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 // ----------------------------------------------------------------------------
  15 // headers
  16 // ----------------------------------------------------------------------------
  17
  18 // For compilers that support precompilation, includes "wx.h".
  19 #include "wx/wxprec.h"
  20
  21 #ifdef __BORLANDC__
  22     #pragma hdrstop
  23 #endif
  24
  25 #if wxUSE_IMAGE && wxUSE_LIBPNG
  26
  27 #include "wx/imagpng.h"
  28
  29 #ifndef WX_PRECOMP
  30     #include "wx/log.h"
  31     #include "wx/app.h"
  32     #include "wx/bitmap.h"
  33     #include "wx/module.h"
  34 #endif
  35
  36 #include "png.h"
  37 #include "wx/filefn.h"
  38 #include "wx/wfstream.h"
  39 #include "wx/intl.h"
  40 #include "wx/palette.h"
  41
  42 // For memcpy
  43 #include <string.h>
  44
  45 #ifdef __SALFORDC__
  46 #ifdef FAR
  47 #undef FAR
  48 #endif
  49 #endif
  50
  51 // ----------------------------------------------------------------------------
  52 // constants
  53 // ----------------------------------------------------------------------------
  54
  55 // image can not have any transparent pixels at all, have only 100% opaque
  56 // and/or 100% transparent pixels in which case a simple mask is enough to
  57 // store this information in wxImage or have a real alpha channel in which case
  58 // we need to have it in wxImage as well
  59 enum Transparency
  60 {
  61     Transparency_None,
  62     Transparency_Mask,
  63     Transparency_Alpha
  64 };
  65
  66 // ----------------------------------------------------------------------------
  67 // local functions
  68 // ----------------------------------------------------------------------------
  69
  70 // return the kind of transparency needed for this image assuming that it does
  71 // have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
  72 static Transparency
  73 CheckTransparency(unsigned char **lines,
  74                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
  75                   size_t numColBytes);
  76
  77 // init the alpha channel for the image and fill it with 1s up to (x, y)
  78 static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);
  79
  80 // find a free colour for the mask in the PNG data array
  81 static void
  82 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
  83                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);
  84
  85 // is the pixel with this value of alpha a fully opaque one?
  86 static inline
  87 bool IsOpaque(unsigned char a)
  88 {
  89     return a == 0xff;
  90 }
  91
  92 // is the pixel with this value of alpha a fully transparent one?
  93 static inline
  94 bool IsTransparent(unsigned char a)
  95 {
  96     return !a;
  97 }
  98
  99 // ============================================================================
 100 // wxPNGHandler implementation
 101 // ============================================================================
 102
 103 IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
 104
 105 #if wxUSE_STREAMS
 106
 107 #ifndef PNGLINKAGEMODE
 108     #ifdef __WATCOMC__
 109         // we need an explicit cdecl for Watcom, at least according to
 110         //
 111         // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
 112         //
 113         // more testing is needed for this however, please remove this comment
 114         // if you can confirm that my fix works with Watcom 11
 115         #define PNGLINKAGEMODE cdecl
 116     #else
 117         #define PNGLINKAGEMODE LINKAGEMODE
 118     #endif
 119 #endif
 120
 121
 122 // VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
 123 //     First, let me describe what's the problem: libpng uses jmp_buf in
 124 //     its png_struct structure. Unfortunately, this structure is
 125 //     compiler-specific and may vary in size, so if you use libpng compiled
 126 //     as DLL with another compiler than the main executable, it may not work
 127 //     (this is for example the case with wxMGL port and SciTech MGL library
 128 //     that provides custom runtime-loadable libpng implementation with jmpbuf
 129 //     disabled altogether). Luckily, it is still possible to use setjmp() &
 130 //     longjmp() as long as the structure is not part of png_struct.
 131 //
 132 //     Sadly, there's no clean way to attach user-defined data to png_struct.
 133 //     There is only one customizable place, png_struct.io_ptr, which is meant
 134 //     only for I/O routines and is set with png_set_read_fn or
 135 //     png_set_write_fn. The hacky part is that we use io_ptr to store
 136 //     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.
 137
 138 struct wxPNGInfoStruct
 139 {
 140     jmp_buf jmpbuf;
 141     bool verbose;
 142
 143     union
 144     {
 145         wxInputStream  *in;
 146         wxOutputStream *out;
 147     } stream;
 148 };
 149
 150 #define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))
 151
 152 // ----------------------------------------------------------------------------
 153 // helper functions
 154 // ----------------------------------------------------------------------------
 155
 156 extern "C"
 157 {
 158
 159 void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
 160                                           png_size_t length )
 161 {
 162     WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 163 }
 164
 165 void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
 166                                           png_size_t length )
 167 {
 168     WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 169 }
 170
 171 void
 172 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 173 {
 174     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 175     if ( !info || info->verbose )
 176         wxLogWarning( wxString::FromAscii(message) );
 177 }
 178
 179 // from pngerror.c
 180 // so that the libpng doesn't send anything on stderr
 181 void
 182 PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 183 {
 184     wx_png_warning(NULL, message);
 185
 186     // we're not using libpng built-in jump buffer (see comment before
 187     // wxPNGInfoStruct above) so we have to return ourselves, otherwise libpng
 188     // would just abort
 189     longjmp(WX_PNG_INFO(png_ptr)->jmpbuf, 1);
 190 }
 191
 192 } // extern "C"
 193
 194 // ----------------------------------------------------------------------------
 195 // LoadFile() helpers
 196 // ----------------------------------------------------------------------------
 197
 198 // determine the kind of transparency we need for this image: if the only alpha
 199 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 200 // create a mask for it, we should be ok with a simple mask but otherwise we
 201 // need a full blown alpha channel in wxImage
 202 //
 203 // parameters:
 204 //      lines           raw PNG data
 205 //      x, y            starting position
 206 //      w, h            size of the image
 207 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 208 //                      (NB: alpha always follows the colour bytes)
 209 Transparency
 210 CheckTransparency(unsigned char **lines,
 211                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 212                   size_t numColBytes)
 213 {
 214     // suppose that a mask will suffice and check all the remaining alpha
 215     // values to see if it does
 216     for ( ; y < h; y++ )
 217     {
 218         // each pixel is numColBytes+1 bytes, offset into the current line by
 219         // the current x position
 220         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 221
 222         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 223         {
 224             // skip the grey or colour byte(s)
 225             ptr += numColBytes;
 226
 227             unsigned char a2 = *ptr++;
 228
 229             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 230             {
 231                 // not fully opaque nor fully transparent, hence need alpha
 232                 return Transparency_Alpha;
 233             }
 234         }
 235
 236         // during the next loop iteration check all the pixels in the row
 237         x = 0;
 238     }
 239
 240     // mask will be enough
 241     return Transparency_Mask;
 242 }
 243
 244 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 245 {
 246     // create alpha channel
 247     image->SetAlpha();
 248
 249     unsigned char *alpha = image->GetAlpha();
 250
 251     // set alpha for the pixels we had so far
 252     png_uint_32 end = y * image->GetWidth() + x;
 253     for ( png_uint_32 i = 0; i < end; i++ )
 254     {
 255         // all the previous pixels were opaque
 256         *alpha++ = 0xff;
 257     }
 258
 259     return alpha;
 260 }
 261
 262 void
 263 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 264                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 265 {
 266     // choosing the colour for the mask is more
 267     // difficult: we need to iterate over the entire
 268     // image for this in order to choose an unused
 269     // colour (this is not very efficient but what else
 270     // can we do?)
 271     wxImageHistogram h;
 272     unsigned nentries = 0;
 273     unsigned char r2, g2, b2;
 274     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 275     {
 276         const unsigned char *p = lines[y2];
 277         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 278         {
 279             r2 = *p++;
 280             g2 = *p++;
 281             b2 = *p++;
 282             ++p; // jump over alpha
 283
 284             wxImageHistogramEntry&
 285                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 286
 287             if ( entry.value++ == 0 )
 288                 entry.index = nentries++;
 289         }
 290     }
 291
 292     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 293     {
 294         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 295
 296         // use a fixed mask colour and we'll fudge
 297         // the real pixels with this colour (see
 298         // below)
 299         rMask = 0xfe;
 300         gMask = 0;
 301         bMask = 0xff;
 302     }
 303 }
 304
 305 // ----------------------------------------------------------------------------
 306 // reading PNGs
 307 // ----------------------------------------------------------------------------
 308
 309 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 310 {
 311     unsigned char hdr[4];
 312
 313     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 314         return false;
 315
 316     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 317 }
 318
 319 // convert data from RGB to wxImage format
 320 static
 321 void CopyDataFromPNG(wxImage *image,
 322                      unsigned char **lines,
 323                      png_uint_32 width,
 324                      png_uint_32 height,
 325                      int color_type)
 326 {
 327     Transparency transparency = Transparency_None;
 328
 329     // only non NULL if transparency == Transparency_Alpha
 330     unsigned char *alpha = NULL;
 331
 332     // RGB of the mask colour if transparency == Transparency_Mask
 333     // (but init them anyhow to avoid compiler warnings)
 334     unsigned char rMask = 0,
 335                   gMask = 0,
 336                   bMask = 0;
 337
 338     unsigned char *ptrDst = image->GetData();
 339     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 340     {
 341         // grey image: GAGAGA... where G == grey component and A == alpha
 342         for ( png_uint_32 y = 0; y < height; y++ )
 343         {
 344             const unsigned char *ptrSrc = lines[y];
 345             for ( png_uint_32 x = 0; x < width; x++ )
 346             {
 347                 unsigned char g = *ptrSrc++;
 348                 unsigned char a = *ptrSrc++;
 349
 350                 // the first time we encounter a transparent pixel we must
 351                 // decide about what to do about them
 352                 if ( !IsOpaque(a) && transparency == Transparency_None )
 353                 {
 354                     // we'll need at least the mask for this image and
 355                     // maybe even full alpha channel info: the former is
 356                     // only enough if we have alpha values of 0 and 0xff
 357                     // only, otherwisewe need the latter
 358                     transparency = CheckTransparency
 359                                    (
 360                                         lines,
 361                                         x, y,
 362                                         width, height,
 363                                         1
 364                                    );
 365
 366                     if ( transparency == Transparency_Mask )
 367                     {
 368                         // let's choose this colour for the mask: this is
 369                         // not a problem here as all the other pixels are
 370                         // grey, i.e. R == G == B which is not the case for
 371                         // this one so no confusion is possible
 372                         rMask = 0xff;
 373                         gMask = 0;
 374                         bMask = 0xff;
 375                     }
 376                     else // transparency == Transparency_Alpha
 377                     {
 378                         alpha = InitAlpha(image, x, y);
 379                     }
 380                 }
 381
 382                 switch ( transparency )
 383                 {
 384                     case Transparency_Mask:
 385                         if ( IsTransparent(a) )
 386                         {
 387                             *ptrDst++ = rMask;
 388                             *ptrDst++ = gMask;
 389                             *ptrDst++ = bMask;
 390                             break;
 391                         }
 392                         // else: !transparent
 393
 394                         // must be opaque then as otherwise we shouldn't be
 395                         // using the mask at all
 396                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 397
 398                         // fall through
 399
 400                     case Transparency_Alpha:
 401                         if ( alpha )
 402                             *alpha++ = a;
 403                         // fall through
 404
 405                     case Transparency_None:
 406                         *ptrDst++ = g;
 407                         *ptrDst++ = g;
 408                         *ptrDst++ = g;
 409                         break;
 410                 }
 411             }
 412         }
 413     }
 414     else // colour image: RGBRGB...
 415     {
 416         for ( png_uint_32 y = 0; y < height; y++ )
 417         {
 418             const unsigned char *ptrSrc = lines[y];
 419             for ( png_uint_32 x = 0; x < width; x++ )
 420             {
 421                 unsigned char r = *ptrSrc++;
 422                 unsigned char g = *ptrSrc++;
 423                 unsigned char b = *ptrSrc++;
 424                 unsigned char a = *ptrSrc++;
 425
 426                 // the logic here is the same as for the grey case except
 427                 // where noted
 428                 if ( !IsOpaque(a) && transparency == Transparency_None )
 429                 {
 430                     transparency = CheckTransparency
 431                                    (
 432                                         lines,
 433                                         x, y,
 434                                         width, height,
 435                                         3
 436                                    );
 437
 438                     if ( transparency == Transparency_Mask )
 439                     {
 440                         FindMaskColour(lines, width, height,
 441                                        rMask, gMask, bMask);
 442                     }
 443                     else // transparency == Transparency_Alpha
 444                     {
 445                         alpha = InitAlpha(image, x, y);
 446                     }
 447
 448                 }
 449
 450                 switch ( transparency )
 451                 {
 452                     case Transparency_Mask:
 453                         if ( IsTransparent(a) )
 454                         {
 455                             *ptrDst++ = rMask;
 456                             *ptrDst++ = gMask;
 457                             *ptrDst++ = bMask;
 458                             break;
 459                         }
 460                         else // !transparent
 461                         {
 462                             // must be opaque then as otherwise we shouldn't be
 463                             // using the mask at all
 464                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 465
 466                             // if we couldn't find a unique colour for the
 467                             // mask, we can have real pixels with the same
 468                             // value as the mask and it's better to slightly
 469                             // change their colour than to make them
 470                             // transparent
 471                             if ( r == rMask && g == gMask && b == bMask )
 472                             {
 473                                 r++;
 474                             }
 475                         }
 476
 477                         // fall through
 478
 479                     case Transparency_Alpha:
 480                         if ( alpha )
 481                             *alpha++ = a;
 482                         // fall through
 483
 484                     case Transparency_None:
 485                         *ptrDst++ = r;
 486                         *ptrDst++ = g;
 487                         *ptrDst++ = b;
 488                         break;
 489                 }
 490             }
 491         }
 492     }
 493
 494     if ( transparency == Transparency_Mask )
 495     {
 496         image->SetMaskColour(rMask, gMask, bMask);
 497     }
 498 }
 499
 500 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 501 // C++ object destruction is non-portable) - I don't see any dtors here
 502 #ifdef __VISUALC__
 503     #pragma warning(disable:4611)
 504 #endif /* VC++ */
 505
 506 bool
 507 wxPNGHandler::LoadFile(wxImage *image,
 508                        wxInputStream& stream,
 509                        bool verbose,
 510                        int WXUNUSED(index))
 511 {
 512     // VZ: as this function uses setjmp() the only fool-proof error handling
 513     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 514
 515     unsigned char **lines = NULL;
 516     png_infop info_ptr = (png_infop) NULL;
 517     wxPNGInfoStruct wxinfo;
 518
 519     png_uint_32 i, width, height = 0;
 520     int bit_depth, color_type, interlace_type;
 521
 522     wxinfo.verbose = verbose;
 523     wxinfo.stream.in = &stream;
 524
 525     image->Destroy();
 526
 527     png_structp png_ptr = png_create_read_struct
 528                           (
 529                             PNG_LIBPNG_VER_STRING,
 530                             (voidp) NULL,
 531                             wx_png_error,
 532                             wx_png_warning
 533                           );
 534     if (!png_ptr)
 535         goto error;
 536
 537     // NB: please see the comment near wxPNGInfoStruct declaration for
 538     //     explanation why this line is mandatory
 539     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 540
 541     info_ptr = png_create_info_struct( png_ptr );
 542     if (!info_ptr)
 543         goto error;
 544
 545     if (setjmp(wxinfo.jmpbuf))
 546         goto error;
 547
 548     png_read_info( png_ptr, info_ptr );
 549     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 550
 551     if (color_type == PNG_COLOR_TYPE_PALETTE)
 552         png_set_expand( png_ptr );
 553
 554     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 555     if (bit_depth < 8)
 556         png_set_expand( png_ptr );
 557
 558     png_set_strip_16( png_ptr );
 559     png_set_packing( png_ptr );
 560     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 561         png_set_expand( png_ptr );
 562     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 563
 564     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 565
 566     if (!image->Ok())
 567         goto error;
 568
 569     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 570     if ( !lines )
 571         goto error;
 572
 573     for (i = 0; i < height; i++)
 574     {
 575         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 576         {
 577             for ( unsigned int n = 0; n < i; n++ )
 578                 free( lines[n] );
 579             goto error;
 580         }
 581     }
 582
 583     png_read_image( png_ptr, lines );
 584     png_read_end( png_ptr, info_ptr );
 585
 586 #if wxUSE_PALETTE
 587     if (color_type == PNG_COLOR_TYPE_PALETTE)
 588     {
 589         const size_t ncolors = info_ptr->num_palette;
 590         unsigned char* r = new unsigned char[ncolors];
 591         unsigned char* g = new unsigned char[ncolors];
 592         unsigned char* b = new unsigned char[ncolors];
 593
 594         for (size_t j = 0; j < ncolors; j++)
 595         {
 596             r[j] = info_ptr->palette[j].red;
 597             g[j] = info_ptr->palette[j].green;
 598             b[j] = info_ptr->palette[j].blue;
 599         }
 600
 601         image->SetPalette(wxPalette(ncolors, r, g, b));
 602         delete[] r;
 603         delete[] g;
 604         delete[] b;
 605     }
 606 #endif // wxUSE_PALETTE
 607
 608     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 609
 610     // loaded successfully, now init wxImage with this data
 611     CopyDataFromPNG(image, lines, width, height, color_type);
 612
 613     for ( i = 0; i < height; i++ )
 614         free( lines[i] );
 615     free( lines );
 616
 617     return true;
 618
 619 error:
 620     if (verbose)
 621        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 622
 623     if ( image->Ok() )
 624     {
 625         image->Destroy();
 626     }
 627
 628     if ( lines )
 629     {
 630         for ( unsigned int n = 0; n < height; n++ )
 631             free( lines[n] );
 632
 633         free( lines );
 634     }
 635
 636     if ( png_ptr )
 637     {
 638         if ( info_ptr )
 639         {
 640             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 641             free(info_ptr);
 642         }
 643         else
 644             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 645     }
 646     return false;
 647 }
 648
 649 // ----------------------------------------------------------------------------
 650 // writing PNGs
 651 // ----------------------------------------------------------------------------
 652
 653 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 654 {
 655     wxPNGInfoStruct wxinfo;
 656
 657     wxinfo.verbose = verbose;
 658     wxinfo.stream.out = &stream;
 659
 660     png_structp png_ptr = png_create_write_struct
 661                           (
 662                             PNG_LIBPNG_VER_STRING,
 663                             NULL,
 664                             wx_png_error,
 665                             wx_png_warning
 666                           );
 667     if (!png_ptr)
 668     {
 669         if (verbose)
 670            wxLogError(_("Couldn't save PNG image."));
 671         return false;
 672     }
 673
 674     png_infop info_ptr = png_create_info_struct(png_ptr);
 675     if (info_ptr == NULL)
 676     {
 677         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 678         if (verbose)
 679            wxLogError(_("Couldn't save PNG image."));
 680         return false;
 681     }
 682
 683     if (setjmp(wxinfo.jmpbuf))
 684     {
 685         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 686         if (verbose)
 687            wxLogError(_("Couldn't save PNG image."));
 688         return false;
 689     }
 690
 691     // NB: please see the comment near wxPNGInfoStruct declaration for
 692     //     explanation why this line is mandatory
 693     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 694
 695     const int iColorType = image->HasOption(wxIMAGE_OPTION_PNG_FORMAT)
 696                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_FORMAT)
 697                             : wxPNG_TYPE_COLOUR;
 698     const int iBitDepth = image->HasOption(wxIMAGE_OPTION_PNG_BITDEPTH)
 699                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_BITDEPTH)
 700                             : 8;
 701
 702     wxASSERT_MSG( iBitDepth == 8 || iBitDepth == 16,
 703                     _T("PNG bit depth must be 8 or 16") );
 704
 705     bool bHasAlpha = image->HasAlpha();
 706     bool bHasMask = image->HasMask();
 707     bool bUseAlpha = bHasAlpha || bHasMask;
 708
 709     int iPngColorType;
 710     if ( iColorType==wxPNG_TYPE_COLOUR )
 711     {
 712         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_RGB_ALPHA
 713                                   : PNG_COLOR_TYPE_RGB;
 714     }
 715     else
 716     {
 717         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_GRAY_ALPHA
 718                                   : PNG_COLOR_TYPE_GRAY;
 719     }
 720
 721     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(),
 722                   iBitDepth, iPngColorType,
 723                   PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 724                   PNG_FILTER_TYPE_BASE);
 725
 726     int iElements;
 727     png_color_8 sig_bit;
 728
 729     if ( iPngColorType & PNG_COLOR_MASK_COLOR )
 730     {
 731         sig_bit.red =
 732         sig_bit.green =
 733         sig_bit.blue = (png_byte)iBitDepth;
 734         iElements = 3;
 735     }
 736     else // grey
 737     {
 738         sig_bit.gray = (png_byte)iBitDepth;
 739         iElements = 1;
 740     }
 741
 742     if ( iPngColorType & PNG_COLOR_MASK_ALPHA )
 743     {
 744         sig_bit.alpha = (png_byte)iBitDepth;
 745         iElements++;
 746     }
 747
 748     if ( iBitDepth == 16 )
 749         iElements *= 2;
 750
 751     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 752     png_write_info( png_ptr, info_ptr );
 753     png_set_shift( png_ptr, &sig_bit );
 754     png_set_packing( png_ptr );
 755
 756     unsigned char *
 757         data = (unsigned char *)malloc( image->GetWidth() * iElements );
 758     if ( !data )
 759     {
 760         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 761         return false;
 762     }
 763
 764     unsigned char *
 765         pAlpha = (unsigned char *)(bHasAlpha ? image->GetAlpha() : NULL);
 766     int iHeight = image->GetHeight();
 767     int iWidth = image->GetWidth();
 768
 769     unsigned char uchMaskRed = 0, uchMaskGreen = 0, uchMaskBlue = 0;
 770
 771     if ( bHasMask )
 772     {
 773         uchMaskRed = image->GetMaskRed();
 774         uchMaskGreen = image->GetMaskGreen();
 775         uchMaskBlue = image->GetMaskBlue();
 776     }
 777
 778     unsigned char *pColors = image->GetData();
 779
 780     for (int y = 0; y != iHeight; ++y)
 781     {
 782         unsigned char *pData = data;
 783         for (int x = 0; x != iWidth; x++)
 784         {
 785             unsigned char uchRed = *pColors++;
 786             unsigned char uchGreen = *pColors++;
 787             unsigned char uchBlue = *pColors++;
 788
 789             switch ( iColorType )
 790             {
 791                 default:
 792                     wxFAIL_MSG( _T("unknown wxPNG_TYPE_XXX") );
 793                     // fall through
 794
 795                 case wxPNG_TYPE_COLOUR:
 796                     *pData++ = uchRed;
 797                     if ( iBitDepth == 16 )
 798                         *pData++ = 0;
 799                     *pData++ = uchGreen;
 800                     if ( iBitDepth == 16 )
 801                         *pData++ = 0;
 802                     *pData++ = uchBlue;
 803                     if ( iBitDepth == 16 )
 804                         *pData++ = 0;
 805                     break;
 806
 807                 case wxPNG_TYPE_GREY:
 808                     {
 809                         // where do these coefficients come from? maybe we
 810                         // should have image options for them as well?
 811                         unsigned uiColor =
 812                             (unsigned) (76.544*(unsigned)uchRed +
 813                                         150.272*(unsigned)uchGreen +
 814                                         36.864*(unsigned)uchBlue);
 815
 816                         *pData++ = (unsigned char)((uiColor >> 8) & 0xFF);
 817                         if ( iBitDepth == 16 )
 818                             *pData++ = (unsigned char)(uiColor & 0xFF);
 819                     }
 820                     break;
 821
 822                 case wxPNG_TYPE_GREY_RED:
 823                     *pData++ = uchRed;
 824                     if ( iBitDepth == 16 )
 825                         *pData++ = 0;
 826                     break;
 827             }
 828
 829             if ( bUseAlpha )
 830             {
 831                 unsigned char uchAlpha = 255;
 832                 if ( bHasAlpha )
 833                     uchAlpha = *pAlpha++;
 834
 835                 if ( bHasMask )
 836                 {
 837                     if ( (uchRed == uchMaskRed)
 838                             && (uchGreen == uchMaskGreen)
 839                                 && (uchBlue == uchMaskBlue) )
 840                         uchAlpha = 0;
 841                 }
 842
 843                 *pData++ = uchAlpha;
 844                 if ( iBitDepth == 16 )
 845                     *pData++ = 0;
 846             }
 847         }
 848
 849         png_bytep row_ptr = data;
 850         png_write_rows( png_ptr, &row_ptr, 1 );
 851     }
 852
 853     free(data);
 854     png_write_end( png_ptr, info_ptr );
 855     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 856
 857     return true;
 858 }
 859
 860 #ifdef __VISUALC__
 861     #pragma warning(default:4611)
 862 #endif /* VC++ */
 863
 864 #endif  // wxUSE_STREAMS
 865
 866 #endif  // wxUSE_LIBPNG