop, int32_t* outBottom,
                             const char** outError, uint8_t* outDivs, bool multipleAllowed) {
    *outTop = *outBottom = -1;
    TickState state = TickState::kStart;
    bool found = false;

    for (int i = 1; i < height - 1; i++) {
        if (tickType(rows[i]+offset, transparent, outError) == TickType::kTick) {
            if (state == TickState::kStart ||
                (state == TickState::kOutside1 && multipleAllowed)) {
                *outTop = i-1;
                *outBottom = height-2;
                found = true;
                if (outDivs != NULL) {
                    *outDivs += 2;
                }
                state = TickState::kInside1;
            } else if (state == TickState::kOutside1) {
                *outError = "Can't have more than one marked region along edge";
                *outTop = i;
                return false;
            }
        } else if (!*outError) {
            if (state == TickState::kInside1) {
                // We're done with this div.  Move on to the next.
                *outBottom = i-1;
                outTop += 2;
                outBottom += 2;
                state = TickState::kOutside1;
            }
        } else {
            *outTop = i;
            return false;
        }
    }

    if (required && !found) {
        *outError = "No marked region found along edge";
        *outTop = -1;
        return false;
    }
    return true;
}

static bool getHorizontalLayoutBoundsTicks(png_bytep row, int width, bool transparent,
                                           bool /* required */, int32_t* outLeft,
                                           int32_t* outRight, const char** outError) {
    *outLeft = *outRight = 0;

    // Look for left tick
    if (tickType(row + 4, transparent, outError) == TickType::kLayoutBounds) {
        // Starting with a layout padding tick
        int i = 1;
        while (i < width - 1) {
            (*outLeft)++;
            i++;
            if (tickType(row + i * 4, transparent, outError) != TickType::kLayoutBounds) {
                break;
            }
        }
    }

    // Look for right tick
    if (tickType(row + (width - 2) * 4, transparent, outError) == TickType::kLayoutBounds) {
        // Ending with a layout padding tick
        int i = width - 2;
        while (i > 1) {
            (*outRight)++;
            i--;
            if (tickType(row+i*4, transparent, outError) != TickType::kLayoutBounds) {
                break;
            }
        }
    }
    return true;
}

static bool getVerticalLayoutBoundsTicks(png_bytepp rows, int offset, int height, bool transparent,
                                         bool /* required */, int32_t* outTop, int32_t* outBottom,
                                         const char** outError) {
    *outTop = *outBottom = 0;

    // Look for top tick
    if (tickType(rows[1] + offset, transparent, outError) == TickType::kLayoutBounds) {
        // Starting with a layout padding tick
        int i = 1;
        while (i < height - 1) {
            (*outTop)++;
            i++;
            if (tickType(rows[i] + offset, transparent, outError) != TickType::kLayoutBounds) {
                break;
            }
        }
    }

    // Look for bottom tick
    if (tickType(rows[height - 2] + offset, transparent, outError) == TickType::kLayoutBounds) {
        // Ending with a layout padding tick
        int i = height - 2;
        while (i > 1) {
            (*outBottom)++;
            i--;
            if (tickType(rows[i] + offset, transparent, outError) != TickType::kLayoutBounds) {
                break;
            }
        }
    }
    return true;
}

static void findMaxOpacity(png_bytepp rows, int startX, int startY, int endX, int endY,
                           int dX, int dY, int* outInset) {
    uint8_t maxOpacity = 0;
    int inset = 0;
    *outInset = 0;
    for (int x = startX, y = startY; x != endX && y != endY; x += dX, y += dY, inset++) {
        png_byte* color = rows[y] + x * 4;
        uint8_t opacity = color[3];
        if (opacity > maxOpacity) {
            maxOpacity = opacity;
            *outInset = inset;
        }
        if (opacity == 0xff) return;
    }
}

static uint8_t maxAlphaOverRow(png_bytep row, int startX, int endX) {
    uint8_t maxAlpha = 0;
    for (int x = startX; x < endX; x++) {
        uint8_t alpha = (row + x * 4)[3];
        if (alpha > maxAlpha) maxAlpha = alpha;
    }
    return maxAlpha;
}

static uint8_t maxAlphaOverCol(png_bytepp rows, int offsetX, int startY, int endY) {
    uint8_t maxAlpha = 0;
    for (int y = startY; y < endY; y++) {
        uint8_t alpha = (rows[y] + offsetX * 4)[3];
        if (alpha > maxAlpha) maxAlpha = alpha;
    }
    return maxAlpha;
}

static void getOutline(PngInfo* image) {
    int midX = image->width / 2;
    int midY = image->height / 2;
    int endX = image->width - 2;
    int endY = image->height - 2;

    // find left and right extent of nine patch content on center row
    if (image->width > 4) {
        findMaxOpacity(image->rows.data(), 1, midY, midX, -1, 1, 0, &image->outlineInsetsLeft);
        findMaxOpacity(image->rows.data(), endX, midY, midX, -1, -1, 0,
                       &image->outlineInsetsRight);
    } else {
        image->outlineInsetsLeft = 0;
        image->outlineInsetsRight = 0;
    }

    // find top and bottom extent of nine patch content on center column
    if (image->height > 4) {
        findMaxOpacity(image->rows.data(), midX, 1, -1, midY, 0, 1, &image->outlineInsetsTop);
        findMaxOpacity(image->rows.data(), midX, endY, -1, midY, 0, -1,
                       &image->outlineInsetsBottom);
    } else {
        image->outlineInsetsTop = 0;
        image->outlineInsetsBottom = 0;
    }

    int innerStartX = 1 + image->outlineInsetsLeft;
    int innerStartY = 1 + image->outlineInsetsTop;
    int innerEndX = endX - image->outlineInsetsRight;
    int innerEndY = endY - image->outlineInsetsBottom;
    int innerMidX = (innerEndX + innerStartX) / 2;
    int innerMidY = (innerEndY + innerStartY) / 2;

    // assuming the image is a round rect, compute the radius by marching
    // diagonally from the top left corner towards the center
    image->outlineAlpha = std::max(
            maxAlphaOverRow(image->rows[innerMidY], innerStartX, innerEndX),
            maxAlphaOverCol(image->rows.data(), innerMidX, innerStartY, innerStartY));

    int diagonalInset = 0;
    findMaxOpacity(image->rows.data(), innerStartX, innerStartY, innerMidX, innerMidY, 1, 1,
                   &diagonalInset);

    /* Determine source radius based upon inset:
     *     sqrt(r^2 + r^2) = sqrt(i^2 + i^2) + r
     *     sqrt(2) * r = sqrt(2) * i + r
     *     (sqrt(2) - 1) * r = sqrt(2) * i
     *     r = sqrt(2) / (sqrt(2) - 1) * i
     */
    image->outlineRadius = 3.4142f * diagonalInset;

    if (kDebug) {
        printf("outline insets %d %d %d %d, rad %f, alpha %x\n",
                image->outlineInsetsLeft,
                image->outlineInsetsTop,
                image->outlineInsetsRight,
                image->outlineInsetsBottom,
                image->outlineRadius,
                image->outlineAlpha);
    }
}

static uint32_t getColor(png_bytepp rows, int left, int top, int right, int bottom) {
    png_bytep color = rows[top] + left*4;

    if (left > right || top > bottom) {
        return android::Res_png_9patch::TRANSPARENT_COLOR;
    }

    while (top <= bottom) {
        for (int i = left; i <= right; i++) {
            png_bytep p = rows[top]+i*4;
            if (color[3] == 0) {
                if (p[3] != 0) {
                    return android::Res_png_9patch::NO_COLOR;
                }
            } else if (p[0] != color[0] || p[1] != color[1] ||
                    p[2] != color[2] || p[3] != color[3]) {
                return android::Res_png_9patch::NO_COLOR;
            }
        }
        top++;
    }

    if (color[3] == 0) {
        return android::Res_png_9patch::TRANSPARENT_COLOR;
    }
    return (color[3]<<24) | (color[0]<<16) | (color[1]<<8) | color[2];
}

static bool do9Patch(PngInfo* image, std::string* outError) {
    image->is9Patch = true;

    int W = image->width;
    int H = image->height;
    int i, j;

    const int maxSizeXDivs = W * sizeof(int32_t);
    const int maxSizeYDivs = H * sizeof(int32_t);
    int32_t* xDivs = image->xDivs = new int32_t[W];
    int32_t* yDivs = image->yDivs = new int32_t[H];
    uint8_t numXDivs = 0;
    uint8_t numYDivs = 0;

    int8_t numColors;
    int numRows;
    int numCols;
    int top;
    int left;
    int right;
    int bottom;
    memset(xDivs, -1, maxSizeXDivs);
    memset(yDivs, -1, maxSizeYDivs);
    image->info9Patch.paddingLeft = image->info9Patch.paddingRight = -1;
    image->info9Patch.paddingTop = image->info9Patch.paddingBottom = -1;
    image->layoutBoundsLeft = image->layoutBoundsRight = 0;
    image->layoutBoundsTop = image->layoutBoundsBottom = 0;

    png_bytep p = image->rows[0];
    bool transparent = p[3] == 0;
    bool hasColor = false;

    const char* errorMsg = nullptr;
    int errorPixel = -1;
    const char* errorEdge = nullptr;

    int colorIndex = 0;
    std::vector<png_bytep> newRows;

    // Validate size...
    if (W < 3 || H < 3) {
        errorMsg = "Image must be at least 3x3 (1x1 without frame) pixels";
        goto getout;
    }

    // Validate frame...
    if (!transparent &&
            (p[0] != 0xFF || p[1] != 0xFF || p[2] != 0xFF || p[3] != 0xFF)) {
        errorMsg = "Must have one-pixel frame that is either transparent or white";
        goto getout;
    }

    // Find left and right of sizing areas...
    if (!getHorizontalTicks(p, W, transparent, true, &xDivs[0], &xDivs[1], &errorMsg, &numXDivs,
                            true)) {
        errorPixel = xDivs[0];
        errorEdge = "top";
        goto getout;
    }

    // Find top and bottom of sizing areas...
    if (!getVerticalTicks(image->rows.data(), 0, H, transparent, true, &yDivs[0], &yDivs[1],
                          &errorMsg, &numYDivs, true)) {
        errorPixel = yDivs[0];
        errorEdge = "left";
        goto getout;
    }

    // Copy patch size data into image...
    image->info9Patch.numXDivs = numXDivs;
    image->info9Patch.numYDivs = numYDivs;

    // Find left and right of padding area...
    if (!getHorizontalTicks(image->rows[H-1], W, transparent, false,
                            &image->info9Patch.paddingLeft, &image->info9Patch.paddingRight,
                            &errorMsg, nullptr, false)) {
        errorPixel = image->info9Patch.paddingLeft;
        errorEdge = "bottom";
        goto getout;
    }

    // Find top and bottom of padding area...
    if (!getVerticalTicks(image->rows.data(), (W-1)*4, H, transparent, false,
                          &image->info9Patch.paddingTop, &image->info9Patch.paddingBottom,
                          &errorMsg, nullptr, false)) {
        errorPixel = image->info9Patch.paddingTop;
        errorEdge = "right";
        goto getout;
    }

    // Find left and right of layout padding...
    getHorizontalLayoutBoundsTicks(image->rows[H-1], W, transparent, false,
                                   &image->layoutBoundsLeft, &image->layoutBoundsRight, &errorMsg);

    getVerticalLayoutBoundsTicks(image->rows.data(), (W-1)*4, H, transparent, false,
                                 &image->layoutBoundsTop, &image->layoutBoundsBottom, &errorMsg);

    image->haveLayoutBounds = image->layoutBoundsLeft != 0
                               || image->layoutBoundsRight != 0
                               || image->layoutBoundsTop != 0
                               || image->layoutBoundsBottom != 0;

    if (image->haveLayoutBounds) {
        if (kDebug) {
            printf("layoutBounds=%d %d %d %d\n", image->layoutBoundsLeft, image->layoutBoundsTop,
                    image->layoutBoundsRight, image->layoutBoundsBottom);
        }
    }

    // use opacity of pixels to estimate the round rect outline
    getOutline(image);

    // If padding is not yet specified, take values from size.
    if (image->info9Patch.paddingLeft < 0) {
        image->info9Patch.paddingLeft = xDivs[0];
        image->info9Patch.paddingRight = W - 2 - xDivs[1];
    } else {
        // Adjust value to be correct!
        image->info9Patch.paddingRight = W - 2 - image->info9Patch.paddingRight;
    }
    if (image->info9Patch.paddingTop < 0) {
        image->info9Patch.paddingTop = yDivs[0];
        image->info9Patch.paddingBottom = H - 2 - yDivs[1];
    } else {
        // Adjust value to be correct!
        image->info9Patch.paddingBottom = H - 2 - image->info9Patch.paddingBottom;
    }

/*    if (kDebug) {
        printf("Size ticks for %s: x0=%d, x1=%d, y0=%d, y1=%d\n", imageName,
                xDivs[0], xDivs[1],
                yDivs[0], yDivs[1]);
        printf("padding ticks for %s: l=%d, r=%d, t=%d, b=%d\n", imageName,
                image->info9Patch.paddingLeft, image->info9Patch.paddingRight,
                image->info9Patch.paddingTop, image->info9Patch.paddingBottom);
    }*/

    // Remove frame from image.
    newRows.resize(H - 2);
    for (i = 0; i < H - 2; i++) {
        newRows[i] = image->rows[i + 1];
        memmove(newRows[i], newRows[i] + 4, (W - 2) * 4);
    }
    image->rows.swap(newRows);

    image->width -= 2;
    W = image->width;
    image->height -= 2;
    H = image->height;

    // Figure out the number of rows and columns in the N-patch
    numCols = numXDivs + 1;
    if (xDivs[0] == 0) {  // Column 1 is strechable
        numCols--;
    }
    if (xDivs[numXDivs - 1] == W) {
        numCols--;
    }
    numRows = numYDivs + 1;
    if (yDivs[0] == 0) {  // Row 1 is strechable
        numRows--;
    }
    if (yDivs[numYDivs - 1] == H) {
        numRows--;
    }

    // Make sure the amount of rows and columns will fit in the number of
    // colors we can use in the 9-patch format.
    if (numRows * numCols > 0x7F) {
        errorMsg = "Too many rows and columns in 9-patch perimeter";
        goto getout;
    }

    numColors = numRows * numCols;
    image->info9Patch.numColors = numColors;
    image->colors.resize(numColors);

    // Fill in color information for each patch.

    uint32_t c;
    top = 0;

    // The first row always starts with the top being at y=0 and the bottom
    // being either yDivs[1] (if yDivs[0]=0) of yDivs[0].  In the former case
    // the first row is stretchable along the Y axis, otherwise it is fixed.
    // The last row always ends with the bottom being bitmap.height and the top
    // being either yDivs[numYDivs-2] (if yDivs[numYDivs-1]=bitmap.height) or
    // yDivs[numYDivs-1]. In the former case the last row is stretchable along
    // the Y axis, otherwise it is fixed.
    //
    // The first and last columns are similarly treated with respect to the X
    // axis.
    //
    // The above is to help explain some of the special casing that goes on the
    // code below.

    // The initial yDiv and whether the first row is considered stretchable or
    // not depends on whether yDiv[0] was zero or not.
    for (j = (yDivs[0] == 0 ? 1 : 0); j <= numYDivs && top < H; j++) {
        if (j == numYDivs) {
            bottom = H;
        } else {
            bottom = yDivs[j];
        }
        left = 0;
        // The initial xDiv and whether the first column is considered
        // stretchable or not depends on whether xDiv[0] was zero or not.
        for (i = xDivs[0] == 0 ? 1 : 0; i <= numXDivs && left < W; i++) {
            if (i == numXDivs) {
                right = W;
            } else {
                right = xDivs[i];
            }
            c = getColor(image->rows.data(), left, top, right - 1, bottom - 1);
            image->colors[colorIndex++] = c;
            if (kDebug) {
                if (c != android::Res_png_9patch::NO_COLOR) {
                    hasColor = true;
                }
            }
            left = right;
        }
        top = bottom;
    }

    assert(colorIndex == numColors);

    if (kDebug && hasColor) {
        for (i = 0; i < numColors; i++) {
            if (i == 0) printf("Colors:\n");
            printf(" #%08x", image->colors[i]);
            if (i == numColors - 1) printf("\n");
        }
    }
getout:
    if (errorMsg) {
        std::stringstream err;
        err << "9-patch malformed: " << errorMsg;
        if (!errorEdge) {
            err << "." << std::endl;
            if (errorPixel >= 0) {
                err << "Found at pixel #" << errorPixel << " along " << errorEdge << " edge";
            } else {
                err << "Found along " << errorEdge << " edge";
            }
        }
        *outError = err.str();
        return false;
    }
    return true;
}


bool Png::process(const Source& source, std::istream& input, BigBuffer* outBuffer,
                  const Options& options, std::string* outError) {
    png_byte signature[kPngSignatureSize];

    // Read the PNG signature first.
    if (!input.read(reinterpret_cast<char*>(signature), kPngSignatureSize)) {
        *outError = strerror(errno);
        return false;
    }

    // If the PNG signature doesn't match, bail early.
    if (png_sig_cmp(signature, 0, kPngSignatureSize) != 0) {
        *outError = "not a valid png file";
        return false;
    }

    SourceLogger logger(source);
    bool result = false;
    png_structp readPtr = nullptr;
    png_infop infoPtr = nullptr;
    png_structp writePtr = nullptr;
    png_infop writeInfoPtr = nullptr;
    PngInfo pngInfo = {};

    readPtr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, nullptr, nullptr);
    if (!readPtr) {
        *outError = "failed to allocate read ptr";
        goto bail;
    }

    infoPtr = png_create_info_struct(readPtr);
    if (!infoPtr) {
        *outError = "failed to allocate info ptr";
        goto bail;
    }

    png_set_error_fn(readPtr, reinterpret_cast<png_voidp>(&logger), nullptr, logWarning);

    // Set the read function to read from std::istream.
    png_set_read_fn(readPtr, (png_voidp)&input, readDataFromStream);

    if (!readPng(readPtr, infoPtr, &pngInfo, outError)) {
        goto bail;
    }

    if (util::stringEndsWith<char>(source.path, ".9.png")) {
        if (!do9Patch(&pngInfo, outError)) {
            goto bail;
        }
    }

    writePtr = png_create_write_struct(PNG_LIBPNG_VER_STRING, 0, nullptr, nullptr);
    if (!writePtr) {
        *outError = "failed to allocate write ptr";
        goto bail;
    }

    writeInfoPtr = png_create_info_struct(writePtr);
    if (!writeInfoPtr) {
        *outError = "failed to allocate write info ptr";
        goto bail;
    }

    png_set_error_fn(writePtr, nullptr, nullptr, logWarning);

    // Set the write function to write to std::ostream.
    png_set_write_fn(writePtr, (png_voidp)outBuffer, writeDataToStream, flushDataToStream);

    if (!writePng(writePtr, writeInfoPtr, &pngInfo, options.grayScaleTolerance, &logger,
                  outError)) {
        goto bail;
    }

    result = true;
bail:
    if (readPtr) {
        png_destroy_read_struct(&readPtr, &infoPtr, nullptr);
    }

    if (writePtr) {
        png_destroy_write_struct(&writePtr, &writeInfoPtr);
    }
    return result;
}

} // namespace aapt