src/common/imagpng.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        src/common/imagpng.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/intl.h"
  32     #include "wx/palette.h"
  33     #include "wx/stream.h"
  34 #endif
  35
  36 #include "png.h"
  37
  38 // For memcpy
  39 #include <string.h>
  40
  41 // ----------------------------------------------------------------------------
  42 // constants
  43 // ----------------------------------------------------------------------------
  44
  45 // image can not have any transparent pixels at all, have only 100% opaque
  46 // and/or 100% transparent pixels in which case a simple mask is enough to
  47 // store this information in wxImage or have a real alpha channel in which case
  48 // we need to have it in wxImage as well
  49 enum Transparency
  50 {
  51     Transparency_None,
  52     Transparency_Mask,
  53     Transparency_Alpha
  54 };
  55
  56 // ----------------------------------------------------------------------------
  57 // local functions
  58 // ----------------------------------------------------------------------------
  59
  60 // return the kind of transparency needed for this image assuming that it does
  61 // have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
  62 static Transparency
  63 CheckTransparency(unsigned char **lines,
  64                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
  65                   size_t numColBytes);
  66
  67 // init the alpha channel for the image and fill it with 1s up to (x, y)
  68 static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);
  69
  70 // find a free colour for the mask in the PNG data array
  71 static void
  72 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
  73                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);
  74
  75 // is the pixel with this value of alpha a fully opaque one?
  76 static inline
  77 bool IsOpaque(unsigned char a)
  78 {
  79     return a == 0xff;
  80 }
  81
  82 // is the pixel with this value of alpha a fully transparent one?
  83 static inline
  84 bool IsTransparent(unsigned char a)
  85 {
  86     return !a;
  87 }
  88
  89 // ============================================================================
  90 // wxPNGHandler implementation
  91 // ============================================================================
  92
  93 IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
  94
  95 #if wxUSE_STREAMS
  96
  97 #ifndef PNGLINKAGEMODE
  98     #ifdef PNGAPI
  99         #define PNGLINKAGEMODE PNGAPI
 100     #elif defined(__WATCOMC__)
 101         // we need an explicit cdecl for Watcom, at least according to
 102         //
 103         // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
 104         //
 105         // more testing is needed for this however, please remove this comment
 106         // if you can confirm that my fix works with Watcom 11
 107         #define PNGLINKAGEMODE cdecl
 108     #else
 109         #define PNGLINKAGEMODE LINKAGEMODE
 110     #endif
 111 #endif
 112
 113
 114 // VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
 115 //     First, let me describe what's the problem: libpng uses jmp_buf in
 116 //     its png_struct structure. Unfortunately, this structure is
 117 //     compiler-specific and may vary in size, so if you use libpng compiled
 118 //     as DLL with another compiler than the main executable, it may not work
 119 //     (this is for example the case with wxMGL port and SciTech MGL library
 120 //     that provides custom runtime-loadable libpng implementation with jmpbuf
 121 //     disabled altogether). Luckily, it is still possible to use setjmp() &
 122 //     longjmp() as long as the structure is not part of png_struct.
 123 //
 124 //     Sadly, there's no clean way to attach user-defined data to png_struct.
 125 //     There is only one customizable place, png_struct.io_ptr, which is meant
 126 //     only for I/O routines and is set with png_set_read_fn or
 127 //     png_set_write_fn. The hacky part is that we use io_ptr to store
 128 //     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.
 129
 130 struct wxPNGInfoStruct
 131 {
 132     jmp_buf jmpbuf;
 133     bool verbose;
 134
 135     union
 136     {
 137         wxInputStream  *in;
 138         wxOutputStream *out;
 139     } stream;
 140 };
 141
 142 #define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))
 143
 144 // ----------------------------------------------------------------------------
 145 // helper functions
 146 // ----------------------------------------------------------------------------
 147
 148 extern "C"
 149 {
 150
 151 static void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
 152                                                  png_size_t length )
 153 {
 154     WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 155 }
 156
 157 static void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
 158                                                  png_size_t length )
 159 {
 160     WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 161 }
 162
 163 static void
 164 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 165 {
 166     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 167     if ( !info || info->verbose )
 168         wxLogWarning( wxString::FromAscii(message) );
 169 }
 170
 171 // from pngerror.c
 172 // so that the libpng doesn't send anything on stderr
 173 static void
 174 PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 175 {
 176     wx_png_warning(NULL, message);
 177
 178     // we're not using libpng built-in jump buffer (see comment before
 179     // wxPNGInfoStruct above) so we have to return ourselves, otherwise libpng
 180     // would just abort
 181     longjmp(WX_PNG_INFO(png_ptr)->jmpbuf, 1);
 182 }
 183
 184 } // extern "C"
 185
 186 // ----------------------------------------------------------------------------
 187 // LoadFile() helpers
 188 // ----------------------------------------------------------------------------
 189
 190 // determine the kind of transparency we need for this image: if the only alpha
 191 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 192 // create a mask for it, we should be ok with a simple mask but otherwise we
 193 // need a full blown alpha channel in wxImage
 194 //
 195 // parameters:
 196 //      lines           raw PNG data
 197 //      x, y            starting position
 198 //      w, h            size of the image
 199 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 200 //                      (NB: alpha always follows the colour bytes)
 201 Transparency
 202 CheckTransparency(unsigned char **lines,
 203                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 204                   size_t numColBytes)
 205 {
 206     // suppose that a mask will suffice and check all the remaining alpha
 207     // values to see if it does
 208     for ( ; y < h; y++ )
 209     {
 210         // each pixel is numColBytes+1 bytes, offset into the current line by
 211         // the current x position
 212         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 213
 214         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 215         {
 216             // skip the grey or colour byte(s)
 217             ptr += numColBytes;
 218
 219             unsigned char a2 = *ptr++;
 220
 221             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 222             {
 223                 // not fully opaque nor fully transparent, hence need alpha
 224                 return Transparency_Alpha;
 225             }
 226         }
 227
 228         // during the next loop iteration check all the pixels in the row
 229         x = 0;
 230     }
 231
 232     // mask will be enough
 233     return Transparency_Mask;
 234 }
 235
 236 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 237 {
 238     // create alpha channel
 239     image->SetAlpha();
 240
 241     unsigned char *alpha = image->GetAlpha();
 242
 243     // set alpha for the pixels we had so far
 244     png_uint_32 end = y * image->GetWidth() + x;
 245     for ( png_uint_32 i = 0; i < end; i++ )
 246     {
 247         // all the previous pixels were opaque
 248         *alpha++ = 0xff;
 249     }
 250
 251     return alpha;
 252 }
 253
 254 void
 255 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 256                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 257 {
 258     // choosing the colour for the mask is more
 259     // difficult: we need to iterate over the entire
 260     // image for this in order to choose an unused
 261     // colour (this is not very efficient but what else
 262     // can we do?)
 263     wxImageHistogram h;
 264     unsigned nentries = 0;
 265     unsigned char r2, g2, b2;
 266     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 267     {
 268         const unsigned char *p = lines[y2];
 269         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 270         {
 271             r2 = *p++;
 272             g2 = *p++;
 273             b2 = *p++;
 274             ++p; // jump over alpha
 275
 276             wxImageHistogramEntry&
 277                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 278
 279             if ( entry.value++ == 0 )
 280                 entry.index = nentries++;
 281         }
 282     }
 283
 284     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 285     {
 286         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 287
 288         // use a fixed mask colour and we'll fudge
 289         // the real pixels with this colour (see
 290         // below)
 291         rMask = 0xfe;
 292         gMask = 0;
 293         bMask = 0xff;
 294     }
 295 }
 296
 297 // ----------------------------------------------------------------------------
 298 // reading PNGs
 299 // ----------------------------------------------------------------------------
 300
 301 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 302 {
 303     unsigned char hdr[4];
 304
 305     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )     // it's ok to modify the stream position here
 306         return false;
 307
 308     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 309 }
 310
 311 // convert data from RGB to wxImage format
 312 static
 313 void CopyDataFromPNG(wxImage *image,
 314                      unsigned char **lines,
 315                      png_uint_32 width,
 316                      png_uint_32 height,
 317                      int color_type)
 318 {
 319     Transparency transparency = Transparency_None;
 320
 321     // only non NULL if transparency == Transparency_Alpha
 322     unsigned char *alpha = NULL;
 323
 324     // RGB of the mask colour if transparency == Transparency_Mask
 325     // (but init them anyhow to avoid compiler warnings)
 326     unsigned char rMask = 0,
 327                   gMask = 0,
 328                   bMask = 0;
 329
 330     unsigned char *ptrDst = image->GetData();
 331     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 332     {
 333         // grey image: GAGAGA... where G == grey component and A == alpha
 334         for ( png_uint_32 y = 0; y < height; y++ )
 335         {
 336             const unsigned char *ptrSrc = lines[y];
 337             for ( png_uint_32 x = 0; x < width; x++ )
 338             {
 339                 unsigned char g = *ptrSrc++;
 340                 unsigned char a = *ptrSrc++;
 341
 342                 // the first time we encounter a transparent pixel we must
 343                 // decide about what to do about them
 344                 if ( !IsOpaque(a) && transparency == Transparency_None )
 345                 {
 346                     // we'll need at least the mask for this image and
 347                     // maybe even full alpha channel info: the former is
 348                     // only enough if we have alpha values of 0 and 0xff
 349                     // only, otherwisewe need the latter
 350                     transparency = CheckTransparency
 351                                    (
 352                                         lines,
 353                                         x, y,
 354                                         width, height,
 355                                         1
 356                                    );
 357
 358                     if ( transparency == Transparency_Mask )
 359                     {
 360                         // let's choose this colour for the mask: this is
 361                         // not a problem here as all the other pixels are
 362                         // grey, i.e. R == G == B which is not the case for
 363                         // this one so no confusion is possible
 364                         rMask = 0xff;
 365                         gMask = 0;
 366                         bMask = 0xff;
 367                     }
 368                     else // transparency == Transparency_Alpha
 369                     {
 370                         alpha = InitAlpha(image, x, y);
 371                     }
 372                 }
 373
 374                 switch ( transparency )
 375                 {
 376                     case Transparency_Mask:
 377                         if ( IsTransparent(a) )
 378                         {
 379                             *ptrDst++ = rMask;
 380                             *ptrDst++ = gMask;
 381                             *ptrDst++ = bMask;
 382                             break;
 383                         }
 384                         // else: !transparent
 385
 386                         // must be opaque then as otherwise we shouldn't be
 387                         // using the mask at all
 388                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 389
 390                         // fall through
 391
 392                     case Transparency_Alpha:
 393                         if ( alpha )
 394                             *alpha++ = a;
 395                         // fall through
 396
 397                     case Transparency_None:
 398                         *ptrDst++ = g;
 399                         *ptrDst++ = g;
 400                         *ptrDst++ = g;
 401                         break;
 402                 }
 403             }
 404         }
 405     }
 406     else // colour image: RGBRGB...
 407     {
 408         for ( png_uint_32 y = 0; y < height; y++ )
 409         {
 410             const unsigned char *ptrSrc = lines[y];
 411             for ( png_uint_32 x = 0; x < width; x++ )
 412             {
 413                 unsigned char r = *ptrSrc++;
 414                 unsigned char g = *ptrSrc++;
 415                 unsigned char b = *ptrSrc++;
 416                 unsigned char a = *ptrSrc++;
 417
 418                 // the logic here is the same as for the grey case except
 419                 // where noted
 420                 if ( !IsOpaque(a) && transparency == Transparency_None )
 421                 {
 422                     transparency = CheckTransparency
 423                                    (
 424                                         lines,
 425                                         x, y,
 426                                         width, height,
 427                                         3
 428                                    );
 429
 430                     if ( transparency == Transparency_Mask )
 431                     {
 432                         FindMaskColour(lines, width, height,
 433                                        rMask, gMask, bMask);
 434                     }
 435                     else // transparency == Transparency_Alpha
 436                     {
 437                         alpha = InitAlpha(image, x, y);
 438                     }
 439
 440                 }
 441
 442                 switch ( transparency )
 443                 {
 444                     case Transparency_Mask:
 445                         if ( IsTransparent(a) )
 446                         {
 447                             *ptrDst++ = rMask;
 448                             *ptrDst++ = gMask;
 449                             *ptrDst++ = bMask;
 450                             break;
 451                         }
 452                         else // !transparent
 453                         {
 454                             // must be opaque then as otherwise we shouldn't be
 455                             // using the mask at all
 456                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 457
 458                             // if we couldn't find a unique colour for the
 459                             // mask, we can have real pixels with the same
 460                             // value as the mask and it's better to slightly
 461                             // change their colour than to make them
 462                             // transparent
 463                             if ( r == rMask && g == gMask && b == bMask )
 464                             {
 465                                 r++;
 466                             }
 467                         }
 468
 469                         // fall through
 470
 471                     case Transparency_Alpha:
 472                         if ( alpha )
 473                             *alpha++ = a;
 474                         // fall through
 475
 476                     case Transparency_None:
 477                         *ptrDst++ = r;
 478                         *ptrDst++ = g;
 479                         *ptrDst++ = b;
 480                         break;
 481                 }
 482             }
 483         }
 484     }
 485
 486     if ( transparency == Transparency_Mask )
 487     {
 488         image->SetMaskColour(rMask, gMask, bMask);
 489     }
 490 }
 491
 492 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 493 // C++ object destruction is non-portable) - I don't see any dtors here
 494 #ifdef __VISUALC__
 495     #pragma warning(disable:4611)
 496 #endif /* VC++ */
 497
 498 bool
 499 wxPNGHandler::LoadFile(wxImage *image,
 500                        wxInputStream& stream,
 501                        bool verbose,
 502                        int WXUNUSED(index))
 503 {
 504     // VZ: as this function uses setjmp() the only fool-proof error handling
 505     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 506
 507     unsigned char **lines = NULL;
 508     png_infop info_ptr = (png_infop) NULL;
 509     wxPNGInfoStruct wxinfo;
 510
 511     png_uint_32 i, width, height = 0;
 512     int bit_depth, color_type, interlace_type;
 513
 514     wxinfo.verbose = verbose;
 515     wxinfo.stream.in = &stream;
 516
 517     image->Destroy();
 518
 519     png_structp png_ptr = png_create_read_struct
 520                           (
 521                             PNG_LIBPNG_VER_STRING,
 522                             (voidp) NULL,
 523                             wx_png_error,
 524                             wx_png_warning
 525                           );
 526     if (!png_ptr)
 527         goto error;
 528
 529     // NB: please see the comment near wxPNGInfoStruct declaration for
 530     //     explanation why this line is mandatory
 531     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 532
 533     info_ptr = png_create_info_struct( png_ptr );
 534     if (!info_ptr)
 535         goto error;
 536
 537     if (setjmp(wxinfo.jmpbuf))
 538         goto error;
 539
 540     png_read_info( png_ptr, info_ptr );
 541     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, NULL, NULL );
 542
 543     if (color_type == PNG_COLOR_TYPE_PALETTE)
 544         png_set_expand( png_ptr );
 545
 546     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 547     if (bit_depth < 8)
 548         png_set_expand( png_ptr );
 549
 550     png_set_strip_16( png_ptr );
 551     png_set_packing( png_ptr );
 552     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 553         png_set_expand( png_ptr );
 554     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 555
 556     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 557
 558     if (!image->Ok())
 559         goto error;
 560
 561     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 562     if ( !lines )
 563         goto error;
 564
 565     for (i = 0; i < height; i++)
 566     {
 567         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 568         {
 569             for ( unsigned int n = 0; n < i; n++ )
 570                 free( lines[n] );
 571             goto error;
 572         }
 573     }
 574
 575     png_read_image( png_ptr, lines );
 576     png_read_end( png_ptr, info_ptr );
 577
 578 #if wxUSE_PALETTE
 579     if (color_type == PNG_COLOR_TYPE_PALETTE)
 580     {
 581         const size_t ncolors = info_ptr->num_palette;
 582         unsigned char* r = new unsigned char[ncolors];
 583         unsigned char* g = new unsigned char[ncolors];
 584         unsigned char* b = new unsigned char[ncolors];
 585
 586         for (size_t j = 0; j < ncolors; j++)
 587         {
 588             r[j] = info_ptr->palette[j].red;
 589             g[j] = info_ptr->palette[j].green;
 590             b[j] = info_ptr->palette[j].blue;
 591         }
 592
 593         image->SetPalette(wxPalette(ncolors, r, g, b));
 594         delete[] r;
 595         delete[] g;
 596         delete[] b;
 597     }
 598 #endif // wxUSE_PALETTE
 599
 600     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 601
 602     // loaded successfully, now init wxImage with this data
 603     CopyDataFromPNG(image, lines, width, height, color_type);
 604
 605     for ( i = 0; i < height; i++ )
 606         free( lines[i] );
 607     free( lines );
 608
 609     return true;
 610
 611 error:
 612     if (verbose)
 613        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 614
 615     if ( image->Ok() )
 616     {
 617         image->Destroy();
 618     }
 619
 620     if ( lines )
 621     {
 622         for ( unsigned int n = 0; n < height; n++ )
 623             free( lines[n] );
 624
 625         free( lines );
 626     }
 627
 628     if ( png_ptr )
 629     {
 630         if ( info_ptr )
 631         {
 632             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 633             free(info_ptr);
 634         }
 635         else
 636             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 637     }
 638     return false;
 639 }
 640
 641 // ----------------------------------------------------------------------------
 642 // writing PNGs
 643 // ----------------------------------------------------------------------------
 644
 645 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 646 {
 647     wxPNGInfoStruct wxinfo;
 648
 649     wxinfo.verbose = verbose;
 650     wxinfo.stream.out = &stream;
 651
 652     png_structp png_ptr = png_create_write_struct
 653                           (
 654                             PNG_LIBPNG_VER_STRING,
 655                             NULL,
 656                             wx_png_error,
 657                             wx_png_warning
 658                           );
 659     if (!png_ptr)
 660     {
 661         if (verbose)
 662            wxLogError(_("Couldn't save PNG image."));
 663         return false;
 664     }
 665
 666     png_infop info_ptr = png_create_info_struct(png_ptr);
 667     if (info_ptr == NULL)
 668     {
 669         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 670         if (verbose)
 671            wxLogError(_("Couldn't save PNG image."));
 672         return false;
 673     }
 674
 675     if (setjmp(wxinfo.jmpbuf))
 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     // NB: please see the comment near wxPNGInfoStruct declaration for
 684     //     explanation why this line is mandatory
 685     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 686
 687     const int iColorType = image->HasOption(wxIMAGE_OPTION_PNG_FORMAT)
 688                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_FORMAT)
 689                             : wxPNG_TYPE_COLOUR;
 690     const int iBitDepth = image->HasOption(wxIMAGE_OPTION_PNG_BITDEPTH)
 691                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_BITDEPTH)
 692                             : 8;
 693
 694     wxASSERT_MSG( iBitDepth == 8 || iBitDepth == 16,
 695                     _T("PNG bit depth must be 8 or 16") );
 696
 697     bool bHasAlpha = image->HasAlpha();
 698     bool bHasMask = image->HasMask();
 699     bool bUseAlpha = bHasAlpha || bHasMask;
 700
 701     int iPngColorType;
 702     if ( iColorType==wxPNG_TYPE_COLOUR )
 703     {
 704         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_RGB_ALPHA
 705                                   : PNG_COLOR_TYPE_RGB;
 706     }
 707     else
 708     {
 709         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_GRAY_ALPHA
 710                                   : PNG_COLOR_TYPE_GRAY;
 711     }
 712
 713     if (image->HasOption(wxIMAGE_OPTION_PNG_FILTER))
 714         png_set_filter( png_ptr, PNG_FILTER_TYPE_BASE, image->GetOptionInt(wxIMAGE_OPTION_PNG_FILTER) );
 715
 716     if (image->HasOption(wxIMAGE_OPTION_PNG_COMPRESSION_LEVEL))
 717         png_set_compression_level( png_ptr, image->GetOptionInt(wxIMAGE_OPTION_PNG_COMPRESSION_LEVEL) );
 718
 719     if (image->HasOption(wxIMAGE_OPTION_PNG_COMPRESSION_MEM_LEVEL))
 720         png_set_compression_mem_level( png_ptr, image->GetOptionInt(wxIMAGE_OPTION_PNG_COMPRESSION_MEM_LEVEL) );
 721
 722     if (image->HasOption(wxIMAGE_OPTION_PNG_COMPRESSION_STRATEGY))
 723         png_set_compression_strategy( png_ptr, image->GetOptionInt(wxIMAGE_OPTION_PNG_COMPRESSION_STRATEGY) );
 724
 725     if (image->HasOption(wxIMAGE_OPTION_PNG_COMPRESSION_BUFFER_SIZE))
 726         png_set_compression_buffer_size( png_ptr, image->GetOptionInt(wxIMAGE_OPTION_PNG_COMPRESSION_BUFFER_SIZE) );
 727
 728     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(),
 729                   iBitDepth, iPngColorType,
 730                   PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 731                   PNG_FILTER_TYPE_BASE);
 732
 733     int iElements;
 734     png_color_8 sig_bit;
 735
 736     if ( iPngColorType & PNG_COLOR_MASK_COLOR )
 737     {
 738         sig_bit.red =
 739         sig_bit.green =
 740         sig_bit.blue = (png_byte)iBitDepth;
 741         iElements = 3;
 742     }
 743     else // grey
 744     {
 745         sig_bit.gray = (png_byte)iBitDepth;
 746         iElements = 1;
 747     }
 748
 749     if ( iPngColorType & PNG_COLOR_MASK_ALPHA )
 750     {
 751         sig_bit.alpha = (png_byte)iBitDepth;
 752         iElements++;
 753     }
 754
 755     if ( iBitDepth == 16 )
 756         iElements *= 2;
 757
 758     // save the image resolution if we have it
 759     int resX, resY;
 760     switch ( GetResolutionFromOptions(*image, &resX, &resY) )
 761     {
 762         case wxIMAGE_RESOLUTION_INCHES:
 763             {
 764                 const double INCHES_IN_METER = 10000.0 / 254;
 765                 resX = int(resX * INCHES_IN_METER);
 766                 resY = int(resY * INCHES_IN_METER);
 767             }
 768             break;
 769
 770         case wxIMAGE_RESOLUTION_CM:
 771             resX *= 100;
 772             resY *= 100;
 773             break;
 774
 775         case wxIMAGE_RESOLUTION_NONE:
 776             break;
 777
 778         default:
 779             wxFAIL_MSG( _T("unsupported image resolution units") );
 780     }
 781
 782     if ( resX && resY )
 783         png_set_pHYs( png_ptr, info_ptr, resX, resY, PNG_RESOLUTION_METER );
 784
 785     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 786     png_write_info( png_ptr, info_ptr );
 787     png_set_shift( png_ptr, &sig_bit );
 788     png_set_packing( png_ptr );
 789
 790     unsigned char *
 791         data = (unsigned char *)malloc( image->GetWidth() * iElements );
 792     if ( !data )
 793     {
 794         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 795         return false;
 796     }
 797
 798     unsigned char *
 799         pAlpha = (unsigned char *)(bHasAlpha ? image->GetAlpha() : NULL);
 800     int iHeight = image->GetHeight();
 801     int iWidth = image->GetWidth();
 802
 803     unsigned char uchMaskRed = 0, uchMaskGreen = 0, uchMaskBlue = 0;
 804
 805     if ( bHasMask )
 806     {
 807         uchMaskRed = image->GetMaskRed();
 808         uchMaskGreen = image->GetMaskGreen();
 809         uchMaskBlue = image->GetMaskBlue();
 810     }
 811
 812     unsigned char *pColors = image->GetData();
 813
 814     for (int y = 0; y != iHeight; ++y)
 815     {
 816         unsigned char *pData = data;
 817         for (int x = 0; x != iWidth; x++)
 818         {
 819             unsigned char uchRed = *pColors++;
 820             unsigned char uchGreen = *pColors++;
 821             unsigned char uchBlue = *pColors++;
 822
 823             switch ( iColorType )
 824             {
 825                 default:
 826                     wxFAIL_MSG( _T("unknown wxPNG_TYPE_XXX") );
 827                     // fall through
 828
 829                 case wxPNG_TYPE_COLOUR:
 830                     *pData++ = uchRed;
 831                     if ( iBitDepth == 16 )
 832                         *pData++ = 0;
 833                     *pData++ = uchGreen;
 834                     if ( iBitDepth == 16 )
 835                         *pData++ = 0;
 836                     *pData++ = uchBlue;
 837                     if ( iBitDepth == 16 )
 838                         *pData++ = 0;
 839                     break;
 840
 841                 case wxPNG_TYPE_GREY:
 842                     {
 843                         // where do these coefficients come from? maybe we
 844                         // should have image options for them as well?
 845                         unsigned uiColor =
 846                             (unsigned) (76.544*(unsigned)uchRed +
 847                                         150.272*(unsigned)uchGreen +
 848                                         36.864*(unsigned)uchBlue);
 849
 850                         *pData++ = (unsigned char)((uiColor >> 8) & 0xFF);
 851                         if ( iBitDepth == 16 )
 852                             *pData++ = (unsigned char)(uiColor & 0xFF);
 853                     }
 854                     break;
 855
 856                 case wxPNG_TYPE_GREY_RED:
 857                     *pData++ = uchRed;
 858                     if ( iBitDepth == 16 )
 859                         *pData++ = 0;
 860                     break;
 861             }
 862
 863             if ( bUseAlpha )
 864             {
 865                 unsigned char uchAlpha = 255;
 866                 if ( bHasAlpha )
 867                     uchAlpha = *pAlpha++;
 868
 869                 if ( bHasMask )
 870                 {
 871                     if ( (uchRed == uchMaskRed)
 872                             && (uchGreen == uchMaskGreen)
 873                                 && (uchBlue == uchMaskBlue) )
 874                         uchAlpha = 0;
 875                 }
 876
 877                 *pData++ = uchAlpha;
 878                 if ( iBitDepth == 16 )
 879                     *pData++ = 0;
 880             }
 881         }
 882
 883         png_bytep row_ptr = data;
 884         png_write_rows( png_ptr, &row_ptr, 1 );
 885     }
 886
 887     free(data);
 888     png_write_end( png_ptr, info_ptr );
 889     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 890
 891     return true;
 892 }
 893
 894 #ifdef __VISUALC__
 895     #pragma warning(default:4611)
 896 #endif /* VC++ */
 897
 898 #endif  // wxUSE_STREAMS
 899
 900 #endif  // wxUSE_LIBPNG