src/common/imagpng.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        src/common/imagepng.cpp
   3 // Purpose:     wxImage PNG handler
   4 // Author:      Robert Roebling
   5 // RCS-ID:      $Id$
   6 // Copyright:   (c) Robert Roebling
   7 // Licence:     wxWindows licence
   8 /////////////////////////////////////////////////////////////////////////////
   9
  10 // ============================================================================
  11 // declarations
  12 // ============================================================================
  13
  14 #if defined(__GNUG__) && !defined(NO_GCC_PRAGMA)
  15 #pragma implementation "imagpng.h"
  16 #endif
  17
  18 // ----------------------------------------------------------------------------
  19 // headers
  20 // ----------------------------------------------------------------------------
  21
  22 // For compilers that support precompilation, includes "wx.h".
  23 #include "wx/wxprec.h"
  24
  25 #ifdef __BORLANDC__
  26   #pragma hdrstop
  27 #endif
  28
  29 #ifndef WX_PRECOMP
  30   #include "wx/defs.h"
  31 #endif
  32
  33 #if wxUSE_IMAGE && wxUSE_LIBPNG
  34
  35 #include "wx/imagpng.h"
  36 #include "wx/bitmap.h"
  37 #include "wx/debug.h"
  38 #include "wx/log.h"
  39 #include "wx/app.h"
  40 #include "png.h"
  41 #include "wx/filefn.h"
  42 #include "wx/wfstream.h"
  43 #include "wx/intl.h"
  44 #include "wx/module.h"
  45
  46 // For memcpy
  47 #include <string.h>
  48
  49 #ifdef __SALFORDC__
  50 #ifdef FAR
  51 #undef FAR
  52 #endif
  53 #endif
  54
  55 // ----------------------------------------------------------------------------
  56 // constants
  57 // ----------------------------------------------------------------------------
  58
  59 // image can not have any transparent pixels at all, have only 100% opaque
  60 // and/or 100% transparent pixels in which case a simple mask is enough to
  61 // store this information in wxImage or have a real alpha channel in which case
  62 // we need to have it in wxImage as well
  63 enum Transparency
  64 {
  65     Transparency_None,
  66     Transparency_Mask,
  67     Transparency_Alpha
  68 };
  69
  70 // ----------------------------------------------------------------------------
  71 // local functions
  72 // ----------------------------------------------------------------------------
  73
  74 // return the kind of transparency needed for this image assuming that it does
  75 // have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
  76 static Transparency
  77 CheckTransparency(unsigned char **lines,
  78                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
  79                   size_t numColBytes);
  80
  81 // init the alpha channel for the image and fill it with 1s up to (x, y)
  82 static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);
  83
  84 // find a free colour for the mask in the PNG data array
  85 static void
  86 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
  87                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);
  88
  89 // is the pixel with this value of alpha a fully opaque one?
  90 static inline
  91 bool IsOpaque(unsigned char a)
  92 {
  93     return a == 0xff;
  94 }
  95
  96 // is the pixel with this value of alpha a fully transparent one?
  97 static inline
  98 bool IsTransparent(unsigned char a)
  99 {
 100     return !a;
 101 }
 102
 103 // ============================================================================
 104 // wxPNGHandler implementation
 105 // ============================================================================
 106
 107 IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
 108
 109 #if wxUSE_STREAMS
 110
 111 #ifndef PNGLINKAGEMODE
 112     #ifdef __WATCOMC__
 113         // we need an explicit cdecl for Watcom, at least according to
 114         //
 115         // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
 116         //
 117         // more testing is needed for this however, please remove this comment
 118         // if you can confirm that my fix works with Watcom 11
 119         #define PNGLINKAGEMODE cdecl
 120     #else
 121         #define PNGLINKAGEMODE LINKAGEMODE
 122     #endif
 123 #endif
 124
 125
 126 // VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
 127 //     First, let me describe what's the problem: libpng uses jmp_buf in
 128 //     its png_struct structure. Unfortunately, this structure is
 129 //     compiler-specific and may vary in size, so if you use libpng compiled
 130 //     as DLL with another compiler than the main executable, it may not work
 131 //     (this is for example the case with wxMGL port and SciTech MGL library
 132 //     that provides custom runtime-loadable libpng implementation with jmpbuf
 133 //     disabled altogether). Luckily, it is still possible to use setjmp() &
 134 //     longjmp() as long as the structure is not part of png_struct.
 135 //
 136 //     Sadly, there's no clean way to attach user-defined data to png_struct.
 137 //     There is only one customizable place, png_struct.io_ptr, which is meant
 138 //     only for I/O routines and is set with png_set_read_fn or
 139 //     png_set_write_fn. The hacky part is that we use io_ptr to store
 140 //     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.
 141
 142 struct wxPNGInfoStruct
 143 {
 144     jmp_buf jmpbuf;
 145     bool verbose;
 146
 147     union
 148     {
 149         wxInputStream  *in;
 150         wxOutputStream *out;
 151     } stream;
 152 };
 153
 154 #define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))
 155
 156 // ----------------------------------------------------------------------------
 157 // helper functions
 158 // ----------------------------------------------------------------------------
 159
 160 extern "C"
 161 {
 162
 163 void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
 164                                           png_size_t length )
 165 {
 166     WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 167 }
 168
 169 void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
 170                                           png_size_t length )
 171 {
 172     WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 173 }
 174
 175 // from pngerror.c
 176 // so that the libpng doesn't send anything on stderr
 177 void
 178 PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 179 {
 180     wxPNGInfoStruct *info = WX_PNG_INFO(png_ptr);
 181     if (info->verbose)
 182         wxLogError( wxString::FromAscii(message) );
 183
 184 #ifdef USE_FAR_KEYWORD
 185     {
 186        jmp_buf jmpbuf;
 187        png_memcpy(jmpbuf,info->jmpbuf,sizeof(jmp_buf));
 188        longjmp(jmpbuf, 1);
 189     }
 190 #else
 191     longjmp(info->jmpbuf, 1);
 192 #endif
 193 }
 194
 195 void
 196 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 197 {
 198     wxPNGInfoStruct *info = WX_PNG_INFO(png_ptr);
 199     if (info->verbose)
 200         wxLogWarning( wxString::FromAscii(message) );
 201 }
 202
 203 } // extern "C"
 204
 205 // ----------------------------------------------------------------------------
 206 // LoadFile() helpers
 207 // ----------------------------------------------------------------------------
 208
 209 // determine the kind of transparency we need for this image: if the only alpha
 210 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 211 // create a mask for it, we should be ok with a simple mask but otherwise we
 212 // need a full blown alpha channel in wxImage
 213 //
 214 // parameters:
 215 //      lines           raw PNG data
 216 //      x, y            starting position
 217 //      w, h            size of the image
 218 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 219 //                      (NB: alpha always follows the colour bytes)
 220 Transparency
 221 CheckTransparency(unsigned char **lines,
 222                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 223                   size_t numColBytes)
 224 {
 225     // suppose that a mask will suffice and check all the remaining alpha
 226     // values to see if it does
 227     for ( ; y < h; y++ )
 228     {
 229         // each pixel is numColBytes+1 bytes, offset into the current line by
 230         // the current x position
 231         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 232
 233         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 234         {
 235             // skip the grey or colour byte(s)
 236             ptr += numColBytes;
 237
 238             unsigned char a2 = *ptr++;
 239
 240             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 241             {
 242                 // not fully opaque nor fully transparent, hence need alpha
 243                 return Transparency_Alpha;
 244             }
 245         }
 246
 247         // during the next loop iteration check all the pixels in the row
 248         x = 0;
 249     }
 250
 251     // mask will be enough
 252     return Transparency_Mask;
 253 }
 254
 255 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 256 {
 257     // create alpha channel
 258     image->SetAlpha();
 259
 260     unsigned char *alpha = image->GetAlpha();
 261
 262     // set alpha for the pixels we had so far
 263     png_uint_32 end = y * image->GetWidth() + x;
 264     for ( png_uint_32 i = 0; i < end; i++ )
 265     {
 266         // all the previous pixels were opaque
 267         *alpha++ = 0xff;
 268     }
 269
 270     return alpha;
 271 }
 272
 273 void
 274 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 275                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 276 {
 277     // choosing the colour for the mask is more
 278     // difficult: we need to iterate over the entire
 279     // image for this in order to choose an unused
 280     // colour (this is not very efficient but what else
 281     // can we do?)
 282     wxImageHistogram h;
 283     unsigned nentries = 0;
 284     unsigned char r2, g2, b2;
 285     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 286     {
 287         const unsigned char *p = lines[y2];
 288         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 289         {
 290             r2 = *p++;
 291             g2 = *p++;
 292             b2 = *p++;
 293
 294             wxImageHistogramEntry&
 295                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 296
 297             if ( entry.value++ == 0 )
 298                 entry.index = nentries++;
 299         }
 300     }
 301
 302     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 303     {
 304         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 305
 306         // use a fixed mask colour and we'll fudge
 307         // the real pixels with this colour (see
 308         // below)
 309         rMask = 0xfe;
 310         gMask = 0;
 311         bMask = 0xff;
 312     }
 313 }
 314
 315 // ----------------------------------------------------------------------------
 316 // reading PNGs
 317 // ----------------------------------------------------------------------------
 318
 319 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 320 {
 321     unsigned char hdr[4];
 322
 323     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 324         return FALSE;
 325
 326     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 327 }
 328
 329 // convert data from RGB to wxImage format
 330 static
 331 void CopyDataFromPNG(wxImage *image,
 332                      unsigned char **lines,
 333                      png_uint_32 width,
 334                      png_uint_32 height,
 335                      int color_type)
 336 {
 337     Transparency transparency = Transparency_None;
 338
 339     // only non NULL if transparency == Transparency_Alpha
 340     unsigned char *alpha = NULL;
 341
 342     // RGB of the mask colour if transparency == Transparency_Mask
 343     // (but init them anyhow to avoid compiler warnings)
 344     unsigned char rMask = 0,
 345                   gMask = 0,
 346                   bMask = 0;
 347
 348     unsigned char *ptrDst = image->GetData();
 349     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 350     {
 351         // grey image: GAGAGA... where G == grey component and A == alpha
 352         for ( png_uint_32 y = 0; y < height; y++ )
 353         {
 354             const unsigned char *ptrSrc = lines[y];
 355             for ( png_uint_32 x = 0; x < width; x++ )
 356             {
 357                 unsigned char g = *ptrSrc++;
 358                 unsigned char a = *ptrSrc++;
 359
 360                 // the first time we encounter a transparent pixel we must
 361                 // decide about what to do about them
 362                 if ( !IsOpaque(a) && transparency == Transparency_None )
 363                 {
 364                     // we'll need at least the mask for this image and
 365                     // maybe even full alpha channel info: the former is
 366                     // only enough if we have alpha values of 0 and 0xff
 367                     // only, otherwisewe need the latter
 368                     transparency = CheckTransparency
 369                                    (
 370                                         lines,
 371                                         x, y,
 372                                         width, height,
 373                                         1
 374                                    );
 375
 376                     if ( transparency == Transparency_Mask )
 377                     {
 378                         // let's choose this colour for the mask: this is
 379                         // not a problem here as all the other pixels are
 380                         // grey, i.e. R == G == B which is not the case for
 381                         // this one so no confusion is possible
 382                         rMask = 0xff;
 383                         gMask = 0;
 384                         bMask = 0xff;
 385                     }
 386                     else // transparency == Transparency_Alpha
 387                     {
 388                         alpha = InitAlpha(image, x, y);
 389                     }
 390                 }
 391
 392                 switch ( transparency )
 393                 {
 394                     case Transparency_Mask:
 395                         if ( IsTransparent(a) )
 396                         {
 397                             *ptrDst++ = rMask;
 398                             *ptrDst++ = bMask;
 399                             *ptrDst++ = gMask;
 400                             break;
 401                         }
 402                         // else: !transparent
 403
 404                         // must be opaque then as otherwise we shouldn't be
 405                         // using the mask at all
 406                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 407
 408                         // fall through
 409
 410                     case Transparency_Alpha:
 411                         if ( alpha )
 412                             *alpha++ = a;
 413                         // fall through
 414
 415                     case Transparency_None:
 416                         *ptrDst++ = g;
 417                         *ptrDst++ = g;
 418                         *ptrDst++ = g;
 419                         break;
 420                 }
 421             }
 422         }
 423     }
 424     else // colour image: RGBRGB...
 425     {
 426         for ( png_uint_32 y = 0; y < height; y++ )
 427         {
 428             const unsigned char *ptrSrc = lines[y];
 429             for ( png_uint_32 x = 0; x < width; x++ )
 430             {
 431                 unsigned char r = *ptrSrc++;
 432                 unsigned char g = *ptrSrc++;
 433                 unsigned char b = *ptrSrc++;
 434                 unsigned char a = *ptrSrc++;
 435
 436                 // the logic here is the same as for the grey case except
 437                 // where noted
 438                 if ( !IsOpaque(a) && transparency == Transparency_None )
 439                 {
 440                     transparency = CheckTransparency
 441                                    (
 442                                         lines,
 443                                         x, y,
 444                                         width, height,
 445                                         3
 446                                    );
 447
 448                     if ( transparency == Transparency_Mask )
 449                     {
 450                         FindMaskColour(lines, width, height,
 451                                        rMask, gMask, bMask);
 452                     }
 453                     else // transparency == Transparency_Alpha
 454                     {
 455                         alpha = InitAlpha(image, x, y);
 456                     }
 457
 458                 }
 459
 460                 switch ( transparency )
 461                 {
 462                     case Transparency_Mask:
 463                         if ( IsTransparent(a) )
 464                         {
 465                             *ptrDst++ = rMask;
 466                             *ptrDst++ = bMask;
 467                             *ptrDst++ = gMask;
 468                             break;
 469                         }
 470                         else // !transparent
 471                         {
 472                             // must be opaque then as otherwise we shouldn't be
 473                             // using the mask at all
 474                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 475
 476                             // if we couldn't find a unique colour for the
 477                             // mask, we can have real pixels with the same
 478                             // value as the mask and it's better to slightly
 479                             // change their colour than to make them
 480                             // transparent
 481                             if ( r == rMask && g == gMask && b == bMask )
 482                             {
 483                                 r++;
 484                             }
 485                         }
 486
 487                         // fall through
 488
 489                     case Transparency_Alpha:
 490                         if ( alpha )
 491                             *alpha++ = a;
 492                         // fall through
 493
 494                     case Transparency_None:
 495                         *ptrDst++ = r;
 496                         *ptrDst++ = g;
 497                         *ptrDst++ = b;
 498                         break;
 499                 }
 500             }
 501         }
 502     }
 503
 504     if ( transparency == Transparency_Mask )
 505     {
 506         image->SetMaskColour(rMask, gMask, bMask);
 507     }
 508 }
 509
 510 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 511 // C++ object destruction is non-portable) - I don't see any dtors here
 512 #ifdef __VISUALC__
 513     #pragma warning(disable:4611)
 514 #endif /* VC++ */
 515
 516 bool
 517 wxPNGHandler::LoadFile(wxImage *image,
 518                        wxInputStream& stream,
 519                        bool verbose,
 520                        int WXUNUSED(index))
 521 {
 522     // VZ: as this function uses setjmp() the only fool proof error handling
 523     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 524
 525     unsigned char **lines = NULL;
 526     png_infop info_ptr = (png_infop) NULL;
 527     wxPNGInfoStruct wxinfo;
 528
 529     wxinfo.verbose = verbose;
 530     wxinfo.stream.in = &stream;
 531
 532     image->Destroy();
 533
 534     png_structp png_ptr = png_create_read_struct( PNG_LIBPNG_VER_STRING,
 535         (voidp) NULL,
 536         (png_error_ptr) NULL,
 537         (png_error_ptr) NULL );
 538     if (!png_ptr)
 539         goto error;
 540
 541     png_set_error_fn(png_ptr, (png_voidp)NULL, wx_png_error, wx_png_warning);
 542
 543     // NB: please see the comment near wxPNGInfoStruct declaration for
 544     //     explanation why this line is mandatory
 545     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 546
 547     info_ptr = png_create_info_struct( png_ptr );
 548     if (!info_ptr)
 549         goto error;
 550
 551     if (setjmp(wxinfo.jmpbuf))
 552         goto error;
 553
 554     png_uint_32 i, width, height;
 555     int bit_depth, color_type, interlace_type;
 556
 557     png_read_info( png_ptr, info_ptr );
 558     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 559
 560     if (color_type == PNG_COLOR_TYPE_PALETTE)
 561         png_set_expand( png_ptr );
 562
 563     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 564     if (bit_depth < 8)
 565         png_set_expand( png_ptr );
 566
 567     png_set_strip_16( png_ptr );
 568     png_set_packing( png_ptr );
 569     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 570         png_set_expand( png_ptr );
 571     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 572
 573     image->Create((int)width, (int)height, false /* no need to init pixels */);
 574
 575     if (!image->Ok())
 576         goto error;
 577
 578     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 579     if ( !lines )
 580         goto error;
 581
 582     for (i = 0; i < height; i++)
 583     {
 584         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 585         {
 586             for ( unsigned int n = 0; n < i; n++ )
 587                 free( lines[n] );
 588             goto error;
 589         }
 590     }
 591
 592     png_read_image( png_ptr, lines );
 593     png_read_end( png_ptr, info_ptr );
 594     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 595
 596     // loaded successfully, now init wxImage with this data
 597     CopyDataFromPNG(image, lines, width, height, color_type);
 598
 599     for ( i = 0; i < height; i++ )
 600         free( lines[i] );
 601     free( lines );
 602
 603     return TRUE;
 604
 605 error:
 606     if (verbose)
 607        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 608
 609     if ( image->Ok() )
 610     {
 611         image->Destroy();
 612     }
 613
 614     if ( lines )
 615     {
 616         free( lines );
 617     }
 618
 619     if ( png_ptr )
 620     {
 621         if ( info_ptr )
 622         {
 623             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 624             free(info_ptr);
 625         }
 626         else
 627             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 628     }
 629     return FALSE;
 630 }
 631
 632 // ----------------------------------------------------------------------------
 633 // writing PNGs
 634 // ----------------------------------------------------------------------------
 635
 636 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 637 {
 638     wxPNGInfoStruct wxinfo;
 639
 640     wxinfo.verbose = verbose;
 641     wxinfo.stream.out = &stream;
 642
 643     png_structp png_ptr = png_create_write_struct( PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
 644     if (!png_ptr)
 645     {
 646         if (verbose)
 647            wxLogError(_("Couldn't save PNG image."));
 648         return FALSE;
 649     }
 650
 651     png_set_error_fn(png_ptr, (png_voidp)NULL, wx_png_error, wx_png_warning);
 652
 653     png_infop info_ptr = png_create_info_struct(png_ptr);
 654     if (info_ptr == NULL)
 655     {
 656         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 657         if (verbose)
 658            wxLogError(_("Couldn't save PNG image."));
 659         return FALSE;
 660     }
 661
 662     if (setjmp(wxinfo.jmpbuf))
 663     {
 664         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 665         if (verbose)
 666            wxLogError(_("Couldn't save PNG image."));
 667         return FALSE;
 668     }
 669
 670     // NB: please see the comment near wxPNGInfoStruct declaration for
 671     //     explanation why this line is mandatory
 672     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 673
 674     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(), 8,
 675         PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
 676         PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
 677
 678     png_color_8 sig_bit;
 679     sig_bit.red = 8;
 680     sig_bit.green = 8;
 681     sig_bit.blue = 8;
 682     sig_bit.alpha = 8;
 683     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 684     png_write_info( png_ptr, info_ptr );
 685     png_set_shift( png_ptr, &sig_bit );
 686     png_set_packing( png_ptr );
 687
 688     unsigned char *data = (unsigned char *)malloc( image->GetWidth()*4 );
 689     if (!data)
 690     {
 691         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 692         return FALSE;
 693     }
 694
 695     for (int y = 0; y < image->GetHeight(); y++)
 696     {
 697         unsigned char *ptr = image->GetData() + (y * image->GetWidth() * 3);
 698         for (int x = 0; x < image->GetWidth(); x++)
 699         {
 700             data[(x << 2) + 0] = *ptr++;
 701             data[(x << 2) + 1] = *ptr++;
 702             data[(x << 2) + 2] = *ptr++;
 703             if ( image->HasAlpha() )
 704             {
 705                 data[(x << 2) + 3] = image->GetAlpha(x, y);
 706             }
 707             else if (( !image->HasMask() ) || \
 708                 (data[(x << 2) + 0] != image->GetMaskRed()) || \
 709                 (data[(x << 2) + 1] != image->GetMaskGreen()) || \
 710                 (data[(x << 2) + 2] != image->GetMaskBlue()))
 711             {
 712                 data[(x << 2) + 3] = 255;
 713             }
 714             else
 715             {
 716                 data[(x << 2) + 3] = 0;
 717             }
 718         }
 719         png_bytep row_ptr = data;
 720         png_write_rows( png_ptr, &row_ptr, 1 );
 721     }
 722
 723     free(data);
 724     png_write_end( png_ptr, info_ptr );
 725     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 726
 727     return TRUE;
 728 }
 729
 730 #ifdef __VISUALC__
 731     #pragma warning(default:4611)
 732 #endif /* VC++ */
 733
 734 #endif  // wxUSE_STREAMS
 735
 736 #endif  // wxUSE_LIBPNG