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 WXUNUSED(png_ptr), png_const_charp message)
 179 {
 180     wxLogFatalError( wxString::FromAscii(message) );
 181 }
 182
 183 void
 184 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 185 {
 186     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 187     if ( !info || info->verbose )
 188         wxLogWarning( wxString::FromAscii(message) );
 189 }
 190
 191 } // extern "C"
 192
 193 // ----------------------------------------------------------------------------
 194 // LoadFile() helpers
 195 // ----------------------------------------------------------------------------
 196
 197 // determine the kind of transparency we need for this image: if the only alpha
 198 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 199 // create a mask for it, we should be ok with a simple mask but otherwise we
 200 // need a full blown alpha channel in wxImage
 201 //
 202 // parameters:
 203 //      lines           raw PNG data
 204 //      x, y            starting position
 205 //      w, h            size of the image
 206 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 207 //                      (NB: alpha always follows the colour bytes)
 208 Transparency
 209 CheckTransparency(unsigned char **lines,
 210                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 211                   size_t numColBytes)
 212 {
 213     // suppose that a mask will suffice and check all the remaining alpha
 214     // values to see if it does
 215     for ( ; y < h; y++ )
 216     {
 217         // each pixel is numColBytes+1 bytes, offset into the current line by
 218         // the current x position
 219         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 220
 221         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 222         {
 223             // skip the grey or colour byte(s)
 224             ptr += numColBytes;
 225
 226             unsigned char a2 = *ptr++;
 227
 228             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 229             {
 230                 // not fully opaque nor fully transparent, hence need alpha
 231                 return Transparency_Alpha;
 232             }
 233         }
 234
 235         // during the next loop iteration check all the pixels in the row
 236         x = 0;
 237     }
 238
 239     // mask will be enough
 240     return Transparency_Mask;
 241 }
 242
 243 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 244 {
 245     // create alpha channel
 246     image->SetAlpha();
 247
 248     unsigned char *alpha = image->GetAlpha();
 249
 250     // set alpha for the pixels we had so far
 251     png_uint_32 end = y * image->GetWidth() + x;
 252     for ( png_uint_32 i = 0; i < end; i++ )
 253     {
 254         // all the previous pixels were opaque
 255         *alpha++ = 0xff;
 256     }
 257
 258     return alpha;
 259 }
 260
 261 void
 262 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 263                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 264 {
 265     // choosing the colour for the mask is more
 266     // difficult: we need to iterate over the entire
 267     // image for this in order to choose an unused
 268     // colour (this is not very efficient but what else
 269     // can we do?)
 270     wxImageHistogram h;
 271     unsigned nentries = 0;
 272     unsigned char r2, g2, b2;
 273     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 274     {
 275         const unsigned char *p = lines[y2];
 276         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 277         {
 278             r2 = *p++;
 279             g2 = *p++;
 280             b2 = *p++;
 281
 282             wxImageHistogramEntry&
 283                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 284
 285             if ( entry.value++ == 0 )
 286                 entry.index = nentries++;
 287         }
 288     }
 289
 290     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 291     {
 292         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 293
 294         // use a fixed mask colour and we'll fudge
 295         // the real pixels with this colour (see
 296         // below)
 297         rMask = 0xfe;
 298         gMask = 0;
 299         bMask = 0xff;
 300     }
 301 }
 302
 303 // ----------------------------------------------------------------------------
 304 // reading PNGs
 305 // ----------------------------------------------------------------------------
 306
 307 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 308 {
 309     unsigned char hdr[4];
 310
 311     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 312         return false;
 313
 314     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 315 }
 316
 317 // convert data from RGB to wxImage format
 318 static
 319 void CopyDataFromPNG(wxImage *image,
 320                      unsigned char **lines,
 321                      png_uint_32 width,
 322                      png_uint_32 height,
 323                      int color_type)
 324 {
 325     Transparency transparency = Transparency_None;
 326
 327     // only non NULL if transparency == Transparency_Alpha
 328     unsigned char *alpha = NULL;
 329
 330     // RGB of the mask colour if transparency == Transparency_Mask
 331     // (but init them anyhow to avoid compiler warnings)
 332     unsigned char rMask = 0,
 333                   gMask = 0,
 334                   bMask = 0;
 335
 336     unsigned char *ptrDst = image->GetData();
 337     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 338     {
 339         // grey image: GAGAGA... where G == grey component and A == alpha
 340         for ( png_uint_32 y = 0; y < height; y++ )
 341         {
 342             const unsigned char *ptrSrc = lines[y];
 343             for ( png_uint_32 x = 0; x < width; x++ )
 344             {
 345                 unsigned char g = *ptrSrc++;
 346                 unsigned char a = *ptrSrc++;
 347
 348                 // the first time we encounter a transparent pixel we must
 349                 // decide about what to do about them
 350                 if ( !IsOpaque(a) && transparency == Transparency_None )
 351                 {
 352                     // we'll need at least the mask for this image and
 353                     // maybe even full alpha channel info: the former is
 354                     // only enough if we have alpha values of 0 and 0xff
 355                     // only, otherwisewe need the latter
 356                     transparency = CheckTransparency
 357                                    (
 358                                         lines,
 359                                         x, y,
 360                                         width, height,
 361                                         1
 362                                    );
 363
 364                     if ( transparency == Transparency_Mask )
 365                     {
 366                         // let's choose this colour for the mask: this is
 367                         // not a problem here as all the other pixels are
 368                         // grey, i.e. R == G == B which is not the case for
 369                         // this one so no confusion is possible
 370                         rMask = 0xff;
 371                         gMask = 0;
 372                         bMask = 0xff;
 373                     }
 374                     else // transparency == Transparency_Alpha
 375                     {
 376                         alpha = InitAlpha(image, x, y);
 377                     }
 378                 }
 379
 380                 switch ( transparency )
 381                 {
 382                     case Transparency_Mask:
 383                         if ( IsTransparent(a) )
 384                         {
 385                             *ptrDst++ = rMask;
 386                             *ptrDst++ = bMask;
 387                             *ptrDst++ = gMask;
 388                             break;
 389                         }
 390                         // else: !transparent
 391
 392                         // must be opaque then as otherwise we shouldn't be
 393                         // using the mask at all
 394                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 395
 396                         // fall through
 397
 398                     case Transparency_Alpha:
 399                         if ( alpha )
 400                             *alpha++ = a;
 401                         // fall through
 402
 403                     case Transparency_None:
 404                         *ptrDst++ = g;
 405                         *ptrDst++ = g;
 406                         *ptrDst++ = g;
 407                         break;
 408                 }
 409             }
 410         }
 411     }
 412     else // colour image: RGBRGB...
 413     {
 414         for ( png_uint_32 y = 0; y < height; y++ )
 415         {
 416             const unsigned char *ptrSrc = lines[y];
 417             for ( png_uint_32 x = 0; x < width; x++ )
 418             {
 419                 unsigned char r = *ptrSrc++;
 420                 unsigned char g = *ptrSrc++;
 421                 unsigned char b = *ptrSrc++;
 422                 unsigned char a = *ptrSrc++;
 423
 424                 // the logic here is the same as for the grey case except
 425                 // where noted
 426                 if ( !IsOpaque(a) && transparency == Transparency_None )
 427                 {
 428                     transparency = CheckTransparency
 429                                    (
 430                                         lines,
 431                                         x, y,
 432                                         width, height,
 433                                         3
 434                                    );
 435
 436                     if ( transparency == Transparency_Mask )
 437                     {
 438                         FindMaskColour(lines, width, height,
 439                                        rMask, gMask, bMask);
 440                     }
 441                     else // transparency == Transparency_Alpha
 442                     {
 443                         alpha = InitAlpha(image, x, y);
 444                     }
 445
 446                 }
 447
 448                 switch ( transparency )
 449                 {
 450                     case Transparency_Mask:
 451                         if ( IsTransparent(a) )
 452                         {
 453                             *ptrDst++ = rMask;
 454                             *ptrDst++ = bMask;
 455                             *ptrDst++ = gMask;
 456                             break;
 457                         }
 458                         else // !transparent
 459                         {
 460                             // must be opaque then as otherwise we shouldn't be
 461                             // using the mask at all
 462                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 463
 464                             // if we couldn't find a unique colour for the
 465                             // mask, we can have real pixels with the same
 466                             // value as the mask and it's better to slightly
 467                             // change their colour than to make them
 468                             // transparent
 469                             if ( r == rMask && g == gMask && b == bMask )
 470                             {
 471                                 r++;
 472                             }
 473                         }
 474
 475                         // fall through
 476
 477                     case Transparency_Alpha:
 478                         if ( alpha )
 479                             *alpha++ = a;
 480                         // fall through
 481
 482                     case Transparency_None:
 483                         *ptrDst++ = r;
 484                         *ptrDst++ = g;
 485                         *ptrDst++ = b;
 486                         break;
 487                 }
 488             }
 489         }
 490     }
 491
 492     if ( transparency == Transparency_Mask )
 493     {
 494         image->SetMaskColour(rMask, gMask, bMask);
 495     }
 496 }
 497
 498 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 499 // C++ object destruction is non-portable) - I don't see any dtors here
 500 #ifdef __VISUALC__
 501     #pragma warning(disable:4611)
 502 #endif /* VC++ */
 503
 504 bool
 505 wxPNGHandler::LoadFile(wxImage *image,
 506                        wxInputStream& stream,
 507                        bool verbose,
 508                        int WXUNUSED(index))
 509 {
 510     // VZ: as this function uses setjmp() the only fool proof error handling
 511     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 512
 513     unsigned char **lines = NULL;
 514     png_infop info_ptr = (png_infop) NULL;
 515     wxPNGInfoStruct wxinfo;
 516
 517     wxinfo.verbose = verbose;
 518     wxinfo.stream.in = &stream;
 519
 520     image->Destroy();
 521
 522     png_structp png_ptr = png_create_read_struct
 523                           (
 524                             PNG_LIBPNG_VER_STRING,
 525                             (voidp) NULL,
 526                             wx_png_error,
 527                             wx_png_warning
 528                           );
 529     if (!png_ptr)
 530         goto error;
 531
 532     // NB: please see the comment near wxPNGInfoStruct declaration for
 533     //     explanation why this line is mandatory
 534     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 535
 536     info_ptr = png_create_info_struct( png_ptr );
 537     if (!info_ptr)
 538         goto error;
 539
 540     if (setjmp(wxinfo.jmpbuf))
 541         goto error;
 542
 543     png_uint_32 i, width, height;
 544     int bit_depth, color_type, interlace_type;
 545
 546     png_read_info( png_ptr, info_ptr );
 547     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 548
 549     if (color_type == PNG_COLOR_TYPE_PALETTE)
 550         png_set_expand( png_ptr );
 551
 552     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 553     if (bit_depth < 8)
 554         png_set_expand( png_ptr );
 555
 556     png_set_strip_16( png_ptr );
 557     png_set_packing( png_ptr );
 558     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 559         png_set_expand( png_ptr );
 560     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 561
 562     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 563
 564     if (!image->Ok())
 565         goto error;
 566
 567     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 568     if ( !lines )
 569         goto error;
 570
 571     for (i = 0; i < height; i++)
 572     {
 573         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 574         {
 575             for ( unsigned int n = 0; n < i; n++ )
 576                 free( lines[n] );
 577             goto error;
 578         }
 579     }
 580
 581     png_read_image( png_ptr, lines );
 582     png_read_end( png_ptr, info_ptr );
 583     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 584
 585     // loaded successfully, now init wxImage with this data
 586     CopyDataFromPNG(image, lines, width, height, color_type);
 587
 588     for ( i = 0; i < height; i++ )
 589         free( lines[i] );
 590     free( lines );
 591
 592     return true;
 593
 594 error:
 595     if (verbose)
 596        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 597
 598     if ( image->Ok() )
 599     {
 600         image->Destroy();
 601     }
 602
 603     if ( lines )
 604     {
 605         free( lines );
 606     }
 607
 608     if ( png_ptr )
 609     {
 610         if ( info_ptr )
 611         {
 612             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 613             free(info_ptr);
 614         }
 615         else
 616             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 617     }
 618     return false;
 619 }
 620
 621 // ----------------------------------------------------------------------------
 622 // writing PNGs
 623 // ----------------------------------------------------------------------------
 624
 625 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 626 {
 627     wxPNGInfoStruct wxinfo;
 628
 629     wxinfo.verbose = verbose;
 630     wxinfo.stream.out = &stream;
 631
 632     png_structp png_ptr = png_create_write_struct
 633                           (
 634                             PNG_LIBPNG_VER_STRING,
 635                             NULL,
 636                             wx_png_error,
 637                             wx_png_warning
 638                           );
 639     if (!png_ptr)
 640     {
 641         if (verbose)
 642            wxLogError(_("Couldn't save PNG image."));
 643         return false;
 644     }
 645
 646     png_infop info_ptr = png_create_info_struct(png_ptr);
 647     if (info_ptr == NULL)
 648     {
 649         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 650         if (verbose)
 651            wxLogError(_("Couldn't save PNG image."));
 652         return false;
 653     }
 654
 655     if (setjmp(wxinfo.jmpbuf))
 656     {
 657         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 658         if (verbose)
 659            wxLogError(_("Couldn't save PNG image."));
 660         return false;
 661     }
 662
 663     // NB: please see the comment near wxPNGInfoStruct declaration for
 664     //     explanation why this line is mandatory
 665     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 666
 667     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(), 8,
 668         PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
 669         PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
 670
 671     png_color_8 sig_bit;
 672     sig_bit.red = 8;
 673     sig_bit.green = 8;
 674     sig_bit.blue = 8;
 675     sig_bit.alpha = 8;
 676     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 677     png_write_info( png_ptr, info_ptr );
 678     png_set_shift( png_ptr, &sig_bit );
 679     png_set_packing( png_ptr );
 680
 681     unsigned char *data = (unsigned char *)malloc( image->GetWidth()*4 );
 682     if (!data)
 683     {
 684         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 685         return false;
 686     }
 687
 688     for (int y = 0; y < image->GetHeight(); y++)
 689     {
 690         unsigned char *ptr = image->GetData() + (y * image->GetWidth() * 3);
 691         for (int x = 0; x < image->GetWidth(); x++)
 692         {
 693             data[(x << 2) + 0] = *ptr++;
 694             data[(x << 2) + 1] = *ptr++;
 695             data[(x << 2) + 2] = *ptr++;
 696             if ( image->HasAlpha() )
 697             {
 698                 data[(x << 2) + 3] = image->GetAlpha(x, y);
 699             }
 700             else if (( !image->HasMask() ) || \
 701                 (data[(x << 2) + 0] != image->GetMaskRed()) || \
 702                 (data[(x << 2) + 1] != image->GetMaskGreen()) || \
 703                 (data[(x << 2) + 2] != image->GetMaskBlue()))
 704             {
 705                 data[(x << 2) + 3] = 255;
 706             }
 707             else
 708             {
 709                 data[(x << 2) + 3] = 0;
 710             }
 711         }
 712         png_bytep row_ptr = data;
 713         png_write_rows( png_ptr, &row_ptr, 1 );
 714     }
 715
 716     free(data);
 717     png_write_end( png_ptr, info_ptr );
 718     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 719
 720     return true;
 721 }
 722
 723 #ifdef __VISUALC__
 724     #pragma warning(default:4611)
 725 #endif /* VC++ */
 726
 727 #endif  // wxUSE_STREAMS
 728
 729 #endif  // wxUSE_LIBPNG